First of all forgive my possible over excitement here, this is my first built and dyno'd supercharged engine.

I'm doing this build to favor an old school hot rod look to have fun and to cruise around in. I've always wanted a huffer sticking out of the hood. The fake shotgun scoop as a pair of eyes on the butterflies:


Run the videos at max resolution to see the numbers more clearly.

The engine is a 406(de-stroked 427), the blower is 5% overdriven on pimp gas.
The builder says with race gas and a 10% pulley the engine should make about 20% more across the range.

I have to detail the engine compartment and get a transmission before I can put it in my car. That's going to drive me nuts after seeing it run

Idling: (about 950)


First Run!


Dyno Monitor
After a few runs, Timing backed to 28* with no effect on Torque


Dyno Room, Larry at the helm

 

Woot! That is a sweet beast!

 

WOW!

 

Looks good. Forgiven, 406 SB is bored 400. Now you need some stiffer springs.

 

Nice numbers!!

Torquey....

That ought to tear up some drive train stuff...

I have always wanted a roots blower through the hood as well...

 

Hi Ganey,
I checked the numbers:

Bore 4.125
Stroke 3.8
Rods 6

Same block with 4" stroke is 427

I opted for a shorter stroke to give the engine quicker "rev"

 

Killer! Boost is always a good thing!


Keep us up to date!


JIM

 

Damn good numbers.... must be the pimp gas you are running.

 

Hey......pimpin' gas ain't easy!!!!

RobbSalzmann, all I have to say is this: Please don't ever floor it while facing east........with that torque curve, you might just stop the Earth's rotation!!!!!! And that would be.....well, let's just say it would be bad, and leave it at that..


Scott

 

You guys don't have pimp gas in your town? Just look for the purple gas pump with a somewhat trashy gal standing next to it, holding it's hose in her hand.

 

Very nice. Congrats!
I think the stock hood should "just" clear.

 

Awesome, love the flat torque curve.

 

There are only two things that determine how fast a motor revs and a shorter stroke is not one of them.

1. Less reciprocating weight.

2. Higher TQ

If you would have went with a 427 you would have exceeded 700 FP of TQ and your hp would have stayed the same only the peak would have been a few 100 rpm lower.

Did you have a boost gage on that motor for the dyno runs?

 

Boost at 5%OD averages about 7psi (range measured is 12-15inHg)
At 10%OD boost is expected to run 11-13psi, and exceed 700ft/lbs on racegas.

I understand your explanation of stroke vs revs, and while the thinking is correct, I think it may be an over simplification - however I will say I know you know more about this than I could forget - and I do enjoy your wisdom on the subjet. I've built a few motorcycle engines over time as well as a few car engines, both turbo and NA. The stroke length discussion is a common subject and seems to have a lot to do with how you want the engine to behave/perform.

For me, adding forced induction was a compensating element for subtracting stroke.

Other factors also weighed on my decision to choose a shorter stroke, including radius of rotation/inertia. Keeping compression at or below 8.5-1 was a challenge in this project. A longer stroke would require the ring landings to be too close (for my comfort) to the piston top to maintain <8.5-1 & clear the valves. I didn't want to foot the bil for custom forged pistons.

Even at this stroke I had to have the chambers milled on a CNC to get from 64 to 75CC. The good news is the head work yeilded better numbers on the flow bench and we think is a contributing factor to the nice flat torque curve and ability to retard timing from 36* to 28* with no measurable effect on tq.

 

Most of the AFR heads are made in your choice of 65 or 75 cc

The 415 ci I build with -21 or -23 cc dished pistons. (Wiseco) I was shooting for like @ 9:1 C/R with 75 cc heads for some power when not under boost

My 434 has a tiny 6 1/4 ATI damper for less rotating weight. I went with a 42 pound Callies pendulum cut crank throws and a 22 pound billet steel flywheel. when out of gear it changes rpm very fast.

When in gear you are then adding all the drive train including the weight of the tires and wheels. So I have billet lighter weight Centerline wheels.

As a more revving faster in gear. Just think about engine TQ. Your present motor under ideal conditions might run mid 10 second quarters. Now the guy in the other lane has a totally tricked out 302 with a 3 inch stroke and he shifts at 8500 rpm and he gets down the track in 13.5 seconds. You both have the same tranny and rear end gearing.

Which motor revved faster?

The only advantage of a shorter stroke is less piston feet per minute at a given rpm. I like hot rice bikes. The other day I was looking at the new Kawasaki zx-10 it makes 201 hp 14,000 some red line and it is 1000cc which is only 60 ci

 

Doesn't a shorter stroke reduce reciprocating weight?

 

Nice numbers congratulations!

 

Not when the manufacturer is using mass produced forged blanks. Call up one of the forged crank places. My light weight 42 pound is 42 pounds no matter if it is 3.00 through 4.125 stroke.

The throws are the same the rod and main journals are the same. They just machine the rod journals to a stroke length.

It still comes down to TQ. Read the definition of TQ. please. It is the ability to accelerate an object. (like the crank shaft) Big race motors can just blip the throttle and hit the rev limiter

 

Why does the old 327's turn 8000 and the 350's like 6500rpm or less.

 

My basic understanding of the main benefit of a shorter stroke for higher rpm is based on reduced linear piston speed in the bore.
A longer stroke requires the piston to travel further in the same given time (rpm)... and the higher the piston speed, the greater the inertial loads on the rods to accelerate and decellerate the piston.

The use of lighter pistons in higher revving stroker motors is advised.

There is also a consideration for the angular displacement created between rod and piston during rotation.
In an engine with the same rod length, a shorter stroke has a reduced angular displacement during a stroke, hence it has slightly lower lateral loads on the piston assembly.
Some say there is a gain in efficiency in converting from linear motion in the bore to circular motion of the crank.
That's where longer rods can be advantageous.