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The 77 cc’s are the ideal minimum. In reality the heads are over 80cc.
If the timing chain checks out, it wouldn’t be much more work to pull the heads. Have them milled and reinstall them with thinner head gaskets. If I remember correctly every .006 machined off is 1 cc’s, it’s no big deal to take .060 off the heads.
Another thing to keep in mind is these engines were originally assembled with steel shim head gaskets that measure around .028 compressed thickness. If the heads were installed without any surface machining your already down on compression with no changes.
If I recall, .005"/cc for 455, .0056/cc for 350. Cutlassefi would be the man to ask.
I'm not really looking to squeeze out every last bit of available compression point. Just want an idea of what the CR is and get a cam recommendation. Sounds like it's somewhere between 9.25 and 9.75 to 1. What cam would be good for a fun street application, maybe a little lope?
I dont know what kind of cam a boat uses so i searched a couple boat forums and seems the jet boat olds455 crew dont mind a comp comp cams xh268, a car cam
a quick search at summit shows a howards cam thats also good for a jet boat !
some boaters said they like to install the cam advanced to take advantage of upper rpms
You could get a degree wheel and map out the cam opening and closing timing to determine what grind it is before jumping into a replacement. You would need the degree wheel when installing a new cam anyway.
You could get a degree wheel and map out the cam opening and closing timing to determine what grind it is before jumping into a replacement. You would need the degree wheel when installing a new cam anyway.
yes. I would like to know when the valves are opening in relation to the compression stroke. The 350 that was in the car had 170# and 455 has 145# with similar pistons. I suspect loss of compression due to cam timing is reason.
Is this a fresh build? Before tearing into the engine, are you sure the timing chain is good, and installed correctly? If the chain is stretched or installed wrong ( pretty easy to do if it’s a timing set with different keyways) your going to have low compression and lousy low end performance.
Any decent 455 should easily destroy tires, especially with 3.23 gears. Olds engines don’t really have a torque curve, if you look at a graph it’s more like a torque plane. The torque starts high, hits its peak, then drops back down to high. You say the cam sounds a little choppy, for the cam to be big enough to noticeably affect performance it would have to be big enough to shake the fenders off.
I’d pull the timing cover off and look at the timing set before pulling the trigger on a cam. Unless your planning to put a roller cam in, I’d avoid messing with the cam if at all possible. Too many horror stories and risks with flat tappet cam break in problems. The cam that’s in it now survived break in, no need to roll the dice unless absolutely needed
I spoke with Mark cutlassefi and after describing the symptoms, he said the Edelbrock carb was likely the problem and he was correct. We rebuilt the original Quadrajet and the now has *****. It will roast the tires all through 1st gear and didn't stop pulling to past 100 where I got off it. Unfortunately the idle isn't working properly and will die if set below 1100 rpm. We took ot off and checked all the ports and the are all clear, so don't know what's wrong, but the cam isn't the problem.
That is probably a pretty aggressive cam, you need to open up the idle passages on your Qjet. Cliff Ruggles book explains it quite well, all the mods needed. You can talk to him, he sells the enlarged idle tubes needed to your specs. Wow, I have never seen a poor running Edelbrock carb on this site, being sarcastic of course. My Innova timing light works great. I love being able to check total advance and set idle rpm and where the mechanical advance comes in with one tool.
Last edited by olds 307 and 403; March 3rd, 2021 at 04:40 AM.
I find its easier to move the distributor at idle and check your setting at the higher rpm. You may have to run the engine up a few times to get it right. It does not matter the rpm as long as its high enough to have stopped advancing. You want to buy a vacuum advance stop.
Looks like this
January 8th, 2021, 12:13 PM
