Mohammed

I’m new to the carb world, need a good combo for my 89 to replace the TPI’d LB9.

Gonna use an L31 from the yard and the is Performer RPM Air-Gap intake what cam and carb should make it a killer? Trans is WC-T5 with 3.42 gears. Don’t have any pollution laws here but I’ll be driving it on the street.

Thanks for your input

scottland

take the heads off, take them down to a machine shop, have them cut the valve guides down, and make the valve seat larger, for a larger valve spring. while the heads are there, you might as well have them drill and tap the rocker stud bosses for screw in studs. should be pretty cheap, call around and get some quotes.

replace the head gaskets (probably a good idea anyway)

a factory L31 has a roller cam, so you might want to go with something like a comp XR270HR-10, or XR276HR-10.

both should give you good power up to about 5500rpm, so it should be plenty streetable.

as for a carb, a holley 4150 650cfm should work just fine, word around the campfire is that mechanical seccondaries are reccomened for a manual car, and vacuum seccondaries are reccomened for a auto car.

five7kid

iTrader: (14)

Holley has a chart on their website that shows what RPM (stall speed) you need to stay above to avoid bog with a given engine & carb size for a mechanical secondary (double pumper) carb. A 650 DP works well on a 350 for fairly low stall.

Mohammed

mate do you have the link for the chart?

Mohammed

Will I get more power with the Holley 750 DP?

AutoRoc

iTrader: (1)

If you want big screaming power here ya go:

A. Use a Holley 750 DP

B. Use an Edelbrock Super Victor Vortec Single plane intake and have it port matched to the Vortec heads you have.

C. Choose a cam lobe from this link and go from there. http://www.carcraft.com/techarticles/116_0311_cheap/ Scroll down and click on the small yellow chart above the Royal Purple oil quarts. Those are some mean cam specs that you would want probably. You can go with larger lift cams if you read D and follow suit.

D. Are you willing to spend money to take that engine apart and modify the heads? It's worth power. You could machine the valveguides down to accept MORE than .485 lift which is the maximum you can run with stock Vortec heads. Also since you'll be choosing a killer camshaft, bigger stiffer springs would be a wise choice. A performance oriented valvejob would be worthwhile also along with pocket porting and smoothing of the runners, maybe even combustion chamber polishing. If that's something you want to do, you can then just get a bigger cam to start with instead of a small .485" lift cam. Aftermarket Roller rocker arms would also enhance high rpm operation while adding power.

This is what the "Cheap Street" racers are doing and ya know...with a 175 shot they are running high 9's and probably making 600+hp...Goodluck!

five7kid

iTrader: (14)

http://www.holley.com/HiOctn/TechSer...fo/TI-225.html

five7kid

iTrader: (14)

A little better WOT off-the-line.

Peak power will be about the same whether DP or VS. It's the rest of the curve that benefits from the DP.