Ideal exhaust diameter on a stock 80

[Hants]

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.

Fools go...

IIRC, Rick said that on his NA truck, he saw a 2lb/minute increase simply by change the MAF.

Assuming that the increase is actual flow increase (and not simply measurement instrument changes), it seems pretty clear that 18hp increase (at the flywheel) is a good guestimate.

Yes, Garrett appears to be quoting ranges for turbo sizing, but air is air. Increase flow by 2lb/minute due to forced induction. Or increase flow due to less restriction. Either way is more air.

I haven't seen anything anywhere that indicates that forced air is more valuable/useful to an engine than the same flow increase due to less restriction.

Back to our originally scheduled program:

Has anyone measured their MAF changes due simply to exhaust changes? For instance, has anyone done cat-back replacements and measured before and after MAF readings? How about high-flow cat replacement? Or LX's fancy JDM replacement exhaust?

 

['74 UA FJ]

I have always wondered why we *need* backpressure. Any theories out there?

Karl

You don't NEED backpressure. It does increase bottom and midrange torque, however. That is a FACT.

 

[turbocruiser]

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

Okay, Scott, I'm diggin this. If you are saying that there is really no real increase in power, then does anything at all from the risk-related perspective apply? You are however acknowledging an increase in the throttle response right? If that is the case is that why you were making a mention of our mid throttle point potential problems? I'm guess I'm trying to get to the mid-point between basically no performance increase and some performance increase. So, not in a confrontational way, but in an interested way, which one is it? Thanks.

 

[ArmyFJ]

I think this is one of the worst hi-jacks ever. Even an attempt to revert it was thwarted.

On the topic, due to the restriction in clearance at the front drive shaft where the exhaust crosses over, I think that those thinking about exhaust need to examine the the cross section area of the pipe.

If there is enough clearance to put 2 2.25 through that spot then there is a CFM advantage over one 3 inch pipe. If you can fit a 3.25 inch pipe then that advantage is gone, and you would need at least 2 2.50 inch pipes. Just a thought.



Matthew

 

[SUMOTOY]

I think this is one of the worst hi-jacks ever. Even an attempt to revert it was thwarted.

On the topic, due to the restriction in clearance at the front drive shaft where the exhaust crosses over, I think that those thinking about exhaust need to examine the the cross section area of the pipe.

If there is enough clearance to put 2 2.25 through that spot then there is a CFM advantage over one 3 inch pipe. If you can fit a 3.25 inch pipe then that advantage is gone, and you would need at least 2 2.50 inch pipes. Just a thought.



Matthew

I'll run both, until the hijack gets surgically removed (Edit: I tried to do it myself). Matthew, IME with duals, you have drag thru that dual 2.25 pipe that tends to favor the 3in single. Go to dual 2.5's, the drag in the smaller pipe is offset by a massive gain in combined cross section.

I tested this in the 300 to 500hp range in the turbo cars. The 20vt audis come with dual 2.25in pipe from the factory. 3in shows a significant improvement, but 2.5in duals are even better. And the resistance thru a dual 2.5 cat setup vs a single 3 was about 4psi difference in reduced backpressure.

What I see a lot of is deletion of dual (parallel) cats replaced with a single 3inch, when at really high catalyst temps thru laminar flow dual cats, the duals (even stock) will show a significant reduction in backpressure pre cat vs a single 3in.

HTH

ST

 

[ArmyFJ]

Then I suppose the question is will 2 2.5 inch pipes fit up there?

Matthew

 

[alkaline747trio]

Army, go single 2.5 from the cats back with whatever, if any, muffler you want...any more than that is a waste on the 3FE IMO. And gut your cats if you can, you wont notice much sound gain.

 

[suprathepeg]

I'd bet that a 2.5 to the muffler and 2.75 out would be a good setup for a 4.5l engine. In the mini trucks with smaller v6 engines 2.25 -2.5 seems to be ideal.

 

[ArmyFJ]

Well I want to keep the cats. I want to be enviro friendly, plus I hate the no cat smell. I have heard the sound is different with a dual set up though is that true? I like a loud diesel sound.

 

[alkaline747trio]

You're not gonna get any sounds out of that 3FE with cats though, the way the exhaust is routed on the 3FE, with straight 3" pipes from the downpipes back would still yeild a very quiet exhaust. You're not gonna get a loud diesel sound, try 2.5 from the cats back w/o a muffler, single pipe.

 

[SUMOTOY]

Then I suppose the question is will 2 2.5 inch pipes fit up there?

Matthew

It's tight man, btdt on exhausts that don't go over the frame! I thought the best compromise might be to run 3in to the muffler, then dual 2.5 to a true dual exhaust with a resonator on each side. I haven't visited this yet, and Man-a-fre has that 3in already mandrel bent, so it could be cheaper to just go 3.

I'll be on this soon, as my supercharger has already blown off the back muffler, and is now leaking thru the cat seals...

SJ

 

[alkaline747trio]

Sumo, the exhaust DOES go over the frame on the 3FE, it goes from the DS over the frame and t-case flange to the PS then back.

 

[SUMOTOY]

Sumo, the exhaust DOES go over the frame on the 3FE, it goes from the DS over the frame and t-case flange to the PS then back.

Yup, which means it's tight. I was referencing my audi turbo dual 2.5 installs where it's tight without going over a frame.

HTH

ST

 

[alkaline747trio]

It fits, but getting the turn over the frame would be difficult with two 2.5s, not worth the money, but if you do your own work it might be worth the trouble.

 

[cadence]

\

I agree with this. Pipe isn't restriction on an 80. On the inline cats (OBDII) it's the cats, on the dual parallel (OBD I) trucks it's the center muffler. On a stock truck, I'd run a high flow center and rear can and leave the exhaust size alone. On manual shift cars, increasing the pipe size can increase HP, usually at the expense of torque. On autobox cars, increasing pipe size just makes great sounds and rarely adds enough ponies to measure.

2.5 is more than enough.

Scott Justusson

Old thread but good info! Let's stay on topic and away from the MAF debate!


Scott says the ODBII in-line cats are the biggest exhaust restriction and I don't doubt it. 90s cat technology probably leaves a lot to be desired in terms of size vs scrubbing/cleaning efficiency vs power output!

Who has fitted a single, large, low restriction (300 CPI or less) cat on thier OBDII 80 series in place of the original twin in-line cats?

Was there a seat-of-the-pants performance benefit?

 

[turbocruiser]

Old thread but good info! Let's stay on topic and away from the MAF debate!


Scott says the ODBII in-line cats are the biggest exhaust restriction and I don't doubt it. 90s cat technology probably leaves a lot to be desired in terms of size vs scrubbing/cleaning efficiency vs power output!

Who has fitted a single, large, low restriction (300 CPI or less) cat on thier OBDII 80 series in place of the original twin in-line cats?

Was there a seat-of-the-pants performance benefit?

First, IMHO, we'd all be better off to totally forget everything Scott ever stated about 80's; 99.99% of it was way wrong. Second, I also stated that the cat's were the primary part of our restriction so that's the .01% I prolly agree about with what he's stated. Third, I installed a single 3" hi-flow cat on my rig and really liked the outcome there. Hope that helps.


Found this thread in the hope it helps.
https://forum.ih8mud.com/80-series-tech/239588-catalytic-converter-option-forced-induction-rigs.html

 

[concretejungle]

Turbo,

My roommy has replaced his exhaust with 3inch. Another local club guy has 2.5 inch. IMHO the 3 inch exhaust is just way too loud. The 2.5 has a much better sound. We have not dynoed either truck, but the guy with the 3inch said when he installed it he had a bit better throttle response but didn't notice much power improvement. He also has Landtank's MAF upgrade and a supercharger.

So, i need an exhaust and i'm really leaning to 2.5inch based on the sound and performance i have seen.

 

[dwrtoy]

I built a nice merge collector for my 80-at the location of the old flange-into a short 3 inch diam "race cat" . From there it's routed into a ATR straight through muff, and dumped out the side rocker.. way the flock too loud. It reved cleanly and freely to the limiter though. I placed a 5" supertrapp disk pack (3" inlet) and played with disks, and could notice a significant seat of the pants difference. 18 disks is perfect in sound and powerspread and revs...i say 3" with a more retrictive muffler than a ATR, otherwise 2.5 would suit the motor better. naturally aspirated of course.

 

[NKP Garage]

We found that 2.5" was ideal for the 1FZFE. 3" may be helpful if you are running a large turbo, but until them 2.5" is your best bet.

 

[yoopercharged]

Holy Hijack!! Is the OEM exhaust pipe on the FZJ 2.25"?