What percentage increase in cost since the first wrench was turned. I've never had a project like this that didn't creep up.

Keep the pictures coming.

 

We achieved 385hp from a 3.6 running ITB's which had better than factory driveability. Engine ran highly modified 964 heads on 993 bottom end with custom camshafts, headers, etc, plus the usual Motec of course. The engine was in the back of a 964RS used and living in the centre of London. Ironically just as we had the engine running perfectly the customer called and mentioned that he was having aircon fitted, so the following week we removed the ITB's and refitted the stock intake and aircon mount/pulley to the engine and remapped it for the ITBs. From memory we managed to squeeze 360hp from it in this guise.

 

Sorry to disappoint chaps.

As said, still comfortably within budget. Nick has been very organised and planned the build/ cost accordingly. This was the most vital (amongst others) assets I needed in order to decide upon the builder when venturing into a project like this one. I personally take costs of this kind very seriously - to that effect I took a lot of time, planning, researching (at my amateur level), meeting and talking with builders before making my decision.

As a result, I have felt in comfortable control of costs, up to date, relaxed (albeit impatient) and assured from the outset that time spent in R&D would not effect cost.

Pictures coming soon hopefully!

From the non expert to the expert's post.

My post was on the basis of non ITB as Jotaking's post was reverent to 'safely achievable' from my interpretation: every day usability - maintenance, servicing etc. Mind you I suppose ITBs are 'every day' useable also, although for a daily driver I would prefer to stick to a more standard induction system. Since my car is a weekend, tourer, streetable track car ITBs were/ are on my radar.

 

Without radical modification the stock intakes (964 resonance flap or indeed 993 Varioram) reduce peak torque above 5000rpm and choke the engine to make its power peak between 6000 to 6700rpm, hence within conventional tuning limits around 100bhp per litre is the most that you could realistically expect to make. Trying as hard as we could with an experimental cam in a 3.75 litre 964 engine running a modified early aluminium manifold, the most we managed to achieve was 382bhp which is around 102hp/l. With ITB's and headers (in crude terms) you open up the airflow through the engine which then moves the peak VE (volumetric efficiency) above 7000 rpm. Hence, for example, if you could make exactly the same torque at a peak power of 7250rpm compared to the stock manifold peak at 6250rpm, if the stock engine made 350hp (97hp/ltre) it will now make 406hp (113bhp/litre). RPMs make power, so the more revs the engine can safely run the more power per litre it will make, which is why Formula 1 are now limiting the peak rpm of engines in order to cap the power outputs rather than running air flow restrictors.

 

Going back to the 'standard engine' thing: These figures above can be achieved at a sensible cost.

One of the biggest problems with going down the ITB route for me is the price!! By the time you've buy your throttle bodies, engine management/ECU, harnesses & wiring, then set it up etc you've literally spent the entire engine cost all over again which I find hard to justify.

I know that quality never comes cheap and there's more to it than just numbers but still.....

Just my opinion of course.

 

Heads did make quite a difference for Daffy. With 964 heads lightly ported we got 340 HP. Just changing out to Gamroths trick heads bumped us to 381. The dyno chart in my build thread has both variants.

I did get Daffy back. I put 1000 street miles on her before going to the track where I blew an oil line in lap 6. I caught it early so no engine damage, just a big oily mess sigh. Your going to love the motor when you get yours back. It's really transformational! Anyone who thinks ITBs and Motec aren't street able don't know one of the right builders. I'll post an update on my thread with some thoughts (don't want to thread jack you!). I will say 1st gear is now useless. Even going 10 mph if you hit full throttle the tires just light up to redline in like zero seconds :-).

Paint may not make her faster but I can't get over how beautiful your car looks! I'm anxious to see you get it back with the new beastly motor.

 

While talking about power output, costs etc with ITB's there is something important missing from the mix imo and that is gearing. Raising both peak power and torque to over 7000 rpm is fine, but it is in large part unusable when run with standard gear ratios.
Redline in 5th would equate to about 180+ which is useless on the road as the engine wouldn't have the torque to cope and useless on track as it would never be used?

 

Who says that the torque is lower? You are making the fundamanetal mistake of assuming that power comes at the cost of mid-range torque; design and build the package correctly and your 8000rpm ITB engine will make more torque than stock from 4000rpm up so it will definitely be faster in every gear, no matter what the gear ratios are, with the added advantage of an extra 1000rpm on top. Sure, the peak speeds in each gear will be higher, but that is not necessarily a bad thing as it also gives you more flexible use on track by holding on to a gear for slightly longer down a straight or through a bend rather than adding an up-down gearchange.

 

Colin, I didn't say the torque was lower or that the car will be slower? My point was that a car modified with ITB will work better with gearing adjusted to suit the new torque / power peaks and this would apply to both a road car or a track car. Given the cost of such an ITB conversion surely mods to the gear ratios would make good cost effective sense.
Running at the UK legal limits on dual carriageway or motorway means the engine is spinning at below 3000 rpm, obviously the ITB setup is not at its best here and driveablity suffers as a result when compared to the standard system.

 

Sorry, obviously I completely misunderstood the above comment. Give me some time and I will drum up a dyno comparison between a 9m ITB engine and stock 964 so you can see how a tuned engine would be faster than stock - even at 3000rpm.

 

You can possibly find a dyno print somewhere that shows decent numbers but WOT figures are a small and not particularly useful part of the story at these revs.
Understand the context of the comments in relation to gear ratios and surely you would agree such G/Box changes would maximize the benefit of an ITB modified engine?

 

I'm obviously having a thick day because I still fail to see how an engine that makes the same or more torque as a stock engine can be slower or less driveable. The stock 996GT3RS has the same 9:31 ring & pinion and similar gearing as a stock 993RS yet you don't hear GT3RS owners complaining because their car is less driveable on the road compared to their old 993RS, do you?

In principle I agree that a close set of gear ratios can make any engine faster, but my personal experience of racing an 8200rpm ITB 993RS and my ingrained engineering principles tell me that running a stock gearbox on such a car is not a disadvantage. In fact I would go as far as saying that in some circumstances running a motorsport 8:32 ring & pinion is a real disadvantage due to the additional gear changes required over the duration of a lap.

 

https://rennlist.com/forums/993-foru...rticle-11.html

....My car does indeed have relatively tall gearing because it has the standard G50/32 993RS CS transmission which is not ideal when combined with an engine that produces peak power above 7000rpm and revs to 8000rpm - I end up with 55mph in 1st gear, 83mph in 2nd, 108mph in 3rd and just 130mph in 4th. Unfortunately the magazine writer ailed to spot this anomaly and posted the times for the standard cars alongside my "off-cam" figures, whereas the 80-90 and 90-100 times for my car were in the order of 1.5 seconds from memory.

As Groucho Marx once said. Those are my principles, and if you don't like them... well, I have others!

 

The 9m 993RS is my car with a 9m 3.82 race engine = 993 crank, Carillos, 9m P&C, 9m Billet heads, 9m ITB, stock 993 headers, Motec which also runs a stock 993RS Clubsport G50/32 gearbox. It was faster than a standard car in every gear.

mph / 964 C2 / 964RS /GT3RS / 9m 993RS

50 to 60 = 2.27 / 1.84 / 1.5 / 1.05
60 to 70 = 2.07 / 1.65 / 1.34 / 0.78
70 to 80 = 2.06 / 1.56 / 1.41 / 0.88
80 to 90 = 2.19 / 1.72 / 1.43 / 1.21
90 to100 = 2.93 / 2.3 / 1.54 / 1.22
100 to 110 = 3.11 / 2.46 / 1.97 / 1.76
110 to 120 = 3.63 / 2.84 / 2.06 / 1.84

60 to 120 =15.99 / 12.53 / 9.75 / 7.69
60 to 130 = na / 17.39 / 12.81 / 9.79

Also interesting are the speeds in each gear at peak RPM of 6800.
964 G50/03 = 42/71/104/136/169
compared to
993RS G50/32 = 47/74/98/120/144/179
In theory the 993RS box should be easly faster in 3rd, 4th & 5th, about the same in 2nd and marginally slower in 1st.

The conclusion I came to is that the journalist had a flea in his ear and was trying to prove a negative point with your road test.

 

On the contrary, this both excellent & informative, I'm learning all the time. My car goes in soon for a similar job and this thread has helped enormously.

Thanks Frank and also to the many other contributors.

Keep the faith

Paul