The Mega Supercharger 4AGZE thread, using twinscrew charger

[knightrous]

You should run a BPV on the twinscrews as they actually compress the air between the rotors, not just push it like a roots (which builds boost by restriction) and it will get hot.

For the IAT/MAT correction, maybe just set it to zero till around 50-60'c then add some additional fuel to add a bit of cooling (as long as it doesn't push your AFR's into silly places ie: 10:1).

[jondee86]

Yeah... a BPV was on my original list, and I wanted to use one of those "mini-style" servo operated butterfly valves. Only problem was I couldn't find a place to fit it in at the design stage, so I left it out. Along the way I picked up the Bosch valve as it had smaller connections. Once the inlet ducting was up and running, I figured out a way to fit it in... tight squeeze

For the Air Temp enrichment I have settled on zero compensation from 35 to 60 deg. Above and below that normal compensation applies. Just trying to eliminate one variable in the operating temp zone (ambient to 60deg) for the charger at the moment. May have to zero it to 70deg when I start pushing the pedal a bit harder. After that the W.I. syatem should keep the temp down.

Cheers... jondee86

[knightrous]

I have one of these BPV's in my setup.

[jondee86]

That's the mini (cooper) type valve that I wanted to use, but there was just no way I could make it fit with my ducting layout. Down the line I might invest in one of these to replace the Bosch valve...



They come with three different springs so that you can adjust the pressure at which the valve closes. It has the same size hose connections as the Bosch valve and should be a straight swap (with a bit of trimming).

Cheers... jondee86

[JustenGT8]

Handy tip that GFB valve....I currently run the butterfly style on my Kenne Bell but I want to improve the intake and that GFB style valve will help heaps with packaging

[jondee86]

So, I have been driving my car and messing around with the tune to get it good enough for a bit of spirited driving. At the moment is fitted with the largest of the three pulleys I have available. From memory, I sized the pulleys to generate 5, 10 and 15psi. However, at the moment WOT @ 5000rpm is only generating 3.7psi (or 25kPa) of boost. Which leads me to wonder what factors are at work here and what effect they might be having on boost level ?

Random thoughts and open for discussion...
1. Intake ducting pre-throttlebody. I'm using the OEM AE86 ducting and for sure it does not look like a low resistance setup. I plan to replace it with a 45deg alloy tube bend and an Apexi cone filter behind the headlight.
2. Ducting before and after supercharger. Not the most efficient setup, but no sharp bends or obstructions. The best I could come up with to fit the available space.
3. Camshaft and valve timing. I'm using OEM GZE/smallport camshafts at OEM timing.
4. Exhaust. Custom 4>2>1 headers into a 60 dia s/s Apexi overaxle catback exhaust.
5. Manifold Air Temperature. No intercooler in the system so MAT typically runs around 60degC for spirited driving at this time of year in NZ. Water injection is currently set to trigger @ 30%IDC, but IDC maxes around 32% for 25kPa boost, so not doing much.

Have to say that even at this piddling amount of boost, the car is already driving the way I believed/hoped it would Lovely fat bottom (if you will pardon the expression) and strong midrange that encourages me to short shift... no need to rev the snot out of it like I did with ITB's. Looking forward to seeing what it will do with the middle size pulley, but first I'd like to see if I can squeeze a bit more out of the current one.

Suggestions, comments and criticisms all welcome

Cheers... jondee86

[knightrous]

What ratios are your pulleys?
At a guess, I don't think they are high enough.

The guy I bought my Autorotor 2087 from used a 88mm pulley with stock 145mm GZE pulley and it only made 8psi. The ratio was just too low (1:1.63) for the size of the supercharger (870cc/rec) IMO and I will be pushing it closer to 1:2 with a 170mm Nevo crank pulley.

[jondee86]

The Sprintex S5-210 is rated at 940cc/rev. From memory my crank pulley is 130 dia and the s/c pulleys are 110, 90 and 75 dia. So ratios of 1.18, 1.44 and 1.73:1 respectively. According to the old Sprintex calculator, at 7600rpm this should give 50kPa, 82kPa and 117kPa of boost, give or take a few kPa.

The thing that makes me curious is that boost is a measure of resistance to flow. Obviously the calculator has to be based on certain assumptions regarding operating conditions, and I guess that the V.E. of the engine might be one of them ? The higher the V.E. then the lower the boost ? I remember reading elsewhere in this thread that someone changed cams in their engine and made more power with less boost showing on the gauge.

I haven't tried pushing the engine to 7600rpm yet, but in the interests of science I will have to do that to see if it generates a higher boost reading. In actual fact I don't really care what the gauge says... it's just something that tells me if the machinery is working properly. How the car drives is the only thing that matters. The three pulleys are to allow me to learn progressively without blowing the engine. And if you look back on the previous page you will see that I have been trying

Cheers... jondee86

[knightrous]

Boost pressure is indeed the measurement of restriction.
Ported heads and different cams can lower that restriction and drop the boost pressure while increasing overall airflow. Looking at the charts for the S5-210, you are running it in the lower regions of it's capacity.





Throw the 1.44 pulley on and try to get it into the 1.6 - 1.8 PR range

[trdee]

all about them pressure ratios!! spin it harder. yes a higher VE will drop the PR. a regular 4A makes a little over 100% VE at the best point in the rev range, so if you base your calcs on 1.6L/rev then the achieved boost will end up slightly lower than expected. this will be exacerbated if you have a ported head or bigger cams or something else to improve VE even further beyond 100%. I note you mention stock cams so this should not be a big factor at the moment.

Also any restriction prior to the supercharger will have a similar effect. Again since the boost value is derived from pressure ratios, if your intake is restrictive then you will have a slight negative pressure pre-supercharger, which means you are now multiplying that pressure ratio from a base value. IE if everything is good and you have no restriction then the intake pressure should be around 100kpa. on a setup making 1.6PR this will net you 100x1.6=160kPA outlet pressure. However if you have a restriction which is dropping the intake pressure to say, 90kPa, then your outlet pressure will be 90x1.6 = 144kPa.

With all this in mind, I would suggest that the stock 4AGE intake is going to start hurting your boost numbers more and more as you push that charger harder and rev the engine harder etc.

Anecdotally, porting the J-pipe, swapping out the 4AGZE TB for a 4AGE TB, and running nice free flowing intake pipes made a HUGE difference to the response and power output of Harreh's car when he was tinkering with the GZE before going turbo.

[jondee86]

Yes... all good info I have a deep seated urge to understand how this shit works, so I'm trying to get my head around all the smaller factors that make a difference. Going to the 90 dia s/c pulley is not far away, but I would like to get the Apexi filter and new intake ducting in place before then. The AE86 stuff is there because I needed a filter to keep crap out, and I had the OEM bits sitting handy.

From what I read it seems that the V.E. curve follows the torque curve. That means (without using a dyno) the V.E. should start to drop after the engine hits peak torque. This suits me as then there is little reason to be pushing the engine to high rpm... short shift and ride the torque curve. And that's the reason I decided to go with a supercharger.

I figure the smaller pulley will require a complete remap as there will be more boost at any given engine rpm. So if the new intake improves the V.E. I will see its effect on my current map. Sure, the s/c will be in a better part of its efficiency range at higher rpm, and then I will have an excuse to start using the 20 litres of methanol I have in the shed

Cheers... jondee86

[knightrous]

Any restriction before the twinscrew will hurt performance for the reasons Vito stated. I'm currently considering a dual throttle body setup to negate any pre-twinscrew restrictions with a 75mm TB on the supercharger inlet and a factory 4AGE TB on the manifold. The idle is to give the supercharger as little restriction as possible without affecting throttle response.

[jondee86]

Too late for me to consider anything elaborate. I'll settle for cutting the intake resistance down as best I can. Eventually, everything between the filter and the exhaust tip will contribute to the system resistance. And as said above, the higher the airflow, the greater the resistance (increases as the square of the velocity if memory serves).

Therefore I expect to see (when I eventually get to the dyno) a long relatively flat torque curve, that starts to drop off gradually after 5000rpm or thereabouts. And that will be fine by me Not quite understanding the dual throttlebody setup tho... you are saying one big one on the inlet to the s/c and one smaller one (blow thru) after the s/c ?

Cheers... jondee86

PS: Photobucket has just had a dummy spit and blocked all my linked pics... they want US$400 a year to unblock them... payable in advance.
Postimage.org seems a decent free alternative

[jondee86]

First decent day for a while so I went for a drive and cranked a few more revs into the old girl to see if she had more to give...



And managed to log 135.6 kPa (5.16 psi) @ 7430rpm before I ran out of road. That's more in line with what I expected, so all's right with the world again And pleased to see that the rpm/MVSS graph is pretty much a straight line, which indicates that the intake ducting is not causing much of a restriction at low boost.

I hope to have the new intake and filter in place in the next week, and then I will repeat the exercise to see if it makes any difference. Oh, and the knock graph shows how much mechanical noise (false knock) this setup makes. The base engine is noisy, and fitting the s/c adds even more... a huge amount at low rpm fading to zero as things get busy. I've pretty much given up any hope of being able to effectively detect knock.

Cheers... jondee86

[trdee]

even stock the knock sensors are a pain in the arse and cause issues etc... tune with knock ears and forget it after that. as an aside, the knock sensor on my 9A goes fucking mental at idle due to the twinplate rattle haha