T2 2.2 to 2.5 conversion how much HP gain?

[Shelby VNT]

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I completely agree here. The 2.5's strength is also it's weakness. High torque is what kills our engines in my opinion. For the reasons already mentioned and the fact that the 2.5 is more prone to detonation because of the excess torque it makes.

How does making excessive torque cause detenation? Isn't it more dependent on the compression ratio, cylinder temp. and a lack of fuel or low octane?

Correct me if I'm wrong, but the 2.5 isn't all that prone to detenation, is it? I always thought the big downside to the 2.5 was that the pistons are less tolerant of handling detonation because the pistons were more fragile by nature of design due to their rather small ring land spacing and the less material. The 2.2 pistons, on the other hand, are more durable and can handle slightly more detenation without damage resulting.

[Ben Paquin]

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Originally posted by Shelby VNT [b]How does making excessive torque cause detenation? Correct me if I'm wrong, but the 2.5 isn't all that prone to detenation, is it

Cylinder pressure creates torque. High cylinder pressure greatly helps the onset of detonation. As rpm rises chances of detonation is lower. 2.5 makes high torque at low rpm.
That's why.

[BadAndy]

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Originally posted by Ben Paquin Cylinder pressure creates torque. High cylinder pressure greatly helps the onset of detonation. As rpm rises chances of detonation is lower. 2.5 makes high torque at low rpm. That's why.

I agree and disagree....or should I say don't understand

Yes cylinder pressure creates torque and yes it COULD help attribute to detonation.....with the help of restriction which is obviously lower at lower RPM

I don't think I understand "as RPM rises chances of detonation are lower" How can the chances be lower as RPM increases when boost and restrictions increase (understanding that timing is retarded at the onset of boost) not to mention more heat is generated.....

I have never experienced low RPM spark knock (detonation) in our cars no matter what motor I had at the time. I do know that the 2.5 is more prone to breakage vs. a similar 2.2 if spark knock happens at high RPM.

[Ben Paquin]

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I don't think I understand "as RPM rises chances of detonation are lower" How can the chances be lower as RPM increases when boost and restrictions increase (understanding that timing is retarded at the onset of boost) not to mention more heat is generated..... I have never experienced low RPM spark knock (detonation) in our cars no matter what motor I had at the time. I do know that the 2.5 is more prone to breakage vs. a similar 2.2 if spark knock happens at high RPM. [/b]

That's a very good point you bring here.
You are correct in your thinking. The reason why chances of detonation are greater at lower rpm is because there is more time for the phenomenon to happen and it has a greater effect when it does because the engine speed is slower. Usually detonation is at it's greatest at peak torque which is usually just before boost stops rising.

It is true that as you rise in rpm and boost you increase intake temps which in turn help create detonation. Now on a correct setup that includes a bigger turbocharger and more exhaust flow, a large intercooler that keeps intake temps reasonable, detonation should be lower at higher rpm. As long you add the correct amount of fuel to compensate for high rpm and high boost.

[4sfed4]

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Originally posted by BadAndy I don't think I understand "as RPM rises chances of detonation are lower" How can the chances be lower as RPM increases when boost and restrictions increase (understanding that timing is retarded at the onset of boost) not to mention more heat is generated.....

As rpms get up there (on a 2.5 in particular) torque is dropping like a rock. Thus, cylinder pressure gets lower and lower with rpm. This holds true with any engine once its past peak torque as peak torque is where cylinder pressure is highest. So, any risk of detonation that you might find due to cylinder pressure is reduced with rpm.

From what I have seen with my buddies with fancy pants standalone engine management systems, they also tend to slowly ADD ignition timing once they get to peak boost all the way to redline since the detonation threshold is increased with rpm.

[4sfed4]

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Originally posted by Ben Paquin The reason why chances of detonation are greater at lower rpm is because there is more time for the phenomenon to happen

Thats exactly why one can advance timing past peak boost since now as rpm is increasing, there is less and less time for the ignition event to proceed. So, you can benefit by starting it earlier (within reason of course).

[glhsken]

a thousand words.


The cars...

2.5L t3/4 twin cooler 50 stage III .63 RP 3 bar cal 3050 lb car that ran a 12.88 @ 108 Hybrid tranny (should increase load the 2.5L likes)

2.2L t3/4 twin cooler 50 stage II .63 RP 3bar cal 2600 lb car 12.5 @ 112

Neither cars cal was optimum.. the 2.2L was off the wideband the entire run, The 2.5L's fuel was good, but due to the swirl head, timing was at 8 base (the 2.2L had a base of 10 initial) Both cars were set-up SAFE.

Both cars were running stock swirl heads 3" exhaust ported exhaust manifolds and 3" exhausts. Both cars are 5 speeds. For that run the 2.2 was at 22 psi the 2.5 between 24 and 25.


The 2.5L made peak torque approximately 200 rpm sooner. Both cars had peaked by 4350 where the plot is shown. from the peak torque point, the 2.2 stayed above the 2.5L for the rest of the run...

[glhsken]

Stole a page out of yor book Larry.


Let's assume both cars weighed the same... From 4400 rpm on which car would pull harder??

By 4400 rpm, the 2.2 had passed the 2.5L torque and stayed there for the rest of the run.

These are both well built, well thought out cars.

[BadAndy]

Quote:

Originally posted by Ben Paquin That's a very good point you bring here. You are correct in your thinking. The reason why chances of detonation are greater at lower rpm is because there is more time for the phenomenon to happen and it has a greater effect when it does because the engine speed is slower. Usually detonation is at it's greatest at peak torque which is usually just before boost stops rising. It is true that as you rise in rpm and boost you increase intake temps which in turn help create detonation. Now on a correct setup that includes a bigger turbocharger and more exhaust flow, a large intercooler that keeps intake temps reasonable, detonation should be lower at higher rpm. As long you add the correct amount of fuel to compensate for high rpm and high boost.

Ahhhh....makes sense to me now as the "winow" for it to occur is larger....... although I don't think it is a problem with our cars.....that's not to say that it won't happen but yet as you are saying it becomes more of a possibility when compared to a 2.2

But how about actually being harder on parts? (rings/bearings)

The rings I understand as they do not have the larger ring land to help absorb the shock/heat of combustion as does a 2.2 piston.....this is probably the biggest contributer .......not to mention the increased stroke.

The (rod I assume?) bearings I also understand to a extent as the 2.5 produces more low speed torque and crank is moving slower so therefore more pressure is exurted at a certain point and it is at that point for a longer period of time...BUT...it isn't like the 2.5 produces that much more low speed torque than a equally equipped 2.2 to the point that increased bearing wear could be measured

[glhsken]

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BUT...it isn't like the 2.5 produces that much more low speed torque than a equally equipped 2.2

Exactly...

Andy, you know both cars in the plot... His car and mine are identical except for the motor size and turbine wheel (his is more free flowing)

He has since changed to a "G" head. I now have an rp stage "let's get it on" head "thumbs up

I did want to add... good thread... this should be a must read thread for people looking at the 2 choices.

Plot pertinants... std correction 0 smoothing... (added for Larry's benefit)

[4sfed4]

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Originally posted by BadAndy BUT...it isn't like the 2.5 produces that much more low speed torque than a equally equipped 2.2 to the point that increased bearing wear could be measured

Sorry...I just cant resist!

This is 2.2 torque! BWHAHAHAHAHAHA

[4sfed4]

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Originally posted by glhsken Stole a page out of yor book Larry.

hehehehehehehe

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Let's assume both cars weighed the same... From 4400 rpm on which car would pull harder??

The car with less torque???

hehehehehheehe

[glhsken]

And where are those bearings now???

(same place my least set went!!!)

[4sfed4]

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Originally posted by glhsken And where are those bearings now??? (same place my least set went!!!)

hehehehehehee....Both sets are in a quiet "forever home" resting place.

My rings are in the same place. They already experienced their version of Hades :big grin:

[4sfed4]

Quote:

Originally posted by glhsken Plot pertinants... std correction 0 smoothing... (added for Larry's benefit)

Ohh! I forgot about the "Adler correction factor standard".

In that case----

Heres the same run as above



EDIT - On the above plot, the bottom axis is MPH and not rpm. 4400 rpm = 84 mph

Thus, 405.88 hp at 4400 rpm = 484 ft lb = not good for rings or bearings :big grin: