New Turbo build let’s talk about crank stroke’s
 

Hello everyone bout to start a short block build for 1000 flywheel street car.Im personally leaning towards a 4 inch stroke.Whats everyone running and why?

My 9.5" Short Deck Twin Turbo engine will have a 3.5" stroke crank (Moldex did the crank).

My Standard Deck 10.240" block will use a 4" crankshaft with a Vortech YSi Centrifugal Supercharger.

(neither of these engines will be used for drag racing)

Years ago The Butlers and Travis Quillen built a 482 Engine with a 4.25 stroke crank.
Travis has mentioned several times that he should have gone with the 4" crank to me.

I assume that was because he had plenty of power and possibly the 4.0" crank might have allowed a more consistent launch with the 63 tempest (6.27 @ 228 mph) if I remember correctly was their best ET and MPH.

Tom V.

I also think that a short stroke crank is the only way to go on a turbo build. Turbos like a load and a short-stroke crank will allow cylinder pressure to build without the longer stroke's mechanical advantage working against that effect.

As we all know, there is such a thing as too much torque and by moving the horsepower peak up a bit, there is a chance to launch more efficiently and let the midrange and top-end power come in at a point where the chassis is much more effectively putting the power to the ground.

I remember watching Marty Palbykin's car run at Norwalk in 1996. The car didn't launch violently, but the mid-range acceleration was astonishing. As I recall, he ran 196 mph with the transmission shifting from first to third- something went wrong with second gear. He ran a 3.75-inch stroke and I really think that is the sweet spot for a high-boost application. From what I have seen, strokes above four inches are counter-productive for traction and I would suspect that they artificially hinder top-end power production.

3.75 or smaller ...

Don, The crank in Marty's 1967 400 block was a RAM AIR IV-SD 3.75" stroke Forged crankshaft.
It was cleaned up by Moldex Crankshaft and I sold it to him thru Moldex.

It was a Kellogg Crankshaft Forging. Similar to the Pontiac 366 cid forged cranks which I still have several of. Unfortunately those 366 cranks, (which are made of the same special material as the RAM AIR IV-SD 3.75 cranks) will not allow a stroke larger than 3.5 inches. Stock stroke dimension was 3.375" (3-3/8 inch stroke).

So Marty P had a very rare Kellogg/Moldex forged 3.75" stroke Pontiac Crank in his engine.

Tom V.

This precisely how we are building the engine combo for my sons new car, 4.50" bore x 3.75" stroke, we don't want excessive low end torque as it's a limited tyre class,and even with power management it can be difficult to control on a less than perfect track.

Thanks for the info I think we all can agree long strokes aren’t your friend.My goals are not only a decent time on the track but as street able as possible and with some reliability mixed in.In fact this is a very general statement but if I can get to 500 flywheel and 15 pounds of boost I think I’ll be close to my goal.Just as a after thought if I could get it all done at 5500-6000 I’d be happy!

I ran several simulations using Allan Lockheed's Engine Expert and I think that a tall-deck build using a 303 crank would make for a killer high-boost turbo combination. The long rods would keep piston speed in a very reasonable range at high rpm. The only drawback might be the amount of time the piston is at TDC. It might increase the opportunity for detonation if fuel quality is low and charge-air temperature was not kept under 100 degrees.

Since Luhn Performance made 862 HP at 5300 rpm with a Vortech Centrifugal Supercharger (13 psi of boost) and a very basic 455 type engine, I do not see where a street boosted engine at 15 psi of boost could not make 500 hp with a very basic 400 cid engine and 3.75 stroke.
Years ago with the same sized Vortech Supercharger on a 281 cid engine we made 762 hp at 7000 rpm. You could make 500 hp with a 326 engine.

Tom V.

5-8 lbs of boost should do it with a turbo. I ran 10.80 in a 3,400 car with 6-7 lbs with steel heads and a small hydraulic cam with a out of date b & m street charger!


GTO George

Guys should of been a little more clear I’m looking for 1000 flywheel.Just a general statement of 500 flywheel n/a plus 15 pounds should get me close to that.Im in the process of ordering a lower end from butler and the goal is as streetable as possible and low rpm.My thing is with boost you can have it all reasonable street manners and decent power.Going with a 4 inch stroke it works out to a 434ci.

You’re probably going to need at least 20 lbs of boost to get those hp numbers and a damn good crank and rods.........you’re talking 1,400 flywheel hp. I like moldex billet crank and gapless rings.


GTO George

Use the garret boost advisor - it will tell you much boost is needed for a certain power output.

.........or talk to someone with experience!



GRO George