KPG

Buddy, here is the math concerning Todd Z's 9.67 at 149 MPH TT...
(BMEPxDisplacement)/150.8 X Absolute Pressure. Jean has provided the 167 BMEP figure...Todd's car was a 3.6l so displacement is 220ci and assuming they ran 1.5 bar( it may be more) here is the equation:
(167x220)/150.8 x 2.5= 36740/150.8 x 2.5=609.08 Lb/FT MAX That is the base number but Jean has allowed for a 5% increase in BMEP for internal work so that number would be:

(175x220)/150.8 x 2.5=638.26 lb/ft MAX
CJV's 4.3 liter stroker motor would be about 700 lb/ft
If the math is wrong I am positive it will be corrected...

Jean

A time slip certainly does not relate directly to these calculations, there are Qmile calculators out there that will do a better job, reason why I want to keep the quartermile discussion away from it KPG allowing, there are many threads out there discussing it, no point in taking this OT.

A 996TT engine in general with modifications boosting 1.5 Bar will have close to those numbers, could be up a bit or down a bit. One needs to know the depth of modifications however, different or more efficient turbos might bump that percentage a bit (the BMEP was calculated for KKK turbos from the factory since numbers are based on stock P Cars), if displacement is 3.8 ltrs also, whether it is still running on a MAF setup etc.

A 4.3 ltr stroker would give you 760 lbs.ft at 1.5 bar according to the calculation above, CJV's engine could be closer to 997GT3 BMEP territory with all the modifications done to it, depending on the compression it is running.

glpdx

I'm just happy how my measly 996 Turbo throws me back in my seat harder than any other car I've driven. If it can do that with less torque than the N.A. Porsches, great! Whatever it's doing, I like it.

Jean

You have 60% more torque than a N/A engine!

glpdx

I should have rephrased. My personal, and only, dyno has always been how hard the car feels like it's pulling. Every upgrade, I notice a BIG difference. Ignorance is bliss, I suppose.

The more I read, the less motivation I have to actually take any measurements.

Mikelly

I'm glad to see that my numbers fall well within the chart... Makes me feel very good about the combo I purchased and the data included by the previous owner.

Having owned a number of high HP bikes and cars, and having been completely WOWed when I drove Morticia, I'm glad I bought this car... Your info is very informative... Another data point to validate the claims.

Mike

Woodster

Jean,

Great info as always!
Could it be that a 996tt motor's torque max's out but due to some new higher spinning
motor builds that the peak HORSEPOWER (not torque) is much higher?

Marty

Jean

Mikelly

Marty

Thanks. Of course, this is (peak number) torque related, not HP, this is why performance is not directly related to them in the strict sense, things like area under the curve etc.. are not part of this equation.

951M471 CarreraM491

yawn

DublinOh

It seems like you are comparing a N/A engine to a turbo engine at zero boost. Turbos have lower compression so less power without boost.

Jean

Dublin, correct, I think I mentioned that before, compression, more restrictive intake, head design, intercooler losses etc.. Turbo vs turbo engine however is an accurate comparison, once one takes into consideration changes in setup and corrects by some factors. The changes to BMEP will be somewhat limited however with modified turbo engines vs. stock turbo numbers.

LAT

Jean;

coming back to this post for some clarity with regards to the BMEP of my 800 Nm RS engine at 1.2 bar.

What does it calculate out to?

Thanks bud.

Jean

wow it's been a while!

Those are some very impressive numbers, coming from RS Tuning dyno!

Tricky one

The calculated BMEP for a 993TT engine is approximately 156 as seen on my first post, I also estimated that a 5% improvement on this number is very good.

If I do the calculation based on your 800NM and 1.2 Bar, I find that the BMEP is 183. This means that your 3.6 engine has an efficiency of 18% above the normal engine, which for me is impossible, especially knowing that RS engine dyno gives very accurate numbers.

If you look at the chart that I had posted (below) you will see that 590lbs of torque (800NM) are equivalent on the 993TT line to over 1.55 bar of boost, assuming no improvement whatsoever in efficiency vs.stock engine (no exhaust, intake, etc..)


The two possible explanations are as follows:

1- This 800NM torque was measured in overboost mode (RS Tuning specialty, ala 997TT), therefore, while the specs say 1.2 bar, it might have seen those numbers in the few seconds where the ECU goes into overboost at maybe 1.5 Bar, like TB993TT used to have.

or

2- Your engine does not have stock compression.

My calculation of compression would be as follows...
800NM of torque is equivalent on my chart to 1.5bar of boost approximately. You are saying that the boost is 1.2 Bar, the difference is in the compression IMO:

A stock engine has 8.0:1 compression, therefore if your engine had stock compression, at 1.2 bar your effective compression (boost plus engine compression) would be:
1.2 + 1 (atm)= 2.2 x 8 (compression) = 17.6

According to the chart above, to reach 800NM, your boost should be more like 1.5 bar equivalent and not 1.2 bar..
- Effective compression = 1.5+1 (atm)= 2.5 x 8 (compression) = 20

Working it backwards, take the resulting 20 effective compression calculated and convert it into 1.2 bar....20/(1.2 +1)= 9.1 compression ratio.

I hope the above is clear.

My conclusion is that your engine might have some efficiency improvements such as twin plug, exhaust, intake mods, etc.. therefore increasing its efficiency by maybe 5% vs. a stock 993 engine. Then , compression has been increased to 9.0:1 or close to it, and it is running at 1.2 bar. This would take you to 800NM.
The only other option if compression was not increased, is that your engine has produced 800NM while in controlled overboost mode at close to 1.5 Bar.

Does it make any sense to you?

LAT

I follow your reasoning and can offer the following.

1. The engine is a single plug design
2. Compression test was 172 lbs, which is high for an 8.0:1 engine.
3. I have no way at present to verify boost however will do so with my big hand held coming off some manifold attachment later this summer.

So far the only culprit is compression.

You agree?

Jean

LAT

I would say 90% chances are that is has higher than stock compression. Not sure how to read that 172psi, sounds too high but it is very difficult to know what your static compression is exactly with a test. Where all cylinders consistent?

Your best source to know exact numbers is the builder, if he still has the build sheets in one of his files..