Angle Milling vs Straight milling heads
Thread Starter
Racer
Joined: May 2001
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From: Tampa Bay Area
Angle Milling vs Straight milling heads
What are the pros/cons of angle milling the heads? I am looking at bumping my cr up from 9.8 to 10.8 and I was wondering if I should angle mill or straight mill.
Are there any concerns that are involved with angle milling? Other than matching the intake to the same angle that the heads are milled to.
TIA
Are there any concerns that are involved with angle milling? Other than matching the intake to the same angle that the heads are milled to.
TIA
Race Director
Joined: Jan 2003
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From: State of Confusion
just a few random thoughts.....
how much are you gonna whack off those heads to bump the CR a full point?
depending-upon what angle you'd be milling them at (in-relation to the OEM angle), I'd think the water-jackets might-not line-up properly.....
the bolt-holes in the head wouldn't be in-line with the holes in the block (exaggerated, the bolts would have a 'kink' in them at the head/block mating-surface).....
if your pistons have eye-lets cut for valve-reliefs, the valves wouldn't be in-line with them, either.....
and off-the-shelf headers may not fit the chassis / steering components as-well.
Just my $.02-worth.....
how much are you gonna whack off those heads to bump the CR a full point?
depending-upon what angle you'd be milling them at (in-relation to the OEM angle), I'd think the water-jackets might-not line-up properly.....
the bolt-holes in the head wouldn't be in-line with the holes in the block (exaggerated, the bolts would have a 'kink' in them at the head/block mating-surface).....
if your pistons have eye-lets cut for valve-reliefs, the valves wouldn't be in-line with them, either.....
and off-the-shelf headers may not fit the chassis / steering components as-well.
Just my $.02-worth.....
Race Director
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From: State of Confusion
Originally Posted by ram82fire
Had enough of this weather yet out there in west Pa ? 
Today is mid-40s and sunny, so I fired-up the '82 and let it idle for a while in the bright sunshine, but on-the-whole, this weather would gag a maggot.....
Melting Slicks
Joined: Dec 2000
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From: Wichita, KS
You will always have to have any new manifolds (intake and exhaust) trimmed to fit your angle milled heads.
The heads will be hard to sell if you decide to upgrade later.
You may need custom length pushrods to maintain the correct relationship between the rocker and valve.
The heads may need the pushrod holes opened up to clear the pushrods resulting in a need to machine the heads for guideplates.
10.8 to 1 is a lot of compression for stock steel heads.
Can you make enough change with a steel shim (.015 thickness) head gasket to be happy?
The heads will be hard to sell if you decide to upgrade later.
You may need custom length pushrods to maintain the correct relationship between the rocker and valve.
The heads may need the pushrod holes opened up to clear the pushrods resulting in a need to machine the heads for guideplates.
10.8 to 1 is a lot of compression for stock steel heads.
Can you make enough change with a steel shim (.015 thickness) head gasket to be happy?
Thread Starter
Racer
Joined: May 2001
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From: Tampa Bay Area
Originally Posted by 1979toy
You will always have to have any new manifolds (intake and exhaust) trimmed to fit your angle milled heads.
The heads will be hard to sell if you decide to upgrade later.
You may need custom length pushrods to maintain the correct relationship between the rocker and valve.
The heads may need the pushrod holes opened up to clear the pushrods resulting in a need to machine the heads for guideplates.
10.8 to 1 is a lot of compression for stock steel heads.
Can you make enough change with a steel shim (.015 thickness) head gasket to be happy?
The heads will be hard to sell if you decide to upgrade later.
You may need custom length pushrods to maintain the correct relationship between the rocker and valve.
The heads may need the pushrod holes opened up to clear the pushrods resulting in a need to machine the heads for guideplates.
10.8 to 1 is a lot of compression for stock steel heads.
Can you make enough change with a steel shim (.015 thickness) head gasket to be happy?
The 9.8 is the resultant of 9.3:1 pistons w/ 64 cc chambers and .025" head gaskets. If I went with a .015" shim gasket what would my compression be?
So how many thousandths would I have to shave to get a whole point or compression (not angle milled)? Could factory heads take that? Could I mill some and use a shim to get close to 10.5:1?
Thanks all.
Race Director
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From: State of Confusion
Originally Posted by mean8t
The 9.8 is the resultant of 9.3:1 pistons w/ 64 cc chambers and .025" head gaskets. If I went with a .015" shim gasket what would my compression be?
I'd think your resultant CR would be higher than 'just' 9.8:1:
in-fact, I'm guessing it'd be well-over 10:1 already, and damn-close to 10.5 as-is.
Maybe this site can shed some light on this subject:
http://www.smokemup.com/auto_math/compression_ratio.php
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Drifting
Joined: Oct 2000
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From: Shawano WI
The only "con" to angle milling a head is that every demension and clearence has to be checked and corrected to be sure that things are correct. This can drive the cost up considerably from flat milling.
From your sig. it looks like you are reffering to vortec heads. 060 casting Vortec heads can generally be flat cut .040 or angle cut .075 but must be sonic checked to be sure of deck thickness. A .040 flat cut will reduce chamber volume be approx. 6cc's. A .075 angle cut will reduce chamber volume by approx. 9.5 cc's.
To accuratley tell you how much has to be cut to raise commpression by 1 point you have to be more specific as to exactly what you have now. Bore, stroke, chamber volume, head gasket, deck height, piston cc (or what you beleive you have for pistons, 2 relief, 4 releif, dish,dome?) Then I can tell you what cc chamber you will need to get to the desired CR.
Pete
From your sig. it looks like you are reffering to vortec heads. 060 casting Vortec heads can generally be flat cut .040 or angle cut .075 but must be sonic checked to be sure of deck thickness. A .040 flat cut will reduce chamber volume be approx. 6cc's. A .075 angle cut will reduce chamber volume by approx. 9.5 cc's.
To accuratley tell you how much has to be cut to raise commpression by 1 point you have to be more specific as to exactly what you have now. Bore, stroke, chamber volume, head gasket, deck height, piston cc (or what you beleive you have for pistons, 2 relief, 4 releif, dish,dome?) Then I can tell you what cc chamber you will need to get to the desired CR.
Pete
Thread Starter
Racer
Joined: May 2001
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From: Tampa Bay Area
Originally Posted by Pete79L82
The only "con" to angle milling a head is that every demension and clearence has to be checked and corrected to be sure that things are correct. This can drive the cost up considerably from flat milling.
From your sig. it looks like you are reffering to vortec heads. 060 casting Vortec heads can generally be flat cut .040 or angle cut .075 but must be sonic checked to be sure of deck thickness. A .040 flat cut will reduce chamber volume be approx. 6cc's. A .075 angle cut will reduce chamber volume by approx. 9.5 cc's.
To accuratley tell you how much has to be cut to raise commpression by 1 point you have to be more specific as to exactly what you have now. Bore, stroke, chamber volume, head gasket, deck height, piston cc (or what you beleive you have for pistons, 2 relief, 4 releif, dish,dome?) Then I can tell you what cc chamber you will need to get to the desired CR.
Pete
From your sig. it looks like you are reffering to vortec heads. 060 casting Vortec heads can generally be flat cut .040 or angle cut .075 but must be sonic checked to be sure of deck thickness. A .040 flat cut will reduce chamber volume be approx. 6cc's. A .075 angle cut will reduce chamber volume by approx. 9.5 cc's.
To accuratley tell you how much has to be cut to raise commpression by 1 point you have to be more specific as to exactly what you have now. Bore, stroke, chamber volume, head gasket, deck height, piston cc (or what you beleive you have for pistons, 2 relief, 4 releif, dish,dome?) Then I can tell you what cc chamber you will need to get to the desired CR.
Pete
Glensgages: The pistons I am using are .030 over flat-top four-valve relief hypereutectic federal mogul pistons that with 64cc chambers make 9.3:1 cr. Here is the link.
http://www.jegs.com/cgi-bin/ncommerc...59&prmenbr=361
It is a standard bore and stroke 355. Chamber volume is 64 cc. Head gasket is .025" compressed thickness. I am not sure of the deck height.
Drifting
Joined: Oct 2000
Posts: 1,825
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From: Shawano WI
Here is the way I beleive the CR on those pistons is caclulated
Bore - 4.030
Stroke - 3.48
Compression Height - .025
Piston Volume 8.755
Head gasket volume - 9.2 (.041 thickness)
Chamber Volume 64cc
This will give you a 9.35 CR
You are using a .025 head gasket (5.6cc's) which will give you a 9.707 CR.
If you go to a .015 head gasket (this will still give you a .040 quelch) you will have 9.948 CR
If you flat mill .025 off of the heads you should end up with a chamber size of 60cc's. Using a 60cc chamber and a .015 gasket should give you a 10.41 CR which is about the upper limit you would want to run with those heads.
The only other thing you would need to do is check port alignment on the intake manifold and possily a change in pushrod length to correct geometry.
Pete
Bore - 4.030
Stroke - 3.48
Compression Height - .025
Piston Volume 8.755
Head gasket volume - 9.2 (.041 thickness)
Chamber Volume 64cc
This will give you a 9.35 CR
You are using a .025 head gasket (5.6cc's) which will give you a 9.707 CR.
If you go to a .015 head gasket (this will still give you a .040 quelch) you will have 9.948 CR
If you flat mill .025 off of the heads you should end up with a chamber size of 60cc's. Using a 60cc chamber and a .015 gasket should give you a 10.41 CR which is about the upper limit you would want to run with those heads.
The only other thing you would need to do is check port alignment on the intake manifold and possily a change in pushrod length to correct geometry.
Pete
Thread Starter
Racer
Joined: May 2001
Posts: 472
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From: Tampa Bay Area
As far as pushrods are concerned if I mill the heads then the pushrods might be too long and I would have get a pushrod length checker to determine if I need to get new pushrods. Am I on track here?
Thanks,
Josh
Thanks,
Josh
Drifting
Joined: Oct 2000
Posts: 1,825
Likes: 56
From: Shawano WI
Josh;
You are on track. You made need a slightly shorter pushrod after milling the heads. Most small blocks have too short of a pushrod to begin with, so after milling everything you may end up at the correct length. It is something you should be sure to check.
Pete
You are on track. You made need a slightly shorter pushrod after milling the heads. Most small blocks have too short of a pushrod to begin with, so after milling everything you may end up at the correct length. It is something you should be sure to check.
Pete
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I use angle milled heads a lot. It's the best way to get a lot of chamber size reduction with the least amount of metal removed. It also "usually" picks up airflow slightly by moving valve angle.
Most issues are no big deal if you have a good machinist. There is more to it than just whacking the heads...that's the easy part. Any machinist worth using will spot face all the head bolt holes to make sure the faces are square with the deck. There is anough room in the head bolt hole for the bolt to go at a slight angle..just correct the flat are where bolt head goes.
Also, any GOOD machinist would never recommend milling the intake manifold. What needs to be done to do it right is to mill the intake face of the heads. That way no matter what intake you want to use, you can bolt any unmodified one to it you want and not worry about it. Otherwise you have an albatross with the heads and intake permanently "married" together.
The exhaust will likely be a non-issue. You will be lowering the ports slightly, but not enough to make much difference.
All that said, flat milling is a simpler way to go about things, but usally does not produce the same results.
You really need to find out deck height for sure. A .025 miscalculation can mess you up here.
JIM
Most issues are no big deal if you have a good machinist. There is more to it than just whacking the heads...that's the easy part. Any machinist worth using will spot face all the head bolt holes to make sure the faces are square with the deck. There is anough room in the head bolt hole for the bolt to go at a slight angle..just correct the flat are where bolt head goes.
Also, any GOOD machinist would never recommend milling the intake manifold. What needs to be done to do it right is to mill the intake face of the heads. That way no matter what intake you want to use, you can bolt any unmodified one to it you want and not worry about it. Otherwise you have an albatross with the heads and intake permanently "married" together.
The exhaust will likely be a non-issue. You will be lowering the ports slightly, but not enough to make much difference.
All that said, flat milling is a simpler way to go about things, but usally does not produce the same results.
You really need to find out deck height for sure. A .025 miscalculation can mess you up here.
JIM
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Most of the time, I'm starting from scratch figuring out geometry, so not much to comapre to.
But usually on deals where you are cutting heads on an existing combo where geometry is already correct, it's not an issue. As compared to flat milling, you are removing the majority of the metal from the exhaust side of head. The intake/pushrod side remains about the same.
It takes at least a .050 change in pushrod length to move things around much usually. So, most likely it won't be an issue unless you go crazy on milling.
But as with any cam or head change, you need to check to make sure.
Most large race shops stock pushrods in .050 increments, so they are easy to find. I use Reher Morrison. But I'm sure Jegs and Summit can get them too is needed. But again, likely you'll be OK.
JIM
But usually on deals where you are cutting heads on an existing combo where geometry is already correct, it's not an issue. As compared to flat milling, you are removing the majority of the metal from the exhaust side of head. The intake/pushrod side remains about the same.
It takes at least a .050 change in pushrod length to move things around much usually. So, most likely it won't be an issue unless you go crazy on milling.
But as with any cam or head change, you need to check to make sure.
Most large race shops stock pushrods in .050 increments, so they are easy to find. I use Reher Morrison. But I'm sure Jegs and Summit can get them too is needed. But again, likely you'll be OK.
JIM
