Poor 348 performance...

T

Tmart

Member
Hi,
I'm posting for my neighbor, Ted. His car has just come out of a 7 year top to bottom restoration. He's done 98% of all the work. The "new" 348 replaces the original 6 cylinder engine.

348 in a 1940 chevy 2 door sedan.
1959 4 bbl passsenger car block and heads.
Standard bore, honed, new rings and pistons(stock compression).
Heads redone. ss valves.409 valve springs. Fel pro stock gaskets.
Stock distibutor, acccel pointless conversion. Accel super stock coil .Manifold vac. advance.
Stock 3x2 manifold. rochester 2G carbs,rebulit. Fuel pressure regulator and guage. Hi Po pump, new tank and 3/8 feed line to tank.
Dual exhaust, 2.5 inch pipes.

Isky 458 hyd cam installed,....AT O MARK ON CRANK GEAR.

700r4 trans....3.70 diff. gears

150 miles on rebuild.

Runs, smooth idles nicely. Poor performance.!!!Tried timing adjustments etc.

His 6cyl 235 1941 dual carb pickup has more power/pick up.


We are suspecting that the crank gear setting was not the right choice.

Any thoughts/experience would be appreciated.

Thanks....Tommy/Ted
 
heckinohio

heckinohio

Member
had one

I had one of these in a '59 Chev convert in 1959. I was the fastest kid on the block at 14.10. 100% stock with shortened advance curve and rejetted carbs and vacuum throttle linkage. Dont know what you did wrong but mine certainly was good.............

You might consider a stock cam........ for 315 hp version. Cant remember the jetting for sure, I think it was .068 in secondarys and .066 in primary. Somebody else come in there on the jetting. You can get too big real quick. A local was running a 360 HP 409 in '61 at the local strip at 14.90, I down sized his jets at the track and he went 13.75. PJH
 
B

buildit

Well Known Member
Supporting Member 8
poor performance

First thing I would check is the advance curve on distributor. About 36 total without vacuum, and all in by 2500, if possible.

Next is the cam timing. If it was just installed at "0" mark, and not degreed in, then you don't know what you have. If you KNOW that the TDC mark on the harmonic balancer is CORRECT, then pull the left valve cover and roll the engine over slowly in the direction of rotation. It is important not to reverse direction while lining up the mark. You want to set up #1 cylinder on TDC at overlap, when both valves are barely open. The ignition rotor should just be starting to clear the the #6 terminal. The intake pushrod should be about .010 to .015 higher than the exhaust pushrod. That's if you have about 4 degrees of advance on the cam. This is much easier to see at the top of the lifters, if checked before the intake manifold is installed. It's just a way to see if the cam is advanced a little like it should be, or is even (not preferred), or if the exhaust pushrod is higher, it is late. It will never run acceptably if the cam is late.

Last, I hope you don't have those little individual chrome louvered air cleaners. When we dynoed a 348 that was was essentially identical to yours a few years ago, these chinese air cleaners would not let the engine make more than 250 HP. When we tossed them in the trash, and redid the engine tune, it ended up making nearly 360 HP.
 
T

Tmart

Member
Thanks for the info.

Yes, he does have the chinese louvered individual air cleaners.

With regard to ignition timing, are you suggesting no vacuum advance at all, (all mechanical), and a total of 36 degrees.

Compression test not done. I suggested it to Ted, but he felt it wasn't the issue.
If this continues, I'll get him to do it.

The cam was not degreed. It was installed at "0". This will be the last thing we check. (easy stuff first).

Not sure on the jetting. I will get some #'s.

I will pass on the info, and give him a hand.

Thanks, I'll get back with results....Tommy
 
petepedlar

petepedlar

Well Known Member
Supporting Member 3
Just my opinion...... throw those air cleaners away. Take it for a drive without them and I'll bet you see a difference.

Dave
 
T

Tmart

Member
From assembly.

Ted put together the long block. (Most probably done correctly).
We used this site to identify his rear main oil leak. (he left out the rubber inserts in the rear main cap) Thanks for the help!!! Very dry now.


I watched , drank his beer, helped, and applauded/commented/assisted.
We're both "certified"/dyed in the whool professionals.

He needed my help to adjust the valve lash. I spun the push rods until a "slight" resistantance was felt (zero lash) , and then the required additional rotation( approx 3/4 turn, can't remember).
Fuel pressure approximately 5 psi. The damn regulator buzzes as it adjusts pressure, ( sounds sub standard to me).

Base timing was set with a timing light. 8 degrees BTDC if I remember correctly.

Idle mixture set with a vacuum guage and tach. (center carb adjustments available only).
Ted has moved the timing around, to the point of ping/detonation without good results.

IN FACT......... the louvered air cleaners are on his pickup truck (my mistake). There are no louvers on the domed covers on the 348 air cleaners ( small, and maybe even worse than the louvered type for air flow.?)

Thanks for your help, I'm working with an older car .....and and old guy........who's my best friend.. ;-) Thanks....Tommy
 
oldskydog

oldskydog

Well Known Member
Supporting Member 10
Besides all the obvious, a restricted or obstructed exhaust will cause and engine to lay down. Any potatoes in your exhaust pipe?:dunno
 
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