Setting compression ratio

[mlrailguy]

I have a 2332 for my sandrail and it seems to ping way too much, with 91 octane gas. I pulled heads and measured deck height, looks to be right at .026. There is also a copper ring on top, in head, which measures about .022. I'm wanting to achieve 9 -9.5 to 1 ratio, recommended by cam maker. What do you guys suggest?
Thanks for advise

[Marc]

.048" piston-to-head clearance is about as tight as I'd want to run with that large of a bore, particularly on a playtoy where I might miss a shift now and then - and it's tight enough that a lack of "quench" isn't your problem.
What are the combustion chamber CCs and what cam? Is the cam installed "straight up", advanced, retarded? What carburetion and ignition/timing settings?

[mlrailguy]

I believe the heads are 55 cc [CB 044 ]. The cam is Engle K8, straight up. dual Weber 48's, and a Pertronix distributor.

[FJCamper]

Hi Mlrailguy,

If you have a 94mm bore by 84 stroke, 55cc heads, and .048 deck, you're already at 10.2:1. You should be pinging.

You need more way deck, about .080, to get down to 9:4.

FJC

[Steve Arndt]

What is your ignition advance at when it is pinging? Back it down some at the torque peak.

[Marc]

The ideal way would be to have some shallow dishes milled into the centers of the piston crowns (2¾" diameter, ~.065" deep would be in the ballpark)...but if you just want to do it cheap & simple replace the existing head gaskets with some .060" thick ones. That'll make the motor a bit wider and change your rockerarm geometry if you don't also get longer pushrods. It should be possible to open the chambers up enough to gain the 6cc or so needed, too, but that's more work than I'd want to do when there are easier options.
Personally I'd want to have just a little more piston-to-head clearance; if you stepped up to .030" head gaskets that'd add close to 1½cc to the unswept volume so you'd need that much less in the chambers and/or dishes and shouldn't require new pushrods.

[mlrailguy]

I kept retarding the timing till it finally quit pinging, but I really felt a loss in the performance. I am on no budget, basically, so will probably go for the 060 copper head gaskets.
spent all my savings on coil over conversion, after stripping splines out of torsion housing :{

[mlrailguy]

Confused a bit now, after rereading Marc's post. Should I go with 60 or 30 haed gaskets?

[Marc]

It'd take .060" gaskets to get below 9.5:1 without doing anything else. I proposed that you go with .030" AND open up the chambers and/or have the pistons dished.
I'm assuming that you have either 1.4 or 1.5:1 rockers with an FK-8 (with the adjuster screw at the pushrod end). If there are shims on the rocker studs there's a good chance that you won't need longer pushrods with the .060" gaskets - you'll probably get away with just removing them, or using thinner ones, to re-establish acceptable rockerarm geometry.

Another dodge when pushrods aren't long enough is to put lash caps on the ends of the valves. Generally speaking if the adjuster is in line with (parallel to) the pushrod at the point of ½ valve-lift you'll be good to go. With stock-style rockers that have the adjuster on the valve end, it should be in line with the valve stem at ~ half lift. The objective is to minimize the side thrust on the stem by "splitting" it so that it's exerted in both directions as the valve travels in order to minimize friction and guide wear. With beefy valvesprings I look for parallelism between ½ and ⅔ lift. If your rockers have rollers on their tips there's another method - do they?

If your budget is tight, a pragmatic approach would be to use the thickest gaskets that you can with the existing pushrods that'll allow decent geometry, taking whatever C.R. you can get and limiting the spark advance if you have to. Don't overlook the geometry, if it's bad it'll heat the oil and wear the guides prematurely - and it'll cost a lot more to replace the guides than it would for a set of pushrods.

[Piledriver]

I have personally seen and also heard of many a SBC or such where the owner popped in much thicker head gasket to drop CR (losing squish) to reduce ping and it ended up much worse.

A high CR/tight squish motor may want a different curve, less total advance and perhaps more initial, t4s tend to be that way.
(27-28 total mechanical and 12 initial tends to work well on a ~stock T4, and that is basically factory spec for total mechanical, they ran heavy vacuum retard and low initial for emissions reasons, it's a great way to heat up the heads quickly at idle)
Also: Monitoring CHT?

The factory timing curve and settings are for a stock motor.
Unless you have one of those you must figure out what the motor wants.

Of course if the CR is simply wayyy too high, you have to deal with that unless E85 is common where you live..

I would dish the pistons, maiking certain to leave ~1/2" of flat deck around the outside edge to keep good squish.

[mlrailguy]

Ok, yes,am running the ratio rockers and they have been shimmed up a bit. Unfortunately there are no shops in my vicinity for doing piston work. sounds like the .060 gasket is most logical way to go for now. At least I won't have to worry about pinging any more.