tired 350 to new 383 swap questions.

[Tuck]

Hello all, I'm new here so go easy as I have fragile ego...

So I've done some searching here and around the interweb and haven't gotten a defintite answer, no one in my area has an answer either because it hasn't been done locally.

I have a '97 GMC 3/4 4WD w 4L80e, the original engine has developed cold knock and is getting worse, has and does run fine, throws no codes or misfires but I've been angling for a rebuild because I love the body style of these trucks.

Looking around for a suitable rebuildable core I ran across an abandoned L31 383 stroker project in long block that was still on the stand. The price was cheap, like desperate "I gotta post bail for my wife" cheap.

He had picked a way too radical cam for my liking so I sold that off and called compcams for a suggestion, they reccommended thier 08-501-8 cam with 212/218 .495 lift 112LSA profile.

Calculating the compression with valve job only Vortec heads yields 9.67:1 comp. My questions are, is that a good cam choice? and most importanly can the factory Black Box PCM be tuned to handle the increased displacment and cam choice? Can the factory injector spider be scaled up to supply the increased displacment too?

This truck is mainly used to haul my street/strip T/A and it is used to haul building materials. I want it to be reliable and have good drivability. So, it's a semi DD work truck that I really like. I would like it to run pump 87 but if that's unreasonable then 93 pump gas is okay too.

Any help??

 

[michael hurd]

From GM Performance Parts description on their long block 383 stroker: the factory computer will adjust quite fine to the larger engine. However, you may consider a tune to get the most out of it. From what I read the factory manifold and spider are good to approximately 400 hp.

If you are sticking to factory vortec heads, that cam may clear ( retainer to guide ) with a different retainer, but I would want to mock everything up and measure the clearances first. IIRC .470 is about the maximum you are going to get with factory retainers, but production tolerances etc, means that's not set in stone.

Otherwise, you are looking at a bunch of machine work to turn down the OD of the guide for smaller PC seals, shorten it, and possibly enlarge the spring pockets at the same time. If you intend to do this on some used heads that need a valve job anyways, you may be better off buying a head that drops in place that would accept that lift, like the Edelbrock E-tec.

 

[Tuck]

Thanks for the reply, and yes, I forgot to mention Im going to have the heads machined to accept better valve springs and to avoid retainer to seal interference.

A differnt head is an option but not one Im prepared to invest in for an over babied tow vehicle.

I just wish I could find a definitve answer about the injector. GM make the claim it will but the HT383e has a half point lower compression than I will, and the HT383 runs a smaller cam than I will. They also state it's for half ton applications only....whatever that means.