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Late 964 heads v. 993 heads for 3.8 rsr build

Hi All -

Assuming that one can machine late 964 heads to have the same port sizes, valves, valve stems as a 993 RS head, are there any other significant advantage for using a 993 spec head for a 3.8 rsr motor instead of using s late 964 one?

For instance, are the 993 heads stronger (e.g. better alloys used) or any other differences like combustion volume, shape of ports, etc.?

Any thoughts on this are appreciated. Thanks.
Old 07-28-2016, 03:05 AM
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Originally Posted by Rusty911 View Post
Hi All -

Assuming that one can machine late 964 heads to have the same port sizes, valves, valve stems as a 993 RS head, are there any other significant advantage for using a 993 spec head for a 3.8 rsr motor instead of using s late 964 one?

For instance, are the 993 heads stronger (e.g. better alloys used) or any other differences like combustion volume, shape of ports, etc.?

Any thoughts on this are appreciated. Thanks.
993 heads are made from RR530, same alloy as the older turbo heads

the rocker pedestals are different, there seems to be fewer issues w/ the 993 versions

I've heard of more issues w/ the ceramic exhaust pot liners on 964 this is more anecdotal than verified as a trend

993 heads have dual pattern header bolts

for 3.8 it's still recommended to weld the fins on the 993 heads

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Old 07-28-2016, 04:37 AM
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I have used them with Ti valves-can't recall the sizes-RSR cams-only minor port work
and cut for interlocking rings. Made around 350 RWHP with 50mm ITBs
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Old 07-28-2016, 04:38 AM
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Thank you Bill and Mark for your responses. I have a core 964 long block and now thinking that I should use 993 heads. One last question is whether I can still use the 964 cam housings with the rockers and shafts with the 993 heads or will I run into issues?

Last edited by Rusty911; 07-28-2016 at 06:11 AM.. Reason: Edit
Old 07-28-2016, 06:08 AM
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One of the most active racing engine builders in our area suggests that, depending on specifics, late 993 heads offer advantages, everything else being equal.

One of my friends has just gone through the process of examining this question and his conclusion was to have his 964 heads properly machined. His application is not 3.8 RSR, but nonetheless he is trying to make every BHP possible based on race class constraints and with respect to bang for the buck.

The last time I checked, none of the active race engine builders or machinists that I know of here in Norcal recommend or implement welding of the fins as Bill suggests is common back East. The builders and machinists to which I refer here have been at it for decades and have vast experience, which includes world championship winning factory 935 team from the 70's and 80's.

During the decade+ I was running a high output 3.8 liter racing engine, I had two early 993 heads develop cracks requiring replacement. I asked around about the experience of others and reached no conclusions about ways to prevent this.

The canvassing process not only included the local experts mentioned above, but also inquiries via a thread in these forums and telephone conversations with several highly regarded engine builders and machinists with pro racing experience both locally and in other parts of the country.

Both times I experienced cracks were during racing weekends when ambient temperatures exceeded 100 degrees. And yes, my oil and engine cooling arrangements were/are fully adequate for these conditions and there were no AFR issues.

In my last rebuild (about a year ago) my builder considered my early 993 heads as timed out (thermally) so they were replaced with 993 RSR heads.

One local machinist that I know gets a large share of the air cooled racing work here locally is German Precision. He has been doing this kind of work for decades and does my work. He might be a good resource for you.
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Old 07-29-2016, 08:34 AM
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What exactly is welded fin wise?
Old 07-29-2016, 09:02 AM
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Quote:
Originally Posted by Mahler9th View Post
One of the most active racing engine builders in our area suggests that, depending on specifics, late 993 heads offer advantages, everything else being equal.

One of my friends has just gone through the process of examining this question and his conclusion was to have his 964 heads properly machined. His application is not 3.8 RSR, but nonetheless he is trying to make every BHP possible based on race class constraints and with respect to bang for the buck.

The last time I checked, none of the active race engine builders or machinists that I know of here in Norcal recommend or implement welding of the fins as Bill suggests is common back East. The builders and machinists to which I refer here have been at it for decades and have vast experience, which includes world championship winning factory 935 team from the 70's and 80's.

During the decade+ I was running a high output 3.8 liter racing engine, I had two early 993 heads develop cracks requiring replacement. I asked around about the experience of others and reached no conclusions about ways to prevent this.

The canvassing process not only included the local experts mentioned above, but also inquiries via a thread in these forums and telephone conversations with several highly regarded engine builders and machinists with pro racing experience both locally and in other parts of the country.

Both times I experienced cracks were during racing weekends when ambient temperatures exceeded 100 degrees. And yes, my oil and engine cooling arrangements were/are fully adequate for these conditions and there were no AFR issues.

In my last rebuild (about a year ago) my builder considered my early 993 heads as timed out (thermally) so they were replaced with 993 RSR heads.

One local machinist that I know gets a large share of the air cooled racing work here locally is German Precision. He has been doing this kind of work for decades and does my work. He might be a good resource for you.
Where were your cracks in your heads?

I have a 3.6 that I run in Texas that just had one head develop a crack in the exhaust area.

I just replaced that head. I'm also working on a 3.8 build.

Both heads setups are 964's in my case.

Unfortunately 90+ degrees is a common track day here in Texas.

I have plenty of oil cooling -- is there anything else I should be considering?

thanks,

Mike
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Old 07-29-2016, 11:38 AM
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The majority of the canvassing I did resulted in a range of responses from "I don't think welding is the definitive answer," to "I'd never do that." As a result I did not look into further details of what Bill has suggested is a standard practice, at least in his area.

If I recall correctly, one of the respondents was Ted at German Precision. Ted does all, or nearly all of the head work for my friend and engine builder, and they both worked together with Jerry Woods and Bruce Anderson (and others) at Garretson/Barbour back in the day. My builder has a fair amount of relative experience with high output 3.6 to 4 liter racing engines.

Further, I concluded that there was just no consensus on anything definitive to do on this potential issue.

Here is a link to my thread in these forums:

Curious about Experiences with Cracked 993 Cylinder Heads used in Racing Engines

Please note that its an old thread. Since then, the local active herd has pretty much moved away from these kinds of motors in favor of our "rocking chair class"' limited 3.6 (GTL) motors, designed for greater longevity and lower operating cost. So our "arms race" appears to be over, at least as far GT engines (lol).

My friend/builder used a 3.0L type of fan/alt for my engine, which has some advantages, including weight, compared to stock 964 or 993 parts, which is an adaptation that is pretty easy to accomplish. Ad many of us have or are fabbing up ducting underneath our aftermarket fiberglass 3.8-style tailbases to feed our fans with as much cool air as possible.

One of our racers has been running a stock 993 fan/alt package, and he is now taking steps toward better cooling, via, at least in part, swapping out his 993 fan for a 993 TT fan, which is a bolt-on change. All in an effort toward lowering the range of cylinder head temps experienced under a variety of running and ambient conditions.

That same racer is using the same engine builder that I use and is having German Precision work up a set of 964 heads right now.
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Old 07-29-2016, 12:56 PM
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Ok, I just spoke with my buddy here locally (referred to as "one of our racers" above). Just a coincidence.

As a result, if you are local and are considering having machining done in our area I conclude that you might benefit from giving Ted a call at German Precision, and also speaking with the folks at JWE. If you do the latter, you will most likely be speaking with my good friend Rich. He is a great guy.

Rich and Jerry Woods may or may not be using German Precision for some of their head work. They may have a different or several favored machinists. But the key for you, depending on the specifics of your application and more detailed questions/concerns, is that they may have some perspective and/or services to offer, from which you may benefit. This may include fin welding as an option or recommendation.

My buddy was looking for late 993 heads to replace his 964 heads which are okay but have stock 964 valves. He wanted to upgrade to big valves, and late 993 heads have bigger stock valves than 964 heads.

His search yielded just a few hits. The scarcity of the available parts resulted in higher-than-justifiable (for him) prices, so he opted to have his heads machined for larger valves, and as I have stated, GP is doing the work. Welding of fins is not part of that work.

If for some reason you decide you have to have 993 heads, you may be able to find some at the Porsche dismantler in Eastern Canada. Another potential resource for parts, with whom I have done some successful business, is Mr. William Knight. You can probably find his contact info in the PP 911 classifieds, or you can ping me via PM..
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Last edited by Mahler9th; 07-29-2016 at 03:55 PM..
Old 07-29-2016, 03:53 PM
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There should be a glut of 964 heads available given that Singer is using aftermarket heads on a lot of their high HP builds. Might be worth having 8 or 10 machined at the same time so in the avent you develop a crack, you have a fresh head that cc's out the same on the shelf ready to go.

If budget allows, the aftermarket Xtreme heads are supposed to be the business on high HP builds.

Last edited by Evan Fullerton; 07-30-2016 at 06:02 AM..
Old 07-30-2016, 05:58 AM
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Wouldn't necessarily help the heads -- but has anyone played with
electrical PC style cooling fans drawing air from the cylinders from underneath?

BTW, my crack was from the exhaust port up into and behind the exhaust port liner.

Mike
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Old 07-30-2016, 02:51 PM
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Thanks guys for the suggestions.

I know Ted and will give him a call at GP to get his thoughts. Perhaps, I'll need to make a decision on an engine builder first as there are some conflicting approaches on what the ideal port/valve size should be, etc.

To give an example, I was just reading on Rennlist that Colin Belton from Ninemeister and Geoffrey Ring actually think the 964 heads flow better and produce more power and torque than 993 heads due to their smaller more efficient ports (with upgraded 993 valves and guides) claiming higher velocity and flow. And Ninemeister's billet heads (which are beyond my budget) also have 41mm intake ports with a special port design and shape that is difficult to replicate with stock 964 and 993 heads.

However, it seems that the majority of builders seem to favor the 993 heads with the larger RS sized valves with additional port work. I like 993 heads in that they have a use a better alloy and have a larger sealing surface as compared to 964 heads. However, since I already have 2 good sets of late 964 heads and no 993 ones, I like the suggestion of talking to Ted and JWE and possibly others to see if the 964 heads will perform adequately for my build before making a final decision on which way to go.
Old 07-30-2016, 04:34 PM
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