I'll be getting some headers next month and needed to know what size to get. I was thinking of 1 5/8" on my stock 350. Many people have told me that you need 1 3/4" headers for a 350 to breathe. I don't race the car and it rarely sees over 3500 RPM so top end horsepower is not as important as drivability. How much torque is lost by the 1 3/4" headers and 3" cat back? I do plan on a different intake and cam but nothing radical. Will 1 5/8" work well up to about 300-350 HP. Thanks

 

You won't really notice the advantages of 1 3/4" headers until around 400 HP. In the July 2000 issue of CHP, the did a 350 Goodwrench build up swapping various parts to see the effects on a dyno.

At 402HP, they swapped the 1 5/8" headers for 1 3/4" headers for a gain of 6 HP on the dyno. You can draw your own conclusions.

 

A lot of 350 guys on all the boards swear that 1 3/4" is the only way to go, but I back Glenn on this subject. I've seen a few dyno tests like the one he's referring to, and the results are close to the same. Even Lingenfelter recommends 1 5/8" on his EFI 383's.

------------------
85 calif. iroc
383/A4
9" rear

 

I totally agree. I am planning to swap my 305 for a 350. I went ahead and did the exhaust work and used 1 5/8 headers on my 305 for the time being. Definitly lost a lot of low end below 3,000 rpm. I think they will be perfect for my 250hp to 300 hp 350 when I put it in. I have picked up quite a bit of torque since I increase my fuel pressure and timing but it is still off from what it was with a basically stock system. Above 3,000 is really great. IMHO I would stay with 1 5/8 especially if you seldom rev above 3,500...bob

------------------
91 camaro RS L03 convert,
t-5, ultimate TBI mods,TBI spacer,SLP 1 5/8 headers,
3"cat back, 3.42 torsen posi,alston SFC's,Global West LCA relocation brackets

 

ok...what about for a 400 small block? it will have about 500 hp when its done but it will work its way up there...and when it gets there...it will get twin turbos...which will erase the need for these headers. what do u think?? will hooker 1 5/8 long tubes pass emissions?? i kinda wanna pass emissions.

------------------
Rick
90 Camaro RS 305 TBI
400 small block, Hooker 1 3/4 super comp long tubes, Random Tech Cat, Hooker aero chamber cat back on the way!!
TH700-R4 with Trans-Go shift kit
MacEwen Motorsports White Gauge Overlays
K&N Filter Charger (wooohooo)
GTS Headlight and Taillight covers
5% Limo Tint all around
Classic White Chevy Bowtie sticker on rear window
www.geocities.com/esvalenz

Man if my camaro were a rice-rocket all those mods would give me what...easily 50-60 hp!!!

 

ok the headers are legal...but will they restrict a 500hp 400 small block?
<bgsound src="http://farts.netcarver.com/sounds/famous/homer.wav" loop="1">
thanks guys

 

Thanks guys, thats what I wanted to hear. I thought that the 1 3/4" would be a bit to much. Looks like I'll be giving SLP a call pretty soon. Thanks again.

 

Check out this website for a Header GP going on right now!
http://www.users.qwest.net/~zjon/z-r...enheadergp.htm

$375 W/Air
$350 WO/AIR

WOW