Compression Ratio and Stall

[johnnytsi]

Starting to think about a new shortblock and am interested in wether or not higher compression would help get up on the converter quicker/easier?

John-

 

[turbotalon1g]

and you didn't post this on link? ::

I've never messed with higher compression back to back on the dyno, but if it makes more TQ then it would work, wouldn't it?

 

[johnnytsi]

and you didn't post this on link? ::

I've never messed with higher compression back to back on the dyno, but if it makes more TQ then it would work, wouldn't it?

was going there next when my Grandkids showed up. We got caught up in watching Kung Fu Panda 2 3D.

AND that is the real question - does a higher compression engine make more torque while off boost?

 

[turbotalon1g]

I'll post on my local forum and see what I hear, there are a few locals that have played with compression ratio.

 

[BogusSVO]

CR has little to nothing to do with converter stall.

The stall of a converter is for when it locks up, larger cams is the main reason to go to a higher stall converter.

 

[johnnytsi]

CR has little to nothing to do with converter stall.

The stall of a converter is for when it locks up, larger cams is the main reason to go to a higher stall converter.

Without Nitrous, I can get my setup to stall at 4200rpm in 12-15 seconds
With an N2o shot, I can get to my 4200rpm stall in 1 second.

I'm interested in ways to get to my 4200 stall in less than 10 seconds without a Nitrous shot.

So - given the cams and converter remain the same, will a higher compression ratio shortblock help my setup get up on the converter quicker?

I'm currently running a 9:1 2.3 S2 cams and a Sinister 10" Max stall converter.

Things on the table are

• Higher compression 2.3
• 2.4 shortblock
• Go back to my fp3 cams
• tweek my cam timing
• Converter change

 

[jrohner]

It should help, how much more compression you need for a noticeable difference I would like to know myself.

 

[Diamond Star Werks]

AND that is the real question - does a higher compression engine make more torque while off boost?

Yes it does.

 

[BogusSVO]

Let me see If I can say this with out sounding too foolish. It has been years since I have been in auto tech school.

The stall of a converter, is to allow for slippage so the engine can get into its working RPM band, or the "Meat" of its power band. Then the converter locks up at its stall rating. (4200 RPMs in your case)

Now there are 3 or 4 main parts built into a torque converter... I forget the proper names, and I am in no means a transmission guy, But building engines I have to have an understanding of how they work.

You must be logged in to view this image or video.

So you have an engine that reaches 4200 RPM in appox 15 secs w/o NO2 and appox 1 sec w/ the Nitrous.

Your goal is to get 4200 RPM w/o the Nitrous in 10 sec or less.

So the engine needs to rev faster.

The way I see it, you need to lessen the rotating assembly in the engine.

This can be done by going to a lightweight assembly, such as a Butcher crank, Alumn. con rods, and ultra light weight pistons.

Now raising the CR may help by a few hundred RPMs, But I doubt you will reach your goal with a bump in CR unless you go thu the roof with it.

The reason I say "May help" is the higher CR will be geting the engine to spin faster due to more force being applied to the piston on the power stroke.

 

[jrohner]

You need more torque to get up on the converter. Weight of the rotating assembly doesn't effect torque, compression does. By your logic a V8 would need a looser converter than a 4 cylinder because it's rotating assembly is heavier.

Put a torque converter in an engine with more torque and it's stall RPM will actually be higher, there is no exact stall RPM of a torque converter because the engine it's bolted to makes a big difference.

 

[BogusSVO]

You need more torque to get up on the converter. Weight of the rotating assembly doesn't effect torque, compression does. By your logic a V8 would need a looser converter than a 4 cylinder because it's rotating assembly is heavier.

Put a torque converter in an engine with more torque and it's stall RPM will actually be higher, there is no exact stall RPM of a torque converter because the engine it's bolted to makes a big difference.

I am saying RPM matters, not torque, and not the weight of rotating assembly.

A V8 (350 SBC) has a fairly low stall about 1800 RPM stock.
I know that my stock converter in a A4LD is about 2200 RPM in a 2.3T Ford
A V8 devlops torque and a much lower RPM band than a 4 cyl.

So with what you are saying a V8 has a higher stall than a 4 cyl?

The stall of a converter is set by the number of fins inside the converter.
More fins= lower stall
Less fins = Higher stall

Now I will agree that a V8 rotating assembly is heavier than that of a 4 cylinder, but a V8 also revs slower than a 4 cyl. and the V8 has a lower redline than that of most 4 cylinders.

Now by lowering the weight of the rotating assembly allows the engine to rev faster. Same reason the 5 speed guys loose the the cast iron flywheel and go to a lighter alum flwywheel.

 

[Diamond Star Werks]

You need more torque to get up on the converter. Weight of the rotating assembly doesn't effect torque, compression does. By your logic a V8 would need a looser converter than a 4 cylinder because it's rotating assembly is heavier.

Put a torque converter in an engine with more torque and it's stall RPM will actually be higher, there is no exact stall RPM of a torque converter because the engine it's bolted to makes a big difference.

Your wrong man. Rotating weight does affect torque and hp. Put. An engine with 300lbs of torque on a stock assembly then put that exact engine with all lightweight components. You gonna tell me there will be no increase at all with all lightweight components?

I think so my friend. Less weight = less loss of energy. Less energy loss equal more functional energy equals more power. More torque/power equals a faster stall.

 

[HighPSI TSi Guy]

I'm going to clarify all the misinformation here..

Converter is just an automatic slipper. Stall speed is NOT where it "locks". DSMs don't even have a lockup type converter (2Gs do, but not under power, it's for cruise only). The stall speed is simply a factor of torque vs the K factor of the converter. More torque = higher stall. How fast it blows through the stall is dependent on K factor and converter diameter. More torque will bring up the same stall faster. A non lockup type converter will NEVER "lock", it has a point at which it is considered "coupled" which is where it has reached it's full efficiency. The same converter will stall at different speeds based on load (even vehicle weight is a factor) and torque. The more boost you make, the more torque you make, the higher the stall speed. The closer you get to the coupling point the more torque it takes to raise the stall speed. The point at which you do not have enough torque to raise the stall speed is the actual stall speed.

To answer the original question, yes, higher compression yields more torque which will bring up the stall faster than a lower compression. Once you get into boost that is where it gets tricky. A lower compression will spool easier, but make less torque. There is a minimum torque required to maintain stall speed. Retarding timing will create a similar effect of the low compression. So IMO it's better to run the compression as high as you want, and then tweak the maps to get the stall up behavior desired.

 

[jrohner]

I am saying RPM matters, not torque, and not the weight of rotating assembly.

A V8 (350 SBC) has a fairly low stall about 1800 RPM stock.
I know that my stock converter in a A4LD is about 2200 RPM in a 2.3T Ford
A V8 devlops torque and a much lower RPM band than a 4 cyl.

So with what you are saying a V8 has a higher stall than a 4 cyl?

The stall of a converter is set by the number of fins inside the converter.
More fins= lower stall
Less fins = Higher stall

Now I will agree that a V8 rotating assembly is heavier than that of a 4 cylinder, but a V8 also revs slower than a 4 cyl. and the V8 has a lower redline than that of most 4 cylinders.

Now by lowering the weight of the rotating assembly allows the engine to rev faster. Same reason the 5 speed guys loose the the cast iron flywheel and go to a lighter alum flwywheel.

This had the potential to be a really good thread, but took a turn for the worst pretty quick with 'bogus' information. Stating lock up and stall in the same sentence like they have something to do with each other pretty much sums up your knowledge of converters (which you stated twice so far). Lock up is with a clutch inside a lock up converter; stall is basically the point when the converter holds the engine back from gaining RPM.


You need torque to get RPM with the torque converter when the car is not moving. A converter reacts to torque not RPM, it's not a centrifugal clutch with weights and springs like whats on your Briggs and Stratton engine, look at the pic YOU posted. Put the stock converter from a 4-cyl Colt into a V8 and it'll stall at 5 grand. A torque converter multiplies torque not RPM, they don't call it an RPM converter for a reason.

With the SAME identical converter, YES the V8 will have a much higher stall. My 4g63 will only hit 2200 RPMs without boost when not moving, yet when I get boost it'll go to around 4000 RPMs, why? A thing called torque.

Weight of the rotating assembly doesn't matter because the engine's RPM's per second of acceleration is very slow when you're getting up on the converter (the smaller engine the worse). Nitrous increases torque, yet you think there is some other reason that it gets you up on the converter faster? It's definitely not making your engine lighter inside. A 2.3 should be harder instead of easier to get up on the converter since the crank is heavier WTF? A diesel engine would never stall because the rotating assembly weighs more than an entire 4g63 longblock, again WTF. My 408 Windsor with 524lbs of torque must suck with an auto since the crank is heavy, wait a sec ... I don't even have to get up on the converter first cause it stalls instantly because of all that torque.

If the engine doesn't matter, why do they always ask every thing imaginable about your engine when you want a converter built? They aren't asking just because they are curious and bored with nothing better to do.



A couple quotes after 2 seconds of Googling (from people that actually make torque converters):

Why is stall speed different with the same converter on different engines?
Engine output is what really determines stall speed for a given converter. For this reason the converter you have been using may not be adequate when you improve performance of your engine. This is particularly true in using an improved camshaft. Improving heads, carburetion, installing turbos or manifolds can all affect stall speed. Remember, you want to have stall speed matched to your particular car combination.
--------
The key point to remember is that stall speed is a balancing act. Stall speed is always a balance between the engines ability to produce power and the converters ability to hold it back. A change to either side will alter the balance and change the resulting stall speed.

The speed at which stall occurs with a given converter is a function of engine peak torque. It is clear that the stall speed on a given converter will not be the same when coupled to a tame small block as it is when coupled to a high performance big block.

 

[johnnytsi]

wow - this went sideways in a hurry

 

[BogusSVO]

I'm going to clarify all the misinformation here..

Converter is just an automatic slipper. Stall speed is NOT where it "locks". DSMs don't even have a lockup type converter (2Gs do, but not under power, it's for cruise only). The stall speed is simply a factor of torque vs the K factor of the converter. More torque = higher stall. How fast it blows through the stall is dependent on K factor and converter diameter. More torque will bring up the same stall faster. A non lockup type converter will NEVER "lock", it has a point at which it is considered "coupled" which is where it has reached it's full efficiency. The same converter will stall at different speeds based on load (even vehicle weight is a factor) and torque. The more boost you make, the more torque you make, the higher the stall speed. The closer you get to the coupling point the more torque it takes to raise the stall speed. The point at which you do not have enough torque to raise the stall speed is the actual stall speed.

To answer the original question, yes, higher compression yields more torque which will bring up the stall faster than a lower compression. Once you get into boost that is where it gets tricky. A lower compression will spool easier, but make less torque. There is a minimum torque required to maintain stall speed. Retarding timing will create a similar effect of the low compression. So IMO it's better to run the compression as high as you want, and then tweak the maps to get the stall up behavior desired.

First, Thank you for correcting the terms I used. I used "lock" where I should have used "coupled"

I do understand, that there is a lock up torque converter and a non lock up torque converter.

Now could you define what the K Factor is?
This is a new term to me and I wish to understand.

After a bit of reading, I also understand that stall, can be refered to in 3 ways.
Brake Stall
Flash Stall
True Stall

Now JohnnyTSI.. Which stall are you referring too?


The reason I brought up going to a lighter rotating assembly is simple.

If I am understanding this correctly, You need torque to "Get up on the converter"

So that means the engine needs to produce the torque needed.

I am sure we can agree that you do not make the same ft/lbs of torque at 1000 RPM that you do at 3000 RPM.

So if the torque band if your engine falls between 3000 - 6000 RPMS, and that is where you need to be for the Sinister 10" Max stall converter to be most effective.

( JohnnyTSI, your dyno sheet was not up for me to view when I looked today, so the numbers are random)

It just makes sense to me to get the engine to rev as fast as you can,to get into the torque band, and a lighter rotating assembly would help achieve this.

I do apologize for taking your thread sideways.

I am always open to learning new ideas and theroys, and sometimes some things may have to be explained at a grade school level so I can see the logic in it.

 

[johnnytsi]

No worries!

The title of my thread should have read: Compression Ratio and Stall times

What I want to accomplish is to minimize the amoutnt of time it takes to get 'up on the converter'.

The longer stall times generates way to much heat! During the early part of a competition it isn't as much of a concern as there is plenty of time for the trans to cool down between races. But as I get further up the ladder in the elimination rounds, the runs get closer together, the less time The transmssion has to cool off between rounds.

I need to figure out how to get my engine to make more torque off boost to shorten the amount of time it takes to get up on the converter and thus help keep temps down.

 

[jrohner]

Have you played with timing and fuel a lot? If my car is a bit rich it takes forever to get up on the converter (or never does). You also need enough timing to keep torque up enough, but not too much either since lower timing spools the turbo at a lower RPM. For the most part my car likes to be on the leaner side with quite a bit of timing. Also, make sure your air filter is not taking in hot air from under the hood, that makes more difference than anything else tuning wise.

 

[Diamond Star Werks]

If your trying to keep trans temp down why not use an external cooler for it?

 

[johnnytsi]

Have you played with timing and fuel a lot? If my car is a bit rich it takes forever to get up on the converter (or never does). You also need enough timing to keep torque up enough, but not too much either since lower timing spools the turbo at a lower RPM. For the most part my car likes to be on the leaner side with quite a bit of timing. Also, make sure your air filter is not taking in hot air from under the hood, that makes more difference than anything else tuning wise.

I'm just now exploring options to get the car spooled without the N2o shot, Lots mor experimentation is in the plans.

If your trying to keep trans temp down why not use an external cooler for it?

I already have a large B&M with a fan on it, I also have a second cooler purchased, Beefing up the trans cooling system is definately in the works.

John-

 

[Boomdeeze]

Interesting thread, would like to see some results as I am going to a 11.5:1 2.0 and need to be able to bring my 9.5" billet TC to stall correctly.

 

[GDNF2ET]

Turbo size and exhaust housing size play a large part in brake-boosting an auto car..
Without an $800 converter or juice, a 35R is the max you can get away with, and thats with the most restrictive, small exhaust housing available...This is my experience with a 2.0 4g63.....