Angle milling benefit

General engine tech -- Drag Racing to Circle Track

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athomp
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Angle milling benefit

Post by athomp » Sun Mar 11, 2018 1:53 pm

I've been reading a little about angle milling heads and I have a question about the benefits of doing it. On a stock iron 23 degree SBC head, notwithstanding the benefit of the CR increase, what would be the potential HP gain (on a totally stock engine) from milling to 22 degrees? I'm referring to the benefit of the valve angle change only vs getting the same CR gain from flat milling. And let's assume I could get this done for free - is it worth doing? This is for a circle track car.

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Re: Angle milling benefit

Post by The Badger » Sun Mar 11, 2018 2:52 pm

I have no experience with angle milling and then dynoing but any gains would probably result from unshrouding the valve from the cylinder wall. How much? I have no idea.

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Re: Angle milling benefit

Post by JoePorting » Sun Mar 11, 2018 2:58 pm

I think it's a waste of time and money, and you'll be ruining a set of heads. Anytime you mill a head and cut into the 35 degree top intake angle you will lose intake flow. Typical lose is around 10 CFM across the lift range.
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Re: Angle milling benefit

Post by Keith Morganstein » Sun Mar 11, 2018 5:45 pm

JoePorting wrote:
Sun Mar 11, 2018 2:58 pm
I think it's a waste of time and money, and you'll be ruining a set of heads. Anytime you mill a head and cut into the 35 degree top intake angle you will lose intake flow. Typical lose is around 10 CFM across the lift range.
Normal Angle milling doesn’t get into the intake valve seat as soon. Normal angle milling is taking more off the exhaust side. Common on a SBC is a .000 to .125” angle mill.

(Unless you are reverse angle milling? That would be a bad idea)
Automotive Machining, cylinder head rebuilding, engine building. Old school shop, semi-retired moonlighter. Can't seem to quit #-o

groberts101
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Re: Angle milling benefit

Post by groberts101 » Sun Mar 11, 2018 6:03 pm

I.. think.. all Joe was pointing at is you're eventually lead to robbing poor peter to pay rich paul.

Short side of the oem head is already horrid and greater compression doesn't usually help matters in that regard. Basically, pressure recovery decays in an already poorly recovered area of the curtain. And then to really fix it we sink the valve which opens the chamber right back up thereby negating some of that compression gain. Only so much material in the short turn to help correct a flat mill.. much less an angle milled head.

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Re: Angle milling benefit

Post by GARY C » Sun Mar 11, 2018 10:58 pm

Most 23* rules allow for + or - 2* for casting flaws so many will roll the head to 21*, you are best off to consider this from the beginning for above mentioned reasons, top cut as well as chamber work needs to be done accordingly.

If the head and chamber have already been ported for a stnd 23* angle chances are you will loose power if you only angle mill.

If your not bound be class rules and don't have heads already I would look into a good used 18* head and intake package.

Power claims are around 15 horse gain if done right or loss if done wrong.
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Re: Angle milling benefit

Post by pdq67 » Mon Mar 12, 2018 12:11 am

Doesn't Holley still sell 20 degree SBC heads?

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Re: Angle milling benefit

Post by rustbucket79 » Mon Mar 12, 2018 1:45 am

In a perfect world starting from scratch I'll take the added compression every time, but your question is vague and lacking in detail to be able to answer. Rules? Smog engine with miles or a purpose built oval engine with races or seasons of races?

Some things to keep in mind. Some castings have thickness issues or just don't have the iron to reliably seal a head gasket by the spark plug once milled. Pushrod length might be wrong afterwards. Intake face angle of head will need to be corrected. Valve to piston may be insufficient. Octane requirements will go up.

A mid pack car won't turn into a front runner just by angle milling the heads. :wink:

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Re: Angle milling benefit

Post by ZEOHSIX » Mon Mar 12, 2018 2:48 am

Angle milling more than 1degree angle usually results in cylinder head fasteners binding in through holes and requires re spot facing the bolt pads in the heads to get them back to parallel......I think ARP still sells a stud set with 3/8" long reduced fastener sized studs to allow for through hole clearance in severely angle milled SBC applications....if you need to drastically reduce a combustion chamber angle milling is the best method to subtract volume from a SBC chamber....but then you live with the side effects and deal with them.

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Re: Angle milling benefit

Post by Schurkey » Mon Mar 12, 2018 3:37 am

pdq67 wrote:
Mon Mar 12, 2018 12:11 am
Doesn't Holley still sell 20 degree SBC heads?
Haven't seen them advertised for years. I can't find them on the Holley web site, or on the Summit web site.

I think they're extinct.

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Re: Angle milling benefit

Post by mag2555 » Mon Mar 12, 2018 6:26 am

What iron heads and with what size Intake valves and flowing how much are all details needed on this question!

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Re: Angle milling benefit

Post by athomp » Mon Mar 12, 2018 6:53 am

Rules state 441, 882 or 993 heads. May be planed maximum .030. No other work allowed. 1.94/ 1.5 valves. Stock .390/.410 cam 8.5:1 CR. 500CFM 2 bbl carb. Stock iron intake.
I'm asking if the 1 degree change in valve angle in and of itself has a benefit. From what I'm hearing it may very well be detrimental and negate some of the benefit of the CR increase. Unless Someone is looking for a large decrease in chamber size it's not worth it. Is that correct?

Thanks


mag2555 wrote:
Mon Mar 12, 2018 6:26 am
What iron heads and with what size Intake valves and flowing how much are all details needed on this question!

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Re: Angle milling benefit

Post by Warp Speed » Mon Mar 12, 2018 7:16 am

JoePorting wrote:
Sun Mar 11, 2018 2:58 pm
I think it's a waste of time and money, and you'll be ruining a set of heads. Anytime you mill a head and cut into the 35 degree top intake angle you will lose intake flow. Typical lose is around 10 CFM across the lift range.
"Ruining"?
That's kinda funny, as every performance cylinder head I have worked on/with for the last 25+ years has been cut into the valve job. LOL

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Re: Angle milling benefit

Post by mag2555 » Mon Mar 12, 2018 7:41 am

A flow bench worked out valve job with back cut valves will pick you up 5 to 8 hp , but the deal is to use new valves with tall margin's so you afford to have the valve work sink the valves a tad yet not drop compression.
Replacement dish faced intake valves need to be avoided!

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Re: Angle milling benefit

Post by Krooser » Mon Mar 12, 2018 4:04 pm

Around here our guy's routinely angle mill oem heads to get the compression up. Most dirt class's mandate an open chamber sbc head.

I think my son's 993 heads have been cut .080 or so... His 355 is around 12-1... the car pulls like a freight train off the corners. The Jones cam helps, too.

Compression is horsepower... I'll trade 10 cfm for 15 HP anyday.
Last place in the B-main is better than anyplace in the grandstands...

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