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Old 12-31-2006, 11:28 AM
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92 C1500 engine swap

I am in the process of an engine swap in my 92 Chevy C1500 and I have 3 questions. Question 1, I am using an early 80's block and early 70's head combo that I had laying around, and now I am to the intake manifold install part. I want to keep this truck TBI, and I have been planning on using an Edelbrock Performer TBI intake (part# edl-3704) but I was told the head to intake mating surfaces on the TBI intake and the older heads are cut at different degrees, and will have a vacuum leak if I put these together. I have set my stock intake on the engine and it appears to line up fine. Has anyone ran into a problem with this before? My 2nd question is I am planning on running an older style long water pump with v-belt accessories and brackets, instead of the hideous cast aluminum brackets and serpentine setup. Since the serpentine water pump runs counter clockwise and the older water pump runs clockwise, is this going to cause any problems with the plumbing of the intake manifold? Question 3, Do I route the heater core return line to the water pump like the older water pump, or to the radiator like the TBI cooling system is designed for? Thank You and Happy New Years!

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Old 12-31-2006, 04:24 PM
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The problem isn't the mating surface angle, its the bolt angle. 87-95 heads are identical to old heads except the center four bolts are at a 72* angle instead of perpendicular to the mating face. Then 96 and up Vortec heads have only 8 bolts at a straight down angle. I wouldn't worry about the TBI. You can retain it for simplicity or smog compliance, but its not a very wonderful piece. The swirl port heads that came with them are downright awful, and the TB itself only flows about 390 cfm. Anything more than about 250 hp and its hurting for air in a bad way. They're not really injectors at all, they're low pressure nozzles. It just wasn't one of GMs better designs.

A Qjet would get you better power AND mileage. Sad but true.

So, the TBI intake will only work on TBI-style heads with the funky centerbolt angle. I've seen guys modify (hog out) the center holes and put TBI intakes on older heads, but its not ideal.

Maybe someone else can chime in here, but don't TPI heads have the same funky center bolt angles? They're not wonderful heads, but at least they're better than swirl ports. That might let him get the TBI bolt pattern with a little better heads.
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Old 12-31-2006, 04:26 PM
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Oh, and the other question. Yes... you put the heater hose in the same place as before. Your serpentine water pump is reverse rotation, NOT reverse flow. The water still goes the same way, but the pump is made to spin backwards. So, you can hook up everything as if the water pumps were the same. The only difference is which direction it spins, but the water paths are the same.
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Old 01-01-2007, 12:05 AM
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Thank you curis73 for the info. Sounds like the cooling will be no sweat. I have been reading a lot about TBI's and I really want to play with it for a while, so it sounds like i may need to go with a 4 barrel duel plane intake with a TBI adapter.
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Old 01-01-2007, 12:48 AM
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Forget a dual plane, vacuum doesn't some into play on the TBI..the fuel isn't pulled through like a carb, it's placed in and waiting to be sucked into the combustion chambers.

A sinlge plane does better with the TBI's.
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Old 01-01-2007, 08:01 AM
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I disagree, flat. The way air moves through the intake is the key, not the vacuum signal to the carb/injectors. Its the way the air/fuel mix moves through the runners that affects intake geometry, not EFI. Just because you remove the carb, doesn't mean you remove the physics associated with how the air moves through the intake.

And if you want to be picky about it, carbs do a better job of atomizing fuel than GM's TBI.
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Old 01-01-2007, 11:43 AM
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The advantage of a dual plane intake on the carb, is just as you mentioned, stronger vacuum signal which allows better metering of the fuel into the plenum..which is needed for idle and low RPM response.

The TBI doesn't require a vacuum signal as the sole reason to meter fuel into the plenum, based on a few parameters in the EPROM (TPS, Engine RPM, and MAP come to mind) fuel is pulse through the injectors into the plenum.

My own experience with TBI is just one car, but with two engines (305, then L05 crate engine) and three intakes..stock, Perfromer and offbrand/overseas single plane, that somewhat looked like a Victor. After the 350 swap and riginal intake, I went to the performer, definitely noticed (via butt dyno) that the midrange pull was stronger through about 5K RPMs. After talking with some guys who did many mods on thier TBi engines, I went to the single plane intake, again, via the butt dyno, I noticed no difference in off idle performance, and the engine pulled much better through mid to upper RPMs than the Performer did. I only took the engine to 5K, since it still had the L05 cam in it, but I think with more cam and a better set of heads (ofcourse) it would have been able to pull higher.

The TBI unit was when it was a 305) ground out some, I switched to 65# injectors with the 350 and made the FPR adjustable..I don't recll everything thing I did, but once the 350 was in, I didn'tdo any further mod's, just worked with what I had.

Anyway, the difference between carb and TBI are more than that, even CFM readings can't be compared, even though both are a wet intake...since TBI "throws" fuel into the plenum where it atomizes with air and the carb dies it simulataneously within the bores.
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