chief455

iTrader: (21)

I have a set of 241 casting heads that were milled .035. I've established the fact this sucks when trying to pick a big cam, so I'm playing it safe with a TR224/563/112 cam
Questions:
1. What will my ratio be with stock pistons/Felpro gaskets?
2. Will 92-93 octane after a tune be good enough?
3 Would octane boost actually do anything - have you used it?
4. Why do this milling?
- will the little compression increase = any power increase on pump gas?

chief455

iTrader: (21)

maybe the night crowd can answer my??s

DenzSS

1. CC your heads, it is pretty simple. Only way to be sure. Once you have that, we can figure out the CR.

2. It should be without a problem.

3. Octane boost does absolutely jack. It only raises the octane by fractions of a point. Either run pump gas or race gas.

4. On a personal note, I loathe milled heads unless there is no other option. It is too easy to screw up the geometry, plus you can end up shrouding the valves even more, having an inopportune squish area, and any other number of issues. Some think it is fine. I don't.

Yes, more compression is a good thing. It will allow you to run a more "aggressive" camshaft, allow for higher cylinder pressures, and a whole other pleasant can of worms. A rough rule is +/-4% HP per point of compression.

chief455

iTrader: (21)

4. On a personal note, I loathe milled heads unless there is no other option. It is too easy to screw up the geometry, plus you can end up shrouding the valves even more, having an inopportune squish area, and any other number of issues. Some think it is fine. I don't.

I am not happy about the milling either. I'm old school - cast iron heads and 9.5:1 on pump gas. Let the portwork, chamber shape and cam do the power making.
Anyway, I have these heads and cams steeper than 225/575 p/v is a problem since I'm not going to mess with the stock bottom end. I'll start with a big cube short block if I crave more power later.
At least it seems my combo will run on pump gas and if I am reading this right - the compression increase may make me up to 4% more powerful than without the milling?

So if I made 400rwhp with unmilled heads, raising my compression 1 point potentially could make 416rwhp? On the same tank of gas?

DenzSS

How much compression you can take on pump gas is a complicated issue.

I can't remember off the top of my head, but I think the limitation on pump gas is around 220psi of cranking pressure. I'm probably off, but I think that's close to the limit you can run on 93 pump.

There is also the squish area, the cam profile, and the chamber design to consider. With a good cam design, I've seen up to 11.5:1CR run very well on pump gas. With a larger bore and less valve shrouding, you can get in the neighborhood of 12:1 and possibly even a little higher.

If you're into engineering, there are a lot of limits you can push.

Yup, that's what I'm saying. 400-416.

chief455

iTrader: (21)

How much compression you can take on pump gas is a complicated issue.

For sure! Good topic.
I went through this lesson while building my pump gas all iron Pontiac motor, and many before it. Same with iron heads - keep the chamber shape to promote swirl into the intake valve, unshrouded, and smooth to eliminate hot spots.
Machined small chamber heads with dome pistons - yikes
Polised open chambers with flat tops and zero deck = yummy
Then consider your mechanical ratio figured by the bore/stroke/deck height/+
(valve relief cc/gasket crushed thickness and actual chamber cc volume) quench area. Now put the cam into the equation!
Lot's of valve overlap keeping the intake valve open while the exhaust begins to open bleeds off some dynamic compression (cylinder pressure) but traditional high lift medium duration cams with "good idle" wide (114 or more) lca can actually build cylinder pressure. While this may be the intent of the cam grinder to make more power, it also just increased your motors chance of being a pinging slug that can't handle any ignition timing!
That was old school stuff.
Now we have the drop a point of compression when you have an aluminum head theory, on top of aluminum blocks! Add strange material used to make pistons dissapate heat, better cam grinding and the 11.5 - 12:1 compression you mentioned might be runable on **** gas today. I'm still leary...

But you have answered my basic question DenzSS !
I won't get the chance to cc those heads because they're going on.
I figured someone might have been here that already did the math - or knows about how many cc per .005 milled on a 241 head equals.
Anyway - I guess I'll be safe with 93, a good tune and hopefuly get my first LS1 into the 11's without anything but heads/cam/headers/converter.
And still get decent gas milage and reliability for the street

robertbartsch

I have 5.7 LS6 castings milled .055.

I'm using a small street cam 220/220, 564/564, 112

1. DO NOT use a big cam for milled heads
2. You can fly-cut the pistons if you insist on a big cam but be careful
3. Compression ratio for me is 11.2 to 1. OK on high test pump gas - no pinging with a mild LS1Edit tune
4. Using thick head gaskets is bad since it tends to promote detonation

robertbartsch

I have 5.7 LS6 castings milled .055.

I'm using a small street cam 220/220, 564/564, 112

1. DO NOT use a big cam for milled heads
2. You can fly-cut the pistons if you insist on a big cam but be careful
3. Compression ratio for me is 11.2 to 1. OK on high test pump gas - no pinging with a mild LS1Edit tune
4. Using thick head gaskets is bad since it tends to promote detonation

chief455

iTrader: (21)

thanks Robert! Sounds like we are on the same page

I'll tell a secret. When building a stroked Pontiac once the block must have been decked too far or the pistons were off because they stuck out of the block .016!!!!
They were custom pistons too thin to shave, the p/v and compression was going to be hazardous. I cheated the system and used double head gaskets.
Custom gaskets for big bore Poncho's at .040 crushed each. That's right - I had .080 gasket thickness!!!!
Well, p/v allowed a wild roller cam, compression came in at about 9.5:1 and the thing dynoed over 600 hp at 6200 and 610tq at 4400 reading 110%volumetric efficiency!!
The motor is 5 seasons strong and many street miles with only spring changes.
Never say Never I guess

DenzSS

You're definitely right--good topic. I'd like to see more like this on here.

Actually, we're running the flattops .022" out of the hole on my 408. A lot of chamber work was done to support that, though.

DenzSS

I did a little looking and I think you should be around a 59cc chamber with .035" milled off of the heads.

If my math is correct, that is going to bump you a little over a full point in compression to about 11.15:1.

Based on the stock piston protrusions I've seen, I'd place it closer to 11.3:1. Just a guess though.

You might check and see how badly the valves are shrouded. Like you stated, that doesn't give you much at all in the way of P to V clearance. It's going to be tight. Kind of an odd squish area too if I'm picturing it correctly post-milling.

I'd think about running a slightly thicker head gasket, maybe with a compressed thickness around .064" or so. That should get your P to V in a little better shape and drop the compression to around 11.0:1, which is a little safer and less on the ragged edge. Your squish is still going to be weird, but there isn't much that can be done about that.

I think the calculations are pretty close, but I'd definitely double check.

chief455

iTrader: (21)

I've had a few guesstimates of 11.3 so I think you are right there. I was told Fel Pro gaskets are thick yet still good. Any ideas on selection there?
I hate the ragged edge!

Pistons out of the hole was not my dream set up either, but I made it work, as you did also

Check this pic of the chamber - it's a bit dark but it actually looks decent in person. It flowed good numbers even at low lift so I don't really think the big mill job hurt much but my cam lift limitations.
Heck - maybe this will keep me from getting them to grind me a 242/242/ - .616/.616 - 110lca advanced to 106 intake centerline
If I had the room I'm just sick enough to try something like that

With 11:1, a TR224/563/112, LS6 intake, ported tb, Jethots and these heads(296cfm at 600 lift) backed by a 4000 stall and 3.73's I hope I get my 3750lb car accros the line in the 11's and can drive it all summer.

DenzSS

Hmm. Doesn't look too bad. Actually, the last Fel Pro gasket I saw had a lower compressed thickness than stock. I'm not up on the Fel Pro gaskets, I usually use Cometic. Good looking gasket, though. If it had a stock compressed thickness, I'd be using it right now.

I don't see any reason why you shouldn't be well into the 11s with driving and traction. Should be a nice ride.

I'm curious to see how mine turns out. I'm still waiting on the last of the parts. LSX intake is on the way and I'm waiting for my lifters to get here. I left them at the shop in WI accidentally. Still have to do a final measurement on the pushrods since the rockers ended up being a 1.95 instead of the 1.9 we were planning on.

chief455

iTrader: (21)

thanks for the supporting words! I'm getting confident my combination is safe and will work well.

Don't you just love the quality control on aftermarket performance parts ?
Never build ANYTHING without checking it!!

Best of luck to you and thanks for a thoughful discussion. Nice after reading bash after bash and lots of arguing

DenzSS

No problemo. Thank you and good luck.