Damn, I didn't understand all that fully.
Being a manual you have more control.
Let's say this big cam peaks at 6300rpm, if it holds that peak till 6800rpm and begins falling off at 6900rpm would this be the best time to shift?

 

You are auto, so I would look at when you make peak torque and try to land right on it or just past it. If you are just falling at 6900, I might hang on to 7200. Just depends on how the converter flashes and where it lands on the upshift.

 

You really ought to for your own satisfaction (and potential change of heart) show up to the dyno with either a holley sniper or a set of mid length runners for the FAST. I have seen post after post that you're worried about giving up midrange. You're really not...you're just shifting the powerband higher. Those are both cheap options that you could easily sell and recoup ~80% of your investment afterward if you don't like the results. The data alone would be well worth the money spent.

The Fast 102 with long runners is going to neuter the top end results a bit. I think you're going to be lucky if it peaks at 6500 and is able to hold flat until 7000rpm. It may start falling off early like before. In reality, you should be shooting for a combination of parts that will peak ~7000 rpm. If you nailed it, great job...but I don't think the fast 102 is going to support it without either shortening the runners or retarding the cam a bunch more. The only thing out of sync right now is the intake manifold....well, that and the torque converter.

We just did a 415 with a victor jr and a holley 850 and made 663@6900 on the engine dyno. It also made 650 at 6300 and 650 at 7400. This was with a 243/257 on 110+2 with .640 lift, FED ported LS3's and 11.4:1 compression on 91 octane. Vacuum pump too. Best power was at 29* spark so we definitely were not limited by spark timing. It stopped making power, but never showed signs of detonation above that.

We were shooting for 700, but are up against the top end just not being big enough to support that much power. Average power is fantastic, and it moves the car down the track extremely well. It really needs a super victor at a minimum.

The old LS3 with the intake and carb peaked at 7400 which is around what was expected out of this one with the extra cam duration and bigger cylinder heads. Average power was up a huge amount. Peak gains were a little underwhelming vs the 376.

 

I will leave that to my tuner.
You and him know more about this than me.

 

Thanks for.the advice.
However, i have had private correspondence with a member on here with a very similar combo to mine.
This gentleman has a 427 with CNC LS3 heads, a large solid roller camshaft and a fast 102mm with the long runners.
When he swapped over to the mid length runners, he lost too much torque off idle all the way to 5500rpm. The torque began evening out 6000rpm.
It made his car feel at least 500lb heavier and he is fitting the long runners back on.
Also, this car will be a street car.
Changing the runners might effect the stall converter and will stall lower because of less power and torque.
I don't want that to happen either.
My aim is for the cam to peak at around 6500rpm and hold till 7000rpm or close to it.
That's all I want.
I like your build though.

 

Nice post!! I have a question for you. Is this the reason a stick car trap higher vs a auto car ?

I find it amazing how a stick car traps a higher mph than a auto but a auto is effortless to drive.

 

It probably is. At least when talking T56 vs 4L60 or 80. I bet the 8 and 10 speed autos have changed the equation though.

Also shows how important driver skills and knowledge are

 

Not going to call no names but some guys on here say you dont need to worry about low end and midrange horsepower/torque to have a fast car.

 

For the street with an auto** I agree about runner length I suppose, but then I wouldn't let yourself be disappointed by the peak numbers. I have a 402 in my rx7 that everyone critiques when I post a dyno sheet, but I've been 130 in the quarter with it which I'm quite happy with. You should never really be doing a pull at 3000 rpm, but with a stalled auto that flashes to ~3200 rpm it'll happen pretty often. You're building to your application instead of trying to hit a dyno number which is the right way to go. With a manual you can change how you drive to utilize the higher rpm powerband. With an auto you're kinda stuck with the long ratios.

Your engine is going to be a beast regardless of what the peak numbers on the dyno say. Your butt dyno should be very happy. The 415 we built feels like an animal compared to the stock bottom end ls3. We were able to tighten the converter which improved efficiency on the finish line and increased mph without having to take rear gear ratio out of it.

Without a 6000 stall converter I wouldn't put the short runners in it. Torque the thing down the road. Ideally you want the stall speed of the converter to be high enough for the RPM to fall into the converter when you shift. You can get torque multiplication benefit off the shift that can be stronger than the gear ratio benefits that Darth mentioned above. I'd consider in the future maybe creeping up on stall speed to ~4500 rpm which shouldn't be too far off your torque peak. I've driven cars that are faster down the dragstrip actually shifting BEFORE peak power to utilize the converter on the gear recovery.

 

Unless you have a lockup converter you're losing ~6% efficiency to slip on the top end. If 6500 rpm with 0% slip is 130 mph, with 6% converter slip 130 mph is now actually 6900 rpm.

Autos also take more power to turn.

They do tend to be faster in ET, and unarguably more consistent.

 

Another reason manual mph better is no slip in converter. But a converter that doesn't fall more than 1000 rpm on shifts is going to run. Better than one that's to tight and drops to far on shifts.

 

Posted before seeing post above mine

 

Its a handful of guys on here that have went from a stick to auto.... then back to the stick. Forgot what member did it on here but his car was faster with the T56 at the track. I was shocked myself when i seen those results.

 

That 3200 is too tight. And the harder you push the motor, the more it will absorb energy. Most really tight stalls are in that 85-90% efficiency zone... which means they actually eat up to 15% of the available RPM from the motor (and with it HP). You want your NA converter to be closer to 95%... it will drive loose but will be much more efficient (think tighter STR or 1.9 or 2.0).

I'd recommend getting a loose 4000 or 4400... like a CircleD 3E or Yank PT. Then it'll be able to rev past 7000 and actually be faster as you will be closer to a manual in efficiency.

For example... an unlocked converter that is 87% efficient with a motor that would otherwise see 550rwhp in a 6-speed would only see 480rwhp unlocked in an auto! Not only that, but if the 6-speed saw 7500 at the input shaft, would only show 6500 at the tailshaft with the auto. One reason why you lose MPH in an auto vs a manual.

A converter that is 96% efficient would be more like 7200 at the output shaft and would show 530rwhp. That's why locked converters typically pick up a pretty large amount over the unlocked converter. Of course, you lose the torque multiplication of the higher stall with it locked, so a properly designed stall should continue to multiply engine torque well past it's flash stall point until it couples and is essentially 1:1... A looser converter does this higher in the RPM range making a higher revving motor otherwise faster. But that's why a high stall car will ET better. It's multiplying the power to the ground better until you get to the top of the range... and then it's falling off and thus making less power at less RPM up top compared to a manual, hurting ultimate MPH capability.

 

Some LSX classes and events are strict on the stick cars. You can be in the same class of racing as a another guy running a automatic and they'll make the stick car add 120 pounds of ballast/weight. To me it dont make any sense at all...

 

When it comes to big cube engines I agree. On a 346, you gotta worry about midrange. On a 418, just build for power

 

Larger motors are going to generate a surplus of low and mid range torque/power compared to smaller motors. If you are going big, it is best to focus big. Otherwise, max out something smaller and more sensible.

The formula for strokers that seems to work best is to aim for the f!ck!ng stars! You end up with beautiful 700hp 400ci engines on off the shelf heads, just have to follow the right recipe for success.

 

Why is this in External. Moving to internal.

 

I wondered about that.... Thanks!

 

Jake are you saying a 3200rpm stall is not enough for my combination? Don't forget this is a street car.
I just spoke to my tuner and according to his calculations, there is a 90% chance the current stall will need to be adjusted.
He goes stall speed might need to be a little higher so I'm guessing the converter will end up being a 3600rpm.
I was very specific that I want it to drive nice in the low end.
Current one drives like stock.