Wondering what compression i should be looking for in a 400 with a 68cam. i will be taking cold readings as the carb has been sent off for rebuild. any info will be greatly appreciated.
From the 1968 Service Manual.Wondering what compression i should be looking for in a 400 with a 68cam. i will be taking cold readings as the carb has been sent off for rebuild. any info will be greatly appreciated.
Thanks Jim, Just sent the Carb out to Cliff to be redone I guess i will be pulling the engine now, I hope its not the block.
You did not say how many miles on the engine or why you decided to do a compression check.Thanks, I needed some positive news. having it refreshed is on the list, it just moved to the top.
I just did this, dished forged pistons and forged rods 30 over on the bore.the milage is a bit of a mystery i would guess around 150,000. I will pull valve cover tomorrow and take a look and see what ti find. Have started to look for a good machine shop in Maine. I am actually looking forward to getting the running gear back up to spec. I will have to make my mid up on weather to put dished pistons in the engine so it will run on pump gas. Have you done this? How big of a reduction of power would there be?
What cam did you use? I have a 68cam (ys 1968 code engine) with a th400 and 3.36 gears (ZG code rear end) . this is all stock. would I need to change the cam and gears? I would like to keep it as stock as possible, but still smoke the tires.I just did this, dished forged pistons and forged rods 30 over on the bore.
Compression ratio is 9.5-1 and the goat runs like a scalded ape on pump gas.
The old 335 HP was tired and now it is around 370 with the cam.
It will smoke the tire going into second with the TH-400 no problem in fact I really have to baby it so it doesn't chirp on the shift.
My experience with different engines is if you just do the top end it puts pressure on the old tired bottom end and you end up doing the whole engine anyway.
Go big or go home.
Hi JIM, just a quick update, I poured some mystery oil in the cylinder and let it sit over night blew it out and tested it. the pressure came up to 180psi. There must have been a stuck ring. thanks for all the advise.You did not say how many miles on the engine or why you decided to do a compression check.
Was it burning oil or smoking out a tail pipe? Running poorly/missing?
You may want to also pull a valve cover to make sure the rockers have not loosened up on that bad cylinder. I am thinking if a valve is not opening fully, your readings may be affected. Once purchased a '68 GTO that the guy thought the engine was bad. It ran, but poorly. Pulled a valve cover and one of the rocker arms has loosened up and gone sideways off the valve. No damage, just put it back on and tightened it up and that car would catch rubber on a hard 1st to 2nd shift of the TH-400. Next time I saw him I told him about it and I could see the regret in his eyes 'cause he thought he was selling a car with a bad engine - cheap.
So, you may want to check a few things just to be sure, could even be a worn cam not opening the valves fully. Otherwise, you need to do the rebuild.
Hi JIM, just a quick update, I poured some mystery oil in the cylinder and let it sit over night blew it out and tested it. the pressure came up to 180psi. There must have been a stuck ring. thanks for all the advise.
OK, good. Didn't want you to think the engine just became "good to go" and then something happened.I still plan on the rebuild, it just made me feel better knowing the block wasn't the cause. still have to deal with the high compression engine vs pump gas problem, so a rebuild is in the near future. will be going with dished pistons hope to drop the compression down to 9.5 and go .30 over on the bore.
Thanks for all the info guys. Time to do my home work and get a package put together. I am leaning toward a sturdy stock like set up as it is a driver and i don't race but still like to smoke the tires. Once I have settled on a package i will post it and have the updates on the progression.