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View Full Version : 355 cid install and exhaust......



Donziweasel
08-02-2008, 10:01 AM
I have had my new engine in for over a week. Here is a couple of pics, but it looks a lot like my old one. Here's why- The nice shiney valve covers did not fit with my exhaust manifolds, so I had to use the stock Merc ones. The intake is black, but is also a Mercruiser, but looks like a dual plane. Came with a MSD distributer that was as high, if not higher, than the carb post. I was really concerned that the hatch would not clear it, I had less than a 1/8 of an inch. Anyone know what kind of Merc manifold that is?

Now I have about 7-8 hours on it and it has broke in nicely. Before I was getting 56 mph @ 4550 rpm with a 19 pitch Vengence and 1.65 gears. Now, getting 61 @ 5100 rpm's with same prop and gears. I guess I have two questions- First, now that I have a 380+ hp 355 CID SBC, would a performance exhaust help that much? I know on a stock engine they have very little effect. I know 380 hp is not that much in regards to some SBC being built, but 2-3 more mph would be nice. Any thoughts?

Second, although I don't mind the 19 Vengence, it definetly has some weird characteristics. Main issue is chine walk over 57 mph. Even driving into the torque, it still walks, and can walk violently if you steer out of the torque. Dropping a little tab settles it down, but also take a few mph off top end. I talked to MP about it and he said he thought a 20 pitch Turbo 1 might settle it down. He also wanted to go one pitch higher as Turbo's will pull more RPM's than the Vengence on the same setup. I think 5100 rpm is about right for this engine. Randy, need to give you a call, but been really busy, will try this week. Can you pm me your phone number?

Other than that, the install went fine with just a little creativity in some areas. Oil PSI is 60 when running, 25-30 at idle. The mid and upper range is amazing. Run 3000 rpms and drop the throttle, the boat JUMPS and pins you in your seat. Scary acceleration. Seems to have good torque curve from idle to 5100. Really happy with the engine and if you are lookng for a crate, I highly recommend Blue Print Engines (also came with a 1 year warranty).

Sold my old engine (350 with 260 hours, Comp Cam, Vortec Heads, Edel Manifold, Holly DBL Pump, probably around 330 hp) for 2000.00. Cost of new engine- $2500.00. $500.00 and some sweat equity got me into a new engine (engine is new, not reman or rebuild). Really happy. Now, how fast will she run at AOTH with 20% more ponies? Anyone want to place wagers? I would think 65 ish, maybe more. Damn altitude and damn bilge to small for a blower.:)

gcarter
08-02-2008, 10:33 AM
Good work and results.
I'm amazed it runs so well at your altitude.
I'm sure there're better props for you. No need to scare your guests, or yourself for that matter.

The Hedgehog
08-02-2008, 10:33 AM
Nice looking setup. You should be happy.

I would think that it will run the heck out of 65. Maybe more. I doubt that you will see very much by doing the exhaust. One benefit to note is that you will save a good bit of weight thus getting more of the hook out of the water. That will help some with the chine walk issues.

I like the idea of a SM system. It would look nice with the Q&Q, lighten up the back and would help the throttle response even more. Who knows, you might even gain a couple of hunderd RPM.

VetteLT193
08-02-2008, 10:46 AM
regarding exhaust, check out the other thread about the 7.4 exhaust. MJ said he gained 100 RPM on his stock 310 HP 454 by going to the GLM aluminum.

It's all about cost/benefit in my opinion. The GLM in your situation would probably be worth it... or find a good used set of Stainless or EMI. It took me a while to find a used set for Small Block, but if your current manifolds are fine you have time to search.

BigGrizzly
08-02-2008, 11:14 AM
On that engine I can say that Stainless marine will help. as for the prop I still have the 20 inch prop you returned and a couple of larger ones of different typs. As for speed The prop you ate using is far from my favorite on a 16 or an 18 classic. I have done many tests on them with various engine combos.

mrfixxall
08-02-2008, 11:45 AM
Prop turbo one or a txp if yo can turn it:) most merc stuff comes from gm and gm get their stuff from edlbroch.. so the answer to your intake question is its probably a edlbroch performer intake with mercs name on it..edlbroch makes most of gms alunimum cylinder heads also..looks good and its about time you hit the 60 mark:D

Donziweasel
08-02-2008, 12:02 PM
Thanks for the advice everyone.

Randy, what have you found are the characteristics and speed differences between the Vengence and Turbo?

BigGrizzly
08-02-2008, 12:11 PM
Got your PM and I am here.

smokediver
08-02-2008, 06:40 PM
1.65 gears with that set up and horsepower ... hmmm .... I am thinking 23 mirage plus ... labbed if you can ... would be a nice bet ... i was turning a 25 with a 1.47 and a few more ponies ... i bet when you get to sea level u r gonna need at least a 23 if not a 25 ... top speed my guess is gonna be 69 or 70 ... if you can turn the 25 ...

Donziweasel
08-02-2008, 07:44 PM
I think it would turn it, the engine is STRONG. Can't wait to get get below a 1000 ft.

ITTLFLI
08-02-2008, 08:57 PM
Looks good DW!.....Good results as well!

kd5cue
08-02-2008, 09:46 PM
Looks good DW!.....Good results as well!i was looking at specs on there web site for that motor looks like most torque is around 4500-4600,,,that where i would prop too:popcorn:

The Hedgehog
08-03-2008, 08:08 AM
I am thinking it should be propped for maybe 5,100 - 5,250. From what I have been told is you don't want it to max at the peak of the torque curve. You want to go a bit past there but you also don't want to prop it out to where the torque curve falls off dramatically. You also don't want to leave a bunch of hp on the table.

When I was doing some prop testing, I noticed that I go most slip around peak torque. At least on V-hulls.

I would be interested to hear what the experts say.

BigGrizzly
08-03-2008, 08:37 AM
Since you asked and others will be looking I will give some insight. The vengeance was a haphazard idea that was designed around a 17 degree v hull, not a deeper hull. It tends to chine walk on deeper Vs and some flatter hulls. Because because og the type of blade pitch progression it has some funny slip characteristics on heavy deep hulls. This causes a hydrodynamic inefficiency. So my educated response would the Turbo and possibly certain Solas props would actually be faster at the same RPMs. When we tested them at Honda, they faired at the bottom of the list on our boat and motor combos. This is not saying it is a bad prop but I have always found something better

BUIZILLA
08-03-2008, 09:38 AM
I would prop it to 100 rpm past the peak HP point, not the peak TQ point...

YMMV

Donziweasel
08-03-2008, 09:43 AM
Here is the dyno sheet-

http://secure2.digitalims.net/blueprintengines.com/orders/photos/dyno_charts/MBP3550CTC_large.jpg

It is still creating 410 ft-pd at 5100. Granted peak is around 4700, I am with Hedgehog, want to go a little past that. 20 Turbo should be about right I would think. Randy, I also agree about the Vengence. The Turbos I tried last year did not chine walk near as bad above 55 as the Vengence. When it did, you could "drive through it". Not with the Vengence! Try and drive through it without backing off the throttle or throwing a little tab and you are in trouble! When I say violent, I mean it is VIOLENT.

Was out yesterday and got into it with a 24-25 ft Eliminator. I was catching him before the walk took the fight out of me. It is hard to believe a 380 horse 16 can run down much bigger and supposedly faster boats. The fact is that altitude works in different ways with different engines. NA vs. Blower, NA falls off faster in power up here. ALSO, BBC vs SBC, BBC falls of much worse, especially carbuerated. Simple really, the more air an engine needs up here, the worse the fall off. Technically, a 4.3 Mag 220 horse will outrun a 5.0 Mag 260 horse up here, go to sea level, the 5.0 wins. Bring a 496 HO 75 mph 22 up here and it will be a close race between the 2 of us. You will struggle to break 63 mph. Your 425 ponies is now less than 330.

smokediver
08-03-2008, 10:18 AM
are you sure on your drive ratio ? i think you have a 1.47 or 1.5 ... not the 1.62 or 1.65 ....

The Hedgehog
08-03-2008, 10:32 AM
I know that it is an 18 but I really like the way a Turbo handled on mine. It really settled down. I did not think that the M Plus was bad, just liked the Turbo much better.

I still don't know why more folks don't use boost on higher altitude lakes.

Donziweasel
08-03-2008, 03:12 PM
I changed the gears from 1.47 to 1.65. I have owned 8 boats out here and everyone I had to change the gears. Before the change, I was turning 4500-4600 with a 19 pitch on the old engine and 4700-4800 with a 15, which was still well over 300 hp at sea level.

For us high altitude guys, setting up a boat is a match between prop, drive gear and hp. All boats come from the factory set up for sea level and will lose 20% or more hp off the bat (some, much more, like my old 7.4 330 horse in a 1997 21 ft Milan. Could barely get on a plane). Most people only have to play a little with props, and I have tried just propping vs. propping and gears. You end up with a 15 pitch or lower. Boat does come out of the hole nice though.:wink:

Rootsy
08-04-2008, 09:42 AM
FWIW, ask Sam Pilato how much he gained by installing SM on his warm 350 in his 16....

Donziweasel
08-04-2008, 10:06 AM
I wouldn't think too much hp, but, stock Merc manifolds way a TON. Could shave some serious weight off the ass end. Might make it handle better too.

I am real happy with the boat right now and don't want to put too much into it as in the next year or two I am moving up to a 18. Boo Boo likes the 18 more than the 22 and since I am torn between the two, I let her decide. Before I even take delivery, it is getting a blower, not going to fight hp loss on this one.

On that note, I will be selling this 16. If anyone wants me to let them know when I am ready to sell it, let me know. 1997 in great shape. 270 hours on the hull, 8 on the engine. Would run 65+ at sea level I would think (might even get upper 60's, or 70 with right prop). Captians call, stereo, trim tabs, etc.....nice Donzi.

Jamie, just out of curiosity, how much hp did it take to break 80?

Donziweasel
08-04-2008, 10:12 AM
I know that it is an 18 but I really like the way a Turbo handled on mine. It really settled down. I did not think that the M Plus was bad, just liked the Turbo much better.
I still don't know why more folks don't use boost on higher altitude lakes.

It is catching on, but the biggest problem is someone to install, tune and service one. Closest place to us is Salt Lake City, 300 miles away and they are at a lower elevation.

BigGrizzly
08-04-2008, 10:14 AM
As for drive gears vs. prop size it is always better to run a prop with more pitch instead of less pitch and more prop RPMs (to a point). On most current pleasure craft hulls-deep Vs especially things get weird above 32 pitch (singles are particularly bad. The smaller pitch props tend to loose efficiency at high prop RPMs.

Donziweasel
08-04-2008, 10:21 AM
I have never been able to run above a 21 pitch on anything out here, and even that is a little high.

BigGrizzly
08-04-2008, 10:30 AM
The point is changing the drive gears was the smart move. If we gear it to use a 15 pitch then gear it to use a 20 pitch. The 15 will come on a plane faster but will be slower top speed and will have worse fuel economy. Now if we are comparing a 25 to a 27 the difference is insignificant. I have proved this many times.

Rootsy
08-04-2008, 11:34 AM
380 at the prop or so (figure 30 - 40 hp loss through the drive)... and an Alpha SS... the SS was worth 8 - 10 mph alone. I was buzzing her way up around 5800 rpm or so... It was fun but still would get away from you if you didn't drive it...

Saw mid 68 mph with the Alpha Gen II and a bit less HP but I had all I could do to hang onto it and still maintain some feeling of actually having "fun" while doing it. It was a real handful, white knuckled ride... That I don't care to repeat.

The 16 was fun but unlike DougL's 18 with about the same HP as above and an SS that'll run low 80's and feel like a caddy cruising down the highway at speed...

Donziweasel
08-04-2008, 08:07 PM
Looked everywhere for over a month for an SS. MP has one I might be able to "borrow" for a while. Would probably push my boat into 70 mph land.

I like my 16, but like yours, it is a handful. It definetly has a very high fun factor driving it. I feel that it is a good boat for a younger person. My back takes a beating in it and our lakes can get rough. An 18 is definetly in my future.

Rootsy
08-05-2008, 10:45 AM
And as I said before, if you were listening to me... you CANNOT just bolt an SS onto your Gen II transom assembly. There is machining and epoxy work that needs to be done to the existing Gen II transom assembly bell housing. You need a Gen I style upper shift shaft and you need to make 2 spacers for the rear trim cylinder cross rod that goes through the drive.

I engineered it and did it to mine and I also did it to Sam Pilato's Gen II transom assy... It must work as he is still running his and I haven't heard a negative thing from him about it.

Donziweasel
08-05-2008, 10:51 AM
I know and was ready to take the plunge if I had found one. Was going to be a winter project. If it had happened, I knew we would be talking some this winter!:smash::wink::)

I figured it out from threads of you talking about your 16, the trippledigits thread (remember, he supposedly cut a alpha down 1 inch higer X than an SS and then ran 700 hp through it) etc.... Still, even with the work, seems like a good way to pick up speed.