Ideal exhaust diameter on a stock 80

[landtank]

My estimate was probably more of a guesstimate. I've recorded over a 2 lb increase in air flow with just changing my MAF. From what I've read that is about 20 HP. As far as exhaust systems, I know absolutely little to nothing of how restricted they are and what can be achieved but guessed that 15 HP would be reasonable because much less than that and it would be hard to feel any difference and people have posted that it does make a difference.

So maybe 30 hp is more reasonable.

 

[SUMOTOY]

My estimate was probably more of a guesstimate. I've recorded over a 2 lb increase in air flow with just changing my MAF. From what I've read that is about 20 HP. As far as exhaust systems, I know absolutely little to nothing of how restricted they are and what can be achieved but guessed that 15 HP would be reasonable because much less than that and it would be hard to feel any difference and people have posted that it does make a difference.

So maybe 30 hp is more reasonable.

Is this 2lbs per hour/per minute/per second? I can do those calculations pretty quickly, but need the time unit, I'm in lbs per hour (per cylinder and total) but can change it fast enough.

I would caution that exhaust systems usually make for a gain in VE at a much narrower rpm. I'm still thinking 35hp on a 200hp motor sounds like a bunch if just doing external engine bolt ons.

Scott Justusson

 

[concretejungle]

Those guys backed it up with dyno runs before installing and then after. First run was stock, second run was with a new exhaust, exhaust manifold, high flow air filter/intake. That yielded 35 poneys.

 

[landtank]

Is this 2lbs per hour/per minute/per second? I can do those calculations pretty quickly, but need the time unit, I'm in lbs per hour (per cylinder and total) but can change it fast enough.

I would caution that exhaust systems usually make for a gain in VE at a much narrower rpm. I'm still thinking 35hp on a 200hp motor sounds like a bunch if just doing external engine bolt ons.

Scott Justusson

Not sure of the time, it's OBDII so it's the standard unit for whatever they dictated.

The stock unit reported 21+ lbs of air flow. So that would be accurate for the 212hp the engine is rated for.

The next run immediately afterwards recorded 23+ lbs. This was actually done on two trucks with near identical results.

Factor in whatever you want for the exhaust, I was guessing as I stated above.

 

[Land Speeder]

In my opinion, no...but others disagree. I'm running gutted cats and a glass pack, 2.5 cats back, feels like it has more torque (starts off better espically when towing) and raw horses (freeway speeds hold easier). Could be just my 3FE, but I dont see why it wouldnt be better on any other engine with propper headers/manifolds that maintain the backpressure.

Got to agree, I'm not scientific but.... I replaced my 2 cats with one catco hi-flow cat, 2.5" tube to a borla muffler with 2.5" tail pipe. It was very noticable power, too much to be placebo.

 

[SUMOTOY]

Got to agree, I'm not scientific but.... I replaced my 2 cats with one catco hi-flow cat, 2.5" tube to a borla muffler with 2.5" tail pipe. It was very noticable power, too much to be placebo.

It's not due to the cats would be my only point. The borla and the 2.5 can help. There is very little backpressure in the dual (parallel) cat setup.


SJ

 

[SUMOTOY]

Not sure of the time, it's OBDII so it's the standard unit for whatever they dictated.

The stock unit reported 21+ lbs of air flow. So that would be accurate for the 212hp the engine is rated for.

The next run immediately afterwards recorded 23+ lbs. This was actually done on two trucks with near identical results.

Factor in whatever you want for the exhaust, I was guessing as I stated above.

At what rpm did you register that 21, or was that peak? I'm guessing peak, and that appears to be air lbs/min at ~4300rpm. Sounds about right.... So if you went up to 23lb/min, and we assume VE hasn't changed (read same rpm for max air lb/min), looks like about 7hp crank, 5whp for that MAF change on a normally aspirated truck. I suspect it's a lot less because the 'restriction' of the MAF isn't significant enough to make any real impact in and of itself

Might be more on a turbo or SC truck, though I'd bet less than 20hp.

This indicates to me that changes to the intake won't gain much on the dyno in and of themselves. Changes to the exhaust side would need the baseline (stock MAF) and the modded MAF to show the gains to the use of the MAF.

IME, 2.75 MAF on the audis will run in excess of 400HP without changing to the larger porsche MAF's. This mod can help a turbo application, but at 8psi, I doubt by much. Still good machine work Rick.


Scott Justusson
94 FZJ80 with supercharger and AFM

 

[Bambusiero]

For whatever it's worth. It's not that back pressure is desireable,
but gas flow velocity IS desirable. When you use tubing too large for
for a given engine, the velocity drops off too much because it the
tubing has such a large volume. Then you loose the scavenging
effect of pressure/vacuum pulses helping the engine pump gases
though it.

So, probably better to have some back pressure and enough velocity
than no back pressure and not enough velocity.

 

[landtank]

At what rpm did you register that 21, or was that peak? I'm guessing peak, and that appears to be air lbs/min at ~4300rpm. Sounds about right.... So if you went up to 23lb/min, and we assume VE hasn't changed (read same rpm for max air lb/min), looks like about 7hp crank, 5whp for that MAF change on a normally aspirated truck. I suspect it's a lot less because the 'restriction' of the MAF isn't significant enough to make any real impact in and of itself

Might be more on a turbo or SC truck, though I'd bet less than 20hp.

This indicates to me that changes to the intake won't gain much on the dyno in and of themselves. Changes to the exhaust side would need the baseline (stock MAF) and the modded MAF to show the gains to the use of the MAF.

IME, 2.75 MAF on the audis will run in excess of 400HP without changing to the larger porsche MAF's. This mod can help a turbo application, but at 8psi, I doubt by much. Still good machine work Rick.


Scott Justusson
94 FZJ80 with supercharger and AFM

There are countless sites on the web that say when estimating HP you multiply the lbs/min by a factor of 10. I stand by my data and my calculations. But feel free to link to a site where this isn't the case.

 

[SUMOTOY]

There are countless sites on the web that say when estimating HP you multiply the lbs/min by a factor of 10. I stand by my data and my calculations. But feel free to link to a site where this isn't the case.

Rick
I set up a spreadsheet a while ago, that used Toyota and TRD own dyno numbers for a stock truck and TRD dyno numbers for various boost on their supercharged application. Given that on a stock truck, it shows 21lb/min at 4300, it appears pretty valid to your actual OBD II measures. When I change the Pressure Ratio from 1.00 (0 boost) to 1.03 (.5psi), I get 23lb/min at the same rpm. When I do that and go back to the HP calculation, it changes by 7hp crank, 5hp wheel.

Up to a factor of 10 can be a factor of a lot less, like a factor of 4? Just changing the size of intake pipe really isn't going to have as high a factor, as say, a change in a cam or other airflow mods *though* an engine. A factor of 4 is really good for a MAF mod. A engine change yielding a higher demand for air will yield a higher factor gain than just matching supply to demand for air. In fact, it shows that Mr. T designed a decent MAF system at the factory for the air demands of the stock truck.

You are welcome to dyno the mod and confirm your numbers. I suspect that your estimate of HP gain is high, but that the low restriction MAF mod is effective to an air (HP:lb/hr increase) factor of 4

Scott Justusson

 

[Romer]

Scott, I think Rick is asking for a web site or other reference to support how you did your calculation and came up with 7HP. Rick isn't going to dyno it and is simply asking for the backup data so he can then run the same calculation and feel good about it. Seems reasonable to me.

 

[turbocruiser]

Since my spreadsheet contains 15 years of proprietary information from my shop, I prefer to go through how anyone else can set up a spreadsheet.

On this list, there is plenty of data that gives psi boost > Hp figures from TRD. There is also the known of 212 at 4350 from toyota. From this data, you can assign air and fuel in CFM, lbs/hr, lbs/min, lbs/sec or any other. You have a lot of knowns (engine sudoku) that can fill in some of the unknowns, like injector size and known hp and torque figures at a variety of boost levels. What you end up with is a 'factor' for air and fuel vs horsepower estimation.

I'm convinced a SWAG factor can be calculated much simpler, and it really doesn't matter which one you choose. Get one, and back the math up to confirm toyotas dyno numbers, then plug the 2lbs of air back in. The MAF mod doesn't give a HP factor of 10, period.

For the nerds on this list up to the challenge, I used VE of 100% at peak torque and 85% at peak HP for the 4477cc I6. I also used 'rolling ramp' lambda number of 1.00 at 1000rpm, .86 for peak torque and .88 for peak HP.

You can take any 'change' and come up with a revised horsepower estimation (the factor is a a relative constant). Or, in the case of Rick giving only a number for air with no unit... I divided my existing normally aspirated lb/hr column by 60 and determined that the unit Rick was measuring was lb/min and that at "21+"(lb/min), it was at peak HP. I could go back and correct to vacuum, but 99% of my time on these spreadsheets is in boost. What I can do, is give Rick the benefit that his mod caused a .5psi pressure increase (= vacuum drop across the MAF) on a Normally Aspirated truck and get the same "23+"(lb/min) he measured at ~4300rpm. That gives a MAF mod HP increase of F4, all else being equal.

I originally made up this spreadsheet for fuel, not air, but it appears to confirm toyotas published numbers, and defined the undefined OBDII unit in the air reading Rick put up. It also shows not much real gain in HP when calculated out. That's not to say that throttle response isn't better, or that driveability isn't better, only that gains in HP is tough to realize on a MAF change in a Normally Aspirated truck with no other mods.

My experience in dyno numbers, as well as the spreadsheet I used, lead me to propose that a HP factor of 10 for a MAF seems optimistic, since there is no real volumetric increase in the engine. Put pressure into the intake, things might be different. Isolating this on the dyno is simpler for those wanting to make the claim of HP=F10 without the math. My spreadsheets only *predict* dyno numbers based on the knowns of the 1FEFZ engine.

Your resident 1FEFZ nerd
Scott Justusson

Scott, holy moly man, why so completely confounding all the time? 15 years worth of whatever at your shop should simply have a bunch of assorted Audi archives (which we obviously could care less about) so what gives with simply answering the question?

Let me add some additional data. With my stock MAF, my measurements maxed out at around 26 lbs at as low as 40% throttle. I could go to as high as 76% throttle and still have same 26 lbs reading with everything essentially in open loop. Now obviously between the 26 lbs reading at 40% throttle and the 26 lbs reading at 76% throttle the rig was still pulling super hard up to that 76% throttle so it is completely clear that the stock MAF simply peaked at measurements around 26lbs.

Now, with Rick's MAF, which is a thing of beauty by the way, I measured as high as 36.6 lbs at 76% throttle and at completely closed loop operation with each and every sensor still feeding data to the computer! Now I realize the reality that the stock MAF was actually allowing more than that 26 lbs through all along but as I reported I really felt a performance increase after adding the Modded MAF. So, we get to all the advertising that you referenced above about manufacturers making claims on power (which I always have acknowledged was probably less than accurate), buuuut, with Safari for example they advertise the HP at 320. So you take my reading with the Modded MAF and you see 36.6 lbs, or, according to Rick's calculations (and everyone else's I've seen save for yours) and yer lookin at around 366 HP. So where was that extra 46 horsies coming from? Or, if it must be matter of confounding things, come up with some specific math, not fuzzy math based on "proprietary spreadsheets" to explain all this. All I'm asking is for you to take the proprietary spreadsheets, the sum of your experience and the sum of your expertise to simply answer the question that came up when you wrote that the Modded MAF cannot have a factor of ten, but should have some factor of "x". As my math professors used to say, "tell me what x is!" Thanks.

 

[Land Speeder]

Holy jeez.
One day when I retire, I hope to not only have time to read these long posts, but also understand them

 

[Beowulf]

Then the question is, does the software in the computer really care what's over 26lb/min?

Would a dyno run confirm whether or not the stock computer will use the data if the flow is over 26 lb/min?

-B-

 

[concretejungle]

Holy jeez.
One day when I retire, I hope to not only have time to read these long posts, but also understand them

times a zillion

 

[turbocruiser]

I really doubt it, this really would be an ECU code cracking exercise. In stock normally aspirated trim the MAF is calibrated to the software so that any reading over 26lb/min is 26lb/min to the tables. I guess you could look at the exhaust gasses (HC) and see what happens above 26 with the two MAF's.

Normally what happens in naturally aspirated sofware is that the open loop tables under WOT are: Max MAF + WOT switch activated + rpm or rpm rate (=max load). So my bet is that even if the computer reads the MAF voltage correctly and translates it to the OBDII port correctly, the software programming is only responding to 26lb/min or more as Max MAF input. I'm also surprised this doesn't pop a code (MAF out of range), but that's usually a turbo software safeguard (leaking pressure hose).

(Edit) Thinking on this more, if there is no code, then chances are really good that the software sees all flow above 26lb/min as 26lb/min. Which means the gain is really accuracy in measure, not increase in software or MAF output performance (read: Both MAF's should register the same MAF up to max output voltage of the stocker)

That said, it would appear that Rick's MAF is a good mod to get more accurate actual airflow readings on a boosted truck. The next step in benefit would be to reprogram the software to differentiate 26lb/min from 36lb/min.

(Edit II). TC/Rick: Can you get a reading of injector pulse? I'd be curious what happens above 26lb/min comparing the two MAF's. If something different is happening, then their might be a change. The only concern I would have *now* is that there is the possibility of a lean condition under part throttle, because normally WOT/preset throttle angle needs to accompany Max MAF reading to go to the WOT tables (open loop). If you have max airflow and no WOTS triggered, then you are closed loop with a lot of air (what TC wrote above). Without a lot more understanding of what's happening in the ECU, I'd proceed with caution here.

SJ

So, Scott, what are you sayin?!?

I'm not sure if the Auto Enginuity reads injector pulse. It reads all sorts of fuel trim things and of course oxygen sensors. I'll look into injector pulse. Basically I've never seen a lean condition last; whether at full throttle or half throttle with lots of load (hills with deliberate dropdown shifts) it is always slightly rich whenever I'm pushing the performance hard. HTH. I'm liking this discussion. Ohh, one of your questions was what other mods were made - it is essentially the Safari setup with turbo and with intercooler, no UniChip, no mod to the fuel system other than restored fuel injectors flowing within .6% between highest and lowest and also a new stock setup FPR. IIRC the injectors are all at around 310 for flow. Thanks.

 

[Curran]

So....
2.5 inches is the best diameter exhaust for a stock FZJ?
Wait a second ... is this still the same thread?

 

[turbocruiser]

It's far enough in now, that only Herr Romer could surgically remove the tangent. Might be worthwhile doing so, but TC can answer the exhaust questions I have and slide us back to the topic thread.

SJ

3" turbo downpipe to 3" ceramic coated exhaust all the way through and a 3" hi-flow hi-performance cat courtesy of Man-A-Fre. Hope that helps.

 

[landtank]

WOW, I left this thing to go check my math and this is what I find?

Using Garrett's site and the Turbo FAQ here I checked my math again.

I WAS WRONG!!!!

It would seem that 10 hp/Lb was a little generous and it's actually 9.10hp/lb of air flow.

So when you calculate TurboCruiser's 36.6lbs it is 333.06hp. I think this is now jiving better with reality.

So since I see slightly more than a 2lbs increase in flow it woul seem that 18.5hp is a more accurate statement.

 

[SUMOTOY]

WOW, I left this thing to go check my math and this is what I find?

Using Garrett's site and the Turbo FAQ here I checked my math again.

I WAS WRONG!!!!

It would seem that 10 hp/Lb was a little generous and it's actually 9.10hp/lb of air flow.

So when you calculate TurboCruiser's 36.6lbs it is 333.06hp. I think this is now jiving better with reality.

So since I see slightly more than a 2lbs increase in flow it woul seem that 18.5hp is a more accurate statement.

Rick are you referencing this from Turbo Tech 103 on Garretts site?

"What is my mass flow rate? As a very general rule, turbocharged gasoline engines will generate 9.5-10.5 horsepower (as measured at the flywheel) for each lb/min of airflow. So, an engine with a target peak horsepower of 400 Hp will require 36-44 lb/min of airflow to achieve that target. This is just a rough first approximation to help narrow the turbo selection options."

First, this is "as a very general rule for a *turbocharged* vehicle", not normally aspirated. On a normally aspirated truck it will be a magnitude less. On a normally aspirated truck converted to turbo it will be less (low boost with low Compressor efficiency). I suspect TC would hit Safaris numbers, or if Safari posted up their actual MAF number at the 320 crank, it would be close or at TC's.

This is a huge swag reference, and is a guideline for for getting into a turbo family size. Using Garretts site...
F9.5 x 36.6lb/min = 347.7 est HP
up tp
F10.5 x 36.6lb/min = 384.3 est HP

That approximate swag varies 36hp or almost 4lb/min.

With that variance, you can't even call 2lbs significant Rick.


Again, I suggest just running some numbers from Corky Bells book, or using the formula for CFM and doing some conversions.

cid x .5 x rpm x Volumetric efficiency/1728 = CFM

Regardless, TC gain on his turbo app has no reference, since we would expect 36.6 to be what the stock MAF 'should' read. Your gain doesn't apply to this guideline, because you don't have a turbo attached to your truck yet. And 2lbs isn't significant to the reference, even if you had it.

Put it on the dyno, using this reference is outside the significance of a 2lb/min increase.

ST