kgkern01

iTrader: (10)

With the new TFS 21* heads out, I have seen some mentioning of rolling stock heads being done to decrease the angle for better flow. Obviously the intake manifold would have to be milled to accept a change in angle, and header clearances could be affected some. So for those with experience with this on our cars, what has to be done to make it work, how far can they be rolled, and what kind of gains could be realized with rolling the heads for a lower angle?

PS - The reason I am curious about this, is that if it is possible to roll the heads say 1-2* and gain say another 10 cfm in head efficiency and not have to use custom headers to do so, then rolling a set of the 21* heads 1-2* may make for some nice extra potential in a smaller runner head.

Discuss amongst yourselves.

bowtienut

iTrader: (1)

23 deg heads are typically angle milled to decrease chamber size beyond that achievable with flat milling, and the "rolling" of the head position is an UNDESIRABLE result of that. Any theoretical flow enhancement is negligible, and you just end up with more machining and assembly labor expense to get the block/heads/intake to mate properly.
Yeah, you could get a little more "roll" angle out of them if you emphasized the "roll" rather than minimizing chamber volume, but unless you go with a custom intake, or something other than an LT1 intake, I doubt you could take advantage of the new angle of the head ports.

kgkern01

iTrader: (10)

Well I'm not talking about a drastic change in the valve angle, I was realistically
thinking about only rolling 1-1.5* at the most. I plan on milling the 21* heads down to about 49cc's anyways for compression, so I'm going to have to mill the intake to match anyway, so if say another 1* or so roll would benefit while they are already getting milled, I say why not?

bowtienut

iTrader: (1)

confused here. I thought you were starting with stock 23 deg heads, and mentioned the TFS 21 deg head simply as a "target" that could be approached by angle milling the stock heads.
It sounds to me now that you're starting with 21 deg heads. Apologies for misreading you.

913MOTOR

iTrader: (1)

Sounds to me like your going to take some expensive castings and end up selling them for scrap aluminum. If you want to have the best heads, go ls1 and get 15*.

Ed Wright

iTrader: (1)

You will not get more than one degree. Angle milling .125" (that is one degree) is about as far as you can go and still have a place for your intake valve to seat, unles you have really tiny intake valves. Any air flow gains from the angle change (I have seen none) would likely be off set by killing the intake seat top angle when it is cut away when angle milling. The power gained from the added compression will more than off set any air flow loss from screwing up the valve job. No way your gonna roll one over two degrees. Doing that in no way compares to a casting designed around the new valve ange. The intake face has to be cut to restore the angle in relation to the head gasket surface, and the intake manifold bolt holes, and head bolt holes all have to be spot faced also.

The headers will be closer to the block at the bottom. Valve reliefs in the pistons need cut to the correct angle also. I have been angle cutting heads for nearly 40 years (it's nothing new) when class rules restricted me to 23 degree heads.

If you are going to buy heads with a new valve angle you may as well step up to 18 degree heads and intake and make some big power.

kgkern01

iTrader: (10)

Well I'm not going for max power on this build, as it is going to be used on a 53k mi stock shortblock. I am looking to get the most compression possible since I will be running E85 though, thus the reason for milling the heads down to about 49cc. TFS said that the heads can be milled down to about 48cc (from 54cc) at .050 flat mill before affecting the seats. So I wondered if angle milling it for 1* would yield any benefit? So basically I should just flat mill them down for compression only and not worry about angle milling 1* to get 20* and just keep the 21*, because you are saying that the benefit is minimal, correct?

Ed Wright

iTrader: (1)

If you are looking for max compression, angle milling will remove more volume, you just have to do the rest I mentioned to get everything back right.

Puck

iTrader: (17)

If you are not going for max power and the heads can be milled that much already there is no reason at all to angle mill the heads. You will add a lot of money and work to your project for little gain.

What pistons will you be running? 49cc is hella small chambers already. Even with E85 that is some crazy compression assuming a -5cc flat top and 30-40 quench.

kgkern01

iTrader: (10)

Well if the gains, if any, aren't worth the hassle or expense then I'm not going to angle mill. With 49cc, stock shortblock, .026 Felpro gasket, and between .020-.030 deck (whatever stock is) that should put me at 12-12.4 on compression. With E85 the compression should be no problem.

Puck

iTrader: (17)

Ahhh stock deck height and pistons. I was assuming a rebuild with some decking done and flat tops.

You'll be more then fine, I will be running that compression on 93 pump gas and many have gone higher .