1984 C10 BBC 427 feels like its lacking in its true performance abilities.

[yellow400ex05]

I've got a 1984 Chevy C10 with a rebuilt 427 1966 block with 68+ heads not sure what year.


just put a new 780CFM quick fuel carburetor on it new 8mm spark plug wires, it actually had 7mm wires on an HEI ignition and you cant even buy 7mm wires with HEI for these anymore, and fresh plugs. Also has a Comp Cam Magnum 282 cam in it, .561 lift unknown if any other modifications, but the front casting pad is blank like its been cut so that's why i believe its been rebuilt. uses a 4 quart pan as well so i believe its out of a passenger car.

its got a TH400 trans, that so far i've been unimpressed with it has no kick down button in the truck due to the fact that it didnt come with a TH400 but a 700R4 originally. Yes I realize I need one

but regardless the truck chirps 1st through 3rd gears fairly easily, but seems to shift too soon it'll roast them off in 1st but it seems sluggish after it shifts and takes forever to wind out 2nd gear and 3rd gear FORGET it, total slug.

could my Factory 3.08 gears and no kick down really be making this truck a bit more lackluster than I'm expecting it to be? also you can feel that before it shifts at about 3000-3500RPMs it starts to pull like a freight train, you can feel the power come on strong then WHAM it shifts, and back to a lugging lackluster engine.

[TwoFiftyShifter]

Yes.

[79Betty]

The 80's were SO undergeaded it's sad. I had a 86 with 2.56's. Unreal! Pull the diff cover n get the ratio. After we know that we can help narrow it down. The diff probably needs new fluid anyway.

[MylilBowTie]

You probably need a 2500 or more stall converter and adjust the shift points with the governor weights and springs.

[geezer#99]

You need to put some timing in the motor with that cam.
What's your timing set up like?
And why not just shift it manually?

[yellow400ex05]

Originally Posted by geezer#99

You need to put some timing in the motor with that cam.
What's your timing set up like?
And why not just shift it manually?

I cant really adjust the timing with a light, because the balancer seems to be spun and when you put a light on it, it says its at 50 degrees advanced. which obviously is wrong, because it wouldn't run, the timing seems to be adjusted well, I'm probably right around 30-35 degrees advanced if I had to guess. my local engine builder whom built a 327 with me fine tuned it by ear, by adjusting the timing manually, and he's been working with GM small blocks and BBC's for years.

and the rear end gears are the stock 3.08's but with a BBC and a TH400 that's best compared to any taller and the lowest would be 3.42's

I guess i could have the springs and weights adjusted, it would be nice to delay the shift a bit more, the truck would seriously get up and go if it did.

And i realize i need a stall, but wouldn't that only help on takeoff only? the truck spins enough when you touch the gas while taking off haha. And if i did a 2500 RPM stall i wouldn't really notice it while driving as it's probably in that RPM range at cruising speeds around 50-55MPH correct? I believe a TH400 has a 2000 RPM stall convertor stock as well.

and I'm pretty sure shifting a TH400 manually isn't a good idea, since they're vacuum operated when you shift you'd have to let off from WOT? they're not like power glides. i don't want to hurt the trans either

[68post]

I'm sure your 3.08 gears are hurting performance with the cam you have and coupled with the fact that it is a single pattern cam with stock exhaust manifolds.

Too bad you don't know the compression, but that's not easily changed - you'd most likely want to change the cam if your compression is too low. You can perform a cranking compression test to see how it fares.

Your timing advance curve and/or your cam advance could also be suspect.

I hope your cam is still in new shape because big block Chevys' are hard on cams and your oil spec needs to be on point !

I doubt you'd hurt a th400 trans, and occasionally shifting it manually will have absolutely no adverse effect on it.

[68post]

Almost forgot to mention it but you'd better replace the dampener if it's slipped - ASAP !!

(I'd drive real easy until then)

[geezer#99]

If you think the damper slipped then find tdc #1 using a piston stop to check the timing marks accuracy. A low compression, big cammed motor will like lots of initial timing.

[yellow400ex05]

that's what we did geezer#99 and then we realized it was messed up somehow. so then we did it by ear, til the sweet spot was found. this engine has been in the truck since 1989, but only has had 15,000 miles put on it in almost 30 years.

I'm using Valvoline VR1 racing oil. oil change receipts go back to 1989 and it says valvoline so with the cam i figured having zinc was a good idea.

and yes I do have stock manifolds, but running stock width 2.5 inch exhaust, no cats and flowmaster chambered mufflers. so its not totally lacking flow but it would probably love a 3 inch exhaust for sure.

ill take care of the kickdown issue first then get a good shift kit, and have my shift points adjusted up a bit and then go from there.

I really can't afford to get an entire new exhaust made for the truck, its got a perfectly fine exhaust on it and it does sound pretty mean.

[Bishops Trucks]

Shifting a 400 trans manually does not hurt them in any way. I have one with a shift kit in it that I had in a 71 longbed truck. It had a GMPP 350 HO/ 330 hp motor. I ran that truck hard and constantly shifted it manually, never had a single problem with it. Have you checked your harmonic balance? Sometimes they go bad (the rubber between the two halves) and start to slip. That could be part of your issues.

[geezer#99]

So if you proved tdc and your timing marks are good, put a light on it. Otherwise you're just guessing.

[pwradder]

if it were mine, i'd get the timing nailed down (with a light). if i still weren't happy with the results, i'd put it on a chassis dyno and see what the numbers are-the cost of doing a couple pulls is nothing compared to beating you're head against the wall looking for a problem that may not be there. good luck with it and keep us posted!