924Board.org

[indi9xx]

Sorry to hear about the intercooler Simon, thats a real pain.

Have you ever thought about a transition heat sink cooler? I have been working on one for the 944 turbo recently as an addition to the small standard intercooler with good results.. they are great for short bursts of boost, but not so good for prelonged constant boost, such as hitting the autobahn for a couple of hours straight on boost... but if the boost is 30 seconds or less with a 50% duty cyle (such as cornering), they work really well and keep the tempretures very predictable and constant.. but above a 50% duty cycle they become a bit redundant. The good thing though is they can be placed almost anywhere and so do not suffer from stone attacks.

I even had a play with fuel coolers recently for increasing boost on a 993 turbo, they allowed us to go much further without knock than we used to, due to getting the fuel to a constant -5 degrees (good for cooling the intake valves and combustion chamber especially)

Did you get my email about the manifold? I am interested if you still have it!

All the best

Jon Mitchell
Independent Porsche Specialists
Bournemouth, UK
jon@9xx.co.uk
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Jon Mitchell
Independent Porsche Specialist
Bournemouth, UK

[indi9xx]

As a short update...

The first phase test car has only just had the head fitted due to a problem sourcing 4 notch follower adjusters as they have been deleted apparently... so we have gone into production ourselves.

Initial results show that torque (by the seat of the pants dyno) is WELL up.... I am not speaking slightly, but the torque was enough to loose traction on the rear tyres while trying to move the car from one workshop to another with very little throttle... No one was more suprised than me by how well this head seemed to work... but the real test will be how it performs through the rev range.. and then the proof of the pudding will be with the rolling road dyno session over the next couple of days.

Keep your fingers crossed, the end is in sight.

PS: We still need a twin carb manifold for the phase two car if anyone has one.
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Jon Mitchell
Independent Porsche Specialist
Bournemouth, UK

[Chrenan]

indi9xx,

Keep us posted on the Phase 1 update, I am still interested in a head swap that will increase performance without having to swap anything else....

Very excited to see dyno results...
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1987 951 - M193 Version for Japan

[Porchenewbe]

Wow... intresting stuff, unfortunatly largly over my head though!!

indi9xx, thats good stuff, please please let us know of every development!

BTW what kind of cost is involved in a head change? Is this a service that u (indi9xx) will offer when (and if) u market ur new head?

Also, i recently fitted a, think it's called a throttle body, (its the thing containing the throttle butterflies) from an audi which is quite noticably bigger, and ground out the inlet manifold to match, just wondered what kind of power increase this has caused? if any..feels faster but still want to beat my brothers MX5, currently very evenly matched!

Sorry for the tangent.

Keep up the good work.

Many thanks.

john.

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Riding a steep learning curve about all that is 924.

My first porsche ... I'm only 19..But loving it (except the insurance) ... quite some car.

[indi9xx]

Hi Porschenewbe.

The audi throttle body with the bigger butterflies do flow more air, but my tests have shown that on a rolling road, the bigger throttle bodies do not improve torque or BHP at all. In fact some losses were seen at lower RPM.

My personal believe is that there are three reasons for this.

1. My own simulations and flow bench testing show that the standard throttle body is sufficient to supply the standard head and cam up to 7200 rpm, or an improvement in flow at 6000 rpm of over 5%

2. The standard air box snorkel end will not flow as much air as the standard throttle body.

3. Simulations with flow figures coupled with real word rolling road tuning, with the standard head and the standard cam profile show that the standard throttle body and plenum design act as a choke, to stop momentary pressure waves from going beyond the throttle body to the fuel metering flap, where these pressure waves will fool the metering head into providing an incorrect mixture.

The 3rd part is quite interesting, many people see the standard fuel injection as being quite crude, hower it is in fact quite advanced and if set up correctly is very good at performing its duties.

Also interesting about the 3rd count, is that if you improve the flow of the cylinder head and increase throttle body size in proportion to the increase in flow, the pressure waves become less of a problem and the intake system begins to benefit from these pressure waves (less backflowing) This is something I want to investigate further and needs more thought, as there could probably be further gains to be made.
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Jon Mitchell
Independent Porsche Specialist
Bournemouth, UK

[indi9xx]

Hi Again Porschenewbe,

One thing I forgot to address with your post... the costs of changing the head.

Budget in spending about £100 in parts (gaskets, cam belt, tensioner etc)

At our workshop you would be looking at about £250 in labour charges for a head swap.. But it seems the national average for a normal garage to swap a head on a 924 would be around £150 plus parts and often the garage either charge more in the end or quote that they "would not do another one of those" simply because they are not used to working on older cars and the associated problems (like seized and rusted manifold to downpipe studs that sheer off, or the fact many do not understand the injection system or even know how to use a stobe light to set up timing these days)

The biggest problem these days is sourcing the various notched lifter adjuster screws, they are getting harder to find, so much so we are thinking of having a load made.

In particular, this was a problem on the phase one car, we needed some 4 notch adjuster screws.. we had loads of 0, 1, 2 and 3 notch adjusters, but no 4 notch ones.

This also leads to much time spent on adjusting the lifters to the correct clearances and selecting the correct adjusting screws.

So be warned, there are pitfalls to changing the head, but its worth it in the end.

We took the car for a longer test drive today, I took along a friend and 924 customer for the ride.. He was quite shocked... especially when we left the ground for what seemed like a couple of seconds but was probably the front wheels off the ground for a fraction of a second, due to the speed we were going when we crossed some undulating bumps in the test road we use.

In particular, he was impressed with one particular test he asked me to perform, which was accelorating in third gear while the engine was at 3000 RPM as he had found that his 924 (and most he had driven) seem to bog down a little, with the RPM to high to down shift and to low to for the engine to take off... in particular, he was interested in this as its a common scenario (3rd gear at around 3000 rpm) for overtaking.. He commented that the test car "Pulled much harder from 3000 rpm", "seemed more willing to rev" (or kept increasing in power the higher the rpm rose), and "pulled him into his seat" where as his 924 "felt much more sedate in comparison"

Needless to say, this customer now wants one of these heads and seeing as he is a painter/decorator and currently decorating my house, I can see him getting a special deal on one )

All this is "seats of the pants" dyno stuff though... which can be missleading.. so the proof for me (and most of you I expect) will be the dyno figures.
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Jon Mitchell
Independent Porsche Specialist
Bournemouth, UK

[Porchenewbe]

Sounds promising so far then! Glad to hear of ur success thus far at least. Just as a general enquiry do u have a shop, or garage or just a work shop as i am in ur area i next month so a visit may be in order?
With regard to the throttle body, i attended the 924 cup round at anglesy last august and sspoke with quite a few of the teams there and mentioned a larger throttle body that i'd seen for approx £150 which claimed 10 bhp. I was told that the audi part was the same unit and could be bought for £25 from an audi breakers, (which is what i did). My qquestion is however, why if no real gain is seen did all of the teams run this item? is there another mod which they are allowed which makes it benifishal, ie new cam shaft?

Also, just as another slightly of the topic question how much do you charge for a general tune up on what i have so far, ie standard but with k&n and audi throttle body?

Finally... not to hold u up further...when do u expect rolling road figures and when do u expect to market this new head?

Whoops...finally, finally! What are these 4 notch adjusters ur talking about?

Many thanks once again

john.
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Riding a steep learning curve about all that is 924.

My first porsche ... I'm only 19..But loving it (except the insurance) ... quite some car.

[indi9xx]

Porschenewbe,

We run a small Porsche specialist garage in Bournemouth, and visitors to the garage are welcome any time. (brownen Road, Charminster, Bournemouth, BH9 1LJ) but call or email us first, just to make sure we have not closed up for the day, its rare, but it happens.

As a form of reference (for everyone, not just you), we are also the official technical advisors to the independent Porsche enthusiasts club (TIPEC), run seminars for members of Porsche club great britain (PCGB) such as our now infamous 944 cam belt seminars.

Your right about the Audi throttle body and the item from places like Porsche shops being the same, I even suspect that the items from Porsche shops for £100 and above, are actually audi items which have just been bead blasted clean..

Off the top of my head, the 924 cup racers should not be running the larger throttle body, I think they have to run the complete stock intake and exhaust. (in fact I dont think they are able to change anything from stock, except removing stuff for weight reduction)... But I do know they are allowed to run a particular piper cam which is sanctioned for use in the race series... which if they do use larger throttle bodies, may work well as a combination.

10BHP from a throttle body and nothing else is a totally dreamed up claim by whoever made it, I would stake my reputation on it, they are talking balderdash unless they managed to rev the engine to about 8000+ rpm

The notched adjusters are tapered screws, which when wound into the side of the valve followers (also known as lifters), adjust the gap between the cam and follower by pressing down on the top of the valve.. from one end to another, they have a finite amount they can adjust by, so if you need to adjust it further, you need the next stage of adjusting screw.. they start off with no notch, and go through to having 4 notches. We are considering making our own replacement screws in the standard range, and adding one more screw to each end of the range (a minis 1 notch and a 5 notch) as from time to time, they would be handy (we have a customer who fitted an aftermarket valve and has too wide a clearance for a 4 notch and making a 5 notch is easier than him taking his head off again!!!)

If you came into the garage and wanted a basic crypton tune (ignition and fuel setup) we would charge you about £35.
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Jon Mitchell
Independent Porsche Specialist
Bournemouth, UK

[indi9xx]

Chrenan,

Dyno results will be forthcomming, hopefully over the weekend if we have time. (weekends seem to become a bit chaotic in our workshop as the weather becomes warmer at this time of year)

First the dyno figures will be published on my yahoogroup (Porsche924-44) and then here at 924.org

Shortly after that (as soon as we get round to it) a scan of the print out from the dyno will be available in the files section of the yahoogroup (Porsche924-44)

If the head does get marketed (or more to the point if more than a couple of people buy one) we will also set up a stock 924 (with the head) as a demonstrator, so anyone thats interested, can go for a test drive before they buy. But thats all a bit down the road yet.
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Jon Mitchell
Independent Porsche Specialist
Bournemouth, UK

[endwrench]

[Porchenewbe]

indi9xx,
Right, well i'll drop u a line when i'm coming down and think i will invest in a tune as theres a disturbing pincking on acceleration after about 2/3 throttle, is this because of the timing set up?
Neway, keep us updated.

Cheers.
john
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Riding a steep learning curve about all that is 924.

My first porsche ... I'm only 19..But loving it (except the insurance) ... quite some car.

[Chrenan]

Good to hear things are moving along nicely. A couple of quick questions, can you tell me where in England Bournemouth is? I may be in Lincoln (landing in London) later on in the summer or fall to visit my Nan, who knows, it would be neat to stop in at your shop. Also, I understand to do this work on the head you must be working with a bare, dissassembled head. Will it be possible to purchase a head with all required components (cam, lifters, pulley etc.) included and as much pre-assembly performed as possible?
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1987 951 - M193 Version for Japan

[Eturbo924]

Hey here is a good test that everyone can do to compare.

Take your modified 924 and get it out onto a nice flat stretch of road.

Then get her up to about 100kph or approx 62mph.

Put it into 3rd gear and floor it. See how long it takes to climb to say 120kph or 75mph. Can you do that with out breaking to many laws over there?

Then each person in their respective locations can do the same to compare their performance to yours.

Easy.... of course the US cars against the Euro cars will not be a very good comparison.. but should still give a slight frame of reference.

Maybe some one else already suggested this... but I was too lazy to read all the posts.

Eric
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1982 924
1992 968
2003 C4S
Parts Parts Parts and More parts.
E-mail me for parts you need!
Drive Fast!

[simsport]

John
I will get the manifold to you, I forgot, sorry.

Just on the torque improvements...........my car was in a 3 car feature many years ago for a mag called World Sportscar.

In a back to back comparison with a well tuned 2.7 911 and 911 turbo it was the quickest from 50-70 in 3rd gear. It seems the mid range can be improved. In my case it was via a slight increase in comp and the use of twin 40 dell's.

Keep up the good work...as I said...if you find time to improve the 931 head shout!

Simon
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Blown is always best!

[Voodoocars]

I have just joined this forum and have got very excited by the talks about this 924 N/A head.If it's any good,I want one!
Are there any plans to take the head to the TIPEC show at Walton this year?
Regards
Ian