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I would think it's pretty straight forward. I suspect attaching it to the center of the rear cradle, the perimeter will be attached to the rear bumper cover. and rear wheel well area.
The tricky part will be what the resulting curvature/bend the diffuser will be to follow the rear bumper cover. Then there is muffler size. My 6" diameter mufflers (with 1/4"-1/2" room above them for trunk clearance) would stick down too far. A 4" oval muffler could work...hmmmm.
You could still fight air getting up in the the tunnel ahead of the rear cradle, which then you look into moving the exhaust pipes up and add a belly pan. Hopefully trapping all that heat won't cause issues. You could add naca ducts to allow some cooling air.
The exhaust tips would still need to exit in the center so the diffuser would either run under them, or the diffuser would be notched to allow the tips to be there.
ORRRR have the tips exit out the slotted vent area in the stock bumper The below picture is a better option for this since it is a simple straight through muffler:
OK my head hurts...all these possibilities.
Last edited by smitty2919; 02-15-2019 at 12:23 PM.
The C6 as stated should be much easier. I have ordered the GReddy exhaust for mine, which should offer a lot more clearance for the diffuser. I am thinking about attaching the diffuser to the muffler hanger bracket bolt holes in the frame at the rear. Then using the leaf spring bracket holes in the rear cradle to attach up front. The sides will have to be attached to the bumper possibly. This I think can be done with drilling some through holes and making a backing plate that will sit on top of the lip of the bumper.
^I like where your head is at. Put rivet nuts in the backing plate, then simply rivet the backing plate to the bumper lip to keep it in place during assembly/removal. Obviously transfer drill the holes through the bumper cover.
Last edited by smitty2919; 02-15-2019 at 02:08 PM.
Yup! Riv nuts work work well, or use weld nuts on the back side of the plate. Riv nuts will stick out of the face on the plate and not give you a flat mounting surface. I have a Beatrush front under tray on my Evo and it uses something similar to this to attach to the front fenders. Works quite well.
I am starting to wonder if it is better to keep the stock diffuser and add a race one below, or remove the factory piece and just have the race diffuser.
i think that will depend on what you do with your exhaust.
this guy ran his out the license plate recess, to allow more room for race diffuser
couldnt find any great pics
but you can look up Jeremy Swensons ZR1. he runs in Gridlife.
this pic shows a mesh panel where our stock plastic is, but doesnt have the race diffuser on below it in this pic. but shows the exhaust better
looks like he ran side bumper exhaust at one time. (Optima)
mesh panel and race diffuser in place
looks like full coverage from the diffuser, and smooth with not to much angle
Last edited by STANG KILLA SS; 02-17-2019 at 11:19 AM.
That looks like a solid setup. You could run the pipes through the diffuser in the center by simply putting a hole there (similar to running it out the bumper on the sides).
To really work well, the vertical strake edges should be as close to the ground as possible when on the track. This causes the problem of not being able to drive on the street and they get beat up on the track. I'd take a lesson from the Gen 5 Viper ACR-E and make the main structures strakes shorter in vertical height but have bolt on sacrificial strakes that extend closer towards the ground and are designed rub and wear out but not damage the main aluminum support strake structure. I'm not sure what the ACR-E sacrificial strake is made of, but I'm guessing some sort of plastic.
Just a thought so you could use the diffuser on the street just by unbolting the sacrificial strakes and reinstalling them when you visit the track.
I'm not 100% sure about this, but for the diffuser to work on a C5/C6, I don't think it needs to curve up to meet the back of the rear bumper fascia to create a seal....as long as the front of the diffuser is connected under the cars flat belly pan to keep air from getting above it, I think you would be ok with a gap between the top of the diffuser and the bottom of the rear bumper/muffler exhaust area.
i think that will depend on what you do with your exhaust.
this guy ran his out the license plate recess, to allow more room for race diffuser
couldnt find any great pics
but you can look up Jeremy Swensons ZR1. he runs in Gridlife.
this pic shows a mesh panel where our stock plastic is, but doesnt have the race diffuser on below it in this pic. but shows the exhaust better
looks like he ran side bumper exhaust at one time. (Optima)
mesh panel and race diffuser in place
looks like full coverage from the diffuser, and smooth with not to much angle
I actually autocross with Jeremy. His current setup as of June 2018 is the exhaust out the license plate area. The side dumps is his old setup.
Yeah, the guys who did Jeremy's diffuser did an amazing job! The one issue that he ran into is heat being trapped above the diff. The trunk pan got hot enough to burn the carpet on his car. Keep in mind his entire exhaust was wrapped. I think having everything sealed off above the diffuser would not be ideal. There still needs to be some airflow up there to allow the diff and exhaust heat to exit.
He had heat buildup even with that mesh screen in above the diffuser? We don't know what the front side of his diffuser looks like and how it is built. If he runs a belly pan and is 100% sealed off under the rear cradle, I could see how the heat builds up.
If the diffuser attaches to the backside of the rear cradle and everything else under the car is stock and still had heat build up that surprises me. That means not a lot of air runs up beside the transmission around the differential.
I really do like his diffuser. It's not too gaudy but again, not sure how functional it is either.
So I have had two friends burn up the carpet in the trunk of there C6's. One was a ZR1 and one was a Z06. Both happened with rear diffusers installed. I am not saying 100% the diffuser is the reason the carpet started to burn, but with the trapped heat and the over pipe of the exhaust being so close to the trunk pan, I would assume it had a lot to do with it.
The ZR1 had a full wrapped exhaust and a full flat bottom. As for the Z06, I believe this was just a full non wrapped exhaust and the same issue happened.
Below shows the burnt carpet and the section of trunk floor cut out of the Z06
Here is the exhaust and rear diffuser setup on the Z06
This is the hole cut in the trunk floor of the Z06 and the fix he did. Just a small section of exhaust wrap on the over pipes and then created a sheet metal cover over the hole.
I believe the best solution is to add heat shield tape above the exhaust on the trunk floor, and wrap the over pipe section. This "should" keep most of the heat away. Owner of the ZR1 says there was no issues with his car until he turned the power way up. Of course as you increase HP and are on a road course a lot of exhaust heat would be produced. The Z06 was probably around 660hp when the issue happened with his car.
02-15-2019, 12:15 PM
The below picture is a better option for this since it is a simple straight through muffler:
