need a heads recommendation Compression related.

[famous bob]

Working this combination with a stock LA deck height, a standard Felpro 8553PT head gasket at .051" thick, 1 cc in the crevice down to the top ring. and .060" over bore, I come up with 9.85:1 SCR. So the 10.5 numbers are not quite right. You are better off than you think...

What you really care about is the DCR (dynamic compression ratio) which varies with the cam and cam timing, and ultimately the effective DCR, which drops with increasing altitude. The altitude in Tulsa is <1000' so you can pretty much forget about any altitude effects. But the cam is going to vary the DCR.

So we need some cam info to say further. If you really need/want to drop SCR and DCR, then this may be a case where an older type, slow ramp, 'long-tailed' cam will be right.

If you want to use E85, check out all the articles online... they will all tell you that E85 can run with much HIGHER SCR's. So E85 on this setup would leave a lot on the table.

As for AL heads, I am not aware of any in that chamber size. But the extra breathing would indeed be nice.

BTW, you can easily add 2-3 cc's to your existing chambers with some valve work and some very mild grinding in the chambers. I've takne 75 cc heads up to 83-84 cc's. (And did not hit water! Whew.) You can polish the chambers to help fight detonation and get out some material at the same time.

The altitude at the airport is 654 ft or so , maybe 1000 ft on one of the hills or okc. ???

 

[rumblefish360]

That is a most excellent question and I never thought about it... but all my three cams have been installed with ICAs of 62 to about 68 degrees. I don't know if that means anything. The 292 had the latest ICA ( up to 76* when retarded),and I couldn't love that cam. The 270 had the earliest and That I did love. I even loved that one straight up, now with an ICA of 65......

Have you not tried anything lower?
We all know (generally speaking) that larger will support more ratio.

No one was talking about Dcr or cylinder pressure. The engine shops were saying 9.5 was tops for 91 gas. I wasn't buying it. I had to work out by calculator and protractor, and write my own formulas for figuring Dcr. Then to top it off, aluminum heads had just come out about that year 1999, so nobody could tell me how that was gonna affect the Dcr. So I winged it, .....

I’m surprised to read this because from one metal to another dynamic compression ratios aren’t effected by metal material. Just cam timing.

IMO, generally speaking, on a broad term as not to zero in on any specifics in the industry or persons within. Because your then potentially laying blame and asking for names.....

I’ll just start with the actual smart people in the biz who have already figured out what kind of cylinder pressures require what kind of fuel. The DCR vs octane = no detionation. Or “pining or knock.” And how the cam timing effects the DCR.

As the smart guys figure this out and pass along the information, it becomes like a grade school game of telephone. Start with 1 message and then it becomes another one at the end. This is the misinformation line that we all are victims too.
These are the wives tails, etc....

The best way to relay this information (or any) is to use the KISS method of Generalization and make a broad statement of compression ratio with octane to use with it. This is where we end up with the general rules of safe ratio with fuel on intended purposes and cam sizes that are good to use within the parameters of operations on the intended purposes of the vehicle and its performance arena.

Going outside these recommended guide lines can invite disaster on a number of levels. The first and obvious one is getting a tank of bad fuel.

When it comes to cams and DCR, it becomes a bit dicey to zero in on a exact pressure. IMO, this is due to having to many thing to flexible in calculations.

1st, actual math of the engine and it’s static compression ratio. (SCR)
2nd, cam timing events in the early days were never published and secret.
Actual data to the public and many speed shops were a big fa ZERO! Just advice from the manufacturers of parts were given and not even from the engineers that designed and tested them.

So, as the general rules and suggestions were passed down, the now familiar standards being what we know them as are still in place for iron heads.
1pt. More for the aluminum.

8-1, regular cars and/or small cams and add on parts.
9-1 most high performance street cars (DD) and light racing
10-1 street strip/heavier racing- 50/50 race fuel
11-1 fuel race fuel for best results.

These general rules can be bent within reason or semi disasters result and should be traveled at your own peril. This is why using the KISS method on ratio/cam is kept that why with the rule bender of to big of a cam use not to exceed the proverbial 1 or 1-1/2 step bigger than suggested. Or you need to increase the ratio for effectiveness to operate the cam as intended. The reverse for a small cam and to much ratio, less cam.

Because fuel is more of a limitation than anything else.

I probably couldda run closer to 200 on 91; others here on FABO have said that they are over 200 on pump gas, with aluminum heads. But I'm quite happy at 177 and 87E10.

Probably. Except you would need more cam.
I have been able to run 93 on a 10-1 with the 292 cam. IMO, it wasn’t a problem.
Your issue with the cam IMO is misuse of a huge Hyd. in the street. I think you didn’t go fa enough in the envelope on that one and the current builds you have seem implausible due to octane level used and listed DCR pressures in psi.

That purple 292/.509 has a listing in the MP speed tips section that IMO, shows your min. For decent usage. That cam is much better served at another point in scr ratio w/higher gears and stall.

 

[rumblefish360]

I lived in every place you listed for at least a year...except Gimli, but my parents live there half the year so I’m there quite a bit.
The only local fuel I have any great luck with is shell premium, I run it in everything except for the newer 5.0 Mustang my wife drives,she just runs regular co-op gas in that thing.
Even in my lawn equipment E87 goes bad in a few months or it gums up the carb jets in no time...I would not dare to even try it in my 9.5 comp 340 with the iron heads.

Though I’d like to know what cam you have in it.

The ultimate question, for every street/ strip gear head.

Well, yes. But there is a fundamental problem with that.
Once it is known, there will be someone
(and by that I mean hoards of people)
that will unknowingly, stupidly or daringly exceed the math by pushing the limits. And then ***** about how it is wrong.

The general guide lines put forth by past engineers should not be bent to hard. If you follow what they suggest, all will be fine. While there is more than likely more to extract from a build as suggested, it can backfire in your face like that cartoon Coyote!

A suggestion for everybody, don’t go nuts, follow the manufacturers suggestions.

The altitude at the airport is 654 ft or so , maybe 1000 ft on one of the hills or okc. ???

I quoted your post because you (knowingly?) make a excellent point in air pressure and this effects how a engine runs and performs.

THIS, I know you get. But I find it amazing how many miss this or ignore it and freak when there altitude changes in a large way. There due diligence and research was (probably) ill done. Combined with changing quality of fuel... OH boy!

This is were you see the “Suggestions” put for ignored and crying men enter.

 

[krazykuda]

Guys, I currently have a 360 that is bored 60 over. the pistons that it came with are KB 190 that figure 10.5-1 with 72cc heads. that is figured at 30 over so I am not sure if being 60 over will help bring the compression down some.

My question is, is there an aluminum head for the SB 360 with a 72cc or bigger chamber so I could get away from the possibility of detonation? I was thinking of going E85 but with the whole setup I could just about switch to aluminum heads and probably get more power.

thanks,

BW

Are you sure that the KB 190 pistons are going to give you 10.5 compression??? How did you figure that out, going by book numbers or actual measuring of your combo????

If I remember correctly the KB 190's with a .065 fel-pro head gasket (the one that comes in the complete engine tear down kit) will get you in the 9.5 compression range...

Check your actual parts and see what your true compression is...

How to Check Compression

 

[nm9stheham]

That is a most excellent question and I never thought about it... but all my three cams have been installed with ICAs of 62 to about 68 degrees. I don't know if that means anything. The 292 had the latest ICA ( up to 76* when retarded),and I couldn't love that cam. The 270 had the earliest and That I did love. I even loved that one straight up, now with an ICA of 65.

IMHO.... Of course it means something.... it means you like plenty of low and mid-RPM torque, and the wide torque band that comes with it. Every torquey 'street' combination that I work out ends up in the 60 to 67 ICA range. It is where the SCR and DCR combination makes for good low RPM torque starting down around 2000-2200 RPM. Combine that with a good breathing system to get a 6k+ RPM top end and you have a solid, usable torque RPM range of 3:1. That is the 'flexible' word that AJ uses; step on the throttle almost anywhere in the operating band it responds and goes.

The later ICA's with bigger cams need to go hand-in hand with even higher SCR's.

The ultimate question, for every street/ strip gear head.

I'll say that strip is different. You can use but only so much torque in 1st gear, limited by the traction. It would take some well-honed driving skills to consistently control gobs of excess wheel torque at launch (though I bet some guys can do it). But those same gobs of excess wheel torque is what you DO want in road race and rally.

So the trade-off to make the cam bigger, and get the later ICA as a consequence with the loss of low end torque, to gain some top end HP, is understandable. But you see guys with too much rear gear to make up for poor low end torque; they get 3/4 of the way down the 1/4 mile and can't accelerate anymore, 'cuz they're topped out. They need that wider torque band and a lower rear gear...or an OD trans.

 

[rumblefish360]

AJ, what is your static compression ratio at?

IMHO.... Of course it means something.... it means you like plenty of low and mid-RPM torque, and the wide torque band that comes with it. Every torquey 'street' combination that I work out ends up in the 60 to 67 ICA range. It is where the SCR and DCR combination makes for good low RPM torque starting down around 2000-2200 RPM. Combine that with a good breathing system to get a 6k+ RPM top end and you have a solid, usable torque RPM range of 3:1. That is the 'flexible' word that AJ uses; step on the throttle almost anywhere in the operating band it responds and goes.

The later ICA's with bigger cams need to go hand-in hand with even higher SCR's.

And that should be said with the smaller cams effectiveness on the street. And the increase in compression ratio with larger cams to off set the lack of DCR.

AJ’s combos would still bennifit from well ported heads to extend the rpm range very well.

I gotta do some math on my stuff later.
I’ll be back.

 

[AJ/FormS]

Comments in the Quote

AJ, what is your static compression ratio at? See post #19


And that should be said with the smaller cams effectiveness on the street. And the increase in compression ratio with larger cams to off set the lack of DCR.

AJ’s combos would still bennifit from well ported heads to extend the rpm range very well.Yeah I suppose, but I'm not looking for any more, Actually I could give plenty up.

I gotta do some math on my stuff later.
I’ll be back.

 

[AJ/FormS]

I lived in every place you listed for at least a year...except Gimli, but my parents live there half the year so I’m there quite a bit.
The only local fuel I have any great luck with is shell premium, I run it in everything except for the newer 5.0 Mustang my wife drives,she just runs regular co-op gas in that thing.
Even in my lawn equipment E87 goes bad in a few months or it gums up the carb jets in no time...I would not dare to even try it in my 9.5 comp 340 with the iron heads.

E87 goes sour faster than that, so I install stabilizer in everything. Shell gas comes, or used to, with stabilizer already in it.
In the car, I burn it up faster than it goes bad so it only gets stabilizer as needed.
You can tell how sour 87E10 is, by its color.

At 9.5Scr and with a cam at least as big as stock, your cylinder pressure might be sub150psi, and even with iron heads I would run 87E10 at that pressure.
My fuel system has never had trouble with this fuel.I have; 750DP, P4007040 Carter pump, soft steel 3/8 lines, EFI jumpers, a 1968 sender with a 3/8 pick-up added, and with and new factory 3/8 sock: no regulator. Tank is also a 1968 model.
This Holley is known to have a fat low-speed circuit. I left it alone.Maybe that is my saving grace. But honestly, I have never, in Manitoba, pumped a bad tankful into her. With every single tankful since the beginning, about 1999 IIRC, It has been business as usual.I think it still has those 1999 Champions in her. RC12YC or something close to that.
Maybe my car is just blessed...

 

[AJ/FormS]

OOps, comment swapped posts

 

[nm9stheham]

I gotta do some math on my stuff later. I’ll be back.

A highly recommended exercise for guys like you who have a long engine-building history to review IMHO. I'll be interested to see what you come up with

I had a solid grip on the SCR, and a fair grip on DCR, in my 351C in 1975 (supported by measurements) but it was good to come back 40 years later, use the soooo-nice-and-easy online calculators, and find both the SCR and DCR were pretty much what I hand calculated way back when. And, it was good to get modern numbers to verify that the low 8's DCR range with iron heads and quench was near the limit... very few people attempted to compute DCR back then so there was little reference to what was OK.

And I also went back to my 7.6 SCR, 300 degree duration cammed Opel 1.9L rally engine (which I did NOT compute up in the early 80's and just 'ran with it', despite being warned that the cam was too big for a good rally engine) and found that the DCR was in the high 5's... OK, THAT explains why it was 'torque-free' below 3700 RPM LOL

The physics have not changed.

FWIW.... THE changes at the N/A hobby level in the last 50 years are:

• The easy online SCR/DCR calculators nowadays that give little excuse to not look at DCR. It just takes care and thorough research to find the right numbers to plug in. (So you don't have the garbage-in/garbage out problem.)
• The reasonable cost AL heads have been a revolution from 40 years ago and boon to higher CR engines.
• The roller cams and XE and Voodoo type profiles where there is little good reason to use the old slooow cam profiles, except to remediate a problem or save some $$ for the budget limited enthusiasts.
• Hyper pistons
• EFI

All the rest is the same physics.. head flow, crank and block strength, rods and bolts, oil pressure, piston selection, quench, header size and length, intakes, ignition timing tuning, etc. There are some better parts, but they are improvements on the good stuff that was already there.

Good discussion!

 

[Wyrmrider]

Ill chime in with some other info in a bit but the cam is an XE274H

old chevy He 274 H or Mopar HL?
did you change to a HR?

 

[Dubs Chops]

Yessir.... and it is good to ask the question. KB makes certain assumptions on their CR number listings. I get their numbers if I assume a Magnum standard block height (rather than a standard LA block height) and a .039" thick head gasket.

BTW running some quick numbers, that flat dome is probably around .040"-.045" high above the compression height; it takes that to make the -1.2 cc head volume with typical eyebrows. That does not quite jive with the KB notes but the numbers say what it needs to be. So OP, if you have assembled the short block, maybe you can confirm that the pistons stick above the block at TDC? Like around .030" for an LA block...?

Taking your xe274 cam, and doing a DCR computation, that ends up at 7.95, with the cam installed dot-to-dot... i.e., with the cam mfr's standard ground in cam advance. Your cranking pressures ought to be around 160 psi, not awfully high, but where you need to start paying attention to everything that could lead to detonation.

FWIW, I've run 10.3 SCR and 8.3 DCR with iron heads on 93 pump at around 1000-2000'; 165-ish cranking pressures at 1000' so a tad higher than your setup. No issues that I could not manage; could not use regular, and I needed to stay conservative on ignition advance. That engine did have mild quench to help fight detonation, which you won't have with the open chamber heads. Put almost 100k miles on it.

(BTW, you don't need as much ignition timing in general with higher CR's, though more advance is usually better for open chamber heads. As I understand things, the higher peak cylinder pressure and better peak timing that you achieve with timing advance comes with the higher CR's to some degree.)

As an exercise, I've computed up some 63 cc Edelbrock closed chamber heads with these pistons. (ProMaxx lists 65 cc's as an option but I don't know of they are still strictly closed chambers. You might inquire.) Put in a .065" thick head gasket to work with my assumed piston height above deck of around .030" (Needs confirming! If I am wrong, all this is wrong.) and get to .035" quench gap. (It is not a prefect quench gap with that dome not going to the edges of the piston top, but it still ought to provide some quench effect.)

With all that (and assuming my thoughts about the piston dome are right... did I say that needs confirming? LOL), the SCR is now
10.6 and DCR is 8.5. Hmmmm.... a few more tweaks, like a .070" head gasket, and a 279 duration cam, like a Voodoo 703, and the SCR is 10.4 and the DCR is now 8.25. Getting pretty safe now with quench and AL heads, though you still need to take the proper care.

BTW, are you stuck with the 91 octane there in Tulsa? And do you have an LA block?

Yes it's an LA block and I'm stuck with 91oct/

PS those last 4 or 5 posts melted my Brain!

 

[Wyrmrider]

read them over again- you'll get it
the other posters are giving you the math basics which is invaluable- otherwise you are just shooting in the dark or at the mercy of the tec line ignoranuses
Most do not know MOPAR some like Hughes and other mopar specialists do- problem is most are racers
quench is one thing it's when the two cold surfaces close together keep preignition and detonation away
squish is when the squeezing of the volume out of the area creates swirl or tumble or turbulence for a better burn
both are valuable
I'm lost
do you own pistons and or heads at this point?
me I'd get the larger closed chamber heads and maybe even open up the chambers around the valves and pick pistons a half ration lower than max so I can run max advance and not have to worry about a tank of bad gas and not have to pick a bigger cam than I need for the torque range that I want jsut to hold down the Dynamic compression
but that's me- however a little too much compression is way too much to have to live with- not a race car or even a saturday night only car

 

[nm9stheham]

Yes it's an LA block and I'm stuck with 91oct/

PS those last 4 or 5 posts melted my Brain!

LOL, well, no one is trying to snow you, but to give you a good basis for understanding why to do one thing or another. If you want. please post specific questions on terms or concepts, and i am sure someone will try to provide a good answer.

 

[Dubs Chops]

read them over again- you'll get it
the other posters are giving you the math basics which is invaluable- otherwise you are just shooting in the dark or at the mercy of the tec line ignoranuses
Most do not know MOPAR some like Hughes and other mopar specialists do- problem is most are racers
quench is one thing it's when the two cold surfaces close together keep preignition and detonation away
squish is when the squeezing of the volume out of the area creates swirl or tumble or turbulence for a better burn
both are valuable
I'm lost
do you own pistons and or heads at this point?
me I'd get the larger closed chamber heads and maybe even open up the chambers around the valves and pick pistons a half ration lower than max so I can run max advance and not have to worry about a tank of bad gas and not have to pick a bigger cam than I need for the torque range that I want jsut to hold down the Dynamic compression
but that's me- however a little too much compression is way too much to have to live with- not a race car or even a saturday night only car

Yes the motor is built and in the car. I posted 1/4 mile results in another thread. this thread was just in discussion of what head options were out there I could consider without swapping out pistons. I got some good info on some eddy's and a taller head gasket earlier in the thread I will probably be following up on during the winter. for now I am getting a manual trans brake valve body since I have no kickdown and need a manual vale body anyways. its shifts are incredibly slow with the kickdown wired all the way back making passes it takes at least .7 to shift after I hit it.