destroked 3.4l "3500"

[Driver_10]

I had originally purchased a set of custom pistons that would accomodate a 5.7inch "4.3l" chevy rod with the hope of a simple build.

I figured that since the 3500 and the 4.3l have the same pin diameter and width, there would'nt a compatability issue. (both have "crank-pin"2.249-2.250 dia and .940 rod width)

Well guess what...After I went and purchased the rods, I soon discovering that the rods were offset and unusable in a 60 motor. So no Im taking a different approach. I decided to to use a 5.850 SBC rod and .070 copper head gaskets. The SBC "large journel" rods use a 2.100 "pin-dia". This gives me a total difference of .150 crank-pin diameter to play with.

The plan is to destroke the steel 3500 crank "3.310" down to "3.192" which will leave the piston sticking .030 proud of the deck. With the .070 headgasket, I will have a perfect quench of .040. As an added bonus, the new stroke will increase the redline to 7511 rpms while maintaining a "safe" 4000 ft/ per sec "piston-speed".

The real kicker is this......

3.720 bore (.020 overbore) + 3.192 stroke = 3.394 or 3.4 liters of displacement. (No kidding. It was a nearly perfect 207 cid)

Heh Heh heh....The old 3.4l being swapped for a...well, even an better 3.4l.

[IsaacHayes]

hahaha. Cool. What compression does that net you?

[Driver_10]

It may have bumped up to 9.5:1 or so. I need to cc the heads and piston dishes first before I can do a calculation.

[Superdave]

why not use 5.7" large journal SBC rods and just grind the crank pins to 2".. seems more logical than popping the pistons out .070" and dealing with copper headgaskets.

you might even be able to gain some stroke, not sure on the compression height of your custom pistons though.

[923.4v6]

I believe you mean sbc small journal rods being 2".

[Superdave]

yah, oops.. i was typing fast at work.. lol

even the 2.1" journal rods would work, i have a 3500 crank here that's got 2.23" rod pins.. just needs a bit more ground off to work..

[Keoki1978]

How about leave the bore at 3.7" and offset gring the crank for a 3.504" and what do you get, a 3.7L. Now thats some shiznit... Thats what I was thinking bout doing with a 3500 block. I originally wanted the VVT engine, but that bore and stroke wont work. Damn, guess you cant have the cake and eat it too...

[Driver_10]

I prefere a higher rpm/ powerband to low-end torque. If I were to offset stroke to 3.504 and use shorter "5.700" con-rods my redline would drop to 6,849 rpms.

The longer con-rods put less frictional stress/wear on the cylinder walls because of the lowered rod angularity. Also, with long-rod configurations the piston will dwell at TDC longer during the power-stroke. This promotes better thermal/mechanical efficiency.

The only draw-back is the loss of low-end torque. ......Oh well!

[Keoki1978]

damn, so how does a 383 sbc rev out to 8000rpms with a 3.75 inch stroke and a 6 inch rod?? How high you expect to rev that thing, with a 3.504 stroke, you'll get it to 7500 rpm's no problem with the right cam. Believe it or not, most jap engines run a bigger stroke to bore and always rev out beyound 8000 all day long.

[Keoki1978]

I was also stating that it sounds better to say you got a stroked out 3500 than a destroked 3500. And our motors got balls man, I have yet to be beat by a honda and said "damn, I got to much low end" Well at the end of the day, you'll be able to rev 200 rpm's more than the next guy here, but you wont be able to keep them tires lite up well into 3rd gear..

[project89]

u think about it to much, go for the cubes not revs, build the bottom end with good stuff and it will rev as high as u want it to.

surley if i can take a 3.1 to an 8k limiter and multiple passes down the track to 7,600-7,800 u should have no problem getting there with stronger parts

[IsaacHayes]

Short stroke does help with reducing the tendency for knock.

But more cubes is nice too.

[Driver_10]

I was also stating that it sounds better to say you got a stroked out 3500 than a destroked 3500. And our motors got balls man, I have yet to be beat by a honda and said "damn, I got to much low end" Well at the end of the day, you'll be able to rev 200 rpm's more than the next guy here, but you wont be able to keep them tires lite up well into 3rd gear..

Theres a couple of factors that you're overlooking. Stroked motors will not safely operate at that high rpm range for any protracted period of time. If they operated at a constant load under those rpms then it would be a short matter of time before failing. My engine should be able to operate at those kinds of rpms for protracted periods without risk of failure. Since I want to get into road racing, this makes a destroked motor combo the winning choice.

Also my car has been lightend by over 300 lbs. (3170lbs) I dont need as much torque to launch. I can also run numerically higher gearing since I wont come crashing disappointingly into a rev limiter. That means I can stay in the throttle longer before shifting.

[gectek]

I have always liked a square setup myself. but honestly, dwell is good, but seriously CI will help. destroking is common, yes. But I can rev my engine (stock BTW) all the way up to 7200 without a problem in the world. granted i dont have the cam/spings for that, but i have higher gearing as well and sometimes it bounces off the rev limiter before 2nd gear. I still can tho. and when i pulled it completely apart, i found the stock crosshatch still in all my bores, bearings look very good for a 200K engine and crank and rods. so, maybe it is a short stroke, but it was all I had.

in reality what he is doing is common place in road racing, but tell me this. when katech does their 500CI LS engines for road racing and lemans and such, do they use a short stroke? one engine they do....the rest, no.

sometimes seriously breaking from the norm is good, unless you are sanctioned. who says you cannot make power reliably at high rpm with a long rod, long stroke, and a big bore, has not looked into the BBCs at all. I have seen them rev to 7500 for entire seasons of the 1320 with no prob at all. smaller engine? how about 402 and 416 LS engines? they have a 4" stroke. we build them all the time for drag cars and road race cars.

[Superdave]

IMO i'd just build it with solid parts and not worry about your redline based on stroke.. other factors like port flow and cam profile are going to play a huge factor in how far it'll rev and/or make power. You'll also need to worry about cavitation in the cooling system and weather or not your oil pump can keep up at those RPM's.