jshuberg

I'm hoping your wrong here

There are several places that claim that higher gains can be made with a custom exhaust. 928 Motorsports claims that up to 55HP gains are possible with headers and a free flow exhaust. That's with their x-pipe and an 85-95 MY, but I am hoping for something respectable with my 84.

I'm planning on adding Euro heads and/or a supercharger in the future, so I'm going to want an exhaust that can scale to that before I do that work. I'm hoping to see some decent gains from the new exhaust alone, but if not it's still worth it in preparation for future work. Either way I'll have some definitive numbers on what the new exhaust can do for me. I'll post the dyno runs after the work is done.

ptuomov

Goes well with that:



Short of removing collapsed cats and pipes, the exhaust unfortunately can't add much with low-overlap cams in a N/A engine. You need high overlap cams and then the exhaust can either hurt or help a lot.

hacker-pschorr

You under estimate how bad the stock US exhaust system is on the 16V's.

I'm not saying 55+ just from exhaust, but 30-40 has been shown to be in the ballpark.

Carl Fausett

From the "what its worth" department, Euro and non-Euro 16v intake plenums side-by-side.

The Euro throttle bodies are larger, the plenum (as shown) and the ID of the intake runners, the intake passageways in the heads, and the intake valves themselves are also larger. Then there are the cams. And some feel (I am one) that the K-Jet-equipped Euro had a different fuel distributor and injectors (although the PET does not agree with that opinion). Oh - and the WUR. - my experience is that the WUR for a Euro would attain a lower control pressure than the non-Euro model, thereby allowing a higher system pressure at the injectors.

mark kibort

you fail to remember that I did a very controlled test of this. 175rwhp for the 84 on the dyno with the stock exhaust.. headers and stock exhaust , with no cat, went to 190rwhp. with the 3.5" rear section and complete removal of the stock stuff, it went to 200rwhp. so, its pretty clear that the stock exhaust system removal is about 10hp, and another 10hp for the headers. nothing even CLOSE to 50hp.

mark kibort

No, I went with a nice set of headers, and a pretty well designed y pipe and saw only 20hp and that's with a single 3.5" pipe from the y to the rear. I cant imagine anyone having a better header and pipe that could give 150% more power than that. its just not realistic. the holbert car already started with 290rwhp, and with no cat to start with. some air box mods, fuel regulator, equal length racing headers, and the same y pipe and 3.5" exhaust to the rear, it got 40hp, but that's with GT cams as well and a few other tune up changes. (coding plug, new plugs, cap rotor, clutch change, removal of all driven componets off the crank pulley but alternator and PS ).

mark kibort

what cams and heads. and then you got 270rwhp out of a US 4.7 with Ljet? is that what you are saying? that's what the euro 4.7 make, with a much larger intake system. and the restriction on the US is significant.
1.5 x 2" is the AFM opening, and the US throttle body is 2.7" diamaeter. square area is pretty close. however, the AFM has a pretty nice bell mouth opening to make it more efficient with flow..... no where near as nice as the euro and the 3.3" diameter MAF inlet or CIS inlet.
I suspect that your cams and heads were worth a LOT! remember Brian was running a 4.5 and getting 260rwhp with trick heads and cams and megasquirt (or equiv). I don't know the intake, but I think it was euroS as well.

the thing about our 928s and all the work, nothing is ever that surprising when you get all the facts.

ptuomov

I haven't tried this, so ignore my musings if there's actual data.

However, my general theory view is that for one to get 30% increase in power from headers and exhaust, you need to have both very high overlap area cams and be moving from a very bad exhaust to a great exhaust.

I've been following the development of some exhaust systems on the web that use the TFX pressure sensor system. Based on seeing a lot of those pressure traces, I've come to the following conclusions, be them right or wrong:

If there's little cam overlap, the only benefits the exhaust is going give are going to come from reduced pumping losses. It's highly unlikely that the existing exhaust is going to have pumping losses that are anything like 30% of the net engine power.

If there is a lot of cam overlap and high compression, then a good exhaust can create say 7 psi exhaust port vacuum at the overlap which will get the intake flow started in a hurry, regardless of what the IVC-IVO intake pulse tuning is doing. But that can only happen with a lot of overlap area.

jshuberg

I'm currently getting 220rwhp with everything stock except Euro cams. If you saw a 20HP gain with new exhaust and headers, I think it's reasonable I might see slightly larger gains. Both since I'm starting with a little more power, and that the the full potential gains from my cams are likely being choked by my old crappy exhaust. The exhaust is 30 years old, has some dents and dings, and is likely not performing the way it did when new.

I'm hopeful I'll see some decent gains in the 25-30HP range, but there's really only one way to know for sure, and that's simply to do it and see. I hadn't considered any EuroS intake upgrades, but after reading the above posts, I think it's worth considering.

Thanks much!

Carl Fausett

Here is the webpage for the headers you are discussing.

http://www.928motorsports.com/parts/headers.php

It does not mention "50 HP" anywhere. Please stop saying we make such claims when we do not.

And Kibort: by your own text you specifically admit you did NOT test the delta before and after just headers alone, you just assume "add another 10 for headers".

Carl Fausett

jshuberg: Can you show me where we claim that?

Even on our Big-Port headers http://www.928motorsports.com/parts/big_port_header.php
I am very careful not to make any specific HP claims. There are too many variables. And as I have explained before - No-one can ever test headers independent of the rest of the exhaust system.
So although you can dyno before-and-after exhaust system mods - it is very difficult to know which of the HP gains are attributed to the headers and which are attributed to the rest of the exhaust system.

It is for these reasons that NONE OF OUR HEADER PAGES/MODELS publish or promise any specific HP numbers.

DKWalser

True. I spent some time this afternoon looking at your header and exhaust pages. I didn't find any specific HP promises on your header pages.

I did notice a promise of 26 HP and 27 ft/lbs of torque gains from your x-pipe. Forgive me if this has been discussed before, but this particular x-pipe is new to me. The others I've seen require ditching the factory cats. Is this a new product?

jshuberg

http://www.928motorsports.com/parts/xpipe.php
I found this when looking through your various exhaust options. Perhaps it's a typo or something, but it is from your site. If I misread or misrepresented what was being said, you have my apology.

Ketchmi

David, it's the same crossover that Roger sells and that I make and sell. I believe that I am the only crossover supplier in the U.S. Dyno sheets are readily available for it from many sources.

I had cats made for this application as it replaces the factory cat setup. You can run with or without depending on your mood and local regulations.

mark kibort

Maybe you misunderstood the text. ill repeat. I changed ONLY the headers, made a cat , y adapter and it went from 175hp to 187hp. It was 12hp. I had to pull out the dyno runs. Then, put on the 3.5" exhaust . it was worth another 12hp. the 3.5" straight through exhaust with a nice Y pipe, is worth as much as going to a good cross over dual exhaust system from what we have seen.

Expecting 30 to 50hp from headers and exhaust is unheard of for V8 engines in the 6500rpm redline and 200 rwhp range. But, I would love to be proved wrong.

post a stock us 84 dyno run with headers and exhaust with only headers and exhaust that makes 270rwp. they don't exist. (up from 200 or even 220rwhp stock)