Anyone with experience comparing the two, I would appreciate your input. She is going back together after #2 rod bearing failure and I am considering an exhaust upgrade along with the 46mm tial ect I am installing. 4" sure seems like over kill, being that a 6+ liter diesel comes with 3" but I am certainly willing to consider it.

Bill

 

Unless you are making MEGA HUGE POWER it is all bragging rights.

 

I considered a 4 inch exhaust, but unless you are making mega power, like 2bridges said, then you really only "need" a 3'' system. Also 46mm tial while good, may be over kill as well. the 38mm works great for just about anything you'll be able to do with your car, unless again, it's a "I have this on my car" kinda thing.

-Darwin

 

if 300 rwhp is huge then get the 3 inch. Check the Lindsey Site for Dyno Charts. There are two of Dave's red 89. One with 3 the other with 4. No other changes, and that car is not what I would consider a huge hp car.

 

well here is the chart

even at close to 374HP - very little difference - negligable at best
less than 4 hp and 10lbs peak

shift in rpm range and yet note they indicate a race master muffler vs edelbrock - hardly a fair comparison. I would wager the race master muffler on 3" would show improvment over edelbrock

 

Here are the Lindsey charts overlayed. Black is 3 inch Red is 4 inch.



The car was set at 15.5 psi boost. It made 16 psi with the 4 inch and the same settings.

 

Does just the 3" or 4" downpipe make any differences?

 

the chart I posted is the actual chart from Lindsey.
only significant change is a 350-500 rpm shift.
and as I mentioned - the 3" is using an edelborck muffler, while the 4" is using flowmaster race. Certainly not equal.


I can't speak to the "overlayed" chart that appears to be modified or a different comparison

 

Not to mention there were differences in temperature and inconsistant boost control between the two runs (which could easily account for the differences in both dynos). Not an accurate comparison IMO. I'll say this much, I had a tapered 4" on my 26/6 awhile back and noticed absolutely no difference from a straight 2.5" (stock with cat eliminated) or a straight 3". On a K26, a 4" exhaust is pointless unless you just want to make more noise (nothing wrong with that ). For a bigger turbo car making good power like over 400whp, you might see a minimal difference over a straight 3". At the SAME boost level, you're not going to see the kind of gains that LR's dynos would lead you to believe.

 

The overlayed Dyno Charts...

These are the dyno charts from the Lindsey Site under the Dyno charts link.

Both charts are from Dave's 89 Turbo with K26/8.

It is my understanding that the ONLY difference in these two dyno runs are the 3 in and 4 in exhaust. The mufflers on both exhausts were Magnaflow for the respective exhaust size. And the Charts are SAE corrected. Dave did a run with boost set at 15.5 psi, swapped the exhaust then did another run. The 4 inch run is listed at 16 psi because that was the peak boost it made with the same settings as the 15.5 psi 3 inch run.

In my opinion that is as straight forward a comparison as you could possibly make.

Increase exhaust size and don't see a change in power, you got leaks and/or other problems.

 

you are making huge oversights. Muffler backpressure alone can have substancial impact on boost chaacteristics.

just the fact that a edelbrock is used on 3" and Flowmaster race on 4" is difference enought to scew the dyno result.
You are buying the propaganda hook, line and sinker

 

More of the restriction is in the kkk hotside than the exhaust.

 

I made 347 hp at 16psi with my current set up (big BB turbo, MAF ect). I run 22 psi now. Not saying I NEED 4" by any means...honestly I don't know what I need. It makes a ton of power with the stock exhaust, but if it will spool up faster blowing into a bigger hole...I'm all for that.

I went with the 46mm tial because I got one for $314 new off ebay (tial verified that it is legit). Also, running the high boost I run, the tech dept at Tial told me I could use the extra cooling of the 46mm.

There are some pretty conflicting views on whether or not the 4" gives any benefit over a 3". Having had some shady dealings with Lindsey, I am not inclined to believe their claims unless someone has verified it themselves. They just seem a lot like Huntley to me. The exhaust will be from fabspeed either way....I think. Hell, at this point I'm not certain a 3" will improve much over the stock exhaust with a raped cat. Which is the reasoning behind my asking the collective.

Bill

 

You run 22psi on pump?

 

No. On the track I run race fuel. On the street, which is seldom these days I may be guilty of pump gas but then it rarely sees full boost on the street for more than a second at a time and at 6000ft the need for octane drops. Still, race gas is the norm.

BTW, I could care less about bragging rights. The way I have approached this car for the last decade is if it doesn't make it go faster, turn better or stop quicker....I am not interested. If a larger exhaust will spool up quicker and give back some of the low end I lost moving up hill 6k feet...I am game. If it's because it's pretty and sounds nice...not interested. I guess the question is, does a larger exhaust give any benefit and if so how large?

Bill