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What R we doing with exh ports?

After a very lengthy discussion with a local Porsche builder and head porter he has inserted some hesitation of the 3.2 heads. He is nearly insistent on starting with 3.3 heads for torque. He strongly feels that the 41mm intake is way overkill for a turbo and that it only highlights the weakness of the exhaust flow. His thoughts are that it will only let more in with the boost to be bottle necked on exit resulting in hotter heads yet. This in combination with the reduced port velocity increases the need to turn up boost magnifying the above problem to gain back the lost torque.

Question: Real world, how much torque is killed in driving with the 3.2 heads at 7:1 compression? Will 3.2 heads really create a pig off boost? I understand port velocity, but if the 3.2 heads are well received as some of the best, why would it be SO BAD for a 3.3?

How/who can make this up on the exhaust port? I saw his numbers and that some of the stock flow balances were awful down in the lower 60% range. This isn't great NA, but is sad for boost. What solutions are out there? I really don't want to trade down to 3.3 heads.

I'm also looking to go TT with smaller GT's to help bring in some low rpm boost flow. I don't plan to go beyond 1 bar and I'm running 91-2 full finned, Carrera cams, 3.2 intake, 993TT HE's. I'm essentially building a TT 3.2 which has been done before, but this engine builder (who isn't necessarily stuck on the way factory the factory did it) just seemed quite doubtful on the whole 3.2 top end under boost. This will be in a 22-2400 lb chassis...not a #3100 930.
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Old 03-03-2007, 08:00 AM
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The 3.3 heads have better metallurgy for boost. Sorry if you already knew this.
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Old 03-03-2007, 10:31 AM
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You won't be downgrading to 3.3L heads if you port them. Both intake and exhuast must be ported and no, you will not lose any torque but gain a ton.
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Old 03-03-2007, 01:00 PM
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My thought is: If I plan to run a 3.2 intake as I do, then won't I have already port matched the 3.3 heads out close to 41mm? Sure by porting the 3.3 head out to 41 we can make the port hopefully more efficient than a as cast 3.2 head. BUT the head porter says the 3.2 already flows too well on the intake side for the exhaust flow potential.

Can't we get the exh to flow adequately to balance this? He says with custom valves HE CAN, but still doesn't feel I should. He's also against the 3.2 intake because of volume and doesn't love big IC's. So I want more opinions if possible. He seems to run against most of the modern grain on Rennlist and here for an EFI turbo engine.

Let me restate: I only meant "downgrade" flow with the fact that I own 3.2 heads and not 3.3 heads. I realize the RR alloy of these and 993 are more heat tolerant but a few guys have made the 3.2's work in much harsher conditions than I'll ever put them through. Did NOT mean to sound offense to the 930 guys
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Old 03-03-2007, 01:26 PM
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gee, i don't know

I am running a 3.2 intake and euro sc heads. I am getting pretty good results.
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Old 03-03-2007, 06:12 PM
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DRV2FST:

What if anything did you do to the heads? How do the ports/flow compare to a 3.2? Did you have to work hard on balancing the exh flow.

Or did you throw this theory to the wind and just run them? SC cams?

Thanks for the replies so far.
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Old 03-03-2007, 06:32 PM
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Dick Elvenrude (sp?) did the work on the heads. I don't know about the ports/flow comparison.
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Old 03-03-2007, 06:50 PM
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Thanks, just reread your thread and you should be proud. Very nice results that'll surely drive very nicely on the street as well as track. I like the use of judicious fabrication rather than just buying more parts.

I also admire creative thinking rather than "cookie cutter" engines that simply emulate 30 year old formulas. We've came so far in some areas technologically that looking back wards for more than to see where we came from seems poorly planned. I love vintage racing, but why build a 934 engine for the street if efficiency is the goal. We're still limited by the same parameters of physics and heat limitations of our heads. This doesn't mean we should use the same designs to manipulate them to the best of our abilities.

Nicely done. I only hope mine comes as close to my goals.
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Old 03-03-2007, 07:18 PM
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Thanks
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Old 03-04-2007, 04:13 AM
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Luke,
The 3.2 heads are some of the best flowing air cooled heads Porsche ever produced. If you are putting this engine in a 2400 lb car, I wouldn't even worry about the torque you are sacrificing. The weight loss will more than offset.
My understanding about the 3.2 heads is they only need a little cleaning up on the exhaust port. A LOT less work to get them optimized than a set of 930 heads.
As mentioned early on, the 930 heads are special alloy heads that retain less heat than to NA heads. But I think the 993TT heads use the same alloy as the 993 NA heads, so that theory may be mute. Porsche was very much in the experimental phase of turbo applications back then. There are a lot of people running the 3.2 heads out there putting out prodigious amounts of HP.
Just match the head work, cams and turbo to your output goals and you will have one awesome rocket!
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Old 03-04-2007, 06:08 AM
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Dave and others,

Thanks for the reassurance and I'll continue with MY ideas versus this particular local builder's (when you live in BFE, there aren't a lot local opinions). Sometimes you can be made to doubt your best plans when an expert questions you straying from the pack. Your statements above were my exact thoughts.

My understanding is that all 993 heads are made out of a material similar to the 930 heads. This is probably due knowledge, price, less efficient fans, larger bores and higher compression that all push head temperatures. Bill V. was discussing this somewhat recently in the engine building forum.
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Old 03-04-2007, 06:32 AM
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The 3.2 head will do anything but make the car a pig off boost. Got to remember, the 3.2 was non turbo and was very drivable at lower rpm without boost. I would say open up the 3.2 exhaust ports slightly and perform any other nesecary mods (guides, valves) and have a blast. N/A flow charactoristics are improved when boost comes into the picture. Not to mention the car will drive nicley around town depending on the cams selected.
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Old 03-04-2007, 06:51 AM
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