Rapid spool turbo with on-board compressed air in exhaust
 

Hello all, I am posting some information on the system I built to rapidly spool the turbo using on board compressed air into the exhaust manifold. My first time posting so please forgive if I break a rule or two. I normally don't post anything on a public forum however I posted a couple videos showing the system in action and many people have contacted my son asking questions about it on facebook thinking he was me since we share the same name. I dont do facebook but have spoken with Pat and Lars on this forum so thought I would post the system details here for others to duplicate if they want.

First a little info on the car. Its basically a junkpile 99 miata that I like to tinker on. the engine is a 1.8l with 1mm over wiseco pistons, chinese h beams rods and arp hardware. Fueling is e85 with id1000 injectors and walboro e85 pump. I use lucas ethanol treatment to help mitigate water absorption and corrosion. I also use topend lube since its a dry fuel. Turbo setup is a chinese gt3076 clone at around 30lbs boost. Tranny is a jatco e4n71, Mazda calls it a nc4ael. Its highly modded and built by me with good bands and frictions with 2 extra frictions in the clutch pack used for third gear. The engine and turbo setup has been together about three years and the tranny maybe 2 years. I beat on this regularly. Rear tires on the car currently are nitto extreme drag 245/50/16 radials. It took some serious hammer action to fit these puppies...

Now to spool shot setup. First I will have to say if you have a good size turbo this system will mainly be beneficial for drag racing or the occasional hit on the street, and most benefit with an automatic tranny. A manual transmission car will be to the left of the compressor surge line with this system on a large turbo at lower rpms. The torque converter of an automatic allows the rpms to blow through the range where surge happens very quickly so its not really and issue. The larger turbos take a lot of air to kick start the spool process rapidly and low rpm. I use a 5 gallon tank mounted in the trunk. In one shot the pressure drops from 140psi to around 90 and system has to charge again for next shot. This is also the reason you would want a belt driven compressor over a 12v system. I initially tried using a viair style 12v compressor. It was loud and took forever it seemed to charge the tank. I switched to a sanden 508 ac compressor I modified to pump air instead of refrigerant and never looked back. It charges the tank quickly and quietly. Volvo gets away with a 12v compressor since they are only charging about a 1 gallon tank, which works for them as they are spooling a tiny turbo. I use some maps on a fic6 to have a tuneable time in which the spool shot solenoid fires. I also use some of the fic maps to control and tune the torque converter lockup.
Please excuse the rough draft drawings. These are my initial drawings when I was designing the system, but they are legible enough I think and they reflect the design of system the way it is now. Also please overlook the cobbled together nature of the setup. My initial intent was to quickly and cheaply throw this system together to test and tp re-do it in a more permanent fashion, however it worked so well I never got around to it and just left it as is.

https://cimg6.ibsrv.net/gimg/www.mia...2a95cfecfa.jpg
This is the basic wiring configuration. I use the switch to arm the system or to disable. you only want this thing active when you need it, otherwise you'll be shooting air at every stoplight. The hobbs switch I use is is a 15psi nc.

https://cimg1.ibsrv.net/gimg/www.mia...41f27f9da9.jpg
This is the basic plumbing setup. I maintain minimum 1/2" from tank to manifold.

How does all this perform? I think it works very well. I have a couple old youtube videos. one has already been posted on Pats compound turbo thread, but Ill post again along with a 0-60 test using the performance expert phone app
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Here is a picture of a 1/8 mile test I did with the dragy device. For those unfamiliar with dragy its a divice that uses high speed gps and a built in accelerometer. For 1/8 mile and 1/4 mile testing the software tries to emulate dragstip timers be factoring rollout and averaging the last 66' trap speed. Many people have tested this while at the strip and found this device extremely accurate, even more so than vbox apparently.
https://cimg9.ibsrv.net/gimg/www.mia...d4cf4459b7.png
I know the 60' is a little soft, but keep in mind this is on the street and not a prepared strip. In fact I always start in 2nd gear and still have to feather the throttle a bit for a couple seconds. Check out the trap speed though, thats indicative that its making decent power.

Below are a few pics of engine and car to further see setup. Again, I know its a hoopty, but I've always had a soft spot for sleeper builds....

https://cimg9.ibsrv.net/gimg/www.mia...5ae2935d29.jpg
pipe into manifold


https://cimg7.ibsrv.net/gimg/www.mia...e151148e45.jpg
sanden 508 compressor


https://cimg6.ibsrv.net/gimg/www.mia...c97c88ac8d.jpg

Sweet, love outside to box projects.

Right on man, that's a pretty novel idea. I'd think some folks may prefer this to misfiring or nitrous for spooling the turbo due to being more gentle on the system.

Just to add a little more information to help people wrap there minds around the spool shot system.

The 15psi nc hobbs switch in wiring diagram is plumbed to the intake manifold. The relay disables compressor operation while the spool shot solenoid is open. The tuneable signal is 12v that i normally set at 2800 rpm, at full throttle and above 13.5psi absolute (just a little below atmospheric pressure). So in operation the relay is energized anytime the previous mentioned conditions are met when the system is enabled. The compressor will not come on when this relay is energized. The hobbs switch opens after 15psi to close the spool shot solenoid to preserve tank pressure since the turbo spools on its own after that anyways.
The way I use this during a test run is brake boost to about 2500rpm to build a little speed in the turbine then release brakes and full throttle, but feathering throttle slightly as necessary. If I hold brakes too long while going full throttle spool shot will happen before brake release and blow tires off badly. I always start in 2nd gear as thats proven quicker for my setup in testing. So a 1/8th mile run just has one shift to third gear. With my tall tires second gear is good to almost 80mph and a little over 80 if I allow the converter to lock, but I usually only allow lockup in 3rd and 4th gears. If I allow converter to lock in 2nd tires will break loose at higher speeds so I keep it disabled for 2nd. Data shows maximum g's usually occur somewhere between 30 and 45 mph depending on traction. Operating this way I hope will preserve my axles and driveline as torque multiplication to the wheels will be much less off the line than if I start in first and tires happen to hook, I may give up a tenth or two in et though but thats ok with me for the time being.

very cool setup :D

Super cool stuff. Thanks for sharing.

Didn't read though everything, wouldn't this throw off your AFRs?

It would throw off the measured AFRs but not the actual AFRs unless you had the ECU set to adjust according to measured. And you would never knowingly set it that way once installing a system like this.

The spool shot only happens at full throttle when its enabled and called for so most ecu's are in open loop and ignore the o2 sensor. You just tune your engine as you normally would without it. When its being used when your gauge shows lean the engine is actually not lean because the air does not run through the engine, just into the exhaust manifold. Plus my testing data shows the spool shot only last for 5 to 6 tenths of a second anyways to kick start the spool process. So for that 1/2 second when its operational it has no significant effect other than a tremendous reduction in spool time. I run a china clone gt3076 and without this system my car is a dog on the bottom end as spool takes forever. With this system, unless i blow the tires off, I usually get somewhere in the mid 3 second range 0-60 on the street as tested on both nitto drag radials and also M&h racemaster bias ply dot drag tires. I have been testing with g-tech (older version), the performance expert app., and the dragy device. The dragy has been independently proven extremely accurate to dragstrip timer data. In my testing all the systems report back very similar results for 0-60 but for 1/8 mile testing the dragy will report back a lower trap speed since the software for it reports an average speed over the last 66' to emulate the dragstrip speed trap timers, whereas gtech and performance expert show speed at end without averaging.

The only real potential drawback I can see is compressor surge for people with larger turbos and manual transmissions. As I mentioned previously its not really problem for automatic cars since the torque converter allows the rpm's to rapidly climb above the area were surging may happen unless you have a very tight converter.

Just did another 1/8th mile test with dragy device. Got my new best time with it. If anyone is looking for a fast responsive gps based device to test acceleration, this tool looks to be a viable alternative to the v-box system for much less money.
https://cimg8.ibsrv.net/gimg/www.mia...0a50672b25.png
https://cimg3.ibsrv.net/gimg/www.mia...27178ea320.png

Wow, that's quick, good trap speed too. Is that a built motor?

Yeah both motor and transmission. Many of the details are in the first post.

Very cool. Reminds me of CAS.

This is sweet! One thing I'd like to know more about is how you converted an AC compressor to an air compressor. That sounds like it could be useful for all sorts of projects. Very cool project!

Basically I did a grease conversion on the compressor. Im using the sandan 508 as are others. This link is a good start Grungles Homepage . I did a few things differently than he did though. I drilled and tapped the suction and discharge ports for npt for easy plumbing. I plugged the oil holes in the center plate as he did, however doing just this you will still get a lot of grease through the center hole where the crankshaft end and bearing pass through. So what I did to stop the grease intrusion to the top of pistons though this area was to cut and form a seal out of a thin piece of sheet metal to seal this center hole in the head gasket area. When you get the compressor apart it will make sense. Im attaching a modified picture from grungles sight to help you visualize this area.
https://cimg9.ibsrv.net/gimg/www.mia...3490e5f73b.jpg
What you want to do is seal the grease from crankcase area from reaching the top of the pistons. Many other people are also adding various oiling schemes in addition, however for me personally I did not find it necessary. I just add a few shots of grease into compressor crankcase and a quick shot of fogging oil into compressor inlet while its running maybe once every couple months. I've seen no signs of complaining from the compressor doing it this way. I have had this compressor setup like this for almost two years.

Very cool idea with the compressed air and its good to see another Jatco MX5/Miata out there its one of the best combo's for a street sleeper

The jatco 4n71 style transmission looks to have some fair potential once modified. My original intention a couple years ago was to convert to a ford c4. I even built one in advance to use. I am comfortable with the older transmissions such as the c4/c6, powerglides and th350/400 as thats what we used back in the day and guys still use them due to huge aftermarket support.... However I decided to get ahold of the jatco to get a look at the internals before I went to the trouble and expense of a c4 conversion. To my surprise the bands, frictions, drums and planetary assembly's were all very similar to the c4's, so I decided to build one up to test. Glad I did... Having a 4th gear and lockup is nice on the street. Its been in close to two years and holding 30 psi well, and Im not gentle on it.

Btw. Mr. mx5psi, The Miata you built is a sweet ride.

Just a quick update to a recent change to spool shot system. I removed the hobbs switch that was used to close spool shot solenoid after a certain boost pressure is reached and replaced it with voltage comparator circuitry and a dash mounted potentiometer so now i have fully tune-able system for both start and end of spool shot firing. The inputs for the comparator are from the pot and the map sensor. My reasoning for doing this follows.

I made some changes to turbo setup and fueling in preparation to hopefully increasing boost from the 30 psi range to closer to 40psi. I swapped the fuel pump to the walbro 525 pump since on paper it looks to be adequate for fuel supply, and also to a 4bar map sensor. I also swapped the clone gt3076 to a clone gtx3076. The gtx has a billet compressor wheel that is 1mm larger so I noticed it took slightly longer to spool to the higher boost regions than the old turbo. So I adjusted the hobbs switch setting from 15psi to maybe 24psi. After doing that the new setup hit much harder to 30psi, actually a little too hard. That got me to thinking hmmmm, wouldn't it be cool to be able to tune that parameter from the drivers seat? So that's why the change from the hobbs switch to the comparator circuit and dash mounted pot for control.
I have some testing and tuning to learn and adjust new system for best traction/acceleration but its looking promising. I've been slowing creeping the boost up a bit, now set in the 35psi range. Traction is more of a problem, even with the drag radials. However i have gotten in a couple 40-70 mph tests with the dragy to compare with previous setup. In only a couple tries I've exceeded my previous best 40-70 by 18 hundredths of a second. I know that doesn't sound like much, but for that short of a span it's actually fairly significant. Once I have it dialed in again to where I can launch from a start Im hoping to increase my 1/8 mile trap speed from 102mph to closer to 104-105 mph when testing with dragy device.

i was thinking about changing my 460 to a 525 did you upgrade wiring ? keen to see what this auto does on higher boost

I wired with 10 gauge straight from the battery to the pump through a 30 amp relay. I drilled and sealed through the pump access cover to pass wires. The 30amp relay gets fairly warm when car runs for a long time so will be swapping for a 40 amp. The walbro 525 looks like it will do the job for me but boy does that sucker pull some amps.