Camshaft and stall speed question

johndougherty · Post by **johndougherty** » Mon Nov 07, 2005 6:48 pm

Im building a 406 small block for my Nova. Hopefully I can make peak power at 6500 rpms. I am using a th350 and a 4.11 rear gear and 27 inch tall tires. I have a 10 inch convertor that I think will stall about 4500 rpms.
If I calculate the rpm drop between the 1-2 shift (using 0 % slippage)
at 6500 puts me back to 3920 in 2nd gear. This is 600 rpm below the convertors stall speed.
Am I hurting acceleration this way? Or, should I use less camshaft and a 4000 stall speed and still shift at 6500?
Thanks,
John

dbusch · Post by **dbusch** » Mon Nov 07, 2005 11:10 pm

it will not go below stall speed of 4500. this is actually good, since it will be multiplying torque (and accelerating harder) until it approaches lock up again.

johndougherty · Post by **johndougherty** » Tue Nov 08, 2005 12:23 am

Thats what I have a hard time believing. If thats true, should I install a 5500 stall speed instead?

Ron E · Post by **Ron E** » Tue Nov 08, 2005 9:06 am

johndougherty wrote:Thats what I have a hard time believing. If thats true, should I install a 5500 stall speed instead?

It's true.
As far as going to a "way loose" converter, funny things start happening. Once, ballparking a customer's new car with a near stock engine, (street 355 no cam, stock heads, probably a 3000 peak Tq motor) with his race converter installed, the combination was consistant even though it would "fall-off" the stall-speed by 300 rpm, or so when the trans brake released but, if it slipped enough to avoid this, it would pick up .01 to.015. Made dialing it in an adventure.

dbusch · Post by **dbusch** » Tue Nov 08, 2005 11:01 am

if you make peak power at 6500, you will want to shift at 7000 rpm. Then, a 5500 stall will be perfect. 1500 rpm drop on the shift is ideal. I ran a 5000 stall shifting at 7000 and the 60 fts were a little slower than they could have been. I suggest getting a 9.5" converter. They are relatively cheap and are versatile enough that they can be made to stall from 3500 all the way to 6400 rpm!!!

67RS502 · Post by **67RS502** » Tue Nov 08, 2005 12:03 pm

I run a "tight" ATI 10", it footbrakes 2500, and flashes just past 4000.
My peak tq is at 4500, and peak hp at 6200. I shift at 6700-6800.
Rpm drop is to about 5400-5500 range - only about 1300rpm.
Meaning that a converter will have some slippage even above its flash
rpm point - and the rpm drop will not be very drastic as the calculated
rpm drop from the trans gear ratios (like a manual trans).
A quality converter will not have a drastic rpm drop, and will keep
an engine in its powerband, while being efficient on the big end.

Ron E · Post by **Ron E** » Tue Nov 08, 2005 12:46 pm

That was a ATI in the car I was describing. It worked great with the engine it was designed for. But, it would drop back with the stocker unless the tires slipped. The race motor was mild, also, but had enough cam along with head work to raise the torque rpm to the 5200 range. The converter picked up some stall speed with the stronger motor, (can't recall amount off hand) but the converter's manners were pretty much exactly what we asked for, as is usually the case with ATI.

Ron E · Post by **Ron E** » Tue Nov 08, 2005 12:52 pm

BTW, that ".01 to .015" in the earlier post should have the zeros deleted. I was never that good.

johndougherty · Post by **johndougherty** » Tue Nov 08, 2005 4:03 pm

Thanks for all the replies!

67RS502, When you shift and the rpm drops to 5200 rpms, does the rpm climb right away, or does it sit at 5200 rpms for a bit and then climb?
BTW, I like both your Camaro and the Luv truck. Especially the truck... the engine looks almost exactly like the one in my Nova. Same valve covers painted black too.

Ron E, Im not sure what <it would "fall-off" the stall-speed by 300 rpm> means. I think you mean, if the convertor held at 4500 rpms on the transbrake, when released it dropped to 4200 rpms and then accelerated?

Ron E · Post by **Ron E** » Tue Nov 08, 2005 4:22 pm

What I meant was instantly if after the brake releases. when the converter flashes to it's stall, say 4500, then it briefly falls back to 4200, It get's back real quickly, but it's real easy to miss. Any kind of play-back tach etc. shows it plainly though.
And, yes, if your stall is 4500, it will sit there untill the car reaches that speed, then the tach climbs as normal. Same happens after each shift.

67RS502 · Post by **67RS502** » Tue Nov 08, 2005 5:47 pm

The rpm drops to 5400 and climbs again... but remember that it only flashes
to 4000, and 5400 is way above the flash.
Thanks
The camaro is my "ex-street race" car mostly just cruise it on the street,
and run at the track some, and the Luv is my work truck, hence the stock
lookin motor and quiet smooth idle;) - kind of a sleeper.

Donovan · Post by **Donovan** » Tue Nov 08, 2005 7:54 pm

John, if you need a new camshaft for your car I know of a great cam grinder. You should try him sometime.

Ron E · Post by **Ron E** » Tue Nov 08, 2005 8:42 pm

OK, I see your point with dual purpose cars. And, yep, if your mechanical ratio drop doesn't take the motor down to the stall-speed, the converter's not so much in the game. A loose converter is a pain on a car that's street driven ....

Ron E · Post by **Ron E** » Tue Nov 08, 2005 8:44 pm

..that camaro is wickedly fast anyhow!

johndougherty · Post by **johndougherty** » Tue Nov 08, 2005 9:53 pm

Donovan,
Hows your brothers Nova running?