i just dont see heads making that much of a sound difference... you sure you dont have a huge exhaust leak?

 

I know exhaust people in town, and know from various exhaust work they have done for me before how much I'd be looking at for a stainless system done the way I would be happy with. Its not cheap. I have Kooks 1 7/8" long tubes, custom ORY, and Borla. All three inch. Honestly, that's not a restrictive exhaust at all. Yes a 4 inch giant mufflex would be less restrictive, and so would true duals, but it really isn't that bad compared to some others I have seen done on boosted motors. If I went with a turbo, I would probably run a cutout anyways, so I wouldn't need to really change the exhaust from its current configuration (minus the hot side stuff for the turbo).

I had AFR 180 heads before with a maxed out D1SC, a HUGE cam, and a very big intake setup. All of that was screaming for more air the small AFR 180 heads couldn't produce (this was clear on the dyno sheets as well). The much larger AFR 227's roll out a LOT more air (difference was 81 RWHP). This is why it is so much louder. I am sure I don't have an exhaust leak. I had a loose exhaust clamp that blew off, and ever since I put it back on I have checked it often just to make sure it hasn't came back off or there is another leak (because its THAT loud, it makes me almost think there is, but there isn't).

 

check your over axle pipe, and make sure its tight, mine loosened up and came un hooked on my mac exhaust, it was just resting on the axle so everything looked ok.

 

Trust me, I've checked every inch. There's no leak. I am running really rich with the supercharger tune, and a leak would be easy to spot from the exhaust dust, even if I wasn't looking as carefully as I did.

 

in Posts: 405

Good exhaust info.....

Hey guys I just got done reading a good article in the May 2005 issue of Popular Hot Rodding Magazine. The article was written by David Vizard who seems to be one of the most accredited and respected people in the automotive performance world. In the article he stated that CFM is a great way to help develop a zero loss exhaust system. For zero loss a exhaust must flow 2.2 CFM per horsepower(This means less than 1% of total power produced by the engine is lost due to back pressure.). From reading the article I think that a lot of people that see gains when going from a 2.5exhaust system to a 3dual system see them because the muffler on the 2.5system didnt flow enough for their application. David stated that per square inch of exhaust tubing there is 115 CFM of flow. So plugging some numbers into the good ole TI-89.. ((3.14 * radius^2)*115[*2 for a dual exhaust system])/2.2 = Max hp supported with zero loss

A 2.75(stock) single system is good for a 310hp engine with zero loss A 3Single system is good for a 370hp engine with zero loss A 3.5Single system is good for a 503hp engine with zero loss A 4Single system is good for a 657hp engine with zero loss A 2.25dual system is good for a 457hp engine with zero loss A 2.5dual system is good for a 513hp engine with zero loss A 3dual system is good for a 812hp engine with zero loss

Now these numbers are assuming that everything else is set up perfectly. The muffler must flow as much as the open pipe or more to get zero loss at the listed hp levels. He also states that using a muffler with a larger inlet/outlet diameter than your exhaust pipe is a great way to get more out of a smaller diameter system since the muffler flow will be able to match the straight pipe flow. Now there are many other things to consider when designing an exhaust system but I figured this would give a great foundation to build on.

Just a side note that he stated that I thought was neat... Just as fish dont feel the weight of water, we dont readily appreciate the weight of air. Just to set the record straight, a cube of air 100 feet square will weigh 38 tons!
This info is from the sticky at the top of this forum and is basically similar numbers to what all of my local shops go by as well when designing a system. If you three inch pipe is a restriction at 380 hp I guarantee you its a decent restriction at 700rwhp. I have watched what the exhaust restrictions have done in my dads various turbo builds both with heat and power. Its not good. I also built my exhaust fully stainless from behind my stepped kooks to the tips and was 600-700 in materials and that includes the trimix gas and wire. I welded it all up except at the headers and behind the xpipe, put bungs in for my dual widebands and built the exhaust under the car laying on my back with car sitting on 10" blocks. It just seems as much money as you obviously have I to it that matching the exhauast to the induction would benefit you in so many ways. Seriously look at the power level of your car vs when a 3" exhaust becomes a restriction. You are over double that level. I bet you would pick up 30hp and have way cooler egt less heat in blower and heads. Plus you could quiet it down from what you experience now.


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Sigh, I hear what you are saying, but I have also seen first hand power levels with different exhausts. I used to have a good portion of my exhaust 4 inches (it was Mufflex). I changed it to 3 inches to be entirely uniform and sure enough next time it hit the dyno I GAINED 10 RWHP.

Not every car is an exact science, not all combos will work the same, having seen several more powerful FI cars than mine with more restrictive exhaust than mine, I really am not concerned with it.

Quite frankly, I was only planning on getting 650 RWHP with my car with the bigger heads. Sitting at 695, even if I loose a few ponies, I really won't be heart broken. A little added traction and a few less ponies will be just fine with me if I am able to fully enjoy driving the car again without fearing permanent hearing loss.

 

We could trade for a while and I bet you might miss your car. Even spraying a 200shot you will have more power than me unless your dyno gives super high readings. Without re-doing your exhaust I would check into a muffler more suited to cancel noise but get it with bigger inlets and outlets and neck them back down to fit your existing pipe and I bet you wouldnt lose much if any power and quiet it down but I would still bring it to a couple shops to quote you a few variations and give suggestions because chances are they know alot more than me. If you ever get it sorted out would love to hear what you did and how well it worked. More than welcome to pm me.


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Just my .02 on this subject.

That article on exhaust sizing states that for the exhaust to have 0 loss the muffler has to flow as much as the pipe when it's not restricted. Good luck with that. A muffler that's designed to quiet an car's exhaust system is going to be restrictive by nature whether it uses baffles, packing, plates, etc... This is why racecars are loud; their "mufflers" are mostly for show or to comply with maximum decibel rules at tracks which have them.

Call911, are you using a good quality band clamp on the exhaust? You want something that will seal the pipe for a good 1-1.5 inches on each side of the break or it will likely leak and rattle. A good quality stainless clamp in 3" will cost you $10-12 but they are worth it.

Something like this.


I have a Mufflex system on my car with the Spintech muffler. It's very throaty but not exactly quiet. I actually had a set of Moroso Spiral Flow mufflers welded into the system between the muffler and the tips (same as I did with my 98 with the LM1) and it's way more bearable. I also run a set of cutouts in the Y pipe right at the end of the Kooks headers. Cops love cutouts.

 

Most of my exhaust has band clamps as shown above. I also have a couple compression clamps (but am considering changing them to band clamps also).

As I've been advocating for a while now, I'll see what the existing fuller can do first before I explore other options. If I have time I may be able to do that today.

 

Just made the swap. I'll go for a test drive in the next few hours. I couldn't find the "small" plate, so I went with the block off plate. This will force 100% of my exhaust to go through my muffler.

If it quiets things down a ton, but I feel a loss in power I am not happy with, I may take it out and drill a hole. If its still too loud after this, I will explore the options of a different muffler.

 

SUCCESS!!!!!!

The car now runs quieter than it was before the heads!!!! I friggin' LOVE cruising around in it now. So glad this simple trick fixed it all.

I was watching my EGT's the whole time and they never got hotter than before, even when I opened it up.

I can tell I lost a little power because I had more traction (not a ton though). I may see if I can find the in between plate to see how it does. Worst case scenario, I can leave the block out plate in and get cutouts for when I want to race (I don't care if its loud then).

 

Well, you have a perfect template there. If nothing else cut a few blanks and drill different sized and shaped holes in them and see which one gives you the sound you're looking for.

 

If I had access to more metal and metal cutting equipment that would be perfect (although I'm sure I could figure something out to make that work).

Honestly, I really love how it sounds now. I've only driven it that once though. There were times I almost thought it was too quiet. I have the in between plate somewhere I will try to find today. I have a feeling though that in the end I will get cutouts for it, so I can have more power and sound on demand.

 

you basically have a cutout... just take the tailpipe and plate off when your at the track.

 

The angle on the pipe will put exhaust through the muffler even with the open plate in or that section off.

If I'm gonna spend the money and effort into a cutoff, it will be back by the headers where it will give me the most gain.