Which intake manifold

[todd1969]

I'm curious if anyone has taken a stock GM TBI manifold and ported it to 46mm (or a little larger), finding any noticeable performance gains versus buying the Edelbrock 3704 intake and simply installing it? I can get a ported stock intake for appx. $150, whereas the Edelbrock is new and costs about $265 and obviously has no mods. I can have it bored out t0 46mm to match my modded TBI unit I will soon purchase.

I had another 1995 GMC X-cab with a 5.7 engine back in 2003 to 2007. I installed a new 3704 intake, but I also added 1.6 Comp roller rockers the same day. Those mods were nicely noticeable...probably worth 40 horsepower on the crank and I'd guess 20 to 25 at the rear wheels. Seemed to increase power all through the power-band and made the stock cam idle a bit better too...sounded a little "macho" thru the tru-duals with 2.5" pipes and Spin Tech mufflers.

I know there are other intakes one can add, but the stocker, or the Edelbrock 3704 are simple bolt on versions. You don't have to rig this or that up, and I like simplicity.

My TBI unit is currently stock, but I am planning on buying a nice modded unit form someone on here or maybe a business we all know of. A pair of flow tested "cop car injectors" will come with the modded (46mm) TBI unit. Again, I know many people put 454 TBI's on their trucks, but I like the simplicity of swapping a stock small black version for a modded SB version.

Thanks!

[goodgollum]

The best bang for your buck for a stock 1995 5.7L/350 c.i. TBI engine is an Edelbrock Performer TBI 3704 intake manifold plus CompCams 1.6:1 roller rocker arms for higher lift from your valves and less friction because of the roller bearings for the rocker arms.

You could spend more money by installing an aftermarket CompCams hydraulic flat-tappet camshaft, but I don't recommend it.

You could install full/equal-length exhaust headers, a high-flow catalytic converter, a high-flow muffler, and a K&N air filter, but I don't recommend that, either.

The main problem is the heads. The heads are GM "swirl-port" heads. The intake ports have a ramp that was intended to "swirl" air flow to improve low-end torque, but the ramp acts as a blockage to higher air flows.

You could install different heads, but then you'd need a custom PROM chip. I recommend Dave Darge at Powertrain Electronics:
http://powertrain.net/

[todd1969]

I've done most of what you suggest, either on this truck or my previous 1995 ext. cab with 5.7 engine. I never did minus a cam change, but did add Hedman elite headers on the previous 1995 but they leaked form the start and I got a bad taste for Hedmans, even though they were 14 ga. metal. When they did not leak, for all of 2 days maybe, they added considerable power on the tru-dual, no cat 2.5" system I had.

*** Does anyone KNOW for sure how large the Edelbrock 3704 intake can be bored out? I've read 46mm, 47, 48, and I've read of some going to 50mm without hitting a water jacket. I'd like to know for sure before buying a $265 Intake, then spending another $35 to %40 to have it bored out to X size. ***

I agree, the 1.6 roller rockers and a real bit of power and the stock heads are absolute trash. My truck has only 94,000 original miles on it, but I am leery of spending much on an engine with almost 100,000 miles. I have owed the truck from about 87,000 miles forward, so I don't know how it was treated before, however I spoil it and maintain it as well as anyone can.

Todd

[goodgollum]

Todd,

I can't help with do-it-yourself throttle body modifications.
I did a couple minor upgrades, then I paid Dave Darge at Powertrain Electronics to make my custom engine work.

Regarding headers, I suggest thick flanges and RF2016 exhaust gaskets.

[Doober]

I would definitely do a cam change, granted tuning, etc. is required. I would also go with a standard dual plane intake with an open spacer to aid in fueking both banks more evenly. The heads have a ceiling, yes, but you can still get around 320hp from them with some mild porting. If your block is tapped for a stock roller cam spider I'd spring for a roller cam, something in the mid-260 range (210-215 @ .050") will make for a good increase in the stock powerband. You can probably get a set of heads for $500-900 new or less used. That'll make for a good running engine that makes more go everywhere from around idle to 5000.