Corvette Kid

At what RPM can I expect the torque to really start coming in with a stroker bottom end added to my current combination? Stage III heads, Hotcam, etc. See sig for full details. Can anyone w/ a similar set-up enlighten me? How about a 396? Thanks in advance.

CFI-EFI

The number one determinant is the camshaft. If you've used the cam previously, the torque and power curves should parallel the old curves from the 350, only higher, in both respects.

RACE ON!!!

Z06_BluByU

Corvette Kid

Curious, I thought the power would come in sooner with a stroker. And so you're also saying the torque curve will continue to a higher RPM?

Rich & Lisa_84

briannutter

Torque will be up the until power peak, but will fall off quicker after that. Horsepower will peak sooner. horsepower won't be up by much unless a bigger bore unshrouds the valves allowing the heads to breath better. Often people "see" an increase in power when the "top end" stays the same from added displacement, but it can be an illusion. Often small c.i. hydraulic lifter combinations need to rev higher and this puts them in vavle float before their true horsepower potential can be seen. putting more displacement under those killer heads will move the curve down into a more valvetrain friendly place.

If you actually compare piston speed between the two different strokes....you'll see a nearly 1:1 relationship between power. As a "for instance" a 6000 rpm 383 has an average piston speed of 3646fpm. the 350 has to turn 6465rpm to match that. The horsepower peak will often move down by that same 465rpm.

basically to say most people that do 383's are doing head/cam/ and other airflow enhancing measures at the same time and that's what gets the big hp numbers.

CFI-EFI

Are you aware of the relationship between torque and horse power? Do you know the formula for horse power.

RACE ON!!!

CFI-EFI

Yes. The camshaft is the brain of the engine. Other factors may limit it's ability to work to it's potential, but it is the controller. Other items, port flow, etc. may become limiters holding the engine back from what the brain has asked for.

I always thought the same, too. There was an article in a recent Hot Rod Magazine, where they built two different engines and tested them side by side. Granted, it IS a complicated subject, with more variables than you can shake a stick at, but I went away believing the biggest influence of EITHER a poke or a stroke, was due more, to the net increase of displacement, and not so much as to how it was achieved.

RACE ON!!!

FD2BLK

Chris,
While your TQ will be differnt due to the HC -vs- my CC 306 here is my Dyno run and you can see it is a prety flat TQ curve. I think most of the mild camed LTx big cube motors produce a simmilar curve, results may vary

briannutter

As for the formula for horsepower...yeah, no big deal. it's to easy to get caught up in. Frankly just compare the torque numbers for any two engines all the way through the rpm range if you're nitpickey. I'll pick the engine that produces it's torque up high In the grand scheme of things, a given cubic inch will produce a relatively "given" amount of torque, but horsepower is VERY independent of displacement. You'll also note that the numbers on either side of "peak" fall off quicker on a big ci engine versus a small one. With perfect gearing and stable valvetrain, the small cubic inch engines will get you down the track *almost* as fast as the big ones....you just turn them tighter. If you look at any professional form of naturally aspirated racing, you'll find a cubic inch limit. F1, Nascar, and NHRA Prostock being the benchmarks and the cubic dollars spent to find it. Warren Johnson has said that every horsepower costs about $50k and they pick up about 20 per year. NHRA and Nascar have found best power by taking the bores out to the very maximum their borespacing will allow and they've shortened the stroke to hit their c.i. limit. 500 ci in prostock uses a 4.685 bore and a 3.6 ish stroke. Nascar uses a 4.185 bore and a 3.3 ish stroke. I should know...I design their pistons. In F1, the bore to stroke relationship is much more toward bore versus stroke because bore spacing is open. The real determiner of horsepower then becomes how long you can keep the valve train stable. Take the cubic inches of 358 for Cup between 1980 and 2005 and all they've done is give it better heads and a superlight valvetrain to go from 600hp to 820hp with the same column of air feeding them. That also means they have to increase rpm every year to use up that air-hence the valvetrain work. There's friction reductions and all that, but you get the idea. All that being said, on the street....bore it and stroke it out to 434 ci and call it a day if you don't care about more wear from sideloading. As for my qualifications to make these statements, I've worked at Wiseco for 6 years in technical sales, CJ Batten's, Scott Shafiroffs, and worked for Judson Massengill before that. I work with the countries best engine builders on a daily basis. I have about 250 engine dynopulls under my belt, quite a few engine builds, and an additional 80 or so chassis dyno pulls......but that's taught me about 5% of everything there is to know about the internal combustion engine

Corvette Kid

Great info guys. Brian, I thought Nascar ran a stock stroke with just an overbore to get to their 358 cid limit. When did this change?