Basically I'm trying to balance the HP/$ ratio....>

I can get a set of new 1 1/2" aftermarket headers for $50.00 less than the 1 5/8's for my 84 L69.

How much of a difference is the 1/8" going to make?

What size are my stock headers?

 

1st, you don't have headers as OEM, they are called exhaust manifolds. They are roughly 1-1/4" (not too sure) with 2-1/4" connection to the Y-pipe on L69s (smaller on LG4s) . Second, for a stock LG4 to lightly modded L69 I would recommend 1-1/2" primary headers. Anything more serious than a seriously modded L69 up would require 1-5/8" primaries. If you plan on only doing intake, exhaust with the headers, go with 1-1/2" primaries. If your plans call for a serious L69 (or a 350 in the future), go with 1-5/8" primaries. As for brand, I'm biased towards either MACs (1-5/8" on my '94) or better yet SLPs (1-3/4" on my '84).

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George P. Lara
1984 "L69 A4"
Soon to be 357, T5, 3.70
1994 LT1 M6
SCCA, SCFB, SC3GFB

[This message has been edited by MRZ28HO (edited February 19, 2001).]

 

I wish I could cut and paste that onto every question about header size.

Remember bigger isn't always better. A street engine operates below 5000 rpm and is usually below 3000 rpm most of the time. Small tube headers like 1 1/2" build torque and that's what you feel driving stoplight to stoplight. Larger tube headers will help a bigger or more modified engine but only at higher rpms. My best times (below) were with 1 5/8" long tube headers shifting at 6400 rpm. The extra cost of 1 3/4" would not have made much of an improvement to justify the extra cost.

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Follow my racing progress on Stephen's racing page
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87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
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87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

Yes, but Stephen, you're at altitude. Your air/fuel requirements are a lot different.

I dunno why anyone would put 1 1/2" headers on a V8 engine. Unless they do all their driving below 3000 rpms. I'd think they'd be just as restrictive as exhaust manifolds. Your exhaust valve is 1 1/2" in diameter too. A 1 1/2" header primary is only 1 1/2" on the outside, it'll be smaller on the inside. That means your exhaust gas comes out of the port on the head, and into a smaller tube. Exhaust gas likes to expand, not contract.

I'd get 1 5/8" headers for your 305. But its your money.

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West Coast GM Shootout 2001!
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=-

 

1 5/8 headers are pretty versitile. You can use them on basically any slightly modded engine you'll put in. Which means in the long run, you won't end up trashing the 1 1/2s for 1 5/8s later on because they are too small. One set of headers is much cheaper than two sets.

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1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 Trans Am T-tops
4-bolt main 350, performer intake, headers, Holley 650, T-5, hayes clutch, dual elec. fans and 3.23's.
Daily driver and restoration
13.98 @ 101