1985-e1986 Head Specifications
Thread Starter
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
1985-e1986 Head Specifications
Can someone point me to a thread or reply about the
following questions regarding the 1985-e1986 iron L98
head
- Casting number
- Intake port volume
- Chamber volume
- In/ex valve sizes
Unmodified flow numbers would be a bonus.
Thanks,
Ken R.
.
following questions regarding the 1985-e1986 iron L98
head
- Casting number
- Intake port volume
- Chamber volume
- In/ex valve sizes
Unmodified flow numbers would be a bonus.
Thanks,
Ken R.
.
Thread Starter
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Also came across the following comments
.
Originally Posted by LD85 12-02-2002
The stock 85 heads were 462624's and can be ported to flow well but
they are supposed to be crack prone. This is why the people that used
iron heads before aluminum was affordable went to the 441's, they
were able to be ported well and they were sturdy.
they are supposed to be crack prone. This is why the people that used
iron heads before aluminum was affordable went to the 441's, they
were able to be ported well and they were sturdy.
Thread Starter
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
While we're on the subject, how about a quick check
on what happens to compression if the heads get changed?
An '85 is reported to have 9.0:1 compression.
All I know is that
- the heads have 76cc chambers,
- the bore x stroke is 4.00" x 3.48"
- the gasket is about 0.040" compressed
I'll guess there is about 0.020 deck clearance
Using these numbers and then changing the chamber
size from 76cc to
- 68cc = 9.88:1 compression
- 64cc = 10.34:1
- 62cc = 10.59:1
- 60cc = 10.86:1
- 58cc = 11.13:1
- 56cc = 11.43:1
No guarantees. I just used the back of the napkin ...
.
on what happens to compression if the heads get changed?
An '85 is reported to have 9.0:1 compression.
All I know is that
- the heads have 76cc chambers,
- the bore x stroke is 4.00" x 3.48"
- the gasket is about 0.040" compressed
I'll guess there is about 0.020 deck clearance
Using these numbers and then changing the chamber
size from 76cc to
- 68cc = 9.88:1 compression
- 64cc = 10.34:1
- 62cc = 10.59:1
- 60cc = 10.86:1
- 58cc = 11.13:1
- 56cc = 11.43:1
No guarantees. I just used the back of the napkin ...
.
Thread Starter
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Now, suppose an '85 owner happened to have a set of
'128' aluminum heads laying around. How good are they
and could these be a bolt-on replacement for the '624'?
Well, 128's have 58cc chambers. So if the compression
calculation above is correct - without other changes, the
compression will jump to 11.13:1. Highish for an A4 using
pump gas on the street. (If I HAD to use them, a long
duration cam might help me slide by by lowering the dynamic
compression.)
Here is a nice evaluation of the 128 head. Notice his
remarks about maximum valve lift of 0.480" because of valve
retainer-to-guide clearance.
'128' aluminum heads laying around. How good are they
and could these be a bolt-on replacement for the '624'?
Well, 128's have 58cc chambers. So if the compression
calculation above is correct - without other changes, the
compression will jump to 11.13:1. Highish for an A4 using
pump gas on the street. (If I HAD to use them, a long
duration cam might help me slide by by lowering the dynamic
compression.)
Here is a nice evaluation of the 128 head. Notice his
remarks about maximum valve lift of 0.480" because of valve
retainer-to-guide clearance.
Originally Posted by Davemc1963-87conv 10-20-1985
...[D-113 and 128's] have substantially different characteristics, especially
on the exhaust side. The inlet ports however I believe flow very
similarly. I know they also 'look' similar. The exhaust ports on
the other hand are substantially different. The 113 heads exhaust port
has a much larger cross sectional area the port is raised and the outlet
is raised slightly compared to the 128's. The CSA of the short side
radius area in the exhaust port of the 128 is rediculously small in stock
form. The port walls however are thick and can be ported to increase
the CSA and flow substantially increased to match or better a 'stock'
113.
The 128 exhaust can be compared to a traditional SBC exhaust port
and responds in the same manner to porting. Maybe the small CSA was
an attempt to increase exhaust port velocity, who knows!
I believe the casting quality of the 113's is better and the ports are
more standardised. By this I mean some 128's have different inlet port
dimensions than others. Not much, but I found subtle differences on
the 128's I have compared to the repeatability I have noticed on 113's
I have seen. However if and when ported, I don't believe the above
would hinder performance much if at all, it would just increse the time
taken to 'match' both heads in relation to each other with regard to
contour, volume and CSA.
Another anomoly the 128's have is the exhaust spring seat is lower
than the intake by approximately 0.128". This is due to the 128's being
fitted with an exhaust valve rotator. Rather than use a longer exhaust
valve, GM's fix was to lower the spring seat the same amount as the
thickness of a rotator. This sometimes causes problems when changing
valve springs/retainers, as you have to shim the spring up that amount.
However, the easiest solution I have found for this is to use
aftermarket valves (pro-flows to increase flow) and 0.050" reduced
height valve keepers. Obviously this will depend on which springs you
fit and seat pressure you want. I am led to believe GM had to move
away from this silly set up in order to raise the the exhaust port as
found in the 113's. They also did away with the exhaust rotator too.
The combustion chambers of the two heads is very similar. I couldn't
tell the difference visually, although I have never CC'd 113's, the 128's
I have measured dead nuts on 58cc.
With regard to retainer to guide clearance, I can only comment on my
current 128's, because I have not measured 113's, but in stock form
there is only enough clearance to run a cam with about 0.480" lift and
that is marginal if you are running proper guide seals and not just
o-rings.
on the exhaust side. The inlet ports however I believe flow very
similarly. I know they also 'look' similar. The exhaust ports on
the other hand are substantially different. The 113 heads exhaust port
has a much larger cross sectional area the port is raised and the outlet
is raised slightly compared to the 128's. The CSA of the short side
radius area in the exhaust port of the 128 is rediculously small in stock
form. The port walls however are thick and can be ported to increase
the CSA and flow substantially increased to match or better a 'stock'
113.
The 128 exhaust can be compared to a traditional SBC exhaust port
and responds in the same manner to porting. Maybe the small CSA was
an attempt to increase exhaust port velocity, who knows!
I believe the casting quality of the 113's is better and the ports are
more standardised. By this I mean some 128's have different inlet port
dimensions than others. Not much, but I found subtle differences on
the 128's I have compared to the repeatability I have noticed on 113's
I have seen. However if and when ported, I don't believe the above
would hinder performance much if at all, it would just increse the time
taken to 'match' both heads in relation to each other with regard to
contour, volume and CSA.
Another anomoly the 128's have is the exhaust spring seat is lower
than the intake by approximately 0.128". This is due to the 128's being
fitted with an exhaust valve rotator. Rather than use a longer exhaust
valve, GM's fix was to lower the spring seat the same amount as the
thickness of a rotator. This sometimes causes problems when changing
valve springs/retainers, as you have to shim the spring up that amount.
However, the easiest solution I have found for this is to use
aftermarket valves (pro-flows to increase flow) and 0.050" reduced
height valve keepers. Obviously this will depend on which springs you
fit and seat pressure you want. I am led to believe GM had to move
away from this silly set up in order to raise the the exhaust port as
found in the 113's. They also did away with the exhaust rotator too.
The combustion chambers of the two heads is very similar. I couldn't
tell the difference visually, although I have never CC'd 113's, the 128's
I have measured dead nuts on 58cc.
With regard to retainer to guide clearance, I can only comment on my
current 128's, because I have not measured 113's, but in stock form
there is only enough clearance to run a cam with about 0.480" lift and
that is marginal if you are running proper guide seals and not just
o-rings.
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So if one takes a 86e, replaces the heads with 128's, the compression will soar to 11:1? Might be a problem if the valves start touching the piston tops eh?
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Advanced
Joined: Jan 2004
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From: Anchorage Alaska
624 head
Originally Posted by Slalom4me
While we're on the subject, how about a quick check
I'll guess there is about 0.020 deck clearance
.
I'll guess there is about 0.020 deck clearance
.
Burning Brakes
Joined: Sep 2006
Posts: 1,202
Likes: 3
From: MD
That bit about the 624 heads being prone to cracking is old, I believe. The 624 castings have been used since the 70s on different GM production cars. I believe that the cracking problem was in the earlier 624s, but was fixed by modern production techniques. Has anyone actually heard of a vette cracking a 624 head?
Burning Brakes
Joined: Jun 2006
Posts: 1,096
Likes: 28
From: Baltimore MD
Originally Posted by coupeguy2001
I put 113 heads on a stock 86, pinged all the time. 58cc heads. but after 3000 rpm, lots of torque.
Thread Starter
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Originally Posted by rel3rd
was that happening with stock timing, and/or with a chip, or what??
Originally Posted by JrRifleCoach
So if one takes a 86e, replaces the heads with 128's, the compression
will soar to 11:1?
will soar to 11:1?
Originally Posted by JrRifleCoach
Might be a problem if the valves start touching the piston tops, eh?
is that the valve heads will be positioned roughly similarly and that the
difference in cc's derives from the chamber shape. A rough
measurement from the gasket surface to the valve face for each style
of head would indicate whether piston-to-valve clearance of the 128
casting is in the ball park or if further checking is necessary.
My vote is that the OEM retainer-to-guide clearance is going to
present the restriction to lift.
.
Burning Brakes
Joined: Jun 2006
Posts: 1,096
Likes: 28
From: Baltimore MD
Originally Posted by rel3rd
was that happening with stock timing, and/or with a chip, or what??
Originally Posted by Slalom4me
Perhaps it was 11:1 (+/-) compression.
I'm in the market for some aftermarket heads, and want to go as high on the compression as possible and I don't plan on a cam change, but obviously, I don't want detonation as a regular by-product of doing so.
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From: Athens AL
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Originally Posted by rel3rd
I understand where the compression would be. The reason I ask is because I thought LT1's have 11:1 compression from the factory (maybe I am wrong?). I am just curious as to why they can get away with it, and an L98 can't. Or maybe the engine's cooling system configuration is better for the higher compression ratio? I don't know? That's why I asked.
It is the cooling configuration, yes. Coolant hits the heads in the opposite sense to a Gen I SBC.
Burning Brakes
Joined: Jun 2006
Posts: 1,096
Likes: 28
From: Baltimore MD
Originally Posted by vader86
10.5:1, up from 10.25:1 for the last L98s
It is the cooling configuration, yes. Coolant hits the heads in the opposite sense to a Gen I SBC.
It is the cooling configuration, yes. Coolant hits the heads in the opposite sense to a Gen I SBC.
That's my luck and what I figured.
I guess it's back to plan A, which is/was 64cc heads and a little over 10:1 to be safe and headache (and death rattle) free.
