[SuperMattyP]

I'd like to hear from the "experts" about the 968. I'm curious about a few things and I'll try to lay out my questions in a very clear and easy to understand way. Then after some discussion I'll get into what I'm wanting to do with this car.



1. How strong are the engine internals? Any weak links?



2. What is the average amount of power a stock block can handle under FI? (i.e. limits out around 300whp)



3. What do the 968 owners use for fuel/timing control in FI upgrades? What are the pluses and minuses to these systems?



4. This is my first experience with a transaxle vehicle. What are the weak links in the drivetrain when increasing power?



5. How much is the average aftermarket FI kit for a stock block 968? Any links? I've seen one or two that look very nice lately.

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[SuperMattyP]

22 views and no help? Come on guys. I'm here to learn. Teach me.

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[flash]

lol - i've been considering just how to answer those very broad questions



how weak is weak? which internals? there are already known issues with some of the "internals"



is FI fuel injection or forced induction? (carbs are used on some of the race cars) average power? turbo? roots? centrifugal? the block really isn't the issue though anyway



question 3 is driven by the answer to #2, but the answers are many for either



there are plenty of weak links in the drivetrain, from stem to stern - however, the driver and application are key components in determining what breaks



again, on the presumption that FI is forced induction, as there are many different types of setups, and most not being in "kits", it is really impossible to answer this question - however, most people have spent about 15k doing theirs by the time they were done



i think you need to focus your questions more on the specific - the ones you have lain out are very broad and general - it is pretty clear to me that you intend to max out power - i have to presume that you have resolved the chassis issues which very seriously limit the amount of power you can put to the ground - determining the application will help in answering questions regarding maximums and failures and such



as an example, i'm pretty sure i can build a 700hp 968 engine - lol - it will last about 30 seconds

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[Fox944]

check out,



powerhaus.com



they do excellent Turbo work & have kits for the car.



The block is one of the strongest parts of these cars.

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[SuperMattyP]

I didn't realize my questions were as vague as you pointed out. Let me try to clarify.



1. I'm not looking for "all out power". I was interested in making my own turbo system for the vehicle and wanted to know if there was a fairly universal breaking point. In the mazda community I come from most stock engines can't hold over 250whp. Surely there are exceptions but 250whp is typically the highest you can go and still be safe.



2. As far as chassis issues to be worked out first I'm not sure what you mean. What problems do the cars currently have in putting power to the ground?



3. I was thinking of fabricating my own rear mount turbo and was needing info so I could start figuring out what size turbo to use.



4. As for fuel management the type of FI (yes forced induction) shouldn't matter. Boost is boost. Some people tune turbo cars with AFC's and others use full standalones. Some just use simple RRFPRs. I was just curious what most after-market turbo cars were using for management.



Obviously I'm not interested inspending $15k for a turbo kit if I'm balking at spending $15k on the car itself. I have a local STS dealer near me who is selling universal kits for $2700 that have to be custom-fabbed and you must supply your own EMS. I figured $3k for the kit and other needed supplies and then an EMS of somekind...anywhere from $250-$1200. There is your sub-$5k turbo kit.



Again, like I said I'm not looking for all out power or anything. Just a nice kick in the pants. Hell, I'd run a straight nitrous system if the car has proven it's ok with that.

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[flash]

250 at the wheels is a no brainer - i haven't dynoed it lately, but i'm not that far away from there now normally aspirated - i know others have already gotten there without any boost (albeit in a race car)



the chassis has a lot of rubber bushings that need to go away for any real power to be able to get to the ground - it also needs to be stiffened up quite a bit to really handle real torque - you ahve to remember that the front suspension is early VW rabbit, and the rear is super beetle - the car never really got a lot of reinforcement since its inception as a 924, but it got 1000 lbs more weight



without doing the chassis work, you get a lot of twist and snap, and ultimately an unstable and unpredictable car - tighten it up, and it can be a ton of fun



as for boost is boost, i would talk to the guys doing these things - the management systems are STILL not perfect, even after years of people trying to work this stuff out - it seems to take quite a bit to get them working right - there are quite a few different approaches they have used



a bit of quick reading will also bring you to the issues of intake temps - they very greatly depending on the type of unit you use - centrifugal units add much less heat than a turbo - there are plusses and minuses to each



the rear turbos have been talked about - gene and i looked at this a couple of years ago - they are interesting, but i don't understand how they could get around the lag - this is a large bore engine, that takes a lot to develop boost, resulting in lag on traditional systems - i am still trying to figure out how they can get around that - plumbing is probably going to be an issue too - where the heck would you run the pipe? - there isn't any room in the center area, because of the torque tube - the dual resonant manifold may prove to be a challenge too - would you be swapping it out for the 951 manifold?



eric and i have talked about nitrous - no reason it wouldn't work - just a pain to meter and have to fill



don't get me wrong - there are people out there making kits, doing these things on a number of cars, and there are a few different options - this particular engine seems to be a lot more challenging to blow than most though, which has been the topic of many heated discussions



the fact taht it has been such a problem, and teh similar desire for just a bit more oomph, is exactly what has brought me to trying to work out a low boost centrifugal unit myself



let us know what you figure out - we are all looking for the "plug and play" kit

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[SuperMattyP]

I'm by no means in the works with a kit or anything. I'm just trying to learn everything I can so I can see if it's even a viable option.



I'd prefer a centrifugal SC or even a new rotrex blower but typically you'll find the headunit on those will cost just as much as the entire STS turbo kit.



I was VERY skeptical about lag as well. I think the best way to overcome this is through proper turbo sizing. Choosing a turbo that will spool quick enough to be helpful is a big deal. Also the wastegate just dumps to atmosphere after a short DP. I don't see the trim of the turbo causing serious backpressure issues.



I've used Zex kits in the past with great success. Zex aren't the most powerful kits on the market but it's my opinion they are the safest. The rule of thumb for nitrous is not to add more than 50% of your original BHP. So for us a 100hp shot should be safe. Having such high compression I wouldn't feel safe at that level not without serious fuel control and Zex just uses the FPR to increase line pressure through the injectors. I don't see a 50hp shot being too bad. What do you think?

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[flash]

having done a few nitrous kits (and blown up a few motors in the process), i think this engine can safely handle about 75 from the bottle - with the new gradual throttle setups, it should be fairly streetable too - the hassle of filling it would be a pain, and where to put the tank is an issue, but if you can work that out, it sure would be a quick way to power



as for the rear turbo kit, the things that stopped us, beyond the obvious questions of lag, were the routing of the big pipe, how to get it back into the manifold, and what effect the existing manifold itself, with its own 4 lbs of boost, would have in the final equation - just seemed like a lot of work to figure out, with not a lot of known data to point us in the right direction

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[SuperMattyP]

how does an NA engine make it's own 4psi? What am I missing here?

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[flash]

lol - you have a pm

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[saxman]

the easy solution to a rear mounted turbo and lag issues is the use of a vnt turbo... acts like a super small turbo to get things going, and gets bigger to control boost instead of using a wastegate.



I can go into a lot more detail regarding these if someone so desires... I was about this ] [ close to putting on on the honda prior to deciding to sell it to move a bit up market to a 968.







Matty P, the intake manifold uses very very carefully designed resonance waves to boost up some pressure. They same concept is done with ITB's, although not to that high of pressure afaik. It's a difficult concept to explain in a few short paragraphs.

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[flash]

yup - as far as i know this is the only car to utilize dual resonance - the intake air actually cycles through a second time, which they said makes 4 lbs of boost - plenty of cars use resonance, many new ones utilizing variable resonance through varying size runners, but not dual resonance - this was a big thing for porsche, and part of their big sales campaign

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[SuperMattyP]

If I were to install a boost gauge on the car it would register 4psi? That is the oddest thing.



I don't want to bring up a new thread or anything but the way I understood it was that atmospheric pressure is 14.7psi. So an engine seeing "4psi" would in theory be showing 18.7psi....but 4psi on a pressure gauge.



That's a very interesting concept. I'd love to see more about that. I'm into quirky crap like that..

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[flash]

i suppose if you could get the tap at the right spot, after the second loop, then yes, you would see the boost - i have the stuff that says right in it ".3 bar or 4 psi"

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[saxman]

I wonder if you get 4 psi across the board, or if it's at certain resonance frequencies, as you would get with itb's

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[PorscheDude]

I think the pressure increase is felt from 4100 RPM and up. This is the "kick" people refer to.

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[94SilverCab]

Smokiemon,



Once again I find myself agreeing with you. I was under the impression that the "kick" was the vario cam and was later corrected that it was a result of the intake.



Reagrds,



Jay

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[saxman]

[quote name='smokiemon968' post='38673' date='Jul 23 2007, 04:52 AM']I think the pressure increase is felt from 4100 RPM and up. This is the "kick" people refer to.[/quote]

generally with a valve resonance wave, at least in the the itbs, you get a primary, secondary, and tertiary boost of power at different frequencies...



in other words, you'd get a boost in pressure at (for example) 6000 rpm, a smaller one at 5000 rpm, and an even smaller one at 4000 rpm. It's not really a case of it hits at a certain rpm and pulls strong to redline.



Again, this is the case with an itb set up, I'm not sure how the physics of the dual resonance intake work.

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[Fox944]

[quote name='94SilverCab' post='38674' date='Jul 23 2007, 09:03 AM']Smokiemon,



Once again I find myself agreeing with you. I was under the impression that the "kick" was the vario cam and was later corrected that it was a result of the intake.



Reagrds,



Jay[/quote]





The vario-Cam kicks in @ 5,500RPM if im not mistaken.

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[PorscheDude]

Vario-Cam actually "kicks in" or is energized under 1500 RPM then de-energized thru 5400 RPM and "kicks in" or is energized again at 5500 RPM.

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