Jean

Welcome Marty.
LAT's 580BHP CTR2 adjusted BMEP is 175 but he knows that already

Jussi

That 8.5 hp / lb/min is quite low reading. I have heard this value is normally between 9.5 and 10.5.
So if somebody's 993TT engine is from the worst end of this scale, lets say only 9.5 hp / lb/min and
your OBD MAF measurement gives max. reading 424 g/s which is 1526 kg/h and 56.1 lb/min that makes the very familiar horsepower reading : 533 hp!
That is also the reading what RS Tuning has been said they have on their tuned 993TTs.
This is also the same value what I have got from my tuned 993TT (with the stock MAF).
And it is also the max value of the stock 993TT MAF which it can be measured.
So as speaking in Jean's words with all respect : "Do you really have horsepower, or you have been told you do"
So if you have the tuned 993TT with MAF based Motronic and "over 550hp", do that simple and cheap powertest with OBD scanner and tell us results.

Rassel

Don't want to open a can of Perkele here, but can dual K24's really produce 56.1 lb/min consistently?!

K16's I recall push 24 lb/min and K24's push 28 lb/min.

But to be honest - that's in "perfect mode". Real world I have my doubts the K24's are up for the job in the long run.

Anyone got figures for K16/24 hybrids?

Jussi

Perkele!
I don't know if dual K24 can produce that amount.. but I promise, dual GT2871R can

Maybe MOD or TB or somebody else can tell more about K24s capability to produce air(=>Torque/Horsepower) by doing this OBD MAF test..

Rassel

Wow..
Don't want to go OT - but your internal mods I guess are quite extensive..

Jean

js

A stock 993TT will give you about 8.5 hp/lb, a 996TT will get you to 9.3 according to engine dyno datalogs, it is not hearsay.

As far as the MAF, stock MAF will take a 996TT to 490HP, after that you need to "kludge" the calibration, or change to a bigger one.

The K24 turbos that TB and others are using are not K24 compressors, they are much larger hybrids. The 533PS upgrade they have is a bit more than an ECU remap on stock MAF.

Jussi

Ok, don't want to go too much OT with engine mods..

My point is that everyone can estimate their true horsepower with cheap OBD datalogger.
With your max air flow result (in lb/min), you just multiply that value by 8.5
(or 9 or 9.5 if you have internal mods like head work, cams, twinspark etc)
I like to see others result vs horsepower you have been told you do - there must be correlation in those values or otherwise you have been told BS

This Air Flow measurement comparision should be interesting thing - almost like that popular "times from 60 to 130" -thread..

Edited: if your OBD reader gives values in g/s like mine, then use following factors :
1.257 (for 9.5, with very good flow improvement mods)
1.19 (for 9.0, with some improvement)
1.124 (for 8.5, stock engine)

TB993tt

The difference between 8.5 and 9.5 on an engine flowing say 1550kg/h is 57hp so it is going to be pretty important to get this multiplier correct otherwise the data is fairly flakey - where are these "flow multipliers" from and how accurate are they ?

TB993tt

Just got this from a Superflow engine dyno site !
Brake specific air consumption (BSAC) is a measure of how many pounds of air it takes to make 1 hp for 1 hour (lb/hp-hr). The lower the number, the better: It should be in the 6s or lower if the carb is set up right; a 5.55 BSAC number is really good. However, because BSAC varies per engine displacement and power level, there isn't any hard and fast "correct" value

If this is right then we are looking at the BSAC from the wrong direction. It is the BSAC number which determines how much power your engine can make out of the mass of air delivered - so it is pretty pointless comparing kg/hr readings as for example my engine may have a BSAC of 6 and only need 1550kg/hr of air to produce say 560hp and another engine may need 1600kg/hr to make the same power due to its inferior set up......

Jussi

TB: don't let these different numbers disturb you - they are the same thing.

I show you a little math:
when I and Jean speak about 9.5hp / 1lb/1min this comes to form
9.5hp/(1lb*60hr) which means that 1/1lb*9.5hp/60hr and invert that and you'll get final form 1lb * 60hr/9.5hp which is 6.3 in that BSAC number.
So, trust me and you can estimate your car's horsepower with measuring MAF value. Factor 8.5 which is for stock 993TT (tested in engine dyno) gives very poor value 7.06 and factor 9.5 gives reasonable value 6.3 which is from my car and tested also in engine dyno.
I have better value because I have headworks, RS cams, TS, custom made large and freeflow exhaust system and also bigger inlet for turbos - only IC is still stock but it is still stock only because of you. You have kept me off from crappy FVD/Cargraphic/etc ICs

Addition: you can't measure that 1600kg/h with stock MAF and either that 1550kg/h - these numbers are beyond its limits.
So, only way you can get much bigger horsepower reading from max 1546kg/h value is just because your engine flows better, it has better X hp / 1lb/min value!
If you have super hyper free flow system and it gives you 10.5 hp / 1lb/min then it makes real 596 hp..
..but Jean doesn't like that 10.5 number

Jean

The maximum my pressure sensing/low air restriction/No MAF engine could hold at peak HP level is 8.5, dropping from 9.1 at 6K RPMS, so anywhere between 8.5 and 9.1 is reasonable for a modified engine at close to max HP. These are numbers based on engine dyno datalogs. The measurement is quite straightforward.

Todd K. has seen a maximum of 9.3-9.5 on modified 996TTs at peak HP.

This is not relevant to torque calculations on this thread however, as it is HP related.

TB993tt

I still don't get how you can estimate the hp from a given MAF engine ?

If the max possible (if this is proven due to physical restrictions) flow number is 1546kg/hr then the hp number surely depends on the BSAC number which could be anywhere between 8.5 (giving 483hp) or say 10.5 (giving 596hp)......One only knows the true BSAC number if the true Porsche equivalent power output is known and we all know what a grey area that is
BTW if my maximum flow IS 1546kg/hr then my engine's BSAC is 10.1hp/lb/min so I would expect higher flow numbers than the 1546 unless RS really has worked some magic

Jussi

You can estimate if you measure max MAF value with OBD scanner when you accelerate full throttle in 4.gear or 5.gear and then multiply that with ... lets say, moderate factor 9.5.
I've been always said you can _estimate_, so it is not exact or absolute true value because everybody's engine, tuned or not, are different (=> X hp / lb/min value is different).
BUT, then we can at least compare these values against each others. Like I have measured that 424g/s and I have about 533hp.
My opinion is that this is very interesting - car physics.

This is electrical restriction. It is max value in Motronic's ROM 1x256 table : 4.98V=1546kg/h

Lets make this thing right or my way
so first you measure that MAF value and then you have reliable horsepower measurement from (RS) dyno. Now you can estimate this BSAC number or better said, "X hp / lb/min" -value.
For example you have measured that 429g/s value and RS Tuning has dynoed your car and got 562hp. You can now estimate that your engine's flow capacity(also efficiency) is 9.9 hp / lb/min which is very good value !

TB993tt

Yes, of course I understand that I will be able to work out my BSAC after getting the max kg/hr reading from the hammer, but I KNOW mine will be correct.
What I am saying is doing this is a little pointless. For example if one asked one of the Andial boys who thinks they have 58Xhp to measure theirs then they would doubtlessly come up with a 10.5 or whatever which is a pretty pointless number so the flow rate proves ziltch in this context......

It would be interesting and worthy of discussion however if my car (or others) manage to flow more than the 1546kg/hr number

Jussi

Yes, it is interesting. I'd love to see how much air flow these RS tuning's car can get and also how much Andial ones or Kevin's Stage X, etc.
And if you also publish dyno hp reading, then we can make a list from best X hp / lb/min values..
Another point is that if you don't have that dyno proved hp value, you just have previous owner's promise: "it has at least 600hp" then you can test that value with MAF value * 9.5 or whatever would be average values from our dyno proved cars.. That is my original point : "do you really that hp values, or you have just been told you do"