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Secret F233
03-25-2002, 11:34 AM
My brother in law is wanting me to get a Chevy 400 block & build a destroked motor out of the 400 block & my existing 350 5.7L. Has anybody here tried this & what are the advantages to a destroked engine I really have NO IDEA :confused: thank you?

I'm at 4000lbs dry w/a Stringer 800 drive?

BERTRAM BOY
03-25-2002, 06:08 PM
It's funny that you posted this question now. I just came across an article from an old "Chevy High Performance" magazine(Oct 2000).
They do a comparison between a destroked 400 using a 350 crank(377) and a 383 stroked 350.
Here are the results,I hope you guys can read this.
BERTRAM BOY :D :D :D

http://www.donzi.net/photos/cwind03.jpg

BigGrizzly
03-25-2002, 08:13 PM
Geez isn't the Merc Scorpion engine a 377 cid.
The number are good, but what is the real life power in a boat. I would go the 383, need the grunt ot ypu'll twist it to 6000 amd tan out goes the drive. In my race rngines I do big bore and short stroke keeps piston speeds down, however my street stuff is the other way.
Randy

MOP
03-25-2002, 08:51 PM
Being and old fart boat mechanic of too damn many years keep your RPM down on boat engines. They last longer, with the help of the guys up here you can make it run. You can pump a lot of torque, prop it a little under 5K light that should still hold you for a load. Remember lower piston speeds less heat, less wear and tear. You can E-Mail any cam company you like and let them spec a cam for your application, they usually do a good job.

Phil / Long Island

Looped
03-25-2002, 08:54 PM
Randy,
I think that the Scorpion setup just so happens to be a coincidence with the CID figure. I’m pretty sure that the Scorpion 377 is a standard bore 350 (4.0” bore) and a 383 type of crank in it (3.75” stroke) making it a 377 cid engine. Here is the math for it:

Number of cylinders x 0.7854 x bore x bore x stroke = CID
8 x 0.7854 x 4.0 x 4.0 x 3.75 = 376.992 <- fixed a user glitch :D
After rounding it off it comes to a 377

So it’s basically a non-bored 383 sbc.

CDMA
03-25-2002, 09:00 PM
Looped that is right.

Chris

Looped
03-25-2002, 09:36 PM
Chris thanks for backing me up, it's been a while since we talked about the Scorpion engine on this board so I wasn't sure.

As I've been told many times, always go for the longest stroke so that you can get the best torque out of the block. That is why I went for a bored 30 over 350 block and the 3.875" crank making it a sbc 395 but I like to call it a stroker 396 :D . If Chevy can forget to tell the public back in late 1970 that they bored the bbc 396 0.30 over and made it a 402 cid without telling anyone and still keeping the 396 tags I think I can get away with a .08 cid slip. :D :D

AVickers
03-26-2002, 09:31 AM
The old 302 CanAm Chevy engine (remember the Z-28 in 68?) was a "destroked" 327 (2-bolt 327 block, 265/283 small-journal, forged crank). In the next couple of years they went to a large-journal block/crank -- the crank was proprietary to the 302. This was a great high RPM 5L engine that was a gas to drive, but it really made its power when it was wound up tight -- probably too high for most marine applications. (It also had a lot of valve overlap that would be difficult, given the wet exhaust systems on our boats.)

The 307 (another late-60s engine), on the other hand, was a 283 block with a longer-stroke 327 crank.

Same general capacities -- very different engines. A good 327 would out-perform either (except at extremely high revs). A good 350 will out-perform them all in a number of ways -- 350s make good power, after-market parts are plentiful and relatively cheap -- especially at around 5000 RPM.

It would seem that the best overall power producer for a boat from a small block (limiting yourself to something like 4500 -- 5000 RPM) would be a 400...if you could find a good block. The only problems I can think of is that there might be cooling problems, given the siamesed cylinders and the engine is externally balanced.

Short of that (and at the RPM range suggested for outdrives), it would seem that a stroked 350 would be better to have than a destroked 400.

Looped
03-26-2002, 10:11 AM
Yup, the 302’s were great motors. I have a “010” block with a 3” “822” crank setup down stairs waiting for another project. After I bought it I found out that the torque would not be there for marine use so it’s just sleeping for now :D . You can tell if you have a real 302 crank by a notched out area on the outer flange.

Remember, never get ride of anything because you will always find a use for it later on…… :rolleyes:

GEOO
03-26-2002, 01:21 PM
Looped, 396 Cool, a 3.875" Crank. Sound's like a tight package. What cam, heads, rods, carb or injected? Tell me more!!! GEOO

Looped
03-26-2002, 02:16 PM
Geoo,

I bought another 3970010 350 4-bolt race prepped block from an ex-strictly stock race car owner, Thunder Racing forged 4130 crank, 6” rods are required so that I don’t get into any machine work on the block for clearance but I have not decided on “H” or “I” beams(only a few will clear), I have new Vortec “062” heads and will probably go with Comp Cam Magnums for roller rockers. I have not bought the cam/lifter setup yet but chances are it will be a Comp Cam roller/hydraulic combo and maybe gear driven timing. It will be a performer intake/carb setup but I have not gotten that far yet.

Having to buy almost every single part for this restore (nothing really usable) I am all over the place on buying parts for this thing. If I see around 380 – 400hp I will be more than happy. I will not have the motor put together until the restore is close to being finished so that it will be freshly built and not sitting around for a while and not turned over.

Finding out that my Contract is over in the next Month or two for my job, it kind of put a freeze on buying big parts for it until something else comes around.

Secret F233
03-26-2002, 03:16 PM
WOW great Information & Ideas keep it comming Im learning a lot now !! :D

GEOO
03-26-2002, 04:09 PM
Sound's like a fun project. I think my old 383 with a 3.75" crank needed some block grinding? Double check all your clearances. GEOO

Secret F233
03-26-2002, 04:24 PM
This is gona ROCK i can't wait to show this stuff to chad thanks again & keep it coming!! :D :cool: :D

BERTRAM BOY
03-26-2002, 05:19 PM
Madpoodle and anyone else who cares, here is the parts list.
BERTRAM BOY :D :D :D

http://www.donzi.net/photos/cwind04.jpg

Looped
03-26-2002, 08:51 PM
Geoo,
What I meant was there are a few rods made that will clear all areas of the block and if it gets too close I can grind down part of the screw caps (just a wee bit) to make enough clearance if need be (the pan maybe a different story).

Having to buy everything from deck parts to engine parts to fuel lines, I’ve just been bouncing around with whatever part I get at a good price at the right time. Sure is going to be a mess when it comes down to crunch time with all of the little parts I forgot to buy. eek!

Craig

MOP
03-26-2002, 10:11 PM
Had to stick my 2/Cents in again! If you think about it the real issues you dicide, $$ first then go for a little longevity or go for more speed what ever your buget will handle. Being and old OMC mech that 800 I have seen hooked to some pretty big stuff. If the 800 has much time on it get it torn down and checked out. If its got 400 to 600 hours its due.

Phil / Long Island

Looped
03-27-2002, 07:45 AM
A few of the well known rod manufactures state that certain 6" rods that they make will clear a 350 block with a 3.875" crank. For crucial things like this I will have the machine shop decide on what’s best and you're probably right. What the heck do I know; I’m just along for the ride on this one.

Forrest
03-27-2002, 10:38 AM
To do a 383 you will need to grind some clearance in the block for the rods in areas near the bottom of the cylinders. One reason to grind a little from the corner of the big end of the rods is for cam clearance, otherwise you may need to go to a reduced base-circle camshaft which is somewhat prone to breaking. You must rebalance after removing any material from the rods.

Also, consider that with a 400 block you will need to run a closed cooling system since marine head gaskets don't exist for that block. 350 blocks are cheap and plentiful.

For those who don't know, a 350 block with standard bore (4.000") with a 400 crank measures out to 377 cubic-inches. The 383 is the same but bored to 4.030", which is what you usually see. Since Mercruiser uses new blocks that are standard bore, their stroked small-block engine measures 377 cubic inches.

Secret F233
03-27-2002, 10:41 AM
NICE!!! Thanks fella's you guys have this down to a science :D ...

CDMA
03-27-2002, 11:05 AM
Now this may be dumb but I am just shooting from the hip. If you toss out the displacment advantages isn't the stroker better because the "arm" of the crank is longer hence more torque....inquiring minds want to know. :)

Chris

AVickers
03-27-2002, 11:36 AM
That's the point. When you "stroke" an engine, you're installing a longer crank arm. Given the same area of the piston top (to receive the pressure of combustion), this gives you more torque.

Unfortunately, nothing is free... At a given RPM, you have to move the piston farther. This requires a higher piston velocity which eats up energy accelerating and decelerating the mass of the pistons and rods. It also limits the upper reaches of RPMs (where horsepower is made) in that at some point, longer-stroke engines just can't turn as fast as short-stroke engines -- all other things being equal. In some cases, it also changes the relationship of the components -- rod length and piston-to-rod angles at mid-stroke are also factors in engine design that limit what you can do. Clearance is also a potential problem -- note rod bolt pads (for cam clearance) and slots cut in the bottom of the cylinders (for rod clearance) in the 400 SB.

BigGrizzly
03-27-2002, 09:06 PM
RandyI won't tell you but I know why Poodle knows this. The rpm thing is a mute point at this point with any current production outdrives at this time. I saw pieces of a 6300-RPM Bravo1 last week. The boat now has a complete Imco outdrive on it now- nice piece of equipment.

If you look at Cliff's chart the Realistic 5000->5600-RPM data The HP and torque are so close there is no usable difference. Now go to the 3000->3600 RPM Cruise data. Now make your own conclusion. For me the 383 has it in he real life usable engine power. In the real world would be more practical faster(all around) and efficient

Randy