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Old 08-16-2005, 07:52 PM
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Exhaust question for super/turbo members

I'm going to upgrade my exhaust/engine combination in the future, and thought I would ask you boosted bretheren a few questions...There is not too much specific information on supercharged engines and exhuaust sizing/ideas...Here is what I am running now. This is a STREET application. I only run at the track roughly once a year for tuning/bragging purposes.

89' S-10, 355ci, 8.5 static cr, 142 Weiand SC pushing 6psi, 750 Mighty Demon Blower carb, smallish Comp Nitrous HP cam (218*/230* @ .050), factory heads reworked with 2.02/1.60 stainless valves blah blah blah...Limited to 6000rpm...

Now to the exhaust. Right now I am running the Hedman shortie swap headers, with 1.5" primaries and 2.5" collectors, 2 1/4" true duals with off-brand turbo mufflers. I realize that the factory heads are restricting the ability of this engine, and am looking into 190 AFR's sometime in the future, but want to get the exhaust situated first.

Are the 1.5" primaries too small in this application? Keep in mind that the longest primary LENGTH on this header is like 18" which will lower restriction. Sanderson has a 1 5/8" and a 1 3/4" primary size available that will fit this chassis. From what I have gathered, when you are supercharged, header/exhaust system tuning goes out the window and you want the largest free flowing exhaust possible correct? No loss of low end torque?

Also, I would prefer that my next set of headers are coated. With boost and retarded timing I know exhaust temps can skyrocket, and don't want to have the headers "flake up"...Do any of you guys have suggestions/experience there? I'm thinking it may be better to get "plain" headers and have them coated by a third party so I can get what I want.

I'm thinking 1 5/8" primaries, (keep in mind the primary length is almost non-existent) Jet-hot coated, full 2.5" mandrel exhaust with cut-outs for the occasional strip pass/cruise night, Dr. Gas X-over next, then Hemi Super Turbos with full tailpipes for that quiet cruise in the neighborhood... Suggestions? Comments?

Oh yeah...here's the junker... http://groups.msn.com/gearheadspoorboys/huffeddime.msnw

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Old 08-17-2005, 11:25 PM
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i'd use minimum 1 5/8" primaries and 3" secondaries/exhaust. if your headers are getting real red hot than probly go to 1 5/8" if not than ur probly ok if they are id try 3" exhaust with low restriction race mufflers I have a 671 blown 408 chrysler in progress in my 73 roadrunner 9.6 to 1 compression 10psi of boost and i probly over killed on my exhaust with 2 1/4 primaries and 4" secondaries/exhaust and getting 10 series flows 4" in/out with a 5" tip in front of tires (if you are wondering this car is street legal)
aron

p.s. how do u like your Mighty Demon Blower Carb

Last edited by goosesgarage; 08-17-2005 at 11:33 PM.
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Old 08-18-2005, 06:54 AM
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Exhaust size.

CapnKirk,

You're borderline between 2-1/2" & 3" exhaust. Going too large can hurt your performance. Since your heads are a restriction you could probably go large, and not hurt too much, but may loose performance if you went with better heads and stayed in the same boost range. I'd get a better set of headers with larger primaries, and go with a good 2-1/2" or 2-3/4" system.
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Old 08-18-2005, 10:05 AM
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I have to second what both previous replies said and suggest combining them... With your small cam AND the blower I have to believe you have no lack of low end torque.
Like Tech was implying, going to big with the exhaust (on naturally aspirated motor) WILL hurt the low end but, with your set-up, I think this may be a good thing. Bleeding off some low end will help the truck hook up and going bigger on the system will improve upper RPM breathing once you upgrade your cyl. heads. It really boils down to how the truck performs NOW and what you want it to do once you get it sorted out...
Mark
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Old 08-18-2005, 01:10 PM
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i would think if you work on your exh. that your heads would be ok unless they are complete junk.the exh. you have is to small.i may have it backward but i always thought the bigger "1 5/8 and up" with long tubes gave you better low and mid range breathing and the short tube got good marks on the upper end.i would think if you use 1 5/8's-1 3/4's with 3'' back to the mufflers and the mufflers 3-3.5" with what you have just for raing would be the way to go.worry about new heads after all that is do and you can see how they really breath.the heads won't breath if the exh. is choking them.
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Old 08-18-2005, 04:33 PM
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With new heads in your boosted application I think you'd be fine with 3" exhaust. At 6 PSI boost you are running just under the 50% mark for air increase. Meaning you are packing about 50% more air into and out of the system than a NA engine running at atmospheric pressure. As such, you'll need an exhaust that can sufficiently keep up with it. Now, as you are running a boosted application, in my opinion, I'd err on the large side and go with a 3" exhaust for future purposes. A 2.5 inch would do, but would it do when you decide to up your boost level a few pounds?

In most applications (at least in my experience) you wont feel the different on a NA engine making moderate power (300+) switching between 3" and 2.5" (or vice versa). And like I said, since this is a boosted application, I wouldn't worry about a few HP on the low side of the powerband. Build your exhaust for when you are making maximum boost. Dont limit your higher boost/RPM flow just to gain the 3 or 4 hp on the low end.
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Old 08-18-2005, 06:04 PM
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Thanks for all the great replies!

The Demon Blower Carb really does run great. I had tried to modify another pre-existing carb for blower use, and in all honesty it was over my head. I am very picky on run-ability and I just didn't feel confident modifying things with a pin-vise. This is a really nice carb and runs great straight out of the box - however I will soon be in the process of fine tuning everything.

Low-end torque is DEFINATELY not a problem, and after everyones' helpful replies I am seeing that a larger size header would be beneficial. The larger primaried headers use 3" collectors, so I think I'll just try to keep the the pipes 3" all the way back. I just hope there is enough room to cram everything in. (Oh well, none of the other stuff was supposed to fit in there either! )

Nobody really replied about header coatings just yet. Have any of you blower guys had experience with the ceramic-style coatings flaking off or discoloring badly from increased exhaust temps from the supercharger? My existing headers are just painted black with extreme temp paint, and seem to be holding up well.

Again, thanks for all the great replies. This thing is a street terror now, and It's only gonna get worse!

Last edited by jameskirk1; 08-18-2005 at 06:09 PM.
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Old 08-18-2005, 06:58 PM
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While I havent used Ceramic headers on a boosted application, Id be pretty confident in saying that almost any quality ceramic coating is going to outlast the super high temp paints on the retail market today. My ceramic headers seem to put off less ambient heat and hold more of it in the piping.
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