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Stupid inlet spacers

Having joined the dark side from a NA background, I am dumbfounded by the pathetic size of the inlet tract on our turbo motors. 32mm !!!!
I know that with a bit of boost this restriction can be overcome, but letís get real here, as much as we donít like to admit it, a large percentage of our driving really is in the rev range where we are off boost (and way down the power curve).
While I have my motor apart Iím doing lots of ďwhile Iím in thereĒ type stuff and one thing thatís high on my list of things to do is to improve power below 3,000 rpm.

It just seems so obvious to me that the inlet manifold branches, inlet spacers and head ports should be opened up. Thereís plenty of room to do this in the manifold and the heads but the stupid plastic inlet spacers are a real problem.

Bruce Anderson notes in his book that the inlets should be opened up from 32mm to 36mm but doesnít elaborate further. Boring out the spacers by 4mm will reduce the wall thickness from 4mm to 2mm.
Can anyone report on the longevity of spacers that have been bored out to 36mm?

Iíd like to go as far as possible here Ė maybe bore out to 38mm. This would leave a wall thickness of 1mm, which on its own is getting a bit flimsy. To reinstate some strength, I am looking at filling the spaces between the flanges with some kind of epoxy or liquid metal (see shaded areas in photos).
Has anyone else tried this? If so, what type of material is best to use? Obviously it has to be able to handle head temperatures and be compatible with the plastic spacer.



I have also considered boring out the entire center tube in the spacer and replacing it with a steel tube. 1-5/8Ē ERW tube with a 1/16Ē wall would be good (for the ROW, thatís about 41.3mm OD x 1.5mm WT).
If I did this, I would still need to bond whatís left over of the original spacer flanges and injector mount to the steel tubing. Iíd need to notch the tube to clear the injector as well.
Has anyone tried this approach?
Old 07-02-2008, 08:13 PM
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I am in the middle of a head stud R&R right now and could not agree with you more. Why, oh why, did Porsche use 32mm ports, spacers and that intake manifold. Clearly the manifold was a packaging issue, but what the heck. I don't planning on porting the heads this time around but will spend a few cycles trying to port match from the intake to the heads. SHoudl be interesting. I am surprised there is not an aftermarket spacer that is bigger and would locate the injector???
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Old 07-03-2008, 08:09 AM
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Boring to 34mm i think is the largest you can get away with i believe thats what mine are and they are still prone to cracking, it would be hard to find anything that
would bond good to that sort of plastic.

The alternative is purchase the aftermarket aluminum spacers that are already 36mm, i cant off the top of my head remember the source of these.
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Old 07-03-2008, 08:10 AM
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TurboKraft has a solution, but it's more geared for EFI and adapting your stock "pancake" intake manifold for use with EFI injectors:
http://www.turbokraft.com/catalog/product_info.php?cPath=1_41_48&products_id=100


Performance Devlopments also created billet injector blocks...I'll find a picture.
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Old 07-03-2008, 08:42 AM
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Here are the pictures from Neil Harvey - Performance Developments. His blocks were designed to take either a CIS injector or an EFI injector:
http://performancedevelopments.com/company.php



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Last edited by sand_man; 07-03-2008 at 09:01 AM..
Old 07-03-2008, 08:50 AM
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I think you'll have to get aftermarket aluminum ones to go bigger.
I don't think building them up with Devcon or JB weld epoxy and hogging them out would last long.

They used small ports on the 930 to speed up intake velocity at lower speeds.
That improves low speed driving, makes a smoother idle and keeps CIS fuel spray from the injectors atomized better.
Hydrocarbon and CO Emisions are probably lower because of this.
Old 07-03-2008, 09:21 AM
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I think Pat Williams Racing also did some blocks.
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Old 07-03-2008, 10:32 AM
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FYI, I found this in my collection of turbo related pictures - can't remember where I saved it from. USE AT YOUR OWN RISK:

I think these are the drawings for a spacer meant to go under one of these metal fuel/intake blocks...but perhaps the dimensions are useful?
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Last edited by sand_man; 07-03-2008 at 11:19 AM..
Old 07-03-2008, 10:43 AM
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Quote:
Originally Posted by JFairman View Post
I don't think building them up with Devcon or JB weld epoxy and hogging them out would last long.
I tend to agree, that's why I'm nervous about this approach.
The other issue is if I go for the max port size, there's no turning back once I've ported the manifold and heads.

Quote:
Originally Posted by JFairman View Post
They used small ports on the 930 to speed up intake velocity at lower speeds.
That improves low speed driving, makes a smoother idle and keeps CIS fuel spray from the injectors atomized better.
Hydrocarbon and CO Emisions are probably lower because of this.
I figured there had so be some sound engineering reason behind the small port size - damn it - don't you just hate those Germans!!

It would be interesting to hear from anyone who has gone with larger ports to see if they have noticed any adverse affect on driveability. Considering that this is what I'm trying to improve, Mr Fairman may just have tipped the proverbial bucket of cold water on this subject if he is correct.

As far as HC and CO emissions are concerned, in Western Australia they are an environmental issue only. We don't have to worry about smog tests.
Old 07-03-2008, 04:23 PM
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I have larger ports, my insulators are bored out to i believe 34mm and the 930 intake is honed to match, I am using 79 SC heads with large ports and valves and SC cams so they are far removed from the turbo heads and cam that it would be hard to compare. My engine has plenty of guts down low.
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Old 07-03-2008, 05:58 PM
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Quote:
Originally Posted by billjam View Post
While I have my motor apart Iím doing lots of ďwhile Iím in thereĒ type stuff and one thing thatís high on my list of things to do is to improve power below 3,000 rpm.
...
It just seems so obvious to me that the inlet manifold branches, inlet spacers and head ports should be opened up.
+1 what JFairman says...

Chap, you might need to revisit gas flow theory...

Small inlet tracts, small throttle body and small valves all make for better throttle response - and more torque & tractability - at lower RPM because the velocity of the gas at part throttle is faster than it would otherwise be. Downside is that it strangles the motor at the top end.

Big problem on an N/A motor, not so much with forced induction.

Opening up the ports and using larger valves doesn't improve low end, it improves the top-end by allowing more gas to flow at large throttle openings, but at the expense of off-boost response and tractability.

Stock 930 is pretty docile off-boost. Stick to the cams and leave the rest of the top end alone if you want a better street car, IMHO (but definately use after-market rod bolts if you're in there anyway).

SC cams are said to have better low & mid-range than 964 - which have slightly more top-end (IIRC, SC are the hottest you can use with N/A CIS because of the reversion pulses, the 964 have too much timing/overlap). SC cams are hot enough to make the idle lumpy. Tweaking the idle up to 1050 RPM makes it a lot happier...

Use good headers, intercooler and a decent modern turbo, and it gets academic quite soon anyway - my motor makes .5 bar @ 2,500 RPM under load. And with short gearing and 8:1 as well, a 930 will kick you right in the pants from idle without any boost in sight.
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Old 07-03-2008, 11:51 PM
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Quote:
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My engine has plenty of guts down low.
Yeh, but that's your monster 'teener, right? What's that motor pushing around, 2200 pounds? Less?

That's gotta really move...
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Old 07-04-2008, 12:10 AM
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Hello!

Reason for 32mm ports is off-boost torque. Engine has 7:1 C/R and is a pig w/o boost, delivering staggering 120hp w/o the huffer.

Porsche used those strangled intakes to improve gas velocity and thus cylinder filling at low load.

Frankly, whole intake system on 930 is a mess. Pancake plenum flows badly and uneven. Cylinder 1 has noticeably lower flow than cylinder 3 etc. CIS barn door is also in a way. It's a small wonder you can get 300hp from this.

Only way to do it "right" is to fit Carrera intake, but then you'll find out that ports don't match. I believe sand_man's drawing is an adapter between Carrera intake and 930 heads.

Unfortunately, 930 heads won't match perectly with Carrera intake even when ported so tuning a 930 engine with Carrera intake is PITA-job.

Frankly, I believe cheapest way to do right from start (if hunting big HP) is to sell 930 engine and do a turbo conversion of Carrera engine or fit Carrera heads from start. Crank and rods are the same anyway.
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Old 07-04-2008, 02:08 AM
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Thanks for all the input. I'm quite impressed with the depth of knowledge available on this forum. It can help save newcomers heaps of $$ and time.

I was beginning to think there was more to this than meets the eye. I guess it comes from years of playing with NA engines where inlet size has a slightly different effect on power.

Keeping in mind that I'm not hunting big horsepower (= not wanting to spend mega bucks) but just wanting to improve low range performance, it looks like SC cams might be a better option than pissing around with the inlet tract.
I already have a K27 7200 turbo and larger intercooler ready to fit. (Its a B6 and yes, I have already gone through the pain of fitting it to my other car so I have all the fitting problems sorted! I am just swapping it between cars.)

Spuggy suggests "good headers, intercooler and a decent modern turbo". I'm not sure that the K27 7200 fits the bill but it's got to better than the standard issue.
As far as headers are concerned, I do have a set of new "Going Super Fast" headers available to me at a good price. We are getting off the topic of inlet spacers, but if there's any opinions about the merits (or otherwise) of these headers compared to Euro headers, I'd be interested to hear them.


With hindsight, I guess the subject of this thread really should have been "how do I get more off-boost power and maintain driveability without spending megabucks?".

I just noticed the date at the bottom of my screen. It's just another day for us in the ROW, but happy Independence Day to those who think they live in the centre of the universe from one who does!
Old 07-04-2008, 06:43 AM
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Be aware that GSF headers hang down "much" lower than the stock system. You will end up scraping the collector from time to time.
Also, the turbo catch tank gooseneck is too long and will need to be shortened by about 1 inch.
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Old 07-04-2008, 06:48 AM
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Billjam, my 79 930 stock isolators had an ID of 38mm. Compare these to a set of 1989 930 isolators I had which were far smaller, about 32mm. For effective use of the 38mm isolators you would port the manifold openings and cylinder heads, though you may no longer be interested in doing this.

Last edited by Jim2; 07-04-2008 at 07:48 AM..
Old 07-04-2008, 07:45 AM
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Quote:
Originally Posted by 911nut View Post
Be aware that GSF headers hang down "much" lower than the stock system. You will end up scraping the collector from time to time.
Also, the turbo catch tank gooseneck is too long and will need to be shortened by about 1 inch.
Thanks for that info Jim. The GSF headers look well-made, albeit a bit boxy looking, but these are the sort of problems I don't really want to get involved with if there's not much to be gained.
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Old 07-04-2008, 07:05 PM
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Quote:
Originally Posted by Jim2 View Post
Billjam, my 79 930 stock isolators had an ID of 38mm. Compare these to a set of 1989 930 isolators I had which were far smaller, about 32mm. For effective use of the 38mm isolators you would port the manifold openings and cylinder heads, though you may no longer be interested in doing this.
It's interesting that Porsche reduced the size of the isolators at some stage.
It kind of indicates that they may have had some power or driveability issues as implied by beepbeep and spuggy.
However, I am still inclined to go a little bit in this direction - I'm leaning towards boring out to 34mm.
Old 07-04-2008, 07:20 PM
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Originally Posted by beepbeep View Post

Unfortunately, 930 heads won't match perectly with Carrera intake even when ported so tuning a 930 engine with Carrera intake is PITA-job.

Frankly, I believe cheapest way to do right from start (if hunting big HP) is to sell 930 engine and do a turbo conversion of Carrera engine or fit Carrera heads from start. Crank and rods are the same anyway.
Nice stuff beepbeep. Do the Carrera heads and intake bolt onto a 930 case? How do the Carrera head port sizes and valves compare to the 930's? I read somewhere that pre-'80 SC heads are the best?

This whole head and intake manifold business sounds like a lot of work. Can the 930 pancake manifold be used up to 500hp?
Old 07-04-2008, 07:55 PM
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Quote:
Originally Posted by iamchappy View Post
Boring to 34mm i think is the largest you can get away with i believe thats what mine are and they are still prone to cracking, it would be hard to find anything that
would bond good to that sort of plastic.
The alternative is purchase the aftermarket aluminum spacers that are already 36mm, i cant off the top of my head remember the source of these.
I am leaning towards a 34mm bore as a compromise situation. This will reduce the wall thickness from 4mm to 3mm.
Can you elaborate on your cracking problems?
The spacers I removed from the engine after 22 years of use were fairly degraded, cracked and flaky at the head end but were still air-tight.
Old 07-04-2008, 07:58 PM
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