350/290 crate, torque converter suggestion.

[72LB]

I recently put a 350/290 hp crate engine in my truck am having a heck of a time with the rpm range between idle and in gear. I initially tried a couple different carbs , different timing and even different springs in the distributor, the end result it drives great but the idle vs in gear idle is terrible. I was told that with this engine the stock converter needs to be changed but I can't find anything on it and my trans guy says it shouldn't matter. I know several have done this addition, what did you use for a torque converter?

[RustyPile]

We need more information about the engine, in particular, the came profile.. Contact the company who built the engine or the spec sheet that came with the engine.. One of the two will have the suggested torque converter stall speed..

[sick472]

Rusty is on to something there...a good converter shop will want to know "everything" about the motor, rear gears, tranny gears, and tire size too in order to recommend the right one. Can it be done without that info? Sure, If your feeling lucky (or don't mind throwing good money after bad). Don't ask me how I learned that lesson!

[weq92f]

.
Are you having to set the idle high in Park/Neutral so that it doesn't stall/die when you put it in gear?

Could be a number of things...check this thread...

http://67-72chevytrucks.com/vboard/s...d.php?t=720661

-klb

[72LB]

It's a GM crate engine and trying to find someone at GM to talk to is useless.
350/290 HP Engine Specifications:
Displacement: .............................................. 350 cubic inches
Bore x Stroke:.............................................. 4.00 inch x 3.48 inch
Compression ................................................ 8.5:1
Block: ........................................................... Cast iron, four-bolt intermediate mains
Cylinder Head: ............................................. Cast iron
Valve Diameter (Intake/Exhaust): ......... 1.94"/1.50"
Chamber Volume: ........................................ 76cc
Crankshaft: ................................................... Nodular iron, 2 piece rear seal
Connecting Rods: ........................................ Forged, powdered metal, 3/8” bolts
Pistons: ........................................................ Cast aluminum
Rings: ........................................................... Cast iron
Camshaft:..................................................... Hydraulic flat tappet
Lift: ......................................................... .450" intake, .460" exhaust
Duration: ................................................ 222° intake, 222° exhaust @ .050" tappet lift
Centerline: ............................................. 114° ATDC intake, 114° BTDC exhaust
Rocker Arm Ratio: ....................................... 1.5:1
Timing Chain: ............................................... 8 mm single roller design

Originally Posted by weq92f

.
Are you having to set the idle high in Park/Neutral so that it doesn't stall/die when you put it in gear?

Could be a number of things...check this thread...

http://67-72chevytrucks.com/vboard/s...d.php?t=720661

-klb

That thread doesn't really help, I've checked for vac leaks several times and none found. From the paperwork: (The Normal engine manifold vacuum for the 350/290 HP engine is 10-12" Hg at idle (650-750 rpm), I have 15-16".

[68 P.O.S.]

What is your timing set at?

Which distributor are you running? How many degrees of mechanical advance, how many degrees of vacuum advance?

Which carb are you using?

What is your idle rpm in park and in gear?

[72LB]

Originally Posted by 68 P.O.S.

What is your timing set at? 12 deg atm

Which distributor are you running? HEI

How many degrees of mechanical advance, how many degrees of vacuum advance? Not really sure on that but have around 30 total.

Which carb are you using? Had three on it started with a Holley SA 650 then 1406 EDL and now with a QF Brawler 670 which has been the best so far.

What is your idle rpm in park and in gear? Around 1100 in park and drops to 500 in gear.

I had to borrow a tach as mine took a dump and it will be a bit before I can get another one. Also with the HEI I ended up using 1 med and 1 light spring to get it to drive right, runs fantastic at the moment it's just the idle that's funky.

[garyd1961]

I hate to sound negative but that engine isn't a good choice for a truck. Personally I don't think it is a good engine for anything with it's low compression and fairly big cam. I'm not saying it can't be made to run ok but it doesn't have much low end power.
I would try advancing the initial timing and see if it helps.

[RustyPile]

Originally Posted by 72LB

It's a GM crate engine and trying to find someone at GM to talk to is useless.
350/290 HP Engine Specifications:
Displacement: .............................................. 350 cubic inches
Bore x Stroke:.............................................. 4.00 inch x 3.48 inch
Compression ................................................ 8.5:1
Block: ........................................................... Cast iron, four-bolt intermediate mains
Cylinder Head: ............................................. Cast iron
Valve Diameter (Intake/Exhaust): ......... 1.94"/1.50"
Chamber Volume: ........................................ 76cc
Crankshaft: ................................................... Nodular iron, 2 piece rear seal
Connecting Rods: ........................................ Forged, powdered metal, 3/8” bolts
Pistons: ........................................................ Cast aluminum
Rings: ........................................................... Cast iron
Camshaft:..................................................... Hydraulic flat tappet
Lift: ......................................................... .450" intake, .460" exhaust
Duration: ................................................ 222° intake, 222° exhaust @ .050" tappet lift
Centerline: ............................................. 114° ATDC intake, 114° BTDC exhaust
Rocker Arm Ratio: ....................................... 1.5:1
Timing Chain: ............................................... 8 mm single roller design





That thread doesn't really help, I've checked for vac leaks several times and none found. From the paperwork: (The Normal engine manifold vacuum for the 350/290 HP engine is 10-12" Hg at idle (650-750 rpm), I have 15-16".

That cam is oh so wrong for that engine on so may fronts.. Low compression, small valves, etc.. The lift is ok for heavy vehicles that need low end torque to get moving. But the duration kills off what torque is there, plus that center line isn't helping.. Changing to a "milder" cam would do wonders for that engine.. Other wise, heads with bigger valves and/or smaller chambers are necessary.. Compression needs to be at least 1.5 points higher.. And as someone else stated, better rear gears more suited for higher RPM operating range..

The following is only a WAG, but I'd suspect a torque converter stall speed around 1900 -- 2200 would "free up" the engine at idle..

[72LB]

Originally Posted by RustyPile

That cam is oh so wrong for that engine on so may fronts.. Low compression, small valves, etc.. The lift is ok for heavy vehicles that need low end torque to get moving. But the duration kills off what torque is there, plus that center line isn't helping.. Changing to a "milder" cam would do wonders for that engine.. Other wise, heads with bigger valves and/or smaller chambers are necessary.. Compression needs to be at least 1.5 points higher.. And as someone else stated, better rear gears more suited for higher RPM operating range..

The following is only a WAG, but I'd suspect a torque converter stall speed around 1900 -- 2200 would "free up" the engine at idle..

I plan to change the heads and cam in the future (have been reading the Hot Rod article about this engine), surprisingly it runs real good. I've had a couple guy's tell me to put at least a 2000 stall converter (th400) in just haven't found anything on it being correct.

[jbarron]

I've got the same motor in mine.
Ended up putting vortec heads on it which helped some.
It needs a lot more timing than you have now. Look for more like 36+ total.
Helps that I have 4:10 gears with a 2200 stall.
Timing is the main thing.
It would start to run hot on long trips in the summer with the timing set to where factory says.

[72LB]

Originally Posted by jbarron

I've got the same motor in mine.
Ended up putting vortec heads on it which helped some.
It needs a lot more timing than you have now. Look for more like 36+ total.
Helps that I have 4:10 gears with a 2200 stall.
Timing is the main thing.
It would start to run hot on long trips in the summer with the timing set to where factory says.

Might have to get a timing tape. Where do you have your initial timing set at?

Also are you running manifold or timed vac to the dist?

[72LB]

Well I bumped the timing up a couple deg's but it didn't help any. Going to have to look at torque converters.

[geezer#99]

At what rpm did you check your initial timing?
A higher stall won’t help much. You’ll still have a high idle rpm in park and in gear.

[72LB]

My tach went south so it's by ear today. I went with the drop from plugging the dist, somewhere between 7-800 range. Going to try to borrow a tach this weekend.