1 1/2" headers to small for 350?
#2
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Yeah they will. You might see gain from going to a 1 5/8"..but at the 300hp level it won't be a hell of alot.
As a very general rule for matching header primariy size to a motor:
300hp and under use 1 1/2"
300-400hp use 1 5/8"
over 400hp use 1 3/4"
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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports
As a very general rule for matching header primariy size to a motor:
300hp and under use 1 1/2"
300-400hp use 1 5/8"
over 400hp use 1 3/4"
------------------
"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports
#3
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If you can you should go for 1 3/4" headers as that way your set for more house already.
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1989 Trans Am GTA, 5.7L TPI, TH700-R4, T-Tops, dual cats, 9-bolt rear, 3.27, Dynomax muffler, K&N
1992 Camaro RS, 5.0L TBI, T-5, T-Tops, 3.08, L69 Dual Snorkel, K&N - Sold
Theme song for my GTA Cake - The Distance
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1989 Trans Am GTA, 5.7L TPI, TH700-R4, T-Tops, dual cats, 9-bolt rear, 3.27, Dynomax muffler, K&N
1992 Camaro RS, 5.0L TBI, T-5, T-Tops, 3.08, L69 Dual Snorkel, K&N - Sold
Theme song for my GTA Cake - The Distance
#5
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Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
I had 1 1/2" shorties on my 383 but had poor heads on it. When I put some better heads on the engine and went to 1 5/8" full lengths, I was running 11.8's at 117 mph. The 1 3/4" would have been nice but the extra cost didn't justify the larger size. Unless it's a full race engine, 1 5/8" should do you fine.
Most people who install 1 3/4" headers on their cars would probably make more HP and torque if they went to 1 5/8" since driving on the street doesn't put you in the RPM range to get the full use out of the larger headers.
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87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block
Best ET on a time slip: 11.242 altitude corrected to 10.89
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Member of the Calgary Drag Racing Association
87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley
Most people who install 1 3/4" headers on their cars would probably make more HP and torque if they went to 1 5/8" since driving on the street doesn't put you in the RPM range to get the full use out of the larger headers.
------------------
Follow my racing progress on Stephen's racing page
and check out the race car
87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block
Best ET on a time slip: 11.242 altitude corrected to 10.89
Best MPH on a time slip: 121.52 altitude corrected to 125.89
Altitude corrected rear wheel HP: 497.9
Best 60 foot: 1.546
Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association
87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley
#6
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Car: 82 camaro SC
Engine: 350
Transmission: 700r4
At 300 hp, 1 1/2 will be just fine. 1 5/8 will see very little gain on the top end and probably lose a little on the bottom.
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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, currant red metallic paint. Lots of other stuff...
82camaro
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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, currant red metallic paint. Lots of other stuff...
82camaro
#7
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iTrader: (1)
I want to build up an L98 to run 11's-12's and still be good on the street, and I think I'll be putting SLP 1 3/4's and 3" exhaust on it. They should be able to get more higher RPM HP from the TPI while a good TQ converter and a cam that will work good for both, makes use of that lower RPM TQ that the TPI makes also.
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89 RS
STILL Looking For:
An 87 IROC-Z28 350 TPI
[This message has been edited by IROCZTWENTYGR8 (edited August 27, 2001).]
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89 RS
STILL Looking For:
An 87 IROC-Z28 350 TPI
[This message has been edited by IROCZTWENTYGR8 (edited August 27, 2001).]
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#8
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Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
TPI dies out after 5500 rpm and that's where 1 3/4" headers will start to show an improvement. Unless you're constantly spinning the engine to 6000 rpm or have some sort of supercharger installed then just go with 1 5/8". A large tube header will kill the bottom end torque that a TPI produces.
Bigger isn't always better. Headers are an extension of the exhaust ports in the head. Small unported heads won't benifit from large tube headers and will actually create a drop in low end torque. That low end torque is what you use driving from stoplight to stoplight.
I wouldn't even consider 1 3/4" headers for a SBC unless you have a minimium of a 406 with aftermarket heads.
Bigger isn't always better. Headers are an extension of the exhaust ports in the head. Small unported heads won't benifit from large tube headers and will actually create a drop in low end torque. That low end torque is what you use driving from stoplight to stoplight.
I wouldn't even consider 1 3/4" headers for a SBC unless you have a minimium of a 406 with aftermarket heads.
#9
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Car: 90 IROC
Engine: 406
Transmission: GMPP 93/4L60
Axle/Gears: 9 bolt 3.27
I agree with you Steven....There was a 406 buildup last year in one of the mags. It had Iron eagle heads putting out 425-450 horsepower. They tried swapping a set of 1 5/8 for the 1 3/4 headers.
They gained some topend but the over all numbers dropped. So they used the 1 5/8s it was going to be a street motor and they were going for torque. It still made almost 450 horsepower with the 1 5/8s
Lingenfelter uses the stock corvette 1.5 factory headers on his vettes because they cost little in the way of power. His words not mine.....
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Black 90 IROC, L98, A4, 323 gear. SuperRamed 406 in the works!
They gained some topend but the over all numbers dropped. So they used the 1 5/8s it was going to be a street motor and they were going for torque. It still made almost 450 horsepower with the 1 5/8s
Lingenfelter uses the stock corvette 1.5 factory headers on his vettes because they cost little in the way of power. His words not mine.....
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Black 90 IROC, L98, A4, 323 gear. SuperRamed 406 in the works!
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