Oppinions please, realistically, how much difference would upgrading make??

[Guest bastaad525]

Okay... I've gone back and forth on this issue for so long now... every time I think my mind is made up one or two guys give me a new oppinion or info and sway me back the other way.

 

I'm trying to decide, once and for all, whether I should prioritize upgrading to a full 3" exhaust, whether it would be worth it or how much difference it might make over my current setup, and a couple different options I need to consider.

 

I'm hoping some guys who really know a lot about how exhaust flows and how different setups make different amounts of difference, can pitch in here and really give me some good insight.

 

Well, first let me describe my current setup. I'm running the stock downpipe off of the stock turbo. Then, from the downpipe to the differential, I'm running 3" pipe with one slight press bend. Then, from the downpipe, the pipe goes down to 2.5" for those last two 90 degree bends, and those are also press bends. This goes thru a 2.5" straight thru glass pack. It's a long story as to why it ended up like this, which I've typed many a time so will skip this time Suffice it to say it wasn't planned to end up that way.

 

Now, for the longest time I was planning on going with a full 3" mandrel system, but KEEPING the stock downpipe (cost of a custom downpipe was prohibitive).. and going with a Dynomax Bullitt muffler. But some knowledgeable guys have convinced me that going with a full 3" system but keeping the stock DP wouldn't really make a lot of difference. I know the last section is the worst offender, being only 2.5" and press pent thru those two horrible 90 degre bends... but one thing Tim240z mentioned to me that made sense was that having that restriction at the very end of the exhaust wasn't that big a deal as the exhaust has cooled and contracted quite a bit by the time it reaches that point so it probably isn't hurting performance as much as I thought... Makes sense to me.

 

So I'm left thinking... that really the only way I'd benefit from an exhaust system upgrade was if I ditched the stock DP for a custom unit as well, doing the whole thing at once. I know for a fact that even as 'bad' as my exhuast setup is, it's still FAR better than the stock ZXT exhaust, being larger diameter, with a far better muffler, and of course, no cat....

 

So what do you guys think? Worth bothering with right now or worry about other things until the time I can do the DP and full exhaust all at once (IF that time ever comes )? Or do you guys think I'd still gain significant increases in hp or at the least, turbo spool reaction, by running full 3" off the stock DP in place of the pipe I'm running now?

[Brad-ManQ45]

I have a full 3" from stock downpipe back - including cat on my '83 ZXT.

 

Were I you, I would start with the downpipe. Tim240Z was spot on in his recommendation and reasoning. The stock downpipe is definitely more of an inhibitor than your 2.5" stuff hanging far away from the turbo.

[wheelman]

Bastaad,

If it were my decision to make I'd wait on the exhaust and convert to a MegaSquirt system. You've talked about the fuel curve weirdness from the stock ECU several times and how you would like to get rid of it so that's what I'd do first.

 

Wheelman

[Guest ON3GO]

bang for the buck and to get the most power out of your setup.

custom downpipe and a cutout.

 

thats it. keep your exhaust, and when your about to race at the track and etc take the cutout off and your good to go!

 

that was the single best mod i ever did.

 

mike

[Jsquared]

turbos like BIG exhausts. Heck, a naturally aspirated KA24DE made gains across the whole powerband (compared to stock) with a 3" mandrel setup, and at a local dyno, an SR with cams and a stock T25 with a full exhaust made like 30wHP more than an SR with small exhaust, cat, and a T28. Part of that was cams, but at least half was exhaust. Just going from 3" press-bent with a high-flow cat to 3" mandrel with no cat on my little 2-liter turbo engine was noticeable, not so much for peak power gains but from how much quicker the turbo spooled.

 

But I noticed someone said you were having A/F issues with the ECU... in which case I would most certainly advocate waiting on the exhaust and getting the tuning sorted out. All that extra exhaust flow won't do you any good if you get pinging and hole a piston out

[johnc]

Exhaust. And stay away from crimp bends. They typically drop flow about 15% in the best case.

 

I've done a couple turbo exhaust and a few NA exhausts for customers and ALL of them were very, very happy with the results compared to the crimp bent systems they had before.

[Drax240z]

Another vote for exhaust. Awesome results with a 3" mandrel bent system compared to a 2.5" crush system.

[Scottie-GNZ]

Very interesting post and responses. Let me quote myself from my old turboZ wepage of about 7-8 yrs ago:

"I started off with the downpipe and 2.5†press-bent system and ran 106+mph with 15psi boost. After installing the 3†mandrel-bent exhaust and DynoMax UltraFlow muffler, the boost spiked to 16.5psi with no other change.The next successful run was 110.97mph at 17psi. The 3†exhaust, combined with the custom downpipe, gave me one of the biggest performance boost to date. If you do nothing else to your turboZ, this is the one to consider."

 

If you have a 2.5" press-bent pipe making 2 90* bends, you probably have something a little better than a 2" system. ON3GO also made reference to a cutout and that is an excellent option when you take the car to track. Since I recall you not being one that makes it to the track often, probably not an option for you. I have a 3" DP and 3" mandrel that splits into 2 2.5" and I am getting ready to add a 3.5" cutout as close to the DP as possible. Expect a nice increase in power at the track especially with the expected increase in power of the new shortblock. Mine is electric and is probably not an option for the budget-minded, although you will be hard-pressed to "buy" the HP gain another way.

 

Depending on what you are looking for from the car and how it will be drivien, just one upgrade might not be enough and sometimes you cannot do them all at the same time. However, if you really want performance, the 3" exhaust is one you will need.

[Guest bastaad525]

It does seem to me that I'd just be better off upgrading the exhaust when I have the means to do a custom downpipe as well... just doing the whole thing at once or else it's probably not worth it.

 

It kinda sux.. I was so hyped about upgrading the pipe and was very close to doing it and now it's just going back on the backburner for an indefinite amount of time. The downpipe will add quite a bit of cost to the whole thing and is just out of my budget for now. No big deal as even with the stock DP and chop shop pipe I"m running lag is really not much of a problem and it does make very good power... all things being equal I just don't expect it will make some really huge increase in power anyways... if I got 10 hp at the wheels (after turning boost back down to 13psi as I'm sure it will go up a bit with the upgrade) I would be pretty surprised.

 

Next on the list (I hope) is going to be FINALLY installing a full new set of poly bushings, Tim240z offered to give me a hand and a much needed place to do the work as soon as he finishes the project he's on now... hopefully some time this month.

 

And of course this goddamned thing is STILL leaking so now I'm gonna have to do install another friggin oil pan gasket.....

 

 

EDIT: About the air/fuel issues... it's nothing that bad really. The car runs great.... really I'd have no complaints at all except for the oil leaks. It does tend to run quite rich from when boost first comes on at about 2800rpm to about 4000rpm... very much like a fully stock EFI setup does even at stock boost. It then leans out as RPM goes up but never gets leaner than about 12:1 so it's still safe. Off boost it runs great, just like stock, thanks to the RRFPR not adding fuel except on boost.

 

I used to think the rich midrange was a big problem but then someone pointed out that I might actually be BETTER OFF with it running like this. Since my car makes peak torque between 3000-4000rpm, that is also when cylinder pressures are at their highest and most likely to cause detonation, so the extra fuel at that point might actually be beneficial for a little extra safety, considering I'm running on crappy 91 octane. So I'm reluctant to change it as that theory seems to make great sense to me.

 

I could probably free up a little bit of power in the low RPM range if I could 'fix' this issue but really it's not that big of a deal, the car really does run well when pushed, the RRFPR is doing it's job nicely... it's not the perfect solution but for me right now, going with Megasquirt or any of those solutions would be overkill, and again, I don't have the money, or more importantly, the time and inclination, to install, dyno and tune something like that right now anyways.