Opinions please: 3", or 3.5" exhaust??

[BillyGman]

As some of you might already know,I'm building a pump gas low reving 632 C.I. engined 70 Chevelle SS. It will be a street/strip car, but it will see much more street time than it will drag strip time. There aren't any drag strips in my home state anyway, and I hate having to drive out of state, just to get in three passes down the 1320, which is usually the case since it's always so crowded. So I don't want this car to be sluggish in the 2,500-3,000 RPM range. The stall speed I've chosen is merely 3,200 RPM, and I'm running 3.73 gears in the rear.

This engine red lines at only 6,000 RPM, and makes it's peak torque by 4,000 RPM, so I don't want to over-do it with the exhaust diameter.The engine dyno #'s are 800 HP at the crank, and 775 FT/LBS, but the engine is already making 90% of it's torque by 3,000 RPM (715 ft/lbs @ 3,000 RPM). I have a set of headers that I bought for it, that have 2 1/8th inch primary tubes, with 3.5" collectors that are 9" long.

My question is, would a 3.5" exhaust diameter kill some of the low-end and midrange grunt in the 2,500-3,500 RPM range? Do you monster big block guys think I should use a 3" diameter exhaust instead, since the red line is only 6,000 RPM? Or do you think that having anything less than a 3.5" diameter exhaust will kill some of the power between 5,000 and 6,000 RPM? Please help. I need your constructive input.

[TAF]

dual 3 1/2" with a big 3" H-Pipe....and we'll build it for ya if you'd just get that monster down here!

This one was making a little over 800 to the tires....

http://www.mercurymarauder.net/showcase/files/8/3/IMG_3084.JPG

And we built this (with an X-Pipe)...yours should be more "period" with an "H"

http://www.mercurymarauder.net/showcase/files/8/3/IMG_3077.JPG

[Jolly Roger]

My 79 Capri with a 372 cu. in. Vortech YS S/C has a 3 1/2" back to the axles.
I can't see anything less on yours with the cubes that you have.
Just my 4.6 cents worth.;)

[Merc-O-matic]

Just a point of information.....from what I see most of the
big blocks in the Buick Club 455's Stage 1 and Stage 2 (GS's GSX)
all have 3" diameter pipes. Not sure if that helps.:pimp:
When will "she" be finished?

[BillyGman]

When will "she" be finished? I'm not sure, but I'm shooting for some time in July.

BTW Todd, it's funny that you should chime in brutha, because as I was writing that last post of mine, I was thinking of you. Now don't tell me that the silver Mustang in that pic is another one of Marty's secret projects? I just cannot keep up with that boy, and all of his toys. :eek:

Anyway, I do have a 3" exhaust system that came with the car when I bought it. Maybe I'll just slap it on for now, and see how it goes, and what kind of disaster my budget is in when I finish this car. And if I'm not in financial ruin by then, perhaps I can consider taking the long haul to where you're at. That's a longshot though my friend, since I cannot see getting any more than 8 MPG even on the highway with 632 cubes and a 1050 CFM Dominator carb sitting on top. :depress:

One thing that I'll say about X-pipes is that I hate them. I put up with mine on my Marauder, but what I don't like about them is that they give the exhaust note a higher pitch, and if anything, I'd want a lower pitch to the exhaust sound. So an X-pipe is out of the question for my Chevelle. I'd like to go with a 3.5' exhaust, but I don't know if I'll fit 3.5' tailpipes back there with the M/T P315/60/15 drag radials which are 13.5" and 30" tall. And going with a 3.5" diamter exhaust means that I might have to use the Flowmasters, and I hate Flowmasters too. I'd rather have the Dynomax Ultra Flo muffs, but I don't believe that they come in 3.5" and dynomax's 3.5" Thrush glass packs would likely be crazy LOUD!!! Maybe I can run 4 of them. :confused:

[TAF]

Yep...it would be a tight radius over that rear axle with 3 1/2"...but it could be done. I also agree with your thoughts on the X-pipe...that's why I suggested a 3" "H". Also...there are other options for mufflers other than Flowmasters...just get that thing down here...Bryan wants to "play" with it.:D

[BillyGman]

Yep...it would be a tight radius over that rear axle with 3 1/2"...but it could be done. I also agree with your thoughts on the X-pipe...that's why I suggested a 3" "H". Also...there are other options for mufflers other than Flowmasters...just get that thing down here...Bryan wants to "play" with it.:DOkay brutha...we will see what I can do this summer. Right now I've been working seven days a week just to keep up with this project!! Ofcourse the 7 week long labor strike that came about at my workplace two months ago hasn't helped either. I'm still playing catch-up as a result, while at the same time trying to fund this mega HP car project.

But I guess that's us carnuts for ya. When it comes to HP, and G-force, we'll always find a way somehow. ;)

[Tallboy]

Yep...it would be a tight radius over that rear axle with 3 1/2"...but it could be done. I also agree with your thoughts on the X-pipe...that's why I suggested a 3" "H". Also...there are other options for mufflers other than Flowmasters...just get that thing down here...Bryan wants to "play" with it.:D

Todd-I'll be there next week. I'll come back with a full report.

If it's running, I'll just hop in the sumb!tch when Billy isn't lookin' and head your way!!:D

[BillyGman]

Todd-I'll be there next week. I'll come back with a full report.

If it's running, I'll just hop in the sumb!tch when Billy isn't lookin' and head your way!!:D LOL....:baaa: well then I guess I won't be seeing the car anymore after that, because you probably won't want to ever bring it back. ;)

[BillyGman]

okay, I just came across a great article written by the one and only David Vizard concerning exhaust requirements. This guy really knows his stuff, and I've been following his articles as well as reading his books for the past 4 years. You can checkout the link below, but the bottom line is, that he's saying that his extensive testing on exhaust configurations with various V8 engines, has concluded that you need 2.2 CFM of airflow per every one HP.

And a 2.5" diameter open pipe will flow 560 CFM of air. So if you multiply 2.5 by 1.4, you come up with 3.5. This represents a 3.5" diameter exhaust pipe. So then you take the 560 CFM figure (which is for the 2.5" pipe) and multiply that by the same 1.4 figure, you arrive at 784(CFM).

So a 3.5" diamter pipe can flow 784 CFM of air. Since we're talking dual exhaust here, then we simply double that CFM figure.... 784 x 2 = 1568(CFM). Now per David Vizard's test results, we multiply 800 HP by 2.2 CFM...

800 x 2.2 = 1760 so this 632 engine will need an exhaust system to flow a total of 1760 CFM which is close to 200 CFM more than two 3.5" diameter open pipes can flow. So I guess that a 3" diameter exhaust system should be out of the question for my car. And while a 4" diameter would be optimal for drag racing, a 3.5" diameter wouldn't be a bad compromise, since it will flow close to what the requirements will be. And a 4" diameter would definately be very expensive, as well as being very tough to work with concerning back tire clearences, rear end clearences, and ground clearence too.

http://superchevy.com/technical/engines_drivetrain/exhaust/0505phr_exh/

[TAF]

Wow...I don't know about all that cypherin'^^^^...but, I think I said 3 1/2 in post #2.

7-knot, knot...plus 2 X double-knot.....whatever....

[Agent M79]

Good article, Billy. Explained a lot, cyphering and all, I got a few points that I didn't get before.

Does that make me a 'double-nought' Agent, TAF?

[BillyGman]

Wow...I don't know about all that cypherin'^^^^...but, I think I said 3 1/2 in post #2.

7-knot, knot...plus 2 X double-knot.....whatever.... LOL...maybe it's just that some of you good ole boys down south are a bit slower with the math. :D

but yeah, you were right about the 3.5" recommendation my friend. I just need to have info based on dyno testing with various applications before I break the bank even more than I already have, to foot the bill for the exhaust upgrades. My concern is trying to keep this monster quiet enough for actual street driving w/out getting pulled over by the local PD for excessive noise. And another concern of mine is not over-doing it with the exhaust size. I'll be actually driving this monster to work at least one day out of each week from May to November, and because of that, I've deliberately chosen a lower than optimal stall speed, since I know I'll be driving it in traffic.

I know this vehicle will be on the edge for the street, but it's on the street that it will see most of it's life. In fact, I don't even own a trailer for it. To put this whole thing into perspective, consider this....how many street cars that are run on pump gas alone, and are used for the commute to work do you see or even hear of that are churning out 800 HP at the crank, with a redline of only 6,000 RPM, a torque peak that occurs at only 4,000 RPM, and a stall speed of only 3,200 RPM? That's exactly what this car will have. I'm not saying that it will be the best car around, but only that it will be rather unique, and in it's own niche, good or bad. So I don't want to over-do it with the exhaust. I've just heard that the Borla XR-1 race mufflers are amazingly quiet, and so that's what I'll be shooting for. Ofcourse the car will be loud when I hit the throttle hard, and that's fine with me. However, I don't want it to be shaking the windows of every house that I drive by the whole time that I'm just cruising down the road easy. That would be downright annoying to me as well as to everyone around me, and will just draw too much unwanted attention.

[Jolly Roger]

Wow...I don't know about all that cypherin'^^^^...but, I think I said 3 1/2 in post #2.

7-knot, knot...plus 2 X double-knot.....whatever....

Me to____ per post #3.:)

[BillyGman]

Me to____ per post #3.:)Yep...thanks for your input also Roger. It's just a difficult comparisant for me to make between your car and mine even if the power levels are similar, because mine is a naturally aspirated engine, and yours is S/Ced. So it's anything but apples to apples, even when it comes to exhaust system requirements.

[Wagonmaster]

dual 3 1/2" with a big 3" H-Pipe....and we'll build it for ya if you'd just get that monster down here!

This one was making a little over 800 to the tires....

http://www.mercurymarauder.net/showcase/files/8/3/IMG_3084.JPG

And we built this (with an X-Pipe)...yours should be more "period" with an "H"



Saweeeet! How bout' some pic's of the powerplant!! Giddyup!

GT

[BillyGman]

Saweeeet! How bout' some pic's of the powerplant!! Giddyup!

GT yeah, that has to be a 9 second car!!! :banana2:

[Mike M]

I went with 3.5 spintech mufflers right off my collectors and then immediatly into down turned tips that are also oval 3.5 Spintech. I would like to have TAF do the rest of the exhaust out the back but he is too far away and I really think it would be a challenge to get it past the rear suspension and cross member.
The motor made 748 on the dyno so it's VERY loud but sounds sooooo dam good. I reccomend taking a good look at SpinTech because fat pipe will be very close to the ground and the oval pipe gives you a bit more ground clearance.

[BillyGman]

I went with 3.5 spintech mufflers right off my collectors and then immediatly into down turned tips that are also oval 3.5 Spintech. I would like to have TAF do the rest of the exhaust out the back but he is too far away and I really think it would be a challenge to get it past the rear suspension and cross member.
The motor made 748 on the dyno so it's VERY loud but sounds sooooo dam good. I reccomend taking a good look at SpinTech because fat pipe will be very close to the ground and the oval pipe gives you a bit more ground clearance.Thankyou for your input on this Mike, because coming from a monster big block owner like yourself, I take notice of that. My concern is the exhaust being so loud that I might be getting pulled over on the highway, while on my way to work, or especially coming home from work at midnight like I do, and I've heard that those spintech muffs are very loud like you've stated.

Another thing that's uppermost on my mind is that you have a Camaro, and so it must have considerably less ground clrearence than my Chevelle will have. I've chosen a stock suspension height also, and I haven't any intentions of ever lowering the car, so I'm hoping that there won't be any ground clearence issues with my car, like there probably are with yours.

I'm sure that your monster big block does sound great though. I wish that you didn't move out west, because you and I could've done some cruisin' around the tri-state area with our mega-motor cars. :(

Anyway, I'll checkout spintech's site just for some more ideas like you've suggested.

[Mike M]

Ground clearance was a BIG factor in my exhaust. I had tried several mufflers but when I lowered the car down from the lift and looked at it from the side it just didn't look right. My thinking with exhaust is more form over funtion. The SpinTechs are very loud but if I had a complete exhaust it would be much better. Trust me when I say, you have a monster that is going to sound good no matter what you do. Big motors sound great regardless!

[BillyGman]

Trust me when I say, you have a monster that is going to sound good no matter what you do. Big motors sound great regardless! I agree. Nothing like the sound of a mountain motor with a big camshaft, and cavernous bores being emptied out into headers and exiting the tailpipes. I'm getting psyched just thinking about it!!! I gotta go run and get another look at that engine.....