I have a stock 1988 roller cam 318 that I rebuilt some 30,000 miles ago. Stock cam, lifters etc. Dingle ball hone rebuild and freshened up #302 heads. Cast 4bbl intake, Holley 390cfm and a MSD ignition. Runs great, get 14mpg in my Ramcharger with 3.21 gears.
The question is that this dude is loud. I just switched from the dual exhaust to the factory single 2-1/2" exhaust and catalytic converter. I thought that the duals were the reason why it is loud, but not the case. It's loud at the engine especially for a stock Ramcharger.
Another issue I have is It needs 93 octane or the thing will ping like crazy. I have the ignition timing at 10*, total 32 and with vacuum like 50ish. I'm using the med-heavy springs in the MSD distributor and the factory advance stop in the MSD. It doesn't matter what I do timing/distributor wise, it still does this.
Now, i used a stock single link timing set, but I do not remember the brand (I rebuilt it 5 years ago) but it has me wondering if it is off and it has the cam really advanced and causing me to have high cylinder pressure, in turn causing the pinging and such. Every year the dude also fails emission testing with high hydrocarbon and Co2 with my EGR hooked up.
Any thoughts on something I may be missing?
Thanks!
Paul
Elevation Delaware is what? 850 ft ?
Your 318 is gonna be down on power, for several reasons. This means that in the Ramcharger, which may be say 30% heavier than an A-body, she's gonna need a lot of throttle, to get moving. 3.21Hiway gears and tall tires are gonna make it worse as will a factory low-stall convertor.
as would the extra weight of a 4x4 system.
All in all, if that is what you have, you just have a bad combo.
The compression test will steer the guys in the right direction.
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There is
a lot of in-fighting going on, on FABO right now; lots of Alphas.
IMO, the site is in a stage of "going to the dogs", just like many other car-sites are these days; it's just a bad time in FABO's history.
However, there is a very good knowledge base here, and if you tread lightly and co-operate, eventually you will get what you need.
Right now, a compression test will calm them down.
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As for me, I'll just say that detonation, in your case, is likely due mostly to a crappy chamber, and nothing you do will ever let her run on 87E10.
Well ..... maybe not nothing.
Alloy heads should cool the chamber enough to quiet things down.
BTW
To answer your question about cam-timing, you don't have to peel the front of the engine off to check it. You can get a very good idea, using the following method; but it depends on eliminating a couple of variables.
This is not my method. I got it from a Book by Smoky Yunich. It has a name, which I forget, but, what it amounts to is positively locating "Split Overlap".
1) verify the TDC mark on the balancer, using a piston-stop.
2) remove the driver's side valve cover.
3) find split overlap for #1 cylinder.
4) read the advance on the balancer.
a)if you are within 5degrees of TDC, on the advance side, there is no point in degreeing the cam.
b) If the cam is retarded, the pressure will be down, and the power will suck.
c) If the stock-cam is advanced more than 5*, pressure will be up, which makes the bottom end snappier.
d) It's all about the pressure. Which points back to the Compression test.
The variables to watch for are;
1) a slipped TDC mark
2) hydraulic lifters that bleed down during the test.
3) bent pushrods.
4) sunken valve seats or a less than stellar valve job.
The proper way to do this, is to take the intake off and put a straightedge across the lifters. However, I don't see this as any easier than pulling the timing cover. With a stock cam, I have had very good success with a straight edge across the retainers; at least enough to tell me if I want to go thru the trouble of degreeing the cam.
However;
A compression test will definitely hint at the same thing, and by comparison, is just too easy. and
sooner or later, you are gonna need a tach for diagnosis. Mine is right on the dial-back timing light.
I used to run a 73 low-compression LA 318 with open chamber iron heads, in an 84 D100, with 3.23s, a big Thermoquad, 28" tires and with gobs of ignition timing, that did not detonate.
My secret was a 2800 convertor. That combo would roast the tires in First gear. the point is, just have a little patience.
As for a timing curve, you need to read and record your mechanical timing about every 400 rpm, all the way to 4000rpm. Then plot the points on a graph paper. and
The vacuum advance needs to drop out very rapidly; instantly would be good, especially if you have lots of it.
Once again, mine has 22 degrees in it and my total cruise timing can be as high as 56*. The point is, that when you press on the gas pedal, that VA has to decay as fast as possible.
If you don't already have a 2800 stall, or higher, My thinking is, that ou should have, and your cruise rpm should be NOT LESS THAN 2400rpm, which will speak to your gearing and tire size. The 318 may not still get 14 mpgs anymore, but-up, some sacrifices may have to be made. You gotta get rid of the detonation.
Detonation is ignition of an air-fuel mixture from multiple points in the chamber, resulting in an audible shock-wave which usually breaks parts.
The cause is usually excessive heat in the chamber, for the detonation resistance of the fuel.
The heat can come from; Preignition, or from excessive cylinder pressure, lean-running, hot spots in the chamber, or excessive heat in the cooling system.
Going back to your cam-timing question;
It is hard for me to imagine that no matter how far "over-advanced" your cam might be, in the stock 318 engine, that the pressure could get high enough to cause detonation, and yet, the engine would still idle.
I say that because, I have, on purpose, over-advanced LA318 cams, looking for pressure, and they did not detonate. Mind you, the LAs, from 73 on, are 8/1 advertised, engines, which at my 900ft elevation, can barely make 135 psi in the first place. Adding cam advance to the factory lo-C LA318 is a total waste of time. ..... but I had to learn that.
But I also found out that they do not tolerate much cam retard, before the lose power.
BTW
Lean running with hot sparkplugs is an easy way to induce pre-ignition, which quickly leads to detonation.
