[Sporter]

I'm having trouble fitting these under my '67 convertible Firebird. Just not enough ground clearance in most places and my 3" pipes tuck up into the tunnel all the way to the mufflers. Looks like I can mount them on the Warlocks or mount them directly to the pipes at a 90 degree angle or maybe off the pipes before the x-pipe.

Anybody have these on their 67-69 Firebirds? Where did you put them? Thanks.

69 Camaro:


Late model Corvette:


69 Camaro convertible:

[RAJ7395]

Never put them on a bird but I was thinking about adding them to my truck.

My question is why are the the cutouts coming off at a 90 angle from the main pipe? Wouldn't it make more sense to have the inlet split with a Y with one side to the mufflers and the other to the cutout. This way the exhaust flow thru the split would be much less turbulent and thus have reduced back pressure.

RAJ

[Sporter]

I don't know why the Camaro in the first photo did it but the Corvette had no choice due to clearance issues. I have the same problem, no real obvious place to fit the y-pipe for the cutouts. I may have to mount them right onto the pipes just in front of the mufflers or maybe just off the first turn of the pipes before the x-pipe. I was hoping someone else may have a clever solution.

[RAJ7395]

Wish I had a good idea but nothings jumping out at me.

Tough call - I think that for the most good you'd need the dumps as far forward as possible but you don't want to stink yourself out of the car either.

Could you put a Y pipe just upstream of the muffler, switch to a cylinderical cherry bomb style muffler to save width, and fit the valve and cutout tube right next to (in parrallel with the cherry bomb muffler) and dump down before the axle. That way your making the most of the pocket that the stock muffler fits in.

Back in my youth, I used to go to the hardware store and buy straight pipe sections with screw on caps. Then cut and weld the pipe onto the exhaust pipes just aft of the collector to form a dump. Just reached under the car and took off the caps when I got to the track. Cheap, easy, and reliable. If you lose a cap you go to the store and buy another for a $1.

Good Luck!!

RAJ

[Cammer-6]

In the old days we used to swing the collector extension over and rebolt it back to the header.Open headers sound so much better than a cutout. But nowadays every one wants instant gratification,just push a button.

[Flowjoe]

Originally Posted by Cammer-6

In the old days we used to swing the collector extension over and rebolt it back to the header.Open headers sound so much better than a cutout. But nowadays every one wants instant gratification,just push a button.

LMAO, That's funny...where's Freud when you need him?

[dragula81]

You need the DMH low profile cutouts. They're no taller than you're pipe itself but have larger surface area than a normal cuout.

I was actually the first "new" GTO to have these. They fit perfectly on these cars but can be used on any cars. I made a video of my car with them. You can check it out on youtube here: http://youtube.com/watch?v=xoBkEGd2xgg

Give Dave a call at DMH and tell him that Dragula sent you.

[RAJ7395]

Sweet!! Got a link to their site or contact info??

[Sporter]

I spent the day making the cutout fixtures and mocking them to the exhaust in several places. Found the max ground clearance was 5 inches in front of the x-pipe and 4" just after the x-pipe. I decided to mount them after the x-pipe facing down. This will probably compromise the efficiency of them but I'm sure it will be neligible. I wanted to hear the x-pipe through the cutouts as it seems to really smooth out the exhaust.

Mockup before the x-pipe. You can see the trans pan is pretty low:


Mockup on the right pipe in front of the muffler:


Side view. The ground clearance is actually a .25" higher than my deep aluminum trans pan.


Hopefully I can get 'em welded in tomorrow and wire them up for next weeks test and tune.

[dragula81]

Originally Posted by RAJ7395

Sweet!! Got a link to their site or contact info??

dmhperformance.com

[sts]

Mounting them after the x will compromise effiency? You might want to do your homework: I can only go on what I have read, but based on what I have read, combined with just a tad of common sense, mounting the cutouts after the x increases flow--unless of course the newest x-pipe with cutouts after the x are merely another con game by pypes.

[Sporter]

It has to do with the axis of the butterfly valve and the high angle of the cutouts themselves. Mounted before the x-pipe the butterfly axis is parallel to the pipe and the butterfly has its edge to the flow of the pipe. Mounted after the x-pipe the axis is perpendicular to the pipe and when open the butterfly is face-on to the flow. The butterfly actually sticks up into the pipe a wee bit and may try to divert more of the flow out the front of the valve instead of equally before and behind the valve.

Before the x-pipe, parallel axis:


After the x-pipe, perpendicular axis:


Also, the effect of the 90 deg angle of the cutouts is minimized before the x-pipe since its very close to an outside turn in the pipe. After the x-pipe the pipes are pretty straight and I wonder how much flow will really be diverted out the cutouts. Most cutouts have a low exit angle of approx. 30 deg and will divert much of the flow when open. I have not been able to find any material on the effects of a 90 deg exit angle but I spoke with some of the propulsion and aero engineers in my office and they agreed it will flow less. How much less..who knows. Could be insignificant. Bottom line, I'll eat the slight loss in hp to hear the engine through the x-pipe.

Typical cutout and the ones I purchased but could not use:


I made mine from header reducers, I cut them and notched them to fit the 3" pipes:


PS: No comments about the crappy welds.