Marks69BB

Changed from 1 7/8" primaries into 3" collector into 2 1/2" chambered exhaust to 2 1/8" primaries into a 4" pipe (hooker sidepipes) with no mufflers. What should I do - change carb jetting or just adjust carb? It doesn't idle as good as it should and doesn't have the punch that I think it should. Any suggestions? Engine info is in my sig. Thx for any replies! :cheers:

sideoiler

What kind of headers did you install? Do you have completely straight thru 4" sidepipes? I believe a certain amount of back pressure is necessary although I have heard the hooker inserts really cut the flow and cost about 50 hp. I have heard the JCL spiral inserts are good . I am trying to set up my BB exhaust so I am interested to see what solutions the forum comes up with..How loud is it??

Marks69BB

The old headers were Hooker supercomps and the new ones are Hooker combo headers/sidepipes with 4" tubes. Hooker's own inserts are way too restrictive but I was not impressed by the sound files of the JCL baffles so I'm making my own inserts. With straight pipes, they are way too loud for the street but are awesome for the strip - sounds like a Prostock car! :D

69 N.O.X. RATT

I do not think you have enough motor to need 2 1/8 pipes. You have probably cost yourself a lot of torque. You do not have your cam specs and compression, but if it LS-6 stuff with 3.08 gears it is a serioulsy missmatched combination.

Marks69BB

I'm planning on swapping the M20 for a Richmond 5spd to match up with the 3.08s. I'm also planning on having some head work done (or getting new AL heads) and changing the cam. The current cam is unknown but is a very mild street cam - probably the original LS6 crate motor cam. My last chassis dyno was 303rwhp/416tq with a slipping clutch and the cam was finished by 4500rpm. This is the first step in my plan of building a higher hp engine similar to what you are doing and only worked out that way because the sidepipes were free from a fellow vetter. Can you or anyone else help me by answering my original question?

vader86

I think he hit the nail, it doesnt look like you need primaries that large. You lost some low end torque and it makes the engine feel different. Adjusting the jets for more low end power or increasing the fuel pressure probably wont make as much difference as going back to the old headers or a cam change.

69 N.O.X. RATT

I think you are going to have a hard time making those 2 1/8 pipes optimul. I am making 450 rwhp and 470 rwt with my 454 and I have 1 7/8 pipes. For those 2 1/8 pipes to be a good combo I would geusstimate you need to be over 475 rwhp, and want to rev it over 6500 to make max power.

It is hard to tune for a missmatched combo, you could try some carb tuning but it may just exasberate the problem.

The Richmond will help, as will the rest of the planned head and cam work. I just dont know if you want to go as radical as the 2 1/8 call for.

I hate to be the bearer of news you do not want to hear.

Good luck

norvalwilhelm

The best thing to do is sell me the side exhausts at a really good price and go back to the old headers. You are punching a hole in your torque curve. I could live with that because ?????? I would do that for you to help recover some of your costs :) :) :) :)
Have a nice day a email me.

Marks69BB

I guess I'm confused here. :confused:

There are many BB cars running these pipes with big numbers (500+ RWHP & RWTQ) and decent street manners on pump gas. That is my goal. If I have sacrificed low-end torque, should I not gain in mid to high hp range with my current setup? Heck, there are some who have added these pipes to otherwise stock BBs and still raved about them.

According to the specs, I can bore this 4-bolt bowtie block up to 4.495" which, coupled with a longer stroke would mean a 540. Apparently, the previous owner may have already bored it .xx" over since the piston castings I have according to JE are for 500+ cubes (I've never had the heads off so bore, stroke and piston type is unknown). I'm assuming the pistons are flat top considering the >9 cr but what do I know? That's why my perception is that the weak point on this engine is the cam and the low compression since I've heard good things about the heads (14096188 R-port with 116cc open chambers) and the dual-plane intake.

Considering most bang for least money, what would you do next?

69ttop502

I would think with 500 inches no matter what 2 1/8 inch primaries are ok. Also doesn't the fact that the primaries on the swidemounts measure 45 inches make them more forgiving than if they were shorter. They picked up 30 horsepower at the wheels on my car with JCL baffles over an undercar system with good mufflers but only 2 inch pipes. That was with a mild 502. Bill.

Marks69BB

Bill - Did you notice/feel any reduction in low-end torque when you swapped to the sidepipes? Also, did you have to make any adjustments to timing, fuel mixture or did you have to rejet the carb?

69ttop502

Mark, my car felt much stronger and wanted to rev up faster when I went with the sidepipes and JCL mufflers with no loss of low end. But keep in mind the cam in my car then was dead by 5000 rpm's. Because I was doing everything myself and trying to get 3 pulls in I didn't rejet the carb although I am sure my results would have been even better. With my new setup it should be even better. I am going to uncap the JCL baffles as well for even more flow and according to Chuck Harmon not much more noise. I definitely would not be afraid to go into the 2 1/8 inch primary. Leaves you room for more later. Bill.