How do they work for you? Did they help out on the top end any? I am trying to decide if I should go with 1 3/4 or 1 5/8?
Thanks, Gary

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1990 Formula 350

SLP headers right? SLP recommends the 1 3/4" headers for L98 TPI engines, and 1 5/8" for 305 TPI/TBI engines. For a stock L98 the 1 5/8" might be better, but if you plan on going to something better in the future, get the 1 3/4" headers now.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

91Z, for a really modded L98, cam, heads, everything, which would u recommend?? Thanks!!

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Looking For:

87 IROC-Z 350 TPI
84 TRANS AM 305 H.O.

[This message has been edited by IROCZTWENTYGR8 (edited October 29, 2000).]

Take it from me. Get the SLP 1-3/4" headers for a 350 TPI (ESPECIALLY for a modified TPI). I currently have the SLP 1-5/8" headers and they are seriously hurting my topend performance. In retrospect I should have bought the 1-3/4" primary tubes (but - I got a good deal on the used 1-5/8" headers that are on the car now). Doesn't matter now though - I have a set of Hooker SuperComp Long Tube 1-3/4" headers that I will be putting in shortly

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's after installing Hooker LT Headers and reducing weight.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

IROC, the SLP 1 3/4" headers of course!

Thanks guys!! I have a topic on this on the Tech Board, and some guys are saying 1 3/4 and some guys are saying 1 5/8.

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Looking For:

87 IROC-Z 350 TPI
84 TRANS AM 305 H.O.

Definetly buy the 1 3/4", you will get much more from it in the long run. The only reason I am running 1 5/8th on my car is because when I bought them, it was all I could afford.

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission with 2.77:1 Rear End

Current Mods: Edelbrock TES 1 5/8" Headers, Hooker Aerochamber Cat-Back System, Performance Resource Chip with 160* Thermostat, Accel Ignition Components, K&N Filters, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET : 14.32 @ 97.7mph
(corrected for elevation)

Thanks guys, It is stock right now but I do not know if I am going to leave it that way!!
I really wanted something for more top end so it sounds like that is what I am looking for.
Thanks Gary

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1990 Formula 350

I agree what the other say about the 1 3/4.I bought the 1 5/8 because it was all I can afford at the time.If it does lose some in the low end it is very little.

Daz
13.3@104 w/ 2.043 60'

I have a question about the size thing. I have also read that SLP recomends 1-3/4 inch for 350's and 1-5/8 for 305's, BUT John Lingenfelter says in his book that for a street-driven 350 (since they spend most of their time in the low and midrange RPM's) 1-5/8 primaries are the best because they enhance torque in those areas (higher gas velocity.) He says low-mid torque is more important for street-driven cars than the upper-end HP, and goes on to recommend that 1-5/8 primaries can be used for 350 motors making up to 400HP. I think he MAY know what he is talking about! Not flamming anyone but I think it definitely depends on your application. My 2 cents.
John

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84 Firebird with Trans am ground effects- 350 4bbl GM crate motor (LM1), T-Tops, automatic, K&N filter, 180* thermostat, ram-air hood scoop, flowmaster muffler, Accel cap & rotor, MSD Super Conductor Wires. Coming soon: new interior (grey), rear end work, subframe connectors, polyurethane bushings

When I put my headers on in made a huge difference in top end. And there was no noticeable loss on the low end at all. Unfortunately I can't give you any times, because when I was on my way to the track last Fri I spun a rod bearing!!

Oh well, I ordered a new engine yesterday from SDPC. ZZ4 bottom end, Edelbrock 6085 heads and an LT4 Hot cam kit. I can't wait to get this baby between the fenders!!

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Black 88 GTA L98
!Airbox, !IAT, !MAF, !TB, !Plenum, SLP 1 3/4" headers, Dynomax Hi-Flo cat & cat-back, Corvette Servo
14.389 @ 95.2 mph, 2.001 60' {Before headers, new times coming soon)

1 3/4 is the only way to go.

Check out www.headersbyed.com. The creator of this site (Ed Henneman) is in basic agreement with John Lingenfelter, that 1-5/8" tubes on a small block will support over 400 HP. Ed custom designs headers (primary tube size, length, collector size, length, etc.) based on the engine/vehicle combination. I purchased a set of his headers for my 6000 rpm 450 hp 383 with AFR heads and guess what? I got 1-5/8 inch primary headers.

This guy is a bit difficult to work with, but has over 30 years experience. He had one customer with a small block powered racecar and 1-5/8 inch headers that went high 11's in the quarter mile. The customer bought a set of 1-3/4 inch headers and lost almost 0.1 second, even after extensive retuning with the new headers.

I don't mean any disrespect, but people who recommend 1-3/4 inch headers for street driven small blocks typically have little experience with headers with the exception of what they have read in magazines. 1-3/4 inch headers will only benefit small blocks that spend a lot of time making over 450 HP at engine speeds exceeding 6,500 rpm.

John Lingenfelter went 300 MPH at Bonneville in the early nineties with a red small block powered Gen III trans am. I was there. I suggest you follow his recommendations and go with the 1-5/8 inch headers.

Thats good info, thanks!