Camshaft duration and lift specs.

[Dr. David Fleming]

Anyone got the camshaft specifications on lift and duration and overlap for the 454/502 MAG MPI? Could also use the info for the 454mpi.

Crane cams gives the 500EFI cam - Crane 169621 - as cam lift .352 intake/ .359 exhaust; duration intake 292/ exhaust 298 - no overlap spec.

500HP cam - Crane 169611 - as cam lift .339 intake/ .352 exhaust; duration intake 222/ exhaust 230 - no overlap spec.

If this is correct the EFI cam is considerably stronger than the HP - doesn't figure.

Thanks

[mrfixxall]

If you know what the grind number heres the data sheet on all their cams.

[Dr. David Fleming]

mrfixxall,

The grind nos. HR 284-2S-10 1G for the 500HP cam. Grind nos. HR 292-2S-14 1G for the 500EFI cam. These are not on the list you supplied.

Mercruiser service manual does not give the specs for stock cams on 454/502 MAG MPI or the L-29 454 mpi. Someone has got to know?

Thanks

[mrfixxall]

The guy you need to talk to is bob mandera @ marine kinetics..He knows all cam grinds that mercruiser used..

585-654-8583

Fixx

[fogducker III]

The specs I found, not sure if it is what you were looking for...?

454 and 502 Mag is .300 lift and 224* duration. For both exhaust and intake. That is the flat tappet cam.

The roller tappet cam is .342 lift for both intake and exhaust and 227* exhaust duration and 211* intake duration.

[Dr. David Fleming]

Ok guys!

WIth all this potential problem or "water reversion" and "water inversion" in the marine exhaust system and it all being blamed on "high cam overlap". HOw come merc and crane don't publish any fricking overlap specs. Just what amout of overlap is suposed to be a problem?

Hello - we do discuss every aspect of engine tuning on the Donzi Registry - except camshaft specifications? -

This is leaving out the "most important conversation of all!"

Go figure

[BUIZILLA]

Ok guys!

WIth all this potential problem or "water reversion" and "water inversion" in the marine exhaust system and it all being blamed on "high cam overlap". HOw come merc and crane don't publish any fricking overlap specs. Just what amout of overlap is suposed to be a problem?

Hello - we do discuss every aspect of engine tuning on the Donzi Registry - except camshaft specifications? -

This is leaving out the "most important conversation of all!"

Go figureif you look at all the valve timing events, you can figure out the overlap..

[mrfixxall]

Dr.

ok lets use fogdockers specs!

if you Add the intake and exhaust adv durations, then Divide the results by 4 Subtract the LSA lets say its 112 deg then Multiply the results by 2
and thats your overlap..

or if you have the cam card you take the intake opens @ ? BTDC and add the Exhaust closes @ ? ATDC that would be your overlap..

you wont get the rite math form fodockers specs,merc specs are based @ .200

[Dr. David Fleming]

"Valve overlap" is the duration in degrees when both the intake and exhaust valves are open at the same time. The exhaust stroke has about finished and the velocity of the exhaust gas puts a negative pressure condition in the cylinder. The intake valve is opened early to allow the negative cylinder pressure to begin moving the air column into combustion chamber. Inertia being what it is - NEwton F=MxA - it takes time to get the intake to flow so the "valve overlap" is an exhaust boost contition - however minor that may be - improves power - wastes some fuel and in marine engines causes water to get sucked - how I don't know.

Tyler Crockett in his brief explanation to me about the 500HP and the 500EFI made some vague reference to valve overlap. For this reason Marine engines use a special cams.

Except for this vague explanation I have yet to get the entire understanding of the subject.

CMI - David Rank - tells me that they did extensive research on the e-top headers to make sure they would work on the 500EFI with the Crane 169621 cam. This is a cam with 292* intake duration and 298* exhaust duration. But without knowing the lobe centerline and rate of closing and opening the "valve overlap" could be anything. You need the valve events plotted out on paper with a protractor you could figure the overlap.

I think the real issue with "water reversion" is not the overlap, but the "closing event" of the exhaust valve. It would seem it must be closed early enough that the cylinder suction on the intake stroke does "draw water" - not create a negative pressure condition in the exhaust system to draw the water. This "early exhaust valve closing" would of course shorten the effective condition of "valve overlap."

Now this makes sense, but what is the "overlap" number or exhaust closing number that makes a marine cam different from any other?

I am using e-top CMI exhaust with stock cam and have had some minor water condition in the headers last year. So I am dumping the Corsa transom mufflers for CMI transom mount tailpipes with the internal flap making the entire system CMI. Tyler is still trying to push me to the 500EFI camshaft. You wouldn't think headers on an engine with a stock cam would not be an issue?

454/502 MAG MPI cam specs. - intake lift .342/ exhaust lift .342 - intake valve duration 211*/ exhaust duration 227*

500EFI - Crane 169621 - intake lift .352/ exhaust lift .359 - intake valve duration 292*/ exhaust duration 298*

Horsepower of 502MAG MPI - 415 @ 4,800
Horsepower of 500EFI - 475 @ 5000

The cam should be responsible for most of the differences here.

[BUIZILLA]

454/502 MAG MPI cam specs. - intake lift .342/ exhaust lift .342 - intake valve duration 211*/ exhaust duration 227*

500EFI - Crane 169621 - intake lift .352/ exhaust lift .359 - intake valve duration 292*/ exhaust duration 298* you can't compare these two cams using those numbers, the first one shows numbers probably at .050 lift and the second is showing *advertised* numbers, which in the real world don't mean sh1t... you need to compare grind numbers using either .006 or .050 lift equally, then take into consideration the lobe seperation numbers... there is nothing special about marine cams, it's just the choice of lobe grinds in the same catalog or library... auto engines have been using seperation numbers from 111-118 for years, the tighter the LS numbers with a given duration, the choppier the idle manners and the more concern for any reversion characteristics... you can use the exact same lobe profiles on different LS numbers and change the manners drastically... the shortened 10 or 14 part numbers shown are the LS numbers, in this case 110* or 114*...

[Dr. David Fleming]

Budzilla,

I think we are on the same page here in dialing in the issue of cams in marine engines.

What I am missing here are the old dyno tests you used to see run in Hot Rod Magazine. I remember when Eldebrock or someone like Crane would get a big block chevy (bbc) and run dyno tests with all ten or fiveteen cams. Then they would change carbs, manifolds, headers etc. Two or three Holley carbs - 780cfm, 800cfm, 850cfm. They would compare the old Rochester stock carb. Then the cams would be discribed in a way, lift, duration and overlap. They might even throw in a couple of header styles.

Here in "the marine land of 2010" I look at Hot Boat and what do I get - adds and glitz - some babes, some general bullxxxt I could get by going to the boat show. Its no wonder I won't take a subscription - Teague's column and Tyler's are the only thing worth reading. I mean, come on - here is GIL with an exhaust, Stainless Marine, Dana, CMI, Lightening, Harden. Where are the tests and comparisons. What about a baseline on the Holley and then comparison to the Linkefelter fuelie setup on the MAG MPI and the Arizona Speed And Marine. These publishers (clowns) ought to be able to get some of this info out where their customers could use it. They might even sell some of their product and a few magazines. Most as I can tell folks are afraid to mess with their marine engines for lack of understanding of the products. The computor fuel injection has put the whole thing out of reach.

I watched a guy - professional marine mechanic - here in Michigan rebuild a Volvo 7.4 go through the whole engine, put it back in the boat - couldn't get it to run. Then pull the whole engine out again, put it in a truck and take it to Tyler - put it on the dyno - won't run - the frickin fuel injectors were clogged. Half hour cleaning the injectors ran great - you just know what the customer paid for that.

Someone here in the old USA is sleeping at the switch. I think I can handle more than cuzos and Donzi babes. I need some customer service from Mercrusiser and literature from boat mags. I got a laptop and would enjoy hooking it up to the bbc.

[joseph m. hahnl]

This is very interesting, as I have wondered my self why reversion happens,on aftermarket camshafts. Know this is all new to me but I do have a pretty good idea how things work. You can correct me if I'm wrong and I'm sure you will. First off the duration would be determined by the size of the radius and flat at the end of the lobe, obviously the height of the lobe would be the lift. The angle of the lobe placement in angularity on the camshaft would determine the start and finish of the valve relative to piston or crankshaft position.These angles between the exhaust and intake lobes will be what determines overlap.
That would be my understanding of it.

Now I'll do some research:kingme:



Highlights:

Definition: Overlap was once a very common figure but, much like advertised duration, it has fallen from favor as a comparison tool among many cam grinders. Basically, overlap is the number of degrees that the camshaft features with both the intake and exhaust valves open simultaneously. Overlap takes place at the beginning of the intake stroke and also at the end of the exhaust stroke.

Also called lobe displacement angle (LDA), the lobe center has a definite bearing on how a particular camshaft will operate in a specific powerplant. If the lobe center of the camshaft is increased, the valve overlap will be decreased. The overlap decrease is created because the exhaust timing will occur earlier and the intake timing event will occur later in relation to crankshaft position. Conversely, if the lobe center or displacement angle is decreased, overlap increases. Note that lobe center cannot be changed once a camshaft has been ground.


Click on no photo,to see photo
http://static.hotrod.com/_SiteConfigs/_global/images/no_photo_100px.gif (http://www.hotrod.com/techarticles/113_9811_camshaft_tech_valve_timing_piston_movemen t/photo_02.html)[/URL]
The importance of "degreeing" camshafts cannot be over-emphasized. Unless you know the exact relationships between the piston position (crankshaft angle) and the valve lift, neither manufacturer specs nor intentional deviations from these numbers is possible with any degree of accuracy. This Comp Cams checking set is typical of what should be standard in your toolbox.





Definitions:


Definition: Theoretical valve lift is the figure often published in cam manufacturers’ specification charts and is the most common term used to describe the lift of the cam. Theoretical valve lift does not take into account valve lash, valvetrain deflection underload, variables in rocker arm ratio, and so on. Think of theoretical valve lift as maximum valve lift under ideal conditions.


Definition: Net valve lift is the real-world number that your particular powerplant experiences with all variables taken into account. Items such as valve lash, valvetrain deflection, and rocker arm ratio variation are considered when this particular measurement is determined. It should be pointed out that it is virtually impossible for any camshaft grinder to print a true "net" figure on its specification card. The only viable method of determining actual net valve lift is by setting up a dial indicator on the nose of the rocker arm and measuring the lift while the powerplant is in an "operational" mode (but, of course, not running).


Definition: Lobe lift or camshaft lift is the term that describes the amount of lift the camshaft provides without any benefit of rocker arm ratio multiplication factors. For example, a small-block Chevrolet roller camshaft may have an advertised lobe lift of 0.350. If the engine makes use of a standard 1.50:1 ratio rocker arm, the final theoretical valve lift works out to 0.525 (0.350 X 1.5). In the event that the powerplant uses a 1.60:1 ratio rocker arm, the theoretical valve lift works out to 0.560-inch. Think of cam lift as the true amount the camshaft lifts the valve lifter in the respective lifter bore.


Definition: Advertised duration is the most common form of listing specific duration figures. It is measured in crankshaft degrees and basically expresses the length of time that a given valve is open. Unfortunately, this particular figure can be more optimistic than theoretical valve lift. A good portion of the discrepancy regarding advertised duration figures is due to the fact that many manufacturers tend to include the camshaft lobe clearance ramp in their duration figures. For example, a Chevrolet ZL1 camshaft has an advertised duration figure of 359 degrees on the exhaust side. Obviously, this is an extremely stout number and, when you give it some consideration, you can clearly see that the powerplant could hardly run with such a radical camshaft. This is where 0.050-inch duration figures come into play. Measured with the 0.050-inch method, the very same ZL1 grind features a duration figure of 273 degrees. That’s a significant difference.


Definition: The 0.050-inch duration figure is determined when the valve lifter has risen 0.050-inch off the camshaft base circle (opening side) and closed to within 0.050-inch (closing side) on the ramp. This particular duration figure is quite accurate for comparison purposes and in most areas is much closer to true duration than the advertised number. Airflow in the intake or exhaust port is minimal at low lift figures, especially when the clearance ramp numbers are included in the discussion. Since this airflow is almost nil in most situations, the camshaft manufacturers began using the 0.050-inch method to determine a universal number that could be used for camshaft comparison. The newer 0.050-inch number is more accurate and can, at least, be compared without worrying about variables such as ramp clearance.


Definition: Several camshaft grinders have begun to use the 0.020-inch duration figure in addition to the previously mentioned 0.050-inch number. It is primarily a seat duration figure and most often is used to determine valve timing at the seat. This figure is helpful when plotting a specific cam profile on graph paper and also can be of some assistance when comparing various camshaft profiles.


Definition: Overlap was once a very common figure but, much like advertised duration, it has fallen from favor as a comparison tool among many cam grinders. Basically, overlap is the number of degrees that the camshaft features with both the intake and exhaust valves open simultaneously. Overlap takes place at the beginning of the intake stroke and also at the end of the exhaust stroke.



Definition: Lobe center is the amount of camshaft degrees between the point of maximum lift on the intake lobe and the point of maximum lift on the exhaust side of a given pair of cam lobes. As an example, lobe center is calculated for cylinder number one only and does not deviate between number one and the other cylinders in the powerplant. To make a representative sketch of lobe center, draw a line between the very center of a camshaft intake lobe and then draw a similar line through the respective exhaust lobe for the same cylinder. The number of camshaft degrees between these two imaginary lines is the camshaft lobe center.


Also called lobe displacement angle (LDA), the lobe center has a definite bearing on how a particular camshaft will operate in a specific powerplant. If the lobe center of the camshaft is increased, the valve overlap will be decreased. The overlap decrease is created because the exhaust timing will occur earlier and the intake timing event will occur later in relation to crankshaft position. Conversely, if the lobe center or displacement angle is decreased, overlap increases. Note that lobe center cannot be changed once a camshaft has been ground.


Definition: Lobe centerline should not be confused with lobe center or lobe displacement angle. The term "lobe centerline" refers to an imaginary line drawn through each respective lobe but does not combine the separation angle between the intake and exhaust lobes in a given pairing. Lobe centerline can be altered by advancing or retarding a camshaft, while lobe center is a figure that cannot be altered since it is incorporated into the camshaft when it is designed and manufactured.


Definition: A symmetrical camshaft makes use of the same profile on the opening and closing side of a specific lobe. In other words, the opening side of an intake lobe features a shape that is exactly the same on the closing side of the lobe. This term should not be confused with single-pattern or dual-pattern camshafts (see below).


Definition: An asymmetrical camshaft features a lobe shape or profile that is different on the opening side than the closing side of the same lobe. For example, a camshaft could feature a very rapid valve opening profile, but when the valve is closing on the same lobe, the shape could be extremely smooth and gentle.


Definition: Single-pattern camshaft grinds feature identical intake and exhaust lobe configurations. This actually means that the valve timing is the same for both the intake lobe and the exhaust lobe. It should be pointed out that a camshaft can be asymmetrical in design yet still be a single-pattern grind. On the other hand, a camshaft can be symmetrical yet also be a single-pattern configuration.


Definition: Dual-pattern camshaft grinds make use of different profiles on the intake and exhaust lobes. This means that the exhaust lobe and the intake lobe are not identical in shape. A cam profile of this type could feature an asymmetrical lobe on the intake and a symmetrical lobe on the exhaust. It also could be symmetrical in both, asymmetrical in both, or any combination of these types of profiles.

Some links for you ::wrench:

http://www.hotrod.com/techarticles/113_9811_camshaft_tech_valve_timing_piston_movemen t/index.html (http://image.hotrod.com/f/9542979/113_9811_cam02_z.jpg)



[URL]http://www.hotrod.com/sch/02/derterming-overlap-on-a-camshaft/articles/index.html

[joseph m. hahnl]

So what I have gathered. Is that by changing the ratio on the rockers you can gain lift with out altering duration and overlap.:wink:

[BUIZILLA]

So what I have gathered. Is that by changing the ratio on the rockers you can gain lift with out altering duration and overlap.:wink: nope, if you open the valve earlier and close it later with a taller rocker ratio then it DOES affect lift and duration..

[joseph m. hahnl]

nope, if you open the valve earlier and close it later with a taller rocker ratio then it DOES affect lift and duration..

I see, because it's global movement.


you can't compare these two cams using those numbers, the first one shows numbers probably at .050 lift and the second is showing *advertised* numbers, which in the real world don't mean sh1t... you need to compare grind numbers using either .006 or .050 lift equally, then take into consideration the lobe seperation numbers... there is nothing special about marine cams, it's just the choice of lobe grinds in the same catalog or library... auto engines have been using seperation numbers from 111-118 for years, the tighter the LS numbers with a given duration, the choppier the idle manners and the more concern for any reversion characteristics... you can use the exact same lobe profiles on different LS numbers and change the manners drastically... the shortened 10 or 14 part numbers shown are the LS numbers, in this case 110* or 114*...


Ls stands for lobe seperation? so in this case with 114* And 110*,
these are included angles? meaning the 114* LS would have less overlap than the 110*?

[BUIZILLA]

If the lobe center of the camshaft is increased, the valve overlap will be decreased. The overlap decrease is created because the exhaust timing will occur earlier and the intake timing event will occur later in relation to crankshaft position. Conversely, if the lobe center or displacement angle is decreased, overlap increases. Note that lobe center cannot be changed once a camshaft has been ground.



I see, because it's global movement.

Ls stands for lobe seperation? yup
so in this case with 114* And 110*,
these are included angles? meaning the 114* LS would have less overlap than the 110*? yup

[Barry Eller]

Buzilla, here is a list of ComCams offered by CP Performance. I purchased my cam kit from them. I am pasting a section of their HP500 style cams they offer. My cam is part no. 295-012008.

With my GIL Dry Offshore exhaust, reversion is not a problem, and I do have the turbulators for any condensation.

http://www.cpperformance.com/products_comp_cams.aspx

HARDIN/COMP Custom Ground Hydraulic Roller Cam Kits and Retro Fit Roller for B/B Chevy
Note: " K" Indicates Cam & Lifter Kit Part Number - These kits include: camshaft, hydraulic roller lifters, valve springs, retainers, valve locks, seals and assembly lube.
Hydraulic Roller - perfect for a customer seeking HP 500 style performance with a silent choice style exhaust system. Gen 4&5 295-111008 295-111008K 284 284 224 224 .566 .566 112°
Gen 6 295-011008 295-011008K
Hydraulic Roller - this is an incredible camshaft for your late model 454/502 Magnum EFI engine, big power going, yet still EFI compatible Gen 4&5 295-112508 295-112508K 283 290 223 230 .566 .575 114°
Gen 6 295-012508 295-012508K
Hydraulic Roller - this is an upgrade to a HP 500 cam providing maximum torque and horsepower from a long riser wet perf. exhaust Gen 4&5 295-112008 295-112008K 286 294 226 234 .591 .601 112°
Gen 6 295-012008 295-012008K
Hydraulic Roller - great supercharger cam designed for 540 and larger engines, requires dry offshore style exhaust Gen 4&5 295-113008 295-113008K 318 329 252 262 .612 .612 114°
Gen 6 295-013008 295-013008K
Hydraulic Roller - now we're talking large supercharger, 10 lbs. of boost, 540 to 650 C.I., capable of making big HP and still idle. Gen 4&5 295-114008 295-114008K 318 329 256 264 .657 .612 114°
Gen 6 295-014008 295-014008K

[mrfixxall]

Doc! your cam specs.




MERCRUISER # 431-850478
.004 300*/ 300*
.006 288*/288*
.050” 224*/224*
.200” 125*/125*
Lift .483”/. 483”
ICL 109*
LSA 115.5*

[Dr. David Fleming]

mrfixx

Well now that I have graduated from Dr. hahnl's cam university I feel much better. At least I know about lobe separation angle and lobe centerline etc. I still think we are chasing the exhaust closing event. If Dr. hahnl is really serious I am sure he could turn up a few SAE engineering papers on marine cams. That would be great.

What is Mercruiser 431-850478?

.004 lift 300*/300*
.006 lift 288&/288*
.050 lift 224*/224*
.200 lift 125*/124*

valve lift .483/.483
ICL 109*
LSA 115.5*

This is the data I have:

454mpi - intake/exhaust lift - .284/.284
intake/exhaust duration - 209*/209*

454/502MAG MPI - intake/exhaust lift - .342/.342
intake/exhaust duration - 211*/227*

500EFI - Crane Cam 169621 grind HR 292-2S-14 1G
intake/exhaust lift - .352/.359
intake/exhaust duration - 292*/298*

500HP - Crane Cam 169611 grind HR 284-2S-10 1G
intake/exhaust lift - .339/.352
intake/exhaust duration - 222*/230*

[joseph m. hahnl]

mrfixx

Well now that I have graduated from Dr. hahnl's cam university I feel much better. At least I know about lobe separation angle and lobe centerline etc. I still think we are chasing the exhaust closing event. If Dr. hahnl is really serious I am sure he could turn up a few SAE engineering papers on marine cams. That would be great.

What is Mercruiser 431-850478?

.004 lift 300*/300*
.006 lift 288&/288*
.050 lift 224*/224*
.200 lift 125*/124*

valve lift .483/.483
ICL 109*
LSA 115.5*

This is the data I have:

454mpi - intake/exhaust lift - .284/.284
intake/exhaust duration - 209*/209*

454/502MAG MPI - intake/exhaust lift - .342/.342
intake/exhaust duration - 211*/227*

500EFI - Crane Cam 169621 grind HR 292-2S-14 1G
intake/exhaust lift - .352/.359
intake/exhaust duration - 292*/298*

500HP - Crane Cam 169611 grind HR 284-2S-10 1G
intake/exhaust lift - .339/.352
intake/exhaust duration - 222*/230*


Wasn't sure if you were busting my chops with the Dr. thing?
I was serious about trying to help. There's not a lot of info on marine cams, as I'm sure your aware. You did want to now about the overlap .From what I have gathered from Buiz and the limited reading that I have done, As i don't want to make it my career, is that the crane cam 500 hp is @ an included angle of 110* the 500 efi is at 114*. I read an article that stated the 110 is middle of the road and pretty common

If you notice the efi cam with higher lift has less over lap by having the Lobe seperation @114*

Yes, No, I hope that helps some

[The Hedgehog]

I think that this is a good conversation for all (but then I have had a few drinks with a client).

One thing I would like to add is that reversion is also driven by bigger heads and displacement (or at least one). Basically bigger flow = more suction in and out.

[Walt. H.]

One thing I would like to add is that reversion is also driven by bigger heads and displacement (or at least one). Basically bigger flow = more suction in and out.
Well put Hedge!
Now the girls are gonna start paying attention reading between the lines when you say, just stick that big ol'e bump stick in and don't worry about the little details of what might or might not happen. Just don't keep her idling to long or too low.
:rock:
Ya gotta break a few eggs to make a good omelette. :rlol:

[gero1]

there's a marine place in tx that does alot of projects,changing headers n dyno testing and they always post the dyno sheet. i cant remember the web site but some one on here will know it. my bad i lost the icon

[VetteLT193]

One more to throw in the Mix is the 169731 cam. When I did research it seems that it is what most people upgrade to when they rebuild a 500. Grind # HR-226/345-2S-12 This is the cam Eddie is running in his 500.

[Barry Eller]

I found this Mercury Service Bulletin...right click on the x, then click open the link

http://www.pdfoo.com/view_image.php?p=/large-img/p34/289/10390.jpg

[Dr. David Fleming]

Dr. hahnl,

Thanks for the LDA specs for the Crane 169621 and Crane 169611.

It is surprising that with all the trouble they had with the 169611 - duration 222*/230* LDA 110* that Mercury went to 169621 - duration 292*/298* LDA 114*

This is a seriously more radical cam - 169611 was known to revert water easily and 169621 did not. The lobe displacement was almost the same and the duration figures much greater in the 500EFI.

Obviously they got an answer here to the water reversion but what did it?

It is also surprising to me to see how close the stock 502MAG MPI cam is to the 500HP cam.

502MAG MPI - specs out as

duration - 211*/227* (@.50)
lift - .343/.342
LDA - ???*

HP500 - Crane 169611 - specs out as

duration - 222*/230* (@.50)
lift - .339/.352
LDA - 110*

500EFI - Crane 169621

duration - 292*/298* (@.50)
lift - .359/.359
LDA - 114*

In summation at looking at these three cams -

The 502MAG MPI and 500HP cams differ in only 10* intake duration and .005/.010 cam lift.

The difference between 500EFI and 500HP cams is much more significant. These cams differ in intake and exhaust events by an increase in duration of 70*/60* and cam lift of .020/.007. Lobe displacement angle changes by only 4*

Exhaust valve lift changes on all three engines by only .017.

Mostly they are messing with the intake valve lift and major overall duration differences between 500HP and 500EFI.

As I said the HP500 and the 502MAG MPI cams look similar - but do they have similar water reversion issues? I haven't heard much from anyone with the 502 and problems with headers.

And of course we don't have any information on the use of asymetrical lobes on the Crane 169621 or any of these cams.

Sure would be nice to see a LDA on the 502MAG MPI cam.

[maddad]

DR.d, there is something up with the duration numbers you put up there last. There is no chance that they speced a cam with 290+ duration at 050 lift. That sounds more like a "advertised" number. You can't compare these cams until all the data is from the same place.

[Dr. David Fleming]

maddad,

You are correct I used the wrong spec table for the duration of the 500EFI figures. Others were correct. 500EFI duration is 230*/236* @.050 lift on the tappet. 500EFI duration is 284*/292* @.004 lift on the tappet. All these specs are taken from Crane Cams grind profiles on their website.

Variation between 500HP valve duration and 500EFI duration is 8*/6* not nearly so radical. Variation between 502MAG MPI and 500HP is the 11*/3* intake and exhaust I pointed out.

I also noted on the cam cards that the closing event for the exhaust valve @ .050 lift is at 0* BTDC (before top dead center) on the 500HP. Exhaust closing event for the 500EFI @ .050 lift is (1.0)BTDC.

This confirms my guess that marine cams are very un-automotive in design as most cars close the exhaust valve after TDC (ATDC) while the piston is on the intake stroke. Here in the marine engine the exhaust is closed before the piston starts downward and I assume the (1.0) means the 500EFI closes the valve before TDC. (BTDC) This is to keep the suction of the pistons from drafting the exhaust in reverse.

I guess it is surprising that all these cams are somewhat similar at least with regard to automotive cams which can vary wildly with speed and horsepower. Cam selection is tricky because some engines will respond to certain valve activity and some not. It is very easy to get all of the disagreeable aspects of a racing engine with out the benefits of its power. The right camshaft makes a world of difference in usable power, power range and fuel efficiency and general nature of what they are like to drive.

No single variation in an engine produces such a radically different type of operation than the camshaft.

I guess one of the amazing things to me are the number of major off shore boat builders that provide Mercury Racing engines (blue motors) for use by the general public in recreational hulls. Yet the engines are still champions at the track - you sure won't see that in automotive.

Another surprising thing is the Mercruiser 454/502MAG MPI is so generically similar to Mercury Racing 500HP and 500EFI. Aside from a few degrees of cam duration and exhaust headers and slightly better valve gear components, the engines are remarkably similar. Yet they can vary in horsepower by 10-30%. Yet one is in everymans cruiser and the other is in everymans race boat.

ONe would hardly expect the engine of the NASCAR stocker to be so similar to that in his Chevy Tahoe.

Who is Maddy anyway?

[maddad]

Dr.d, Maddy is my daughter Madeline. I call my 18'er Maddy's Daddy's. I came up with the name 11 years ago to keep my then pregnant and raging wife from making me get rid of that piece of junk that was in the yard to long. We'd already decided on the name and it just came out.

[VetteLT193]

This is a seriously more radical cam - 169611 was known to revert water easily and 169621 did not. The lobe displacement was almost the same and the duration figures much greater in the 500EFI.

Obviously they got an answer here to the water reversion but what did it?



110 to 114 lobe separation is not close IMO. 115 degrees is smooth idle. (stock 502 mag is 115.5) 112 degrees you'll start getting some lope. 110 degrees is a not so smooth idle. Most people that own street/strip cars won't go past 110 to maintain drive-ability.

There are other factors that also affect idle but it's a good start to look at lobe.

[Dr. David Fleming]

Vette,

THanks for the Lobe Separation Angle on the 502 MAG MPI cam - where did you find it? I would like to have the cam card on the cam.

I did talk to Crane today. They can grind 169621 for me for $429 bucks and have it in 5 days. This is a lot cheaper than the $839.49 that Mercury Racing wants for it.

The core for this cam is unusual according to John who works there - because of the unique lobe separation and the BTDC closing of the exhaust valve. This is what makes that cam unique in not reverting water.

Crane aparently is back in business and WILLING TO, WANTING TO and WATING TO make all the cams.

Sounds like good news to me.

[The Hedgehog]

Well then buy that cam, do those heads and let those CMI's flow some good tunes. And don't even think about that cam without doing the heads.

[mrfixxall]

110 to 114 lobe separation is not close IMO. 115 degrees is smooth idle. (stock 502 mag is 115.5) 112 degrees you'll start getting some lope. 110 degrees is a not so smooth idle. Most people that own street/strip cars won't go past 110 to maintain drive-ability.

There are other factors that also affect idle but it's a good start to look at lobe.


not true! the cam we run in the 2001 c6 corvette with a 740 bbc is @ 116* lobe separation and trust me it sounds like a prostock!...so the higher the lobe separation is doesn't necessarily mean its a smoother idle...its all the the duration timing built into the cam is what gives you the rough to smooth idle..the lobe separation has a little to do with it but not as much as the duration does..

just my o2

[mrfixxall]

Vette,

THanks for the Lobe Separation Angle on the 502 MAG MPI cam - where did you find it? I would like to have the cam card on the cam.

I did talk to Crane today. They can grind 169621 for me for $429 bucks and have it in 5 days. This is a lot cheaper than the $839.49 that Mercury Racing wants for it.

The core for this cam is unusual according to John who works there - because of the unique lobe separation and the BTDC closing of the exhaust valve. This is what makes that cam unique in not reverting water.

Crane aparently is back in business and WILLING TO, WANTING TO and WATING TO make all the cams.

Sounds like good news to me.


Doc!! crane is not what they use to be.............im telling you call BOB mandara and talk to him,his custom cams are ground on the best blanks money can buy....585-654-8583.............................................. .....

Also if your going with a bigger cam all your doing moving your operating rang up,,if you really want to take advantage of the cam you need to do head work and bump the compression..

[VetteLT193]

not true! the cam we run in the 2001 c6 corvette with a 740 bbc is @ 116* lobe separation and trust me it sounds like a prostock!...so the higher the lobe separation is doesn't necessarily mean its a smoother idle...its all the the duration timing built into the cam is what gives you the rough to smooth idle..the lobe separation has a little to do with it but not as much as the duration does..

just my o2

That's why I said good start... not always the factor but a darn good start generally speaking :wink:

[VetteLT193]

Vette,

THanks for the Lobe Separation Angle on the 502 MAG MPI cam - where did you find it? I would like to have the cam card on the cam.

I did talk to Crane today. They can grind 169621 for me for $429 bucks and have it in 5 days. This is a lot cheaper than the $839.49 that Mercury Racing wants for it.

The core for this cam is unusual according to John who works there - because of the unique lobe separation and the BTDC closing of the exhaust valve. This is what makes that cam unique in not reverting water.

Crane aparently is back in business and WILLING TO, WANTING TO and WATING TO make all the cams.

Sounds like good news to me.

I will try to find the specs again, the 15.5 number comes from memory so don't quote me until I can find the specs. It seems to stick in my head because I can't remember seeing a half number on lobe ever before. I had done the research on this when Eddie was going through the last cycle of rebuilds. He seriously considered going back to full stock on his boat or some flavor of stock but then Cuda had that HP500... then he upgraded that a bit after a bunch more research and parts finding...