brought the gm performance header to be installed
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From: MONCTON
brought the gm performance header to be installed
the mechanic said thats the same header than stock. did i get ripped off? the guy said it was gm performance header. can i have a picture of the stock one and the gm performance.?
another thing is i noticed some buzzing in my exhaust afterwards (im still fully stock)
another thing is i noticed some buzzing in my exhaust afterwards (im still fully stock)
Joined: 12-30-07
Posts: 14,079
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From: NEPA
The GMPP Extrude Honed Manifold is essentially a ported stock manifold.
Look at the inside of the manifold. If the runners & collector are smooth you are ok.
If there are rough castings you got ripped off.
Look at the inside of the manifold. If the runners & collector are smooth you are ok.
If there are rough castings you got ripped off.
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From: MONCTON
ohhh so it looks exactly the same ok. then thats probably why the mechanic was like well thats the same part. but mine had a crack in it so im glad its changed anyways.
what should i expect for performance on everything else stock?
what should i expect for performance on everything else stock?
Joined: 12-30-07
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From: NEPA
It flows 30 CFM more than stock. A member dyno'd one back in the day and gained 4whp & 6wtq.
Last edited by Staged07SS; Nov 29, 2011 at 12:09 PM.
Joined: 05-18-11
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From: West Chicago, IL
Here are some flow numbers to back up Staged's post:
Hi ! Here are my flow calculation for some LSJ engine parts :
ADDED COMMENT : These flow numbers are calculated at ambiant air temperature AND pressure.
Stock Throttle Body (67 mm) : 625 CFM.
EDITED : Stock Head : One intake port : 250 CFM @ stock 0,395" valve lift. One exhaust port : 145 CFM @ stock 0,395" valve lift. Stock head is said by GM to be efficient up to 275 WHP; it is clearly possible to make more WHP than that, but in a unefficient way (several HP losses caused by heat and restriction).
Stock Exhaust manifold ("Header") : 425 CFM.
Stock Downipe (DP) with cat : Plus or minus 370 CFM or less.
Stock Cat-back Exhaust (2,5" inlet to 2,25" outlet with stock muffler) : 300 CFM.
Now here are some replacement parts :
GMPP Exhaust manifold ("Header") : (30 more CFM than stock) : 455 CFM.
Shorty or long tube Header with 1,75" primaries and 2,5" outlet : at least 500 CFM.
Shorty or long tube Header with 1,75" primaries and 3" outlet : at least 725 CFM.
Shorty header with 1,5" primaries and 2" outlet : Waay not enough, who cares LOL.
Stock DP w/o cat : 425 CFM.
2,5" DP with VERY HIGH FLOW cat : plus or minus 450 CFM.
2,5" DP w/o cat : 500 CFM.
2,75" DP with VERY HIGH FLOW cat : plus or minus 475 CFM.
2,75" DP w/o cat : 600 CFM.
3" DP with VERY HIGH FLOW cat : plus or minus 500 CFM.
3" DP w/o cat : 725 CFM.
Stock catback with only the rear muffler replaced (the last portion is still in 2,25" tubing) : 350 CFM.
Stock catback with last portion replaced for 2,5" tubing and straight through muffler : 450 CFM.
2,5" catback : From 450 to 500 CFM (must be a straight through muffler).
2,75" catback : From 550 to 600 CFM (must be a straight through muffler).
3" catback : From 650 to 725 CFM (must be a straight through muffler).
Hope this can help ...
Regards
)
ADDED COMMENT : These flow numbers are calculated at ambiant air temperature AND pressure.
Stock Throttle Body (67 mm) : 625 CFM.
EDITED : Stock Head : One intake port : 250 CFM @ stock 0,395" valve lift. One exhaust port : 145 CFM @ stock 0,395" valve lift. Stock head is said by GM to be efficient up to 275 WHP; it is clearly possible to make more WHP than that, but in a unefficient way (several HP losses caused by heat and restriction).
Stock Exhaust manifold ("Header") : 425 CFM.
Stock Downipe (DP) with cat : Plus or minus 370 CFM or less.
Stock Cat-back Exhaust (2,5" inlet to 2,25" outlet with stock muffler) : 300 CFM.
Now here are some replacement parts :
GMPP Exhaust manifold ("Header") : (30 more CFM than stock) : 455 CFM.
Shorty or long tube Header with 1,75" primaries and 2,5" outlet : at least 500 CFM.
Shorty or long tube Header with 1,75" primaries and 3" outlet : at least 725 CFM.
Shorty header with 1,5" primaries and 2" outlet : Waay not enough, who cares LOL.
Stock DP w/o cat : 425 CFM.
2,5" DP with VERY HIGH FLOW cat : plus or minus 450 CFM.
2,5" DP w/o cat : 500 CFM.
2,75" DP with VERY HIGH FLOW cat : plus or minus 475 CFM.
2,75" DP w/o cat : 600 CFM.
3" DP with VERY HIGH FLOW cat : plus or minus 500 CFM.
3" DP w/o cat : 725 CFM.
Stock catback with only the rear muffler replaced (the last portion is still in 2,25" tubing) : 350 CFM.
Stock catback with last portion replaced for 2,5" tubing and straight through muffler : 450 CFM.
2,5" catback : From 450 to 500 CFM (must be a straight through muffler).
2,75" catback : From 550 to 600 CFM (must be a straight through muffler).
3" catback : From 650 to 725 CFM (must be a straight through muffler).
Hope this can help ...
Regards
)
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Joined: 11-18-08
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From: MONCTON
woah thanks pyro!!!
wow only changing that 2.25 section really opens it up!
well with that in mind... all i need is that highflow cat downpipe, and that 2.5 over axel and then i already have a magnaflow glasspack straight muffler. what do you guys think?
wow only changing that 2.25 section really opens it up!
well with that in mind... all i need is that highflow cat downpipe, and that 2.5 over axel and then i already have a magnaflow glasspack straight muffler. what do you guys think?
Joined: 12-30-07
Posts: 14,079
Likes: 197
From: NEPA
So you would want to replace the stock resonator as well (if you don't want to purchases a full catback exhaust).
Last edited by Staged07SS; Nov 29, 2011 at 02:13 PM.
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