koolrayz

iTrader: (26)

Im starting with a clean sheet of paper. I am curently stock internaly. Im building a forged shortblock and looking at the afr 225 heads. Im wondering if I would be better off using flat dome pistons and milling the heads of should I leave the heads as is and use a high dome piston. looking for 11:1 static compression. from a performance standpoint what is the best option.

CamTom12

iTrader: (1)

Don't domed pistons add more mass to the rotating assembly? Just curious...

Oscar Will

For my money I'd increase the compression through the heads with smaller chambers and/or milling the heads. I think domed pistons inhibit proper flame travel and I'm sure that's been proven many times.

BTL FED

iTrader: (9)

I did domed pistons because I didnt want to cut the deck of the heads, One of the reasons I am going with the AFR heads is that they have a thick deck surface, I didnt want to compromise that by milling them.

Mine is a 408, here is the difference in weight between my domed Nitrous pistons and Normal Forged flattop pistons

Piston type Bore Effective Volume Weight
Flat-top 4.030 -2.0 CC 452 Grams
Domed 4.030 +13.5 CC 508 Grams

btw at 68cc head chambers my motor is around 14.3 to 1 compression

Here is a pic of one

koolrayz

iTrader: (26)

BTL FED, what brand piston is that?
Im thinking along the same lines as far as the integrity of the head. Another thought is once the heads are milled there is no going back. you can always change pistons. Im still concerned with performance though

CHRISPY

I believe AFR is going to be offering a small chamber 225 head?

What displacement are you planning? Stock cubes or stroker/superstroker?

If stock cubes you could run a flat top and hit around 11:1 with that head and no milling if the chamber is small enough. This gives you a few more options.

Tony should be able to clarify on this.

koolrayz

iTrader: (26)

I thought the small chamber was a 66cc. Im still on the fence on whether or not to use a stroker crank with my stock block. My car only has 18,000 miles on it so I should have a perfectly seasoned block. I dont want the weight of the iron block and I dont want to be the ls2 test dummy

RX-Ben

iTrader: (7)

The AFR 205cc head specs @ 66cc

The AFR 225cc head comes in 72cc (currently available) and 62cc (not yet available)

The AFRs have a 3/4" deck!!!!!!!!!!!!!!! You could mill the beejesus out of these and still have a ton of deck left.

A related question with deck milling- how much milling will cause pushrod geometry issues?

Thanks
Ben

2001CamaroGuy

iTrader: (6)

small CC head with flat pistons........domes hurt flame travel........when the AFR 62CCs come out I might grab a pair (would love to have something in the 50CC range)......

Chris@AP-Engineering

iTrader: (-2)

That is a custom Diamond forged piston. That piston was made to handle some serious abuse, it's also gas ported from the top if you look closely.

The LS1 / LS6 domes do no inhibit flame travel as much as say a older SBC with a big dome. Diamond has some pretty big domes that have a very nice smooth dome on them instead of a large dome that looks like a wall to the flame travel. I will agree that a flat top will be the best way to go if you can do it but, I would not sacarfice a lot of deck surface on the head over running a dome in these engines. We have used a lot of domed pistons in the LSx engines and have never seen where flame travel was a problem.

Also remember, when buying a custom piston you can have them lightend to try and get you closer to where you were before. Within reason of course. You can't put a +.150 dome on the piston and expect it to weigh the same as your factory flat top. Keep that in mind.

Mirek

AFR is just milling the 72cc 225 head for their smaller chamber head. So it will be a decked head. Plan accordingly.
They have to re-configer the machines that drill all the other holes before they offer it, etc.... It is much thicker though.

grinder11

iTrader: (1)

Are you sure about this? I have a set of 225's due to be in my garage in the next week or two. I talked to Jason recently and while he didn't go into the differences between the 205's and 225's, he did say it will be awhile before the 225's are available in the smaller chambers. If all there was to it was to mill off .030 or .040 or whatever to arrive at the 62cc spec, I am sure he would have offered me this option, as it wouldn't take but a few minutes to achieve this. I am not sure why the holes would need to be drilled differently, unless the 62's are angle milled, which Jason was very much against doing on my 72's. But if it is a different casting, that is another story completely. However, I can't say for sure what is going on here. I thought AFR was advertising the 225's as having a 3/4 deck, which wouldn't be the case if they were milled to achieve the 62cc figure. And it seems that given the fact that AFR has a clean sheet of paper here to design both sizes, just whacking off material on the deck surface wouldn't be the way they would choose to go, or would it? Maybe Tony or Jason or someone else could post up and enlighten us all! Me anyway!! I agree with the post on the 3/4 thickness being plenty thick and not to worry about milling to achieve the desired compression ratio. Even if you take a .060 cut, it still would be in the.700 range thick-plenty stout. Any time you use a dome you compromise flame travel. I know these engines aren't the same as the original SBC, but all things being equal, and depending just how big the dome you are talking about is, it WILL slow flame travel. For the street, I would shoot for a flat top piston and a zero deck height over a dome and/or milling. A good point on the fact once the heads are milled, you can't go back.

grinder11

iTrader: (1)

By the way, Mirek, where in hell is Berkley? Just curious. I am in North Branch, which most would also ask where in hell is NB!! It's about 30 miles ENE of Flint.You going to the International Auto Show in January? I like the Autorama. But the International is where the new Z-06 is supposed to make its debut, I think. Can't wait-and can't afford either!!

Mirek

Berkley = Royal Oak
I'm right at 12 & Woodward. Try and make it down in the summer. The amount of good competition on Woodward is ABSOLUTLEY INSANE summer nights. Packed.

I wanted the 205's but I also wanted 11:1 & I did not want to mill for numerous reasons so I thought it might be better to go 225's since I assumed I could get a "clean sheet" 225 with a 62cc chamber and get the compression I wanted without all the problems milling can bring (this is when Tony first mentioned the 62cc chamber)
But no.
There are some threads on ARP's "bottoming out" with milled heads, I voiced my concern to Tony and he mentioned to me that he would forward my concern about bolts bottoming out w/ milled heads to the engineer on the 225 in development so I just assume they are milled (I never heard back).

Also when I was at SEMA I talked to AFR and I recall confirming that they were just milling the 72cc head for the 62cc but there is alot of other "math" that has to be done/ machined into the head after you mill it that much. The whole point is if you get the 62cc 225 head you are losing that clearance (.060) so check p/v, check pushrods, deck height, gasket, valve train geometrics, etc...This is my understanding. I will say that It is beyond me why AFR did not just release a 62-63cc head. I understand the Edelbrocks will be 63cc and Trick Flow "did not know" at SEMA time.

Hopefully AFR can confirm this.

cyphur

iTrader: (10)

I just talked to Scott @ AFR, and he confirmed that they will just be milling the 225 castings to acheive the smaller combustion chambers, however he was talking about a 66cc chamber, which was acheived by milling 40 thousandths off the deck. They're just making sure it doens't affect head flow/geometry before they commit to an availability date right now.

Mirek

There you go.

Thanks man.

grinder11

iTrader: (1)

Thanks, CT! And thanks for the invite Mirek. I may take you up on it. By the way, I got the same cam as you (it aint in yet, though!!) but it is a Comp grind made for LPE. Not sure if the ramps are EXACTLY the same, as in duration at .004 lift, .020 lift, etc. It does have .566 lift and no split-222 degrees @ .050 lift I&E. What LSA have you got?

Mirek

112
286 advertised duration lunati grind.

I think that the AFR's high flow numbers and intake velocity may have something to do with the short but tall runner length and when you mill them down(like you have to for the comp bump) you reduce flow to a great extent. Perhaps thats the delay. Who knows I did notice that they now have an asterisk in the catalog that says air flow is effected when milling occurs.

jrp

iTrader: (16)

i did both, 6.6 domes and 5.7 heads milled .020. when all said and done SCR came out to 12.02

heres my piston

screamin' 85 z

Exactly!! Reducing quench space by using a thinner head gasket, decking the block, or reducing head cc's is by FAR better than trying to obtain compression by using a domed piston. Here's an article written by David Vizard..He is one of the leaders in the science behind the internal combustion engine.. Here's what he has to say about it: The entire article can be found here for those that would like more information on the dynamics of compression: http://www.horsepowerjunkies.com/for...ad.php?t=12378

Piston Crowns

Before buying pistons you need to understand that flat-top pistons and small, compact combustion chambers are the racer's most user-friendly choice--by a big margin. Always get all the compression conveniently possible by minimizing the quench clearance and cylinder head chamber volumes before considering domed pistons.
The domed piston may look like an easy short cut to more compression but it does not always deliver the hoped-for power increase. Although intended CR ratio may be achieved, the combustion process may be severely compromised by the presence of the dome. I have seen a piston dome that was a tad too high and cost well over 100hp. Unless you or your engine builder are prepared to spend time developing a piston crown form that works, stick to domes no more than about .001-inch high.