Performance Q&A Tech Section

Our Resident tech guru, Big Mac, tells all.

Kevin McClelland Apr 1, 2009 0 Comment(s)

What does all of this mean to you, Tom? Well, you must live by the same emissions constraints we do here in California. You may install aftermarket performance components as long as they carry a CARB executive order (EO) number. The EO process is a very stringent emissions testing program much like what Detroit must certify its cars by. It's a costly program for the aftermarket parts manufacturers, but it makes their parts legal for sale and use in these states.

You asked about a crate engine. Well, the only truly emissions-legal engine for your truck is a direct replacement L31 small-block. GM Performance Parts offers its HT383E crate engine, which by the letter of the law isn't legal in Mass. However, there's no way the emissions tech in your state can tell that the engine has been swapped unless they disassemble the engine and check the displacement. Do I recommend that you follow these misleading tactics? Of course not! The engine is sold under PN 17800393 and is a direct bolt-in for your L31. To get the most out of this engine, you will need computer tuning done by a professional service because an aftermarket calibrator won't have the proper tune for this engine.

To keep everyone happy and make a very painless refresh of your engine, install a new L31 crate engine from GM. The long-block (PN 12530282) carries a three-year/100,000-mile warranty on parts and labor and will put your truck back to showroom-new in the engine department. Then we would install a few other parts, including a set of GM Performance Parts 1.6 roller rockers (PN 12370839) and a K&N fuel injection performance kit (or FIPK, PN 57-301-2). To tune the engine, go with a Hypertech Power Programmer III (PN 32000). And finally, choose an after-cat exhaust from the manufacturer of your choice for sound and performance. These upgrades to the stock engine will give you an honest 30 additional horsepower and at least 1 mpg gain in fuel economy-you'll see more performance and economy, but this is a safe estimate. Above all, the listed modifications will be in compliance with your state's emissions regulations. Welcome to our new world!

Tale Of Two Engines
I may be in over my head. I have acquired two donor vehicles which I plan to transplant the running gear from into two street rods. One is a '90 van with a 350 TBI engine and a TH700-R4 trans. The other is an '88 Trans Am with a 305 TPI engine and a five-speed. I'd like to install the TPI system on the 350 van engine and run it with the five-speed, and run the TBI system on the 305 with the TH700-R4 transmission. Is this possible, and if so, what needs to be done to accomplish this? Thanks for any help you may provide.
Sonny Davis
Via e-mail

A If you put both engines into a bucket and shook them around long enough I'm sure they would come out the way you'd like! You do have an interesting mix of components to work with here. Let's see if we can get you there.

First, the 350 TBI engine has a great short-block to work with. However, you'll want to change out the cylinder heads. We would take the complete top end off the 305 and camshaft and drop it right into the 350 short. The TPI cylinder heads are about the best iron heads of their day. Now, this isn't much to write home about, but it's what you have. The 305 heads will boost the compression about three quarters of a point and give you standard (not swirl) inlet ports.

Moving on to the 305, swapping the 350 heads onto your 305 will drop your compression. You could pick up a set of swirl-port LO3 305 heads to match the TBI inlet manifold. Also, install the LO5 350 TBI camshaft into your 305. Then you'll have a complete LO3 305 TBI engine.


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