I have a 91 with a 305 tbi that has been converted to tpi. So i still have the tbi heads cam manafolds and y pipe. Im trying to deside between 1 3/4 and 1 5/8 size primaries. When I put this in i also have a 3 inch cat and cut-out to go in with the headers.

Will I lose any power with the 1 3/4 inch compaired to what i have now. I do plain on puting a 350 in later. If I deside to go with the 1 5/8 how much more power will I have with the 305 and how much less will I have with the 350.

If someone has before and after times with slp headers that would be great thanks

 

You are going to want the bigger headers with the 350, so I would just go ahead and buy the SLP 1 3/4 header. I actully plan on putting a set on my 305 this summer as I will be putting in a Minni-ram 383 in the not so distant future. You will not loose power with the 1 3/4 versus the 1 5/8 I DONT THINK but it will be a much better size when you put in that bigger 350 with bigger ports.

As far as time slips with the SLP...I unfortunatly do not know anyone who ran before and after times with the SLP's But I would make a post in the lounge, I bet someone in there has.

good luck,
Erik

 

Unless you plan on making 350HP+ with that 350, I think the 1 3/4" would be a waste, and might even lose a little power. Definately don't put them on a 305. They might make more power than the 1 5/8", but the 1 3/4" would be too much for a stock TBI heads/cam car. The 1 3/4" also have clearance problems.

Compared to the stock manifolds, both the 1 5/8" or 1 3/4" will make a big difference. The whole exhaust setup you stated should add at least 30-35HP on a near stock 305 - no joke! The stock exhaust on the carbed/TBI cars was horrible. A 350 with a decent set of heads and cam will respond much better even. I've seen a few mag tests comparing stock vs headers and 3" exhaust. A healthy 350 (350HP+) gained nearly 65HP from the switch alone.

However, on my car, a change from Edelbrock TES to SLP 1 3/4" made a definate SOTP difference above 4000RPM. I doubt I'm making more than 275HP, so according to my own advice that should not be the case No times for before and after, but it was very noticable.

 

It's the same price between the 1 3/4 and the 1 5/8.

 

I put the 5/8" in my 350 IROC. Like said, unless you're really making some serious hp, then the 5/8 are just fine. I've never heard anything about clearence problems with the 3/4, but hey, its possible. Bigger is not always better. If you do plan on a 383 down the road, you're better off with longtubes anyways.

Before my headers, I had all the mods in the sig plus dual exhaust. I would run a 9.0x-9.1x in the 1/8. After the headers and the 3" catback (don't ask why I switched, guy who worked on the car is a moron) I ran constant 8.9s, with better driving I hit constant 8.8s.

 

Check out the Exhaust board at www.thirdgen.org Nearly 90% of all those who have the 1 3/4" had the #5 primary contact the steering shaft and brake lines.

 

I honestly don't feel it's smart to waste your money on 1 5/8" stuff when you can get 1 3/4" for the same price and then have room to upgrade. Why spend the money twice?

I have the 1 3/4" SLPs on my car...they work great. I don't know what clearance problems there are...although I did have to put a slight dent in one primary to clear the steering shaft.

I would get the 1 3/4" stuff...and work your way into it. Any SLIGHT decrease in performance you'd see with a 305, you'll more than forget about once you go bigger with a better breathing engine. Remember...with a 350 350+hp isn't difficult to attain...

Eric

 

I installed the 1-3/4" versions on my little 305 ONLY because i had them laying around. Another reason is that I believe they make more power than stock manifolds only when the nitrous is being used. I could care less N/A.

Yes 1-5/8" IS a better choice but I have plans that will require severe breathing so I'll be ok in the "future".