No power

[Nick lenz]

Hi guys I have a 90 Chevy 1 ton 4x4 fresh TBI 350 headers and duals with 3:73 gears it runs great but does not seem to have any power. Stamp on starting out is fine for heavy truck but on highway or crushing it just seems to get louder and doesn't really seem to go much. Is this what I should expect because my 98 vortec with with 200000 miles would kill it in race. I know it's not at all close to vortec levels but thought headers and duals would help it get closer.

 

[slowburb]

What size are your pipes?

 

[sntrym]

TBI=crappy cam. You won't have much in the way of top end power no matter what you do to it. I've been able to eek out some extra from my truck's TBI with headers, exhaust with very little, if any restriction, and HEI coil. Even with all that $ thrown at it, I doubt I got more than 10-15 HP out of it. A chip might help too, but it's not going to change the lift and duration of the cam.

I replaced my TBI in my Yukon with a Vortec and the difference is considerable. It was a bit expensive compared to a straight TBI swap but it was worth it without the cost of going full LS swap. I also added a chip.

 

[slowburb]

^^I don't think this is what's to be questioned here. I suspect that the OP knew the behavior of the truck before the fresh motor, and expected more from the new powerplant with headers & duals. I asked what I asked because it's likely that the duals are hurting torque production. Oversized pipes have a tendency to do exactly that; "rob" power instead or produce it.

 

[Nick lenz]

There 2.5 inch pipes. I installed the headers and exhaust and did not notice any difference .

 

[slowburb]

Well, dual 2.50" pipes are more volume than what a stock TBI motor wants. If it's not your entire problem, it's definitely part of it. The truck should not seem gutless.

 

[sntrym]

If the more open exhaust was an issue, he wouldn't have the low end torque. A free-flowing exhaust will reduce low-end torque slightly, but increase flow at WOT, allowing more HP at the top-end. In the case of the TBI motors, they have good torque and no top end, even with a good exhaust. On a 1/2 ton with 3.42 or 3.73 gears, it gets by. On a 1 ton, the lack of top end will be more pronounced.

Now as to this fresh 350, I'm wondering if the cam was a used one that was just reused without checking it. I agree that there should be some top end power, but as someone who has had a TBI for years, it's just not there compared to a Vortec or any newer car with variable valve timing.

The TBI Vortec I have in my Yukon would leave the TBI in my truck in the dust without issue.

 

[slowburb]

If the more open exhaust was an issue, he wouldn't have the low end torque. A free-flowing exhaust will reduce low-end torque slightly, but increase flow at WOT, allowing more HP at the top-end. In the case of the TBI motors, they have good torque and no top end, even with a good exhaust. On a 1/2 ton with 3.42 or 3.73 gears, it gets by. On a 1 ton, the lack of top end will be more pronounced.

Now as to this fresh 350, I'm wondering if the cam was a used one that was just reused without checking it. I agree that there should be some top end power, but as someone who has had a TBI for years, it's just not there compared to a Vortec or any newer car with variable valve timing.

The TBI Vortec I have in my Yukon would leave the TBI in my truck in the dust without issue.

The engine cannot benefit from flow increase beyond its demand. Otherwise we would all be running around with diesel pipes.

I'd sure hate to think a fresh 350 would be sold with a wiped cam lobe.

 

[Justin S]

Define "fresh" for us first, and before doing anything else, you should do a compression test.

 

[sntrym]

I agree, more exhaust capability does not necessarily increase power, but it does not rob it either.