G92Joe

Would the 327 be a better choice than a 350 for a small block turbo application?
My reasons for a 327 would be that the shorter (3.25 vs. 3.48) crank stroke would rev faster to offset turbo lag, it would rev higher, & offer better gas mileage at rpm's below boost levels.
Any thoughts?

89ProchargedROC

with a destroked motor, yes it revs quicker but you need a HIGH redline to achieve the most power. go with a 350 and some GOOD flown' heads and never look back. the only reason i'm going with a 400 instead of 350 is because i'm *going to try* and drive it on the street and the extra cubes help with processing that big Turbo.

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Big Thumper 400 started!
91mm Turbo
GM raised runner heads
PARacing frt suspension
DFI
more as money allows
Always a cool place visit
www.mfba.org

Greg90iroc

what makes you think that a shorter stroke will offset turbo lag? This is not the case man. The larger the stroke the faster the boost will build. think about it the more torque you make down low the quicker boost will build. if there is more exhaust gass flowing at low rpm the turbo will spool quicker. Also a side benifit of the greater stroke is before boost is built teh torque will be greater. Get the 350 or 383 if you can.

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90 IROC l98
last season best corected 13.62 @102
mods
full exhaust, AFPR, pulley, jet stage 1 chip, billet servo, 52mm throttle body, slp runners and some 1.6 RR's and a few other little things.
243 RWHP and 342 RWTQ with hot engine and 90 octain fuel

89ProchargedROC

actually, destroked motors tend to help with turbo lag like he originally send because the faster the motor revs the more load there is and the quicker it comes. the quicker the load/revs the more exhaust velocity you will have and the faster the boost will come.

why do you think most blower/turbo motors god, i mean kenny duttwheiler , builds is a 377 (destroked 400)? for both blower and turbo cars...boost comes quicker.

but turbo lag can be manipulated by header design/length and exhaust housing size too. there are many ways to help turbo lag.

i for one will be using a trans-brake

------------------
Big Thumper 400 started!
91mm Turbo
GM raised runner heads
PARacing frt suspension
DFI
more as money allows
Always a cool place visit
www.mfba.org

JAYDUBB

Since I used to drive around with a normally aspirated 400, I will say this.

Because you are trying to build a street car and the compression ratio may be in the sub 8:1 area, having the 400 is a good thing! Having a 400 will give good off-boost cruising torque. Having the 400 means that she wont be a gutless dog when theres no boost present. Then when the boost builds, LOOK OUT MAMA!

I would not even consider a 327, especially in a 3rd gen! No torque + Heavy car + No converter and gear = a not so happy owner. Sure it will run like a raped ape when the boost hits, but damn its gonna be a wimp without the boost!

Just my .02

No flame intended.






[This message has been edited by JAYDUBB (edited March 04, 2001).]

89ProchargedROC

like i said:

race car motor: 377

semi-street car motor: 400



We will see what happens

kevin v

if the turbo is sized right it will spool fast no matter what size engine. how do you think grand nationals and t-types run so hard with 231ci engines weighing 3500+ pounds. you can't go wrong with either choice in my opinion.

JAYDUBB

Well, most of the really fast GN's out there have larger-than-stock turbos and 3000+ stall speed converters. So yeah, they still build boost quick, but if it wasnt for their converters they would experience EXTREME amounts of lag and be DOGS down low. 8:1 compression is 8:1 compression, no matter how you look at it. And having an itty bitty engine makes things worse.

[This message has been edited by JAYDUBB (edited March 04, 2001).]

kevin v

those little 231's with larger than stock turbos are perfectly streetable with 3000 converters. a 327ci engine would be that much more streetable and would make even more power.

89ProchargedROC

just to let some of you know too.....i know a lot of fast buick V-6 racers and there is one thing that has helped them all tremendously that no one has talked about.....stage right trans-brake (to build boost off the line), many use a small hit of N2O to get going, and many use pressure switches......one setting for foot brake boost 8psi 60' the car and then flip the switch...instant 15psi. its like a cheap electronic boost controller. they have their tricks too.

G92Joe

Some truth may be found in the following: Reference ~ "The Chevrolet Racing Engine" by Bill Jenkins. Chapter 2, "Crankshaft and bearings; stroke displacement selection" goes into it as follows......"there is some degree of performance gain with increase in crank stroke through 3.75"... there is not however a linear increase in output as the stroke goes up. There may be more torque; and with considerable work, it is possible to attain a pretty good Specific Power Curve up to a stroke of about 3.50 inch. Where the restrictions of piston design & induction system design enters the picture, we feel the best compromise is somewhere in the middle ground - a stroke length of 3.25". This provides an optimum rod length of 5.90 inch without restricting the piston design (distance between wrist pin and piston deck; less is better/lighter). This is what we use in our 330 inch Pro Stock engines." They also use the stock #3838495 Tuftrided small-bearing journal, forged 3.25" crank (for reduced bearing surface speed).

Beast5spdGTA

What about engine stresses on the longer stroke motors 383/400? I mean a twin turbo set up is probably looking into the 700+ hp range on race gas and at least 500hp on the street. Would you need exotic engine parts, like rods, crank on the longer stroke engines to make then survive those high stresses? Or better could you get away with cheaper parts in a 350 or 327 and still have some reliablity w/o a very expensive short block? Will the speedomotive sportsman 383 (~$3500 complete short block)advertised price $2150, survive 700-900 hp? I doubt spool up will be a problem with any engine and i also doubt someone will have a turbo set up with a stock trans or rear for that matter(at least not for long=)