200MPH Texas Mile build

[gunpilot]

Been a tuning nightmare fighting the wastegate issue.  Here is what happened:

Huron Speed wastegate comes with a 7lb spring installed, and a 4,14, and 17 spring in the box.  I only want around 10psi, so we started tuning with the installed 7lb spring.  After 3 good pulls of consistent 3lbs of boost, we figured we had a boost leak somewhere.  After investigation, we found the wastegates were opening at 3lbs of boost.  We pulled them apart and found springs that looked just like the 4lb springs in the box.  We figured the wrong springs were installed at assembly.  We contacted Huron Speed, and he informed us that we did in fact have the 7lb springs.  They look REALLY close to the 4lb springs.

Well, they open at 3psi, so they do us no good.  I did not want to put on the 14lb springs because I don't want to harm the motor.  We hooked up a manual boost controller to the 4lb springs, and could only get 7psi before the boost would blow by the controller and actuate the wastegates.  We need larger springs.

A boost controller only controls boost up from spring size, and not down so I did not want to slap in the 14's and give it a try.  We set up shop air on a pressure gauge and tested each of the springs in the Huron Speed gates to see where they open.  The 4lb opens at 1lb, the 7lb opens at 4lbs, the 14lb opens at 7lbs, and the 17lb opens at 12lbs.  To see how that compares to a Tial wastegate, we had one laying around with a Tial 12lb spring in it.  With the same tool, the 12lb opened at 12lbs!  I have no explanation of why the Huron springs actuate way below their labeled numbers, but they do.  This cost us 2 dyno days to figure out.  We did a run with the Huron gates and Huron 14lb springs with no boost controller, and it only gave us 7lbs (just like our tool predicted).

I have since ordered a Turbosmart dual stage boost controller, and left the 12lb (opens at 7lb) springs in.  I will use the 12lb (opens at 7lb) springs as my low boost setting and shoot for 10lbs as my high setting.  7lbs of boost gave us a 550RWHP number and we should be 650+ on 10psi.  That will be 100RWHP at a flick of a switch.

[danameisoj]

got a picture of the dyno graph.  im intersted in seeing the way the t6 responds.. im in debate of swapping into a borg 80mm over my 7875

[gunpilot]

Best I got now

[freeskier7791]

whats preventing you from running higher RPM, I feel like you are not even halfway into the potential of the turbo.

[gunpilot]

Limiter set at 6200 for now while we dial it in. We will shift it to 6800 for final pulls. I’ve heard 7000 is about the safe max on these motors.

[freeskier7791]

Limiter set at 6200 for now while we dial it in. We will shift it to 6800 for final pulls. I’ve heard 7000 is about the safe max on these motors.

I bet you find some power in that final 800 rpm

[gunpilot]

I am also switching out the stock RX-7 4.11 rear end with an Explorer 8.8 with 3.27 gears.  That should spool it up a little differently.

[SuperSlow]

Definitely power to be made the way that torque was still climbing, and the gear swap will help a ton.

You going to Tx2k? I'm just south of Austin and may or may not make the trip out.

[gunpilot]

Quick update. Car has made about 40 pulls, and we can not get over 9lbs or boost. We pressure tested everything and it is good. Has to be a problem with the turbo. We even disconnected wastegates for a wide open pull and only got 8 psi. I just ordered another to replace it and should have it tomorrow. Fingers crossed.

[freeskier7791]

Quick update. Car has made about 40 pulls, and we can not get over 9lbs or boost. We pressure tested everything and it is good. Has to be a problem with the turbo. We even disconnected wastegates for a wide open pull and only got 8 psi. I just ordered another to replace it and should have it tomorrow. Fingers crossed.

Hopefully that fixes it, anything look weird on the existing turbo?

[gunpilot]

Well, it’s less than a week to the race and I finally dropped the rear end to install the 8.8 with 3.27 gears and Detroit tru track. Taking my time to clean it all up. Tuning still not done. I am waiting for new waste gates to arrive. Plan is to finish rear end and finalize dyno on Tues/Wednesday. Down to the wire.

[gunpilot]

If it’s off, gotta clean. Axles were a pain in the butt! RX-7 side would not go over blind C-clip. I ended up measuring splines. New Ronin axles were .2 larger. I did a light sanding and stuck them in the freezer. That did the trick. Light hammer tap seated them nicely. Brace is welded in and painted. Should have time to put it all in tonight and measure for drive shaft.

[freeskier7791]

Looks good, are you gonna be ready?

[blacksi]

If you are cutting it that close, if it were me I'd look for and autocross or track day or something to take the car out on and beat the piss out if it before the mile event.  Just to get anything that isn't quite right to break or rear its ugly head before your cruising down the road at 200mph and have it show up.  With that said I can't wait to see what it will run.

[Cobranut]

If you are cutting it that close, if it were me I'd look for and autocross or track day or something to take the car out on and beat the piss out if it before the mile event.  Just to get anything that isn't quite right to break or rear its ugly head before your cruising down the road at 200mph and have it show up.  With that said I can't wait to see what it will run.

I agree, try to get some hard miles on it before you put your life on the line.
Lots of bad stuff happens when things break at 200+ MPH.

Good luck, I'm looking forward to this run as well.