New Converter, Different Shift Points?
 

First of all, I do not race S/ST, as my screen name would imply. It was the number on my car when I bought it 15 years ago. I don't race SS either although, I've always been impressed with their performance.


My car is a back-halved 67 Barracuda. It weighs 2620 lbs. with me in it. The engine is +.060" 340 w/9.24:1 compression, OEM 596 castings w/1.88" IN valve, roller cam, Victor 340 manifold and Holley 950 carburetor. I run an aluminum drum, 904 transmission w/2.45 1st gear and trans-brake. Dana 60 w/5.57 gear. Either 31.2" or 32.6" tire.


I have been using an 8" ATI converter that hits about 6250 RPM on the brake and it has worked pretty well for the last few years. In an effort to find more MPH and shave some ET, I thought I'd try a little taller tire. It wasn't a horrible move in ET or MPH, except I was running towards the end of the year and was also getting into better air. On my last outing for the year, I was driving into a quartering headwind which, naturally cost me a little MPH but, I realized I was blowing a lot more RPM into the converter.


Fast forward to this year, I decided to swap to a tighter 8" converter and it hits about 5800 RPM on the brake. I take it out to the track, in 2400'-3000' DA air and the 60 ft. is hurting a little and the MPH is down 1 in the 1/8th mile and probably 1.5 MPH in the 1/4. Amazingly, my split times are better to the 330' by .019 sec. and .015 sec. to the 660' and ETs are pretty close.


So, I'm thinking, "Try the shorter tire!" Well, the track prep was awesome and my 60 fts picked up huge but, MPH is still down and my split times are worse.


Anyway, here's my question: Is it typical to have to alter your shift points after swapping to a "better" converter?


Thanks, in advance.

Re: New Converter, Different Shift Points?
 

This isn't a direct answer to your question, but I've always found a looser converter to be quicker and more consistent as long as the finish line RPM is acceptable and not out of the engine's range.

Re: New Converter, Different Shift Points?
 

You are trying to do something you want to do. Listen to your car. It is telling you it doesn't like what you want to do.

Re: New Converter, Different Shift Points?
 

I ran the tighter converter with the taller tire and the 60" to 330' was better, the 330' to 660' was better but, loses MPH in 1/8th mile and the 1/4.


Then, I swap to the 1.4" shorter tire and the 60' is better than ever but, shift recovery is worse than the same converter with the taller tire.


I'm not hearing what it's trying to tell me. I would think the shorter tire would recover on the shifts better than the tall tire. Unfortunately, my last race was all 1/8th mile so, I never ran it out the full 1/4 mile. Looking at the MPH at the 660' doesn't indicate it was going to find anything in the last 660' but, I could be wrong.


I called ATI about sending one of them back. They told me they would be guessing if, they tried to make either one of them better and suggested I just use the one the gives the best ET.


Thanks for the responses, so far.

Re: New Converter, Different Shift Points?
 

Quote: Then, I swap to the 1.4" shorter tire and the 60' is better than ever but, shift recovery is worse than the same converter with the taller tire.

Did it ever occur to you the taller tire had the car going faster at the shift point than the short tire. Think about the physics that comes in play when that happens. The difference in the load on the stator, maybe, Aye... No wonder it wont recover. BTY: there are subtle changes that can be done to a converter that has no effect on stall speed that helps with recovery and TQ multiplication. You could even drop the pump pressure and make the converter act entirely different. Why do you think that any serious Comp racer or serious SS racer has at least two or three converters that all stall within a few hundred RPM of each other?

Re: New Converter, Different Shift Points?
 

What's your criteria that has you believing it's "a better converter"?

The one critical bit of information you omitted and frankly the first and foremost bit of information necessary when discussing converters, in the absence of dyno results is... your cam's duration @ .050?

Without it, there is no meaningful discussion or advice.

Lastly, you have an engine combo that maybe makes 500+HP and 400+ ft/lbs. torque at probably around 5000 RPM. A converter that flashes to 5800 is too loose no mind one that flashes to 6250 IF the goal is to "shave some ET." The fall back RPM is what is most important.

Re: New Converter, Different Shift Points?
 

There is a lot more to a torque converter than just stall speed . There is the torque multiplication, coupling point, and efficiency curve . Maximum torque multiplication happens when there is no output rpm, and decreases to 1 to one at the coupling point . Efficiency is zero at zero output rpm and approaches 100 % when output rpm approaches input rpm (engine rpm) . Since the converter works based on input torque, as you change things like the tire size, or the gear ratios ( both in the trans, or rear end ratio) this effects where on these curves your running . This is why you can see improvements in one part of the run , but lose in other points . As for modifying a particular converter , if you want a higher stall speed, a typical modification is to bend the pump fins towards the negative direction . This will raise the stall speed , but will also increase the multiplication, and the down side will reduce the efficiency . So you may see a better 60 foot time, but may lose mph . There are so many things that can be changed to dial in the "perfect" converter, but as we all know, change the weather, and you may need a different converter combination .

Re: New Converter, Different Shift Points?
 

Bottomline is based on the limited info the OP supplied, both converters are too loose and neither converter is near optimum for the combo. There's no magic required in the year 2016 to get the right converter for a ~ 500HP n/a small block, 1/8th mile bracket car

Re: New Converter, Different Shift Points?
 

Maybe I should have not used "better" and I understand there is more to converters than stall speed. I just figured, I'd tried a couple of different converters with two tire sizes. (basically, a gear change) and hoped it was enough data to give the guy at ATI some direction to go.
It looks like, everybody agrees it could pick up with the "right" converter?

Re: New Converter, Different Shift Points?
 

again, what is your cam's duration at .050?

Re: New Converter, Different Shift Points?
 

IN Closes 63º ABDC @ .050"

Re: New Converter, Different Shift Points?
 

run the other way from whoever told you that cam was what you needed!!:rolleyes:

You are wasting your time with converters with that cam that's at least 40 degrees too big for your 9:1 bracket engine!

FTI, the cam in my 15.5:1 598 has similar duration @ .050.:eek:

Re: New Converter, Different Shift Points?
 

It is a turd! :D

1.2664 60'
3.85 330'
6.058 660'
9.66 @ 135.4 MPH1320'

Re: New Converter, Different Shift Points?
 

a 9.66 best at 2600 lbs. IS a turd!;)

Re: New Converter, Different Shift Points?
 

I think there's more in it. I'm not sure how much quicker I'll
need to go to get a 9.24:1 340 out of that category though. :)

Re: New Converter, Different Shift Points?
 

Dont forget your being held to the standard of class racers.

Re: New Converter, Different Shift Points?
 

I know and am willing to deal with the criticism. I've built everything, mechanically in the
car, ported the heads, intake, spec'd my own cam, etc. I have no problem admitting I
don't know as much as a seasoned class racer so, here I am, looking for answers.

Re: New Converter, Different Shift Points?
 

specing that cam for your combo says you know nothing about cams and their events.

Get the right cam in that engine, then get the right converter.

Re: New Converter, Different Shift Points?
 

Those numbers are not real shabby for something that you built yourself. Non of us started out setting the world on fire. Just keep asking questions and talk to the educated guys about your combo, Talk to the cam companies about a good cam for your combo. Also stick with the better converter companies for a converter that will optimize what you have. Best of luck with your ride and the most important thing is you have fun with it.

Re: New Converter, Different Shift Points?
 

Thanks Mike. It may not have national record power but, I do have a LOT of time and effort in the car.

I have found most cam representatives, I get to talk to, aren't really SS savvy and steer me to grinds in their catalogs.

I'd be real interested to know the cam specs in a cutting edge, low compression 340 super stocker.

I've found, in the past, they don't give out that kind of information and I don't blame them.

Re: New Converter, Different Shift Points?
 

Are Ritter/Weber...the Mopar guys from Upstate NY still around? They might be able
to steer you in the right direction.....

Re: New Converter, Different Shift Points?
 

Kent deals in a lot of surplus NASCAR stuff and marketing his SBM race blocks.

Dave is in Virginia now. He's big into developing pieces and tuning for the GEN 3 Hemi.

I've talked to them in the past. They have been out of SS for several years.

Re: New Converter, Different Shift Points?
 

you don't need or want a super stock spec camshaft for a 9:1 bracket engine.

Re: New Converter, Different Shift Points?
 

Cant be too much different from my 350 chevy suoer stocker,
277/285 @ .050 450 lobe lift and 105 lobe separation. Installed a 99. 1.8 intake and 1.6 exhaust rockers. Mine is a bullet.

Re: New Converter, Different Shift Points?
 

My personal experience just started pulling out duration on the intake and exhaust, most cam company's will put to much duration in on intake and exhaust , a lot depends on cylinder head also. Good luck have fun with it... SS 340 high compression motor is what I have.

Re: New Converter, Different Shift Points?
 

I would listen to guys like Kenny. He has been flogging his 340 for years now and has a pretty good handle on it. I have been involved with the Small MoPar since 1971 but haven't had anything to do with the SS motors (other than TQ carbs) in many years. Cam tech has evolved quite a bit since my low comp 340 has seen the track!
I do find it laughable that a self declared expert who loves to berate everyone who dares to question his expertise on this forum and who runs a high comp 598 Chevy is trying to give you the ultimate advice on a low comp 340. As everyone who has had anything to do with that type combo knows, they have a mind of their own. While your car is about 800 lbs. lighter than the SS version of your car, I think your performance so far is admirable. Jim

.

Re: New Converter, Different Shift Points?
 

I do find it laughable that those without a clue post advising who the op should listen to. Now we find that Chrysler built engines with "minds of their own." :rolleyes:

Re: New Converter, Different Shift Points?
 

Thanks Jim. I appreciate all the input and encouragement. I have pretty thick skin and I'm not trying to make any enemies here.

I still have some work to do and I've learned from this post.

Re: New Converter, Different Shift Points?
 

IF you've learned anything from this thread first and foremost you need to realize your car/combo is not anything like or close to a super stocker and never will be.

Next, picking camshafts is not your forte and your converter can't be right until your camshaft is right.

Last, the good majority of those posting on this forum either can't or won't help you because you are a bracket racer. Matter of fact, a seperate forum was created for bracket racing discussions

http://classracer.com/classforum/forumdisplay.php?f=19

because a few here complained, not wanting a bracket racer answering tech questions and brusing their egos.;)

Re: New Converter, Different Shift Points?
 

Because my car was stripped of it's interior, it will never be a SS legal car and therefore could never be raced in a SS class. GT or otherwise. It's really not set up to be a bracket car either, as 8500-8700 RPM, lap after lap at doesn't lend itself to the typical season. It's just my attempt at ET chasing with an engine I'm familiar with. I know the engine isn't SS legal, to the letter but, I did make some effort to build it, mostly within the constraints of the rules. I can't imagine my car coming close to it's current performance with a camshaft 40º smaller. I have done a little homework and I'll keep beating on it until I feel I've exhausted it's potential. I think high 9.40s @ 137+

Thanks for your input.

Re: New Converter, Different Shift Points?
 

so you're a career test/tuner, what a surprise.:D


your combo with the right cam that without question needs far less duration at .050 than your current 280+, will accelerate your car quicker and faster than it's current performance, with the right converter of course and you'll do it turning less than 8000 RPM!

FYI, all your ET is made in the first 330 feet and 60 foot is EVERYTHING!

Re: New Converter, Different Shift Points?
 

Have to agree that conventional wisdom would say a 280@ .050 cam is going to want at least 11 or 12.1.

Re: New Converter, Different Shift Points?
 

wrong, MORE!

Re: New Converter, Different Shift Points?
 

ok enlighten me so the compression isn't whats wrong with the cam i know theres alot too picking a cam displacement, compression, cylinder head flow, velocity exhuast port vs intake flow low lift vs high lift and whole list more but a general statement a that a bigger cam will work better with more compression i don't see as being completely wrong.

Re: New Converter, Different Shift Points?
 

curious he mentioned ati is ati not one of the better converter companies?

Re: New Converter, Different Shift Points?
 

In my opinion ATI is the best. I have had an ATI converter in my car for all of my career with an auto. There are several others that are good as well.

Re: New Converter, Different Shift Points?
 

I have been dealing with customers for over 45 years that have the same problem you do. I call it testosterone poisoning. Some how the camshaft and cylinder heads are where this disease is usually found. The bigger is better disease. What you have is very little dynamic compression with the low static and the high cam duration @ 50. An engine does not operate on just static compression. the closing point of the intake valve vs the static and other engine parameters makes the dynamic. For instance I have a SS Modified engine that has 15.8 static and a 282 @ 50 cam shaft. Where I have the cam installed it pumps 225 lbs on the 4 th hit. It makes 2.5 hp per cu in. What we are all trying to tell you is the engine may be making hp at high RPM it is not making TQ with that long @ 50 cam and the low (relatively) static compression. That is why it likes the slipping converter. It take cylinder pressure to make power. In dyno terms it is BMEP and it usually happens around peak TQ. The trick to making real power is to extend/expand the RPM band of peak BMEP. To do that you need air and fuel to make the cylinder hotter. It is all about Heat and pressure. You need more pressure...Talk to your favorite cam guy, and no offense, not the minimum wage Cam Help salesman. The guy that knows what a cam does. don't start the conversation out by telling him the size cam you want. You already have the results of that. OK, you have my .02 I'm finished. It is late and my pillow needs some head...

Re: New Converter, Different Shift Points?
 

so based on this, I stated this in post #6 without knowing anything about his cam...

knowing that anybody today can put together a 1.5HP/cu.in bracket type engine with out of the box parts. Well I was wrong. The OP has somehow manage to throw this engine together using these junk heads that don't flow 200cfm and the way wrong cam he chose resulting in an engine that only makes about 1 HP/cu.in. not to mention that the 8700 RPM he's buzzing this grenade to is ~ 2500 RPM past peak HP!

As I stated previously, his current cam is about 40 degrees too big at .050 and we have no clue to how much lift or the LSA. Installing the right cam with ~40 degrees less duration at .050 will make ~ 100 more ft./lbs torque at peak and ~ 60 more HP at peak and peak RPM will be lowered by ~300. This engine will require a shift point of ~ 6200, a converter that flashes to ~ 5000 RPM and be geared to trap ~ 6800 RPM. More importantly it will accelerate his 2600 lb. bucket of bolts quicker and faster than it's current performance!

Re: New Converter, Different Shift Points?
 

I'm listening. Thanks for the input.


I will definitely look into experimenting with different cams. It sounds like it would pay to find a shop that has a dyno that will accommodate something besides a SBC. I've had a few members contact me with some helpful information and I appreciate that.

Re: New Converter, Different Shift Points?
 

I understand cylinder pressure and what components affect it but, I can't figure volumetric efficiency or dynamic compression. I understand what you are trying to tell me but, I do know this..........a N/A 340 will not run better, if it's geared to cross the finish line at 6800 RPM. That would be like switching to a 4.30 gear with my current 31.2" tire just to match 135 MPH. No Way. We have turned the post from shift points to torque converters to camshafts........and I'm completely OK with that. I'm learning! I'm even looking into a different car to try to build a super stocker.





Just guessing, I'm going to say peak HP is about 7000 RPM and Peak TQ probably 5400 RPM.