L31 Conversion Thread

[toolboxchev]

Been doing the rounds, looking for more info on that Jegs Chevrolet Performance motor.

What type of piston do they use in it? Sure you could guess by the compression ratio, yet I am under the influence a long skirted one would be more durable in the long run.

Also who has done this and what specific stuff did you need to get her in and done? Hate to do the find out later thing. I know a cam change can wake them up, suggestions?

[Tator]

Hypereutectic pistons. great for every day use. 9.4:1

Edelbrock dual plane air gap for vortec heads

280 magnum cam

650 DP or Vac sec.

Hooker or equivalent long tubes.

What I would do.

[BCOWANWHEELS]

ALLS GOOD EXCEPT D/P CARB. THERE HARD ON GAS.


Hypereutectic pistons. great for every day use. 9.4:1

Edelbrock dual plane air gap for vortec heads

280 magnum cam

650 DP or Vac sec.

Hooker or equivalent long tubes

BUT I WOULD O/H STOCK 350 MYSELF

What I would do.

[RDrancher]

What 280 cam are you referring to?

[6T7 C10]

I am running a new crate L31 that I installed this past winter. My setup includes the GMPP serpentine belt kit GM12497697, Summit Stage 1 intake manifold 226018, Edelbrock 500cfm carb 1802, Fel-Pro head gaskets 1094, Comp 1.52 rocker arms 1617, Summit HEI distributor 850001R, ram's horn manifolds, and dip stick tube GM12551154. The rest is stock. I have and electric fuel pump SP1130 and electric cooling fans. My dash has the warning lights and I found that a Standard TS81 switch is 240* and fits the head for the water temperature. It is probably running right under or about 300 HP as it is and has strong low-mid range. Hope this helps.

[6T7 C10]

But wait there is more. Oh yeah i remember now. I got a GMPP timing cover w/o the sensor hole 12562818 and a melodized distributor gear ACD10456413.

If I had to do all over again I think I would have used 1.6:1 rocker arms or kept the original ones and put in a HT383 cam 14097395. I originally did not think I was going to get into the engine.

[BCOWANWHEELS]

A comp cams 280 has a real lopy idle poor fuel milage. A great street cam is the melling mtc-1 towing cam

[RDrancher]

Originally Posted by BCOWANWHEELS

A comp cams 280 has a real lopy idle poor fuel milage. A great street cam is the melling mtc-1 towing cam

Yeah that cam looks a little steep for the street.

One combo that's been on my radar is this modified L31 from Pace. It's a grand more than the stock L31, but the head-work has been done to allow running GM's "357" cam, and it still has a GM 12 month warranty. https://paceperformance.com/i-238695...provision.html

[6T7 C10]

Keep in mind the L31 came originally as a factory roller tappet engine. Make sure to spec roller cam and lifters. I think you can make a flat tappet cam and lifters work in that block too but I would shy away from it especially if you have a new crate engine if that is true. The vortec heads flow fairly well for stock at low lifts and low rpm and would require different springs and retainers if the cam plus rocker arm lift gets too high.

[Jrainman]

I have been looking in to Alex's parts .com they have valvetrain spring kits with 4 options for the L31 along with cam and rollor options to suit your needs . you should take a look as to what they offer in performance upgarades for the L31 .

[rcazwillis]

Do the research before you start swapping cams into an L31. Max lift without head work on the valve boss or different retainers and springs is about .450. The 280 has .480 and is a flat tappet. L31 should be a roller cam block. Alex parts has some pieces that will let you increase lift without machining the boss.

I just went through my first set of vortec heads. Machined the valve boss down using Comp Cams tools. I now have enough clearance for .550 off lift. Without some good porting the heads don't flow well past .500. So a cam with about .510 will be what I go with on my engine. Comp Cam has one designed for these heads with .503/.510. Probably what i will use.

[toolboxchev]

Originally Posted by 6T7 C10

I am running a new crate L31 that I installed this past winter. My setup includes the GMPP serpentine belt kit GM12497697, Summit Stage 1 intake manifold 226018, Edelbrock 500cfm carb 1802, Fel-Pro head gaskets 1094, Comp 1.52 rocker arms 1617, Summit HEI distributor 850001R, ram's horn manifolds, and dip stick tube GM12551154. The rest is stock. I have and electric fuel pump SP1130 and electric cooling fans. My dash has the warning lights and I found that a Standard TS81 switch is 240* and fits the head for the water temperature. It is probably running right under or about 300 HP as it is and has strong low-mid range. Hope this helps.

So I take it with Ram Horn manifolds that you have no interference issues with the spark plugs. I figured out a while back the L31 heads have the plug holes moved slightly inboard to the exhaust port side. Did you use any heat sheilds with your Ram Horns?

I would also like to figure out if the cam its equipped with is for a fuel injected setup??? I know they post the specs and figuring out good swap in for a carb motor would be different.

[6T7 C10]

Originally Posted by toolboxchev

So I take it with Ram Horn manifolds that you have no interference issues with the spark plugs. I figured out a while back the L31 heads have the plug holes moved slightly inboard to the exhaust port side. Did you use any heat sheilds with your Ram Horns?

I would also like to figure out if the cam its equipped with is for a fuel injected setup??? I know they post the specs and figuring out good swap in for a carb motor would be different.

Yes I still have the ram horn manifolds and there is no interference issue with the spark plugs. In fact it worked out great. I also used some repop heat shields and they worked fine but I did have to rework the right rear one for use with the oil dip stick tube.

The L31 factory cam does not have a lobe for the fuel pump and the block is not drilled for a pump rod either since they were all fuel injection at that point. I have a 5psi rated electric fuel pump mounted on the frame going to the carburetor.

Hope this helps.