Lemme

This is a graph of my MAF flow (grams per second) for a part throttle, 0-60 mph run on my 87 with the tranny in D with a gear change occurring at 4000 rpm. Is there anything one can conclude from this? Does this show the limit of the engines breathing ability? Is it normal for the air flow to drop so much mid run when the trans shifts up a gear?

bjankuski

It looks normal to me, when the transmission shifts the RPM drop and the air flow drops.

Lemme

Yes it does make sense as one would expect the air flow to be generally proportional to the rpm. As the tranny shifted at 4000 rpm in this example maybe this graph isn't showing the breathing limits of the intake and heads.

Maybe I should just leave it in 2nd and do a run up to 5500 rpm and take another look at the graph. Maybe then I will see it gasp for air!

FLASH92LT1

Since airflow is a function of RPM you'll ALWAYS see a drop at the shift point. Same as you would for Horsepower or Torque.
That willl show a smooth, increasing curve up to your redline.
You're not seeing it "gasping" for air. An engine doesn't "want" more air. It pumps what it is designed to pump.
Why are you watching your airflow?

Rick - '92 LT1

bjankuski

If you run a TPI engine to 5500 I doubt the air flow will decrease as it runs out of breath, instead you will see a decrease in the rate of change in the airflow. (it will level off or increase slowly)

FLASH92LT1

You'll see a drop in airflow at some point. As you pass the engines designed maximum volumetric efficiency the airflow will drop off because the Throttle Body, intake runners, intake ports, valve size, etc., can no longer flow enough to fill the cylinder efficiently at the increasing RPM.

Rick - '92 LT1

Lemme

I keep reading that on an L98 the TPI is the big limitation for horsepower at higher RPM because of the intake runners. In addition people always talk about high flowing intakes, cams, heads and freed up exhausts.

So thats why I am looking at the air flow. I want to see where the 'breathing' problem is so I can improve it.

FLASH92LT1

True! The runners are small and long to increase low end torque but at a sacrifice of higher RPM power.

But you're not going to see it by monitoring the airflow of your engine. That graph is just showing what your engine does. It has no way to show, nor is there any way to interpret, where any problem may be. It is just a graph of airflow.

You could start modding or replacing parts and see how that airflow improves (or not). Change the throttle body, check the new flow. Bolt on some larger runners, check the new flow. Swap heads, check the new flow.

But you won't be able to detect any breathing problems by monitoring it.

Rick - '92 LT1

Lemme

Sorry. I think I am communicating poorly what I am doing here. I am not just looking for a malfunction in the engine. I am looking for performance limitations. As I have done some mods already it would be nice to know whether I am on the right track.

Like many wannabes I am trying to plan ways to get my stock 87 to perform like a z06 for a fraction of the price. By graphing the current performance of the car and by making observations of different parameters vs time etc I hope to be able to set some performance goals for certain parameters.

I want to be able to see where the breathing chokes the performance and then modify it and run another test (as you suggest). I want to understand how to design and/or mod an engine to achieve predefined performance goals. Maybe air flow and torque are directly related!

GREGGPENN

By George, Dr. Watson, I think you've discovered Moriarty's devious plot to capture all of the power in the world. He's going to suck air to gain power! Utterly diabolical!

And, they said it couldn't be done...And, had never been spoken of before!

FLASH92LT1

No, you're doing fine. I am pretty sure I understand what you're trying to do.

What I'm saying is that chart won't show you where that is. Go back and look. Now point out the 'choke point'. You can't. I can't. It can't show a choke point. If it did reach a choke point the airflow wouldn't increase from there and you wouldn't see it.

Now, if you knew someone with higher flow numbers then you'd have an idea of how much air you COULD flow. But you still wouldn't know any 'choke points'. All you could do was follow his sequence of changes and note your flow.

The TPI engine is a whole system designed as a low RPM torque engine with small runners, a small cam, small valve, low flow heads. Its not a big power engine with a small intake meant to 'choke' off power. It was never designed to make power at 5500 RPM.

But you already know the TPI doesn't flow well. Anything you could do to increase it will create more power. I'm sure there's a thread on L98 TPI buildup here somewhere.

BINGO!! You're dead on!! Maximum airflow, and maximum volumetric efficiency, occur at peak torque!!

You could easily get a fraction of the performance of a Z06 for a fraction of the price!!

But seriously.... a 2001 Z06 was 385 HP! That's 135 more than the best TPI. You'd need a 54% increase to reach it. THAT'S a tall order!!

Rick - '92 LT1

tequilaboy

Neglecting frictional losses, the airflow is proportional to hp.

I dug out some old datalogs that were made during a dyno pull. In my case, the airflow peaked about 400 rpm after the hp peak. Even though the airflow was still increasing, the losses were increasing at an even greater rate.

Peak HP was 245 @ 4800 rpm, Peak airflow was 207 gm/sec at 5200 rpm and then declined as a function of rpm.

Lemme

So maybe you think I am a bit of a sucker! You're probably right but I am beyond caring!

Lemme

I think this is something I can compare to. In my graph I hit 207 g/s at 4000 rpm and the airflow was still climbing strongly. Thats why I suggested doing a datalog up to 5500 rpm to see if I can find max airflow.

In another post I saw a member aiming for 320 g/s max! Not sure if it was a L98 though.

Lemme

I think I understand what you are getting at. This is only looking at an input (a major one though) not a test point along the way. Again poor communication on my part to imply I am looking for choke points.

The choke points are already known by people on this forum (and hopefully in time by me). I don't need to rediscover them (Dr Watson!). My goal is to remove them in a cost effective and systematic fashion that takes me in the right direction of straight line performance.

Thanks for your post.

GREGGPENN

I gotta admit I'm one of the most "wordy" people I know, but that's gotta be one of the most techically complex ways of saying: you need to get rid of your OEM runners/intake, greatly improve your heads, then stroke and cam your motor that I've ever seen!

Of course there's NOS or FI too. You're not going to find Z06 performance by doing scans. THAT'S the part you haven't done a good job conveying!

Lemme

I thought it was the most "non-technical" way of conveying it actually. Bit like what an accountant would do! Bang for the buck, performance goals etc ...

You guys have the answers. I admire that. At the moment I have a lot of questions.

I am certainly not looking for performance gains by doing a scan. However, I would at least like to satisfy myself that I have got some bang for my buck so far.

Orr89rocz

YOu wont discover a choke point with the MAF sensor by looking at graphs of the g/s. The ecm is only going to display 255 gram/sec flow max, but that does not mean the MAF is choked out. It will pass MORE air than what it can measure.

LS1 MAF's are about the same diameter but will read up to 512 g/s i do believe. The ecm and sensor are just calibrated and setup to handle that large airflow

My 383 HSR motor peaked the MAF at 4500-4800 rpm. It read 255 and stopped reading. BUT i made 400whp at 6300 rpm and pulled to 6600 without falling off. 4500 rpm is about where I peaked torque. It was flat from 4000-almost 5000
So the 3" MAF was not a restriction. I changed to a 3.5" setup and it did not help power from what I could see at the track.

Lemme

Have you got a spare one of those motors? I think that will help me cut to the chase and get where I want to be pretty quickly! I presume a HSR motor is not an L98! I reckon you must have beaten the 300 g/s mark easily.

Lemme

Actually, I found a better graph that I had done on the same day (5 minutes later) which was at WOT



My conclusion from this is I'm not going to get more than 225 g/s (occurred at 4500 rpm) out of this motor as it is. What would be nice to know is what would a stock 87 be maxing out at? Hopefully less than 225 g/s! Unfortunately I only got my datalogging gear after I'd started modifying. Also what is the best g/s one could expect from a highly modified L98?