I am going to pull the factory heads off of my 360 engine (previously re-worked) and clean things up a bit. Since engine start-up I was getting a good amount of oil past the positive-seal teflon guides and I could tell last time I had the intake off that the valves built up a pretty good amount of "crud" on them.

As well, the intake manifold mating side is looking a little rough, so I figured I'd send them off for a little clean-up. While in the shop I might as well shave them a bit to bump up the static CR.

So here is what I'm looking for: advice regarding the max safe CR (static and/or cranking compression reading) for a set of iron heads, using pump 94 octane fuel.

The cam is Hughes HE3844AL, that's a hydraulic flat tappet, it specs out as follows: .535/.540 lift, 238/244 dur. @ .050", 286/290 adv. dur., 108 LSA.

The motor was compression blue-printed (so precise measurements, as opposed to machinning blue-printed) to give a static 9.8:1 CR. Having done a cranking compression test I saw a steady 165-170 psi. Hughes recommends 165 psi min for this cam.

I think I have some room to go here. This past season I tried mid-grade fuel (91 octane) and had no audible ping. I always run on 94 octane either way though.

What do you guys think?

10.2 is safe with cast iron head on 94 oct. not sure what cranking pressure is safe with cast iron. I know with aluminum head 190-200 is safe on 92-93 oct.

What's the shape of the combustion chamber, round or heart shaped? A thin shave of the head and a thinner head gasket is a cheap up in the compression with the heart shaped combustion chamber. Many of the 1980 + heads were of a swirl design. These heads show a lot of promise with just some gasket matching and simple bowl porting. A better bang for the buck than compression. Did your car come with the A 999? That 2.74 first gear wakes up the motor. The factory iron intakes responds well with some porting in the plenum and runners.

I would not increase the ratio at all. Your better off running slightly light on the compression ratio than having a tad to much. You'll gain more power from better intake/head/exhaust flow.
If it is absolutely needed to mill the heads (& intake if need be) to simply clean up the surface to correct sealing / figment issues, then that's one thing. But not to raise compression.

How much cash and time do you have invested in these J heads now? Seems like they've been a source of headache for since you started the motor for the first time.

You could bump it up to 10.5. It might tolerate 11, but if you go too far it's hard to back track.

If they are open chamber heads then don't try to go up any significant amount unless you have "quench dome" pistons that get you a tight quench area. Even then only perhaps 1/2 to 1 point more. If you have open chamber heads why not just upgrade to some EQ heads, you get more flow, easy to get quench, pressed in hard seats, more efficent burn, no exhaust crossover to heat the intake and chances are you could sell your existing heads to cover a big part of the cost. They can handle 10.5 compression easily.

Guys,

Thanks for all the response so far. Here is the thing, these are re-worked OEM heads, non-fast burn with a resonable amount of port work, max flow is 264@0.550 lift, all DIY work. Due to the original machine work costs (valve job, valve guide liners, etc, etc) I do not want to replace them with another set of aftermarket heads...I already have an upcoming W2 build meant to do that. So these heads are really here to stay for another 1-2 yrs max.

But...since I will be pulling them off I really am looking to push the combo to it's limits. I want to be relatively smart about that though...so given my data points (9.8:1 static CR and dynamic cranking psi) I think I have some room to experiment with.

The car itself already has a 4K stall 9.5" converter, 3.91 gear, 727 trans while the motor is topped off with a Performer RPM intake. All in all it works well I think...but I'd like to push the combo to mid-12s in 1/2 mile...so far the only time out was a best of 13.13 and that was with my Holley Strip Dominator single plane intake.

I considered a move to a roller cam in that "search for power", then a move to a stroker build, but in hindsight, I do not want to rush any of these plans and want to spend some time optimizing my current combination instead.

Anyways, yes, this is very much a bit of an experiment on my part and I'm trying to assess the risk in terms of the CR pursuit.

Mark,
My recommendation to anyone embarking on this type of a project would be to avoid reconditioning of old heads...but, like they say "...hindsight is always 20/20...". I have certainly poured a [censored] load of time and energy into these (mostly due to the porting work), but also thoroughly enjoyed that experience.

The hard teflon valve seals never worked for me...not sure why, but having switched to the polymer ones I have to say the previous oil consumption issues are completely gone. The motor runs strong, I think I may be able to push mid 12s this season, at least that's my goal for now.

I still have the test of my 1.6 ratio rocker arms lined up from this past year when I ran out of time. Heck, what can I say? I am one of these guys who like to play with parts...I am absolutely not the guy who wants to build it once and never have to touch it again. You are right though, it does get a little annoying when the old stuff "acts up"...

Had similar issues running teflon seals and since the switch to poly, that problem is solved and went 10.40`s w/906 iron heads so I understand that deal also. Good luck on the quest for 12`s.............

The most I would push the compression is 1/2 point..
if you go to much you will be pulling timing and in
the end may not gain anything... what head gasket is
on it now.. if its the .039 you can test the .024
thick ones to see if you get any detonation

With new guides and some port work those heads are probably worth $500. Around here milling them .030 costs $200 for a pair. The EQ heads can be had around $700 shipped and ready to install and flow as much as your existing heads with smaller better chambers, a couple hours with your own labor in the garage they will flow a lot more than what you have. Of course this is US dollars and local pricing so that may throw a wrench in my figures.

FYI...I called HughesEngines, spoke with Tim there...he was "neutral", meaning he did not advise me to up the CR, nor did he discourage it. He did point out that 165 psi cranking pressure is what they aim for with this cam and given that I'm running iron heads it may be borderline already.

Once we discussed my experience running a mid-grade fuel (89/91 octane) he was actually surprised that I was able to do that without detonation.

Sooo...given my current cranking pressure readings I'm actually even more curious as to why no audible detonation is occuring. Mind you, by the time you can hear it things have gone really bad...

I'll pull the heads, the valves need cleanup anyways, measure it all out once again and go from there.

Thanks for the input guys!

Audible is generally too late or very bad. Have you read the plugs and looked for peppering or alum. blobs on the porcelain..........?

Detonation isn't as noticeable especially in the higher rpm ranges.

I tore down a running engine some years ago and found rod bearings worn down to the copper on the upper shell, and all in exactly the same spot. The engine had 100K and had never had audible knock, it also had a knock sensor as part of the engine control scheme. Yet, knock is the only explanation for the wear.

R.

I run close to what you have, i have a 360 with flat tops zero decked, worked J heads that are at 59cc, i noticed crud on the valves also. This engine has 11.2 cr cranking psi is at 195/200, with a comp 282 solid FT 244/252 @.050, 520/540 lift on 110 lsa. Only raced it once and it was pig rich ran 12.22 with a 1.66 60' 71 demon 4,400 stall 3.91gear through mufflers at about 3,470 with me in it. The motor has about 11K, i run 93, run very very cold plugs NGK R5672A-9 with msd ignition, with hotter plugs i get yellow on the insulator meaning fast/excessive heat rise, and slight peppering. So far so good for a basic Junk motor, i do love the pop out of the exhaust and the instant throttle response with that hi comp!!

Plugs look good, NGK Vgroove (BKR5E-11), indexed...pretty consistent colour and texture...no sign of peppering or blobs...

Got a close up shot by chance?

Yeeesss sir...I've attached a large ZOOM and re-crop of just the plug tips...no sharpening done, so it may seem a little fuzzy.

Keep in mind, this is the last pic I have when I was trying to work through my oil consumption issues...and as you can tell a couple of the plugs are rather wet...

Man, so does that 59cc chamber bring it down to nearly a closed-chamber format then? I think the flat pad of the open chamber in my heads is very "thin"...taking another .040" off would nearly wipe it out.

According to my calculations, with a 68cc chamber (what I have right now) taking 0.030" off and keeping my current FelPro 1008 gaskets would get me to about 10.47 static CR.


Indeed, very close duration numbers, well, yours would be demeed a size bigger as I understand it (about 5deg more @ 0.050"), so it probably would be inclined to bleed off a bit more pressure.


Nice...yeah, similar combo, I'm a bit heavier and not quite as much stall speed.

No not quite closed chamber so no real quench going on., next engine I build will be right at the limit maybe 185 to 190, they just run so nice if everything is spot on