Dubai944

So, I am currently making 362whp at about 6600rpm, but things drop off after that. The car is great with that power level but, for the challenge of it, I really want to reach a genuine 400whp on the same dyno without any more internal engine changes or alterations to the supercharger setup. 400whp would be a pleasing end point for the development of this particular supercharged engine. After that I might go and play with turbos or a V8, but for now I want to see how many of those missing 38hp I can find with exhaust, intercooler and intake manifold improvements!

I will go up to a 3 inch exhaust from the 2.5 and will have the end tanks on the stock intercooler opened up, but based on discussions with various people in the know I am now really looking for a new intake manifold solution.

The cams I use are designed to make power well beyond where my peak power is now, potentially up to 8000rpm with the right head/manifold combo, but I was told that with the stock 968 manifold they won't make much power over about 6500rpm because the pulse timing gets out of phase and chokes the intake.

I don't want the hassle of ITBs so will stick with a single throttle body. Cutting off the stock intake and welding it to a plenum plate with a more open plenum seems to be the solution employed by most of the aftermarket and custom manifolds I have seen. Runner length, bellmouthing options and plenum shape are all important to get right and without proper flow facilities impossible to know for sure if you have got it exactly right, however, seems worth a try, and I can individually tune cylinders with my setup.

I have a couple of manifolds to play with but before I start cutting them up does anyone happen to have an SFR manifold or something similar already for sale?

Duke

Great results and interesting to see a superchargerd setup, especially one that is a little more than just a bolt-on engine. That is a very nice power/torque curve. No sudden torque spikes that is useless for traction.

Being a supercharger the flat boost level at higher rpms must be related to the supercharger. Upgrading the intercooler is a good idea. The reason why there is a little bottleneck/restriction on the stock IC on the inlet side is to increase the efficiency. If you remove that you will have less pressure drop so the overall boost should rise a little, but at the same time your IAT's will go up slightly.
I would fit a large intercooler with low pressure drop and good cooling. Win win

3" is a good idea especially since you have big cams with lot's of overlap. Need to keep the backpressure low. The intake is more of a guesswork but a general rule is that short runners moves the the powerband up. In your case you don't really need any power below 4000 rpm so I would shorten the runners significantly and do a new plenum with bellmouth's.

Your torque starts to fall off pretty steep, that will be changed by the new intake but I would also look into adjusting the cams on the dyno. A little more retard to increase top end.

Dubai944

Thanks Duke. Maybe I will look at a larger front mounted intercooler. I am just reluctant to change too much not wanting to redo all the ducting I did originally to suit the radiator and stock intercooler, but... possibly the easiest way to pick up a bit more intercooler efficiency.

2bridges

What an awsome little setup
Cool setup, thanks for sharing!

At a glance it would seem you may have belt slip. You certain that is not the case?

max impeller is 80,000 for the C2 - hard to believe that bitch would not be making a ton of heat at that rpm. Most procharger head units with 3"+ inducer are max impeller 60-65,000 until you get to F series

IATs would helpful to gage head unit efficiency.
If you are running near max impeller speed with the stock 951 cooler (less than ideal by todays standards) I expect your IATs are very high.

Meth injection would likely make a huge difference in your specific application.
If Methanol is easily obtainable where you are, that would be where I would go next.
I would use a progressive pump - and measure IAT on dyno - Trigger at 4or 5 PSI , think you will be amazed.

Dubai944

Pretty sure belt slip has been eliminated after three years of customising the pulley setup, tight idlers, braced bracket and 8 rib belt, but if not it can't be improved much more anyway.

My IATs typically average around 30 Celsius above the ambient air temperature and usually a maximum of 40 Celsius above ambient air temperature. Some examples below, first two from recent Australian sessions and third one from Dubai where it was a lot hotter but the increase was still consistent.

That's after running through the supercharger and the intercooler. My IAT is measured just before the throttle body so I really need to add a temperature sender before the intercooler to see how much heat is being made by the charger and how efficient the intercooler is.

I don't know how typical this level of heating is compared to turbo cars? Bear in mind, being a circuit car, the engine is running constantly between about 4000 and 7500 rpm and most of the time at full throttle.

Lakeside Raceway
Ambient Air Temperature 21 degrees C (70 F)
Average IAT 53.5 C (128 F)
Max IAT 63.2 C (146 F)


Queensland Raceway
Ambient Air Temperature 26 degrees C (79 F)
Average IAT 59.4 C (139 F)
Max IAT 67.6 C (154 F)


Previous from Dubai
Ambient Air Temperature 45 degrees C (113 F)
Average IAT 69.9 C (158 F)
Max IAT 85.8 C (186 F)

2bridges

well IATs are not as bad as I would have anticipated considering the track use. Higher than ideal, but your conditions are not ideal.

At 10PSI my procharged LS6 IATs are at or below ambient temp with meth. I have no IAT data without meth for my car.

One other thought comes to mind on the boost flattening up top. Some guys run a restrictor in the fresh air intake of the blower and they pulley down the blower down to make more boost low and then tapper off and restrict (like your car) the top end boost. It exhinits the exact behavior you see.
Seems like a definate possibility your blower intake is a restriction.
If you can test with a nice open bellmouth it should identify if a front side restriction exists if you see more boost in upper rpm.

Dubai944

That's a really interesting piece of information. I never thought about the intake potentially being a restriction. The intake comes from a cone filter sitting just behind the opening at the bottom left hand opening on the bumper panel (right hand side on my avatar) then does two 90 degree turns to reach the inlet. It's quite a long path but hard to get to the back of the charger any other way with the 968 manifold taking up so much room. Something to look at definitely.

Meth sounds interesting but doesn't sound practical for a track car running constantly on boost and sometimes for over an hour at a time. I don't know how big a tank you would need to carry?

2bridges

Oh man if you are making two 90s pre blower I expect you have lots of restriction just in that.
Some are seeing measurable restrictions when using more than a single 45 degree bend.
If your 90s are tight it will be that much worse. Not sure if you want/can run just a screened bellmouth instead, but I would bet that is your missing boost

Meth is probably not the most viable for dedicated roadrace race car.
You would be surprised how little meth it takes to cool the charge, but in your situation almost alwys in boost or on brakes, it would be a fair bit.

Not sure how long your race/sessions are, but yoou would probably need at least a 2 gallon setup and a low level warning system. With meth since it is fuel, you tune needs to account for it. As such if you run out of meth - you will have gone lean and all the ramifications that follow.

Dubai944

Posted this data on Eric's Pressure Drop thread, but wanted to discuss how this relates to my car specifically. This is a sample of pressure drop and temperature drop logged during a track test. The only caveat is it was a short session because I got black flagged for excessive noise. In longer sessions I notice my IATS get a lot higher. I fitted a second map sensor and air temp sensor in the out pipe from the supercharger which is before the intercooler.

Attachment 686305

The results are interesting.

First of all I can now quantify how much the supercharger heats up the intake air. Although I should have installed another temperature sensor pre supercharger to be completely accurate, based on ambient temperatures of 25 to 30 C during the track session, the supercharger is adding up to 100 degrees C of temperature which is a lot, but I don't know how that compares to a turbo?

Secondly the intercooler is doing a really good job of pulling the temperature down, much more than I expected. The price to pay is quite a lot of pressure drop, up to 4psi by the time pre-intercooler boost reaches 12psi above 6000rpm. Seems like a lot of pressure drop at only mild boost levels and I imagine it would just get worse if boost was higher.

I am assuming this means that the intercooler is just too small for the amount of air I am flowing. I have read specs on intercoolers which claim only 1 or 2 psi of pressure drop at full flows over 1000cfm. In theory some of these intercoolers should be able to flow all the air I am pumping with less than 1psi pressure drop. The question is will I still get the same level of decent temperature drop with one of these bigger cores?

333pg333

That's an interesting conundrum Steve. I guess you'll never know the best answer unless you test a few different ones...or change/add something else to the cooling system?

Dubai944

True. Next test though is to open up the intake to the supercharger. Based on 2bridges comments above I have been reading a lot about intake restrictions and their effect on compressors. I now strongly suspect the compressor is being strangled because I currently have a very long 3 inch pipe with two 90 degree bends in it feeding the 3.5 inch intake. The rear fed supercharger is a bitch for access. I really need to get rid of the stock 968 intake manifold to make room for a bigger and more direct air intake, but for now I am trying to see if I squeeze in a proper bellmouth and filter without changing anything else to test the theory. Of course if it does make more boost, the intercooler will also be more of a problem!

thingo

I have found that intake restrictions can have a big effect on compressor behaviour. When I was running a gt3071 on my 951 I was very surprised when it started surging in top gear on the way to the track after a trip to Tasmania. Turned out that driving on an unsealed road(it wasn't on the map!) had clogged my conical air filter, which changed the pressure differentials and moved the surge line way to the right. Cleaning the filter restored normal behaviour.
btw my stock intercooler used to run not much cooler than yours on the track.