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Discussion Starter · #1 · (Edited)
1999 L31 350 vortec in a 3/4ton van. considering a 383 build.

specs:block bored .040, barely decked to .015, 0.041 head gasket, 7cc vr flattops, 5.7 rods, 400 crank, 64cc vortec heads, zz4 cam with 1.5 rockers, stock fuel injection WITH PCM TUNE.

figure it to be 10.5:1 CR static. not sure on dynamic.

will cam bleed enough pressure for pump gas or build too much pressure?

will this run on 87 or 89 octane? if not, what do i need to change? advance or retard timing? deeper dish pistons?

i've read about quench and squish and DCR until my eyes bled. Looking for a barny-style explanatioin. Thanks!
 

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Discussion Starter · #3 ·
looks like 12cc dish would give me 9.975CR and 18cc dish would give me 9.4CR. Is this necessary? I've heard about high CR engines running on 89 octane.... Is that were DCR and squish help out? how is my DCR and squish looking? The cam WILL BE zz4. Will adjusting cam advance help out? at what cost?
 

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Vortecs will be perfect up to about 5000 RPM in a 383. That means your cam should be in the 205-215 duration range (on the intake anyway; probably more on the exhaust side)

With that small a cam, you're looking at 9.5:1 if you want the cheap gas. 10.5:1 will be a bit of a mismatch, but would run fine on 91

I'm running 9.5:1 in a 350 vortec with a 196/206 cam, 111 LSA for a boat. Tops out at 5100 rpms where it makes just shy of 300 hp on 87 octane.
 

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Discussion Starter · #11 ·
Really appreciate the input. I'm looking for torque down in the low and mid rpm's. Peak numbers are not the point in this build. I would prefer 89 octane but 91 would work to I guess. So, 10.5 CR static and 8.4 CR Dynamic then? anything about advancing or retartding cam timing play into this? If so, how? Would it be worth another $150 to get deeper dished pistons to increase volume and decrease CR? what CR is a cam like mine intended for?
 

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I'd say your build is doable with the L31 F.I., you might want to consider the marine intake with external injectors so you can upgrade the flow rate.

What PCM does your van have? The 0411 PCM is more compatible with aftermarket performance parts when compared to the old "black box" pcm, by that I mean there are more tunable tables that are controled via a custom PCM tune.

I had a 10.34-1 compression, LT4 hotcam & 1.6 rockers, L31 injection with the "newer" design injectors, 0411 controlled tuned with HPTuners. I finally gave up trying to get my engine to perform the L31 injection, the non-upgradable 19lb/hr injectors were running out of duty cycle and still couldn't fuel in the higher rev. I instead went carbed, and once I was carbed I put in a bigger cam & vortec heads with 2.02"/1.6" valves and bumped up the compression with a thinner head gasket.
 

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thebigblue said:
Really appreciate the input. I'm looking for torque down in the low and mid rpm's. Peak numbers are not the point in this build. I would prefer 89 octane but 91 would work to I guess. So, 10.5 CR static and 8.4 CR Dynamic then? anything about advancing or retartding cam timing play into this? If so, how? Would it be worth another $150 to get deeper dished pistons to increase volume and decrease CR? what CR is a cam like mine intended for?
You will need the dished pistons. The 8.4 dynamic was from a 9.45 static compression provided by the 18cc dish. If you start with 10.5 static your dynamic will be way too high. Your cam is intended for the 9.5 static, max. With the 9.45 static it will run on 89 octane.
 

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Discussion Starter · #14 ·
decided to go with stock 355. will go with my zz4 cam and springs. also gonna run a set of shorty headers and a wait4me PCM tune.

might back cut the exhaust valves and clean up the flashing in the bowls. if i do the valves i'll use a thinner headgasket to bump static CR a tenth or so.

it's too complicated trying to get stroker working with stock injection. it's my family van so I'm sticking with K.I.S.S.

what do you think those mods will dyno for?

thanks for all the help!
 
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