[Dizturbed One]

CA has a smog stranglehold on engine progress on my 76 GMC Jimmy 4x4. I want to rebuild it soon to bump the compression to help me out on the trails in this heavy old thing. I was thinking just bearings, rings, and valve seals again (just cause it will be apart) along with the new pistons and some better GM heads. I would like to stay on pump gas.

For smog stuff it has AIR tubes and an AIR pump, a charcoal canister, and a vented tank. The truck is a 400SBC/TH350 with 4.10's and 35" MT's. No OD and no lock-up. I know my way around a toolbox, but have built only one motor before now, and know little of what route to go. Truck runs good right now, solid, quiet, cool, doesn't eat oil. A little puff on start-up. Had a full internal rebuild about 6,000 miles ago but I want to go through it again for a little more power, and to fix some leaks from sitting a decade.

Any opinions from guys with experience building engines would be greatly appreciated, I know nothing of various combinations that would produce these numbers without messing with the top end too much to keep the smog ref's happy. I'm just trying to get upwards of 300 lb/ft of torque. Getting 300 horses would be nice... But is not necessary.

[cobalt327]

It's all in the heads. If you use a CARB legal head like Brodix and others make (the Brodix is just an example), along w/a CARB legal cam, carb and headers/exhaust, you can make a LOT more than 300 HP- legally.

[a1supersport]

Wouldn't it be easier to get an older truck (I guess...pre-67 or something?) and go from there? Aren't those older cars/trucks exempt? (Sorry I'm not familiar with emissions-standards).

[Dizturbed One]

Thank you Cobalt, that's what I was really hoping to hear, and had suspected, but do not have enough experience to know. Looks like I'll just be freshening up the build with some new slugs and a different set of heads.

I really want to stay with stock exhaust manifolds and the stock carb though. So I'm hoping it's still feasible with those restrictions. Most headers would give me clearance problems with my front driveshaft, and the Q-Jet I have right now works better than almost any aftermarket carb out there as far as mpg, low RPM performance, and good performance up steep grades.

[Dizturbed One]

Originally Posted by a1supersport

Wouldn't it be easier to get an older truck (I guess...pre-67 or something?) and go from there? Aren't those older cars/trucks exempt? (Sorry I'm not familiar with emissions-standards).

Pre-76 vehicles are smog exempt in California. Ditching it to get a 75 (full convertible top truck which is ugly IMO) isn't an option to me anyways.

This is my first truck and will continue its life with me FOREVER. lol

[cobalt327]

The Q-jet is an excellent carb, as you have found. And there is no reason you can't make well into the 400HP range w/that same Q-jet, possibly w/some tuning. But the basic Q-jet itself will not hold you back from your goals, plus will provide a very responsive engine and the best MPG that you can expect to get from a performance engine, short of a full-on EFI $et-up.

The stock exhaust manifolds are another story altogether. I don't know your reasoning behind keeping them, I will just say that there are CARB exempt headers for that engine should you change your mind.

Being a 4X4, there will be clearance issues w/most "long tube" headers. "Block hugger" or "shorty" headers may fit w/o problems, I'm not positive on this, though- so it would need to be researched. With some exhaust systems, a floor shifter is mandatory, BTW. So swapping exhaust gets complicated, depending on how your rig is equipped as it sits (floor or column shifter, etc.).

A suggestion is to hook up w/a 4 Wheeler club in your area, attend Off Road gatherings and look into the many 4WD and truck forums online (not that we want to lose you here).

Good luck.

[Dizturbed One]

My reasoning for keeping stock manifolds is the fact that I can't find shorty headers with AIR provisions. I've seen one mid-length offer, but I don't think it will be feasible with my truck. Nothing out there gives the kind of clearance that these do while retaining smog requirements.

I don't need it to be as powerful as it can be, just a little more than it is now. So I'm thinking just put some new slugs/rings and some better GM heads with smaller combustion chambers for a compression boost. A mild low-RPM hydraulic cam/lifter setup, and a rebuild/tune on the Q-Jet.

I'll probably be in here this winter asking about heads and a cam combo for it. LOL

[cobalt327]

Originally Posted by Dizturbed One

My reasoning for keeping stock manifolds is the fact that I can't find shorty headers with AIR provisions. I've seen one mid-length offer, but I don't think it will be feasible with my truck. Nothing out there gives the kind of clearance that these do while retaining smog requirements.

I don't need it to be as powerful as it can be, just a little more than it is now. So I'm thinking just put some new slugs/rings and some better GM heads with smaller combustion chambers for a compression boost. A mild low-RPM hydraulic cam/lifter setup, and a rebuild/tune on the Q-Jet.

I'll probably be in here this winter asking about heads and a cam combo for it. LOL

While I do not know how the smog gods will view this, a swap to the L31 Vortec heads and exhaust manifolds would make decent power, w/o breaking the bank. However, I don't know if those exh. manifolds have the correct A.I.R. (or whatever) provisions to match up to your existing system.

What they have, is one large fitting on the driver side manifold, back by the outlet to plumb the AIR pump into. The manifolds look to be maybe a bit larger than earlier Gen 1 SBC log-type manifolds, but I cannot say that w/certainty, as I don't have an older set to compare them to.

That said, there'd prolly not be a significant difference between them and what you have- something like 5-10 HP as a WAG. The Vortec heads lack a heat crossover, so plumbing a functional EGR would be a problem, too. Might be worth some research, in any event.