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Engine Problems?

T

Tire

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Oct 15, 2006
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Topeka KS
High again guys. So far I have recieved good feedback from everyone when I post my problems and let me say a quick Thank you. So here we go again. I have the Blazer driving and all seems well still waiting on a few more parts to finish off the suspension lift and get her where I want her. But I will be picking up my dana 60 front axle and 14 bolt rear on the 9th. With those I should be done few small parts here and there. Now on to my problem with the truck. It had NO balls. I could punch it and it felt like an old junk station wagon going up hill pulling a trailer. This is a brand new 350 i built myself (see where the problems came from :doah: ) about 9.5-1 compresion holley 670 all the goodies etc... I went to a friends house he said my timing was off well as far as that goes the timing has yet to be "on". When you are going down the road at any speed rpm's about 1900-2000 and just barely pushing the petal as you would to maintain a cruising speed the truck makes this high pitched rattle noise. It stops making the sound when you accelerate though. The before mention friend said it was spark plug detonation, knock, something like that and he advanced my timing. Now the truck has tons more power feels like it should but that noise is still there he says the plugs may be fouled or the old gas that was in the truck may have varnished<--? the carb and plugs any and all ideas welcome. Thanks!
 
Okay, first of all, you need to tell your friend that ADVANCING the timing is gonna cause your pinging issues. What you need to do before you worry about anything else is check what your BASE timing is set at. It should be somewhere around 4'.

It sounds to me like your initial problem was cause by WAY too much timing, and I'd be willing to bet that you're gonna need to knock it back a few degrees more to avoid the famous mid-throttle Chevy pinging.

Like I said, let us know where your timing is sitting at idle and take it from there. Good luck, brother.
 
Sounds like I need to head to the parts store and borrow one of thier timing lights and start from scratch again. But If and when I do retard the vaccum timing how will this affect my power? It (the motor) had a significant increase in throttle response and power when he advanced it. You recomend starting the initial mechanical timing at 4 degress but would that change if I told you more about the engine or is that just a chevy standard? Thanks for the quick reply
 
The rule of thumb I've always used is to keep playing with the timing until all the pinging is gone. I would much rather sacrifice a few degrees of overall power if it means my motor won't ping itself to death.

There are other variables you may need to play with, like rejetting or tuning your carb, but deal with the timing first. Keep us posted as to what you find and we'll do our damndest to help you along. :thumb:
 
don't forgett to disconnect the vacuum advance when adjusting the timing...
 
And after you disconnect it make sure to plug it while you're timing the engine.
 
You could just have too high a compression ratio for low grade gas . Alot depends on the cam you used. I would try a tankful of the highest octane fuel.

Get your timing where it should be. If that does not solve the problem, then put the truck on a sniffer, to see if the carb is jetted too lean.

If the problem is still there, after timing and carb mods, then I would say its just a case of too high a comp ratio. If that is the case, then either higher grade gas, or a thicker head gasket.
 
Ok I messed with the timing today (retarded it) following all the advice given and the ping is almost gone it is not noticeable unless you are trying to hear it. I think when i fill the tank again I will put the highest grade in. I should have done that knowing my compression was on the high side. Thanks for the help guys.
 
If you built this engine then give me details as to what parts are in it and i'll figure out your CR and also tell you what i think about the cam choice. I'll need cylinder head CC's, piston CC's of valve reliefs, which head gasket, was the block decked and if so what is the deck height?, and also what cam is in it.
 
Im not sure if the block was decked so lets just say no to that. the pistons are GM flat top forged pistons. I believe they came form a corvette. My reasoning for this is when i got it the engine was not origonal to the truck i was told it came form a corvette maybe camero.. who knows 6 of the 8 were still good the guy at the machine shop I took it to said I was better off replacing the two instead of getting a cheap chinese set. the heads are from a 92 chevy truck so new style I had the intake machined to accept them. they are 64cc, the distributer is a brand new proform w/ HEI coil. the intake gasket was a felpro style, it was supposed to be thinner than a normal one therfore bumping up the compression one half point. the Cam.. oh the cam ... i can't seem to find the part # if i had the book i ordered it out of i would know what to tell you. I have tried to find the part # but I threw away the box a long time ago. It was a RV Cam i am sure that it was a stage 3 RV cam from Crane Cams (at least i know who made it right) I wanted the low end torque for crawling that was my reasoning anyway. All I have to do is take it down to a knowledgable mechanic and all my prob's soleved but I want to do it on my own. (sorta) well i can try for more specifics but this is all off the top of my head thanx btw.. oh it's bored 30 over? I think anyway
 
Well, your CR based on a 4.030" bore with a deck height of .025" (fairly standard) for a non decked block and a compressed gasket thickness of .039" with a 64cc head gets you right at 9.5:1 as you thought. Now the cam has alot to do with the perfomance aspect.
 
While I am on the subject is it normal for the truck to run about 1300 + RPM in park and neutral but get down to about 600-700 rpm in drive and reverse?
 
Sounds like you have a vacuum leak... that would explain the pinging at part throttle as well. Might want to tune with a vacuum gauge. And if those are vortec style heads, you would want a vortec manifold... ditch the one you have and get a edelbrock performer vortec or something similar. In fact, the leak is probably around the head/manifold mating surfaces.
 
Well there's definetly a vacuum leak but i'll be damned to find it. I went out and bought a guage and have tried using starting fluid and a cigarette (and i dont smoke) to try to find this sucker. The guage reads about 19-20 in park and 10 in reverse. I've plugged all the leads out of the Carb to try to limit the options maybe it's time to take it to a mechanic after all.
 
If your heads are vortec, replace your manifold with a vortec style one. You'll kill 2 birds. 1. it'll perform better than a "modified" manifold on vortec heads, and 2. if you install it right you'll probably fix the vacuum leak

What's the cigerette for?
 
another way to check if its a gasket is get some carb clean or similar and spray around the gaskets and see if your idle changes where it does you have the leak
 
fried_guy said:
If your heads are vortec, replace your manifold with a vortec style one. You'll kill 2 birds. 1. it'll perform better than a "modified" manifold on vortec heads, and 2. if you install it right you'll probably fix the vacuum leak

What's the cigerette for?
Click to expand...

A standard intake will not even remotely work on vortec heads so i'm lost as to why you keep saying this to him. :confused: You cannot even modify a standard intake to fit vortec heads.
 
Tire said:
... the heads are from a 92 chevy truck so new style I had the intake machined to accept them.
Click to expand...

I know that you can put a standard intake with vortec heads... but most of the time you get vacuum leaks and the ports never line up. It's not a good idea, but it's been done. I am just assuming that his heads are vortec though. I guess I could be thinking of standard heads with a vortec manifold. But regardless, the leak is probably at the head/manifold mating surfaces if it can't be found anywhere else.
 
Thank you for all your help guys. he was correct i am using new style vortec heads and an older style manifold i just had it (the holes) wobbled so it could be bolted down.. you know trying to save a few cents where ever i could. As far as i can tell it is not coming from around the sides of the manifold but getting to the back is about impossible. looks like a call to summit will solve my problems... but i put the hood back on it so no more easy work area... oh well. thanks again all!
 
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