Louie928

Hi Norbert,
I may have missed it somewhere in the thread, but I don't know what engine you have and reasonable power level you expect. Your clutch housing is an early style which suggests a 16v motor although some people search those out for 32v motors because they are lighter. I've not worked with 16v motors. I have had quite a few people tell me that the 16v motor is sensitive to exhaust pipe size. Too big exhaust pipe and it loses torque. I've had people with 16v motors tell me that the X pipe with 2.5" OD, that's about 2.375" (60mm) ID cost them low and mid range torque. I can't verify that with any dyno tests. On any 32v motor, the 2.5" OD X pipe adds torque everywhere so evidently the engines respond quite differently to exhaust systems and too big on a 16v can cost power.

So, if you have a 16v and presumably the higher performance Euro version, the 60mm is probably ok, even though maybe on the large side. Now where to reduce from the 76mm to 60mm is the question. Usually, the larger diameter collector length makes a difference on where the torque peak happens. The MSDS headers aren't equal length so each cylinder won't behave the same. I just don't know how long the 76mm collector should be. As a guess, I'd say if you want better high RPM performance, have the reducer close to the header flange. If you want better low RPM performance, make the collectors longer. The reducing flange should be as long as reasonably possible so the transition is gradual. I made an X system to connect to a Devek header system on a GT which also had the same size collector as yours. Due to space considerations I made the transition immediately after the collector flange. The system worked really well and made good low end torque as well as good on the top end too. If I had to do it over again I'd do it the same although I didn't try any other configuration. Mostly, I didn't have the room for it. Sometimes you have no choice. For the width of the constriction in the X, keep the 90mm ID size you have now +/- depending on what part of the power curve you want to enhance. What you have now is ok and maybe it doesn't need any change. The outlets of your X section changes direction rather abruptly and might benefit from the more gentle V outlet. I don't exactly know if your X section is 76mm or 60mm. It should be 60mm. Depends on if your engine is supercharged or not. If you wanted to cut your X off in the center and weld on a V like the outlet of the Burn's Stainless, or mine, that would be ok. You'd have very close to Motorsports (Roger sells them now) setup. You may not notice any large improvement. Since you already have what you made, dyno it now, make the change and see if there is any difference afterward. Test and see.

belgiumbarry

thanks again Louie ! yes, it's a 16V , ' 82 europ 928S. Making a track car and i can also drive it on the street ( historic rallys) without huge taxes as it is a "oldtimer" according Belgian laws. ( older than 25 years ) .Got even a vanity plate for it : OPA 007 which means granddad and 007 , well, you know...
got that crazy idea of removing all the ( good working ! ) stuff injection and replaced by 4 Weber IDAs 48 ... a more nostalgic move to oldschool tech as my rallycar was in the 80's...

Now that could be a good idea : cutting the X in center ( which is 60 mm x 90 mm ) and welding a 20° V to after-pipes... i think the entrance is quite "flowing" as one comes from the 2 collectors almost angled at 90°... and yes, the 2 pieces of bend after the X now are rather "abrupt".

Sorry , i didn't mentioned the cars/engine details... for oneselfs it's so obvious to think everybody knows it.

if you have a spare minute, my intro on Rennlist is " Hi from Belgium" thread.

Louie928

Hi,
Ok, I thought maybe this was the car that had the IDAs, but wasn't sure. I'd take some performance measure with the exhaust as it is. Then change the rear of the X to the V and take another performance run. Probably won't change the mixture enough to need any carb work.

belgiumbarry

Hello Louie,

i could do it that way but there's more : we wrongly made the exhaust on the stock car , but now lowered some things don't fit that well anymore , also the ( round) mufflers are to low .. so we will be welding and changing little things, therefore i tought to grab that occasion as also to change the X...
next is a dyno run for the carb setup , so i have all favor to have as much as possible things done to not compromise the "tuning" afterwords....

belgiumbarry

just removed the exhaust for the surgery table
cut the X-piece and prepared 2 "straight" tubes for it.
We are indeed on the "small" side with the X cross section( outside 90 mm for 60 mm tubes ) but Louie mentioned that 16V engines could lose torque if to big... so i keep it as now for the first dyno runs. Must be carefull with torque as i expect to loose already some with the carbs as to a injection system....

Friday evening now, welder to continue on monday....

Louie928

Looks good. Friday evening and you are quitting?? In these cases you are supposed to pull an all-nighter so you can try it on Saturday.

belgiumbarry

oh, Louie, i would... but myself cannot weld ( or sure not good enough )
and my welder on the job had to go home to his wife and kids.... how nice
i have time... the car sure won't be ready besides that exhaust over the weekend...

Louie928

To have a welder on hand is a nice luxury. I was just tweaking you a little.

belgiumbarry

hehe, Louie, than i have the shameless luxury to have 9 certified welders on the pay roll...

belgiumbarry

so they welded the X-V pipe piece today... hope this is what you ment Louie ?

ew928

Looooking Good.

Louie928

Perfect!

belgiumbarry

thanks guys for the nice comments ! i'm really curious for a dyno run....