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Old 12-08-2021, 02:37 PM   #1
rb92673
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Default 2.5" or 3" for Endurance Race

My Lemons car currently is set up with a 2.25" downpipe and exhaust. I am constantly removing the turbo and manifold for various reasons. I would like to redo the exhaust to v-band connections on both ends of the downpipe. I have a t3/t4 turbo with 90+ manifold and stock wastegate. I run about 12 psi of boost. I don't ever really plan on huge boost as it is for endurance racing.

Should I just go with a 3" ATP Ultimate wastegate and 3" all the way? Is there any downside with 3"? I assume I will need to port the hotside more so I don't overboost.

I was going to go with mild steel and attempt to MIG weld it all together myself. Exhaust exit before the passenger rear tire. I had a summit racing turbo muffler, but I blew it out in two races.
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Old 12-08-2021, 03:17 PM   #2
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3" turbo to tail. Just put it in there...don't be nasty.
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Old 12-08-2021, 03:38 PM   #3
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A single 2.5" 16ga pipe supports about 220hp before it BEGINS to be a restriction. I'd say that if the 12lbs is as far as you're going, I'd save the weight and gain the clearance and use the 2.50".
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Old 12-09-2021, 02:20 AM   #4
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I’ve built a few 3”-2.5” systems. 3” with a ATP ultimate gate to the trans x-member, then a nice transition to 2.5” for the rest of the way (over the axle).

For endurance racing I’d just use 3” all the way back with no muffler (or a small resonator or borla can).
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Old 12-09-2021, 11:47 AM   #5
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Originally Posted by Marvelous3 View Post
3" turbo to tail. Just put it in there...don't be nasty.
To late to not be nasty.

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Originally Posted by shoestring View Post
A single 2.5" 16ga pipe supports about 220hp before it BEGINS to be a restriction. I'd say that if the 12lbs is as far as you're going, I'd save the weight and gain the clearance and use the 2.50".
Good to know. Last dyno on the old engine was 200 rwhp, not to worried about weight and as long as it fits on the trailer I am good with clearance.

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I’ve built a few 3”-2.5” systems. 3” with a ATP ultimate gate to the trans x-member, then a nice transition to 2.5” for the rest of the way (over the axle).

For endurance racing I’d just use 3” all the way back with no muffler (or a small resonator or borla can).
I was thinking of a side exit to make it easier. I was going to use v-bands so I could do a straight pipe, and swap in a muffler if the track had noise restrictions (like Laguna Seca).

I assume I need to port the hot side with the 3" ultimate. The hot side is a T3 stage III 63 AR I got from ATP. Right now it boosts to 12 psi even with the wastegate wired open.

Any reason to go stainless over mild steel? My welding skills are non-existent yet.
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Old 12-09-2021, 12:21 PM   #6
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The WG hole should definitely be opened up to around 26-28mm. I just use some spray paint to mark where the flapper sits.

You can get some really thin SS and mild tubing in that size, and it’ll drop a ton of weight compared to using heavier 16ga exhaust tubing. No preference on either material, mild steel is cheaper and generally easier to work with.

To get a decent muffler on a side exit, you will most likely need to add a bump in the floor for clearance. A small glass pack resonator might not be enough, and anything bigger will probably be too big.
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Old 12-09-2021, 12:58 PM   #7
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3" all the way. I use 20ga 304L with 309 filler, and it ends up being really light and pretty darn tough. It's more expensive, but lasts a few seasons longer, so it makes sense. I really like the Borla XR1 line of mufflers, too. Cheap, make good power, quiet, and come in a million flavors. I never buy anything cheaper than those, but sometimes we get roped into using Coast Fab or something fancier. Those are a little nicer, lighter, quieter than the XR1, but a LOT more expensive.
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Old 12-09-2021, 06:47 PM   #8
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Thanks for the suggestions. I ordered some 3" mild steel pipes, bungs and v-bands.
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Old 12-10-2021, 06:05 PM   #9
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I did a little grinding to transition the turbine outlet to the ATP Ultimate WG housing.

https://pbase.com/towerymt/gt2871r

Be VERY careful opening up the hole for the wastegate especially on the area nearest the flapper valve when it's open. I was never sure if mine was catching on the hole at times.

We had one of the ATP housings on our old lemons car, on a a/r .63 T3 turbine housing with the standard (stage 1?) turbine wheel, 60trim t3 compressor wheel in a .60 a/r housing. We ran up to about 14psi on a B230F bottom end.

Build a good support from the downpipe to one of the bell housing bolts. We had the downpipe break at the turbine outlet once during the race, while I was driving. It got really loud inside so I parked it before I totally melted the wiring harness where it comes through the firewall. We fixed it Saturday night at the track...if you get a common u-bolt type exhaust clamp from the parts store, you can take the side of the clamp that has the holes for the u-bolt and weld that onto the downpipe since it fits the shape of the round tubing, then weld on flat stock to flat side of the clamp and attach it through a bell housing bolt.

If you end up running it out the side, be careful with the hangers and routing of the pipe. In my experience running a solid (no flex joint) exhaust out the side, eventually it broke at the end of the n/a header. Even with a 3rd engine mount to reduce the engine movement, there's still going to be vibration & twisting, so think about where you can include a flex joint.

Here's the routing I used on a side exit, non-turbo. We cut a notch, maybe just a blade width not all the way through and welded it to kink the side pipe upward just barely, so it followed the contour of the floor. You could just hammer the floor up if you don't have anything there like the battery.

Also check the rules, I don't know if they've added anything more about exhaust routing, besides keeping it away from the fuel tank in a way that doesn't promote heating of the tank.

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Old 12-11-2021, 04:44 PM   #10
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Thanks for the advice and pictures towery. The Lemons rules state the exhaust must exit after the driver and not heat the gas tank. They also say 92db @ 50ft, but I have only seen them enforce that on a rotary at Sonoma.

Any suggestions on where to put the flex joint? I am thinking on the horizontal portion of the downpipe on the bottom past the bell housing.
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Old 12-12-2021, 05:13 PM   #11
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Use the suggested brace for the downpipe on the bell housing on the vertical section then as you say put the flex pipe on the horizontal section after the bell housing.
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Old 12-13-2021, 12:09 PM   #12
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Use the suggested brace for the downpipe on the bell housing on the vertical section then as you say put the flex pipe on the horizontal section after the bell housing.
Thanks for the confirmation.

Parts are starting to arrive. The opening on the Ultimate Wastegate is HUGE! Those v-bands are going to make my life a lot easier when removing the turbo.
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Old 12-15-2021, 03:44 PM   #13
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We've blown sound at Sonoma with the M52 (and at Thunderhill). It's possible if you try hard enough (and eject enough of the muffler internals).

Best bang for the buck muffler-wise (durability and fitment) in our experience has been the Flowmaster 12518409 "Super HP-2"; we've been getting about a year out of them. I expect you'll probably cook them faster as you're probably? going to be running a bit richer than we do, but they're sturdily built and it's the internals that blow out the back, not the case that splits, so you just slowly get louder... not sure about how they'd work under the 740.

Side exit makes life much easier, but you should consider the exit section as a consumable; everything after the turn-out from the center tunnel will get pounded with debris, and you'll wind up replacing it fairly regularly. Also watch out for any suspension bushings you might route near, for obvious reasons. 8)



My limited turbo experience (DSMs) says that 2.5" is probably right for you at your power levels, and 3" is kind of a nuisance routing-wise. Either way, the exhaust tubing kits from Speedway are a decent bargain if you're going to DIY it...
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Old 12-15-2021, 04:56 PM   #14
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We've blown sound at Sonoma with the M52 (and at Thunderhill). It's possible if you try hard enough (and eject enough of the muffler internals).

Best bang for the buck muffler-wise (durability and fitment) in our experience has been the Flowmaster 12518409 "Super HP-2"; we've been getting about a year out of them. I expect you'll probably cook them faster as you're probably? going to be running a bit richer than we do, but they're sturdily built and it's the internals that blow out the back, not the case that splits, so you just slowly get louder... not sure about how they'd work under the 740.

Side exit makes life much easier, but you should consider the exit section as a consumable; everything after the turn-out from the center tunnel will get pounded with debris, and you'll wind up replacing it fairly regularly. Also watch out for any suspension bushings you might route near, for obvious reasons. 8)

My limited turbo experience (DSMs) says that 2.5" is probably right for you at your power levels, and 3" is kind of a nuisance routing-wise. Either way, the exhaust tubing kits from Speedway are a decent bargain if you're going to DIY it...
Thanks. Running super rich right now, need to fix that. I think I had a flowmaster on there before, but when I took it off all the baffles were just clanging around in it and it was full of holes. I put at least 12 races on it and it was probably dead when I got it.

I am going to try the 3" straight pipe and see how loud it is, might build a second system from the downpipe back with a muffler.

Congrats on an almost win at Sonoma.
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Old 12-15-2021, 07:36 PM   #15
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did someone say flowmasters?
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Old 12-15-2021, 08:01 PM   #16
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Mine sounds awesome at idle lol. NA set up with rsi na cam lol. Need to take flowie off though and get a little quieter one for the annoying decel.
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Old 12-24-2021, 01:14 PM   #17
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did someone say flowmasters?
Shocking, eh?
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Old 12-24-2021, 02:17 PM   #18
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did someone say flowmasters?
You outta be up makin breakfas or sumthin.
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Old 12-28-2021, 11:20 PM   #19
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Before and after. From 2.25 to 3".

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Old 01-05-2022, 03:30 PM   #20
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Before and after. From 2.25 to 3".
So shiny! $500 my azz.
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Old 01-05-2022, 03:47 PM   #21
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so shiny! $500 my azz.
exhausts is exempt. :-p
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Old 01-05-2022, 04:03 PM   #22
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So shiny! $500 my azz.
I think you have proven Volvo wagons are budget exempt.

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exhausts is exempt. :-p
My new shiny coil overs are not, but no Fs given by judge. They worked great BTW.
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Old 01-05-2022, 04:33 PM   #23
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My new shiny coil overs are not, but no Fs given by judge. They worked great BTW.
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Old 03-15-2022, 12:41 PM   #24
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So I went with 3" mild steel exhaust. ATP Ultimate Wastegate, Borla round XR1 3" muffler, and side exit before the right rear wheel. I ported the wastegate hole what I thought was a bunch. Apparently I did not port the wastegate enough or use enough pipe/bends as I had a massive boost increase after 5k RPM, pegging the boost gauge at 20+ PSI. Target boost is 12-15.

Ben suggested running full length over the axle. I am going to port further and try over the axle.

It is much louder than before, but wasn't ear bleeding. Still quieter than the Miatas.
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Old 03-15-2022, 01:23 PM   #25
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What diameter did you open up the WG hole to?
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