Just some tuning info about this blower setup: Turns out it likes a fair amount of idle advance to keep it happy. I had a nice low idle with solid AFR's at 15deg but after revving high or holding a rev, RPM would just smoothly fall to Zero, regardless of fueling. I had a hard time discerning whether it was going rich or lean. I bumped the idle advance up a bit to 20deg and it seems to keep it happier, though it's not perfect just yet. I'm a pretty picky tuner and like cold/warm idle and rev qualities to be perfectly crisp and stable and this blower on e85 with the lag of throttle body injection has it's own learning curve.

seems like there aren't as many empirically supported "rules of thumb" for tuning roots blowers as there are for port injected cars. Like "roots blown fords need 20-25deg at idle" or there will be some people that can cruise at lean AFR's and some say they can't cruise unless it's rich. As an engineer, I like to see data and experiments (if not calculations) to support claims.

 

Yes, this is when engine is warm. I try to do all of my ignition and fuel table tuning with a warm engine, then add in the enrichment compensations for cold engine, colt air temp, stuff like that. There might be a way to utilize the idle valve during Decel to "catch the fall" by cracking it when the RPM drops at a certain rate but I haven't monkeyed with that much yet. People make these run and rev without an idle valve so I'd like to be able to accomplish that.

I haven't heard about e85 having a rough cold idle. My cars both crank up just fine and warm up fine, just have to keep the AFR's in check and it stays happy.

 

Impressive numbers! I've thoroughly enjoyed tuning with e85.

 

While I'm on E10 with a carb, our timing should (maybe) be in the same ballpark. I'm running 20 degrees of static advance, with another 10 degrees of mechanical advance, all in by 2000 rpm. Working well so far. I haven't had time to run a timing sweep on a dyno yet, but it has been a good rough point to begin for me. I'm around 13.0-ish afr at idle, and see up to 16.0 at cruise. Full throttle, I'm consistently 11.5AFR. My only issue is with the slightest throttle input, it goes pig rich maxed AFR guage 10.0. I need to play with the squirters, but no time!

 

Ah okay, so that's similar to what I'm seeing ignition wise. I'll throw a timing light on it to make sure I'm not retarded but it acts better near 20deg. If the timing light checks out, I might add a touch more in there to see if it helps. My fuel table is starting to clean up so tip-in, WOT, and cruise are getting better. I'd much prefer to make calculated changes on a computer than spend time making carb changes.

 

I got lucky. Aside from having to play with the pump shot, my carb is very, very close with the out-of-the box Holley jetting on their supercharger carb.

 

Any updates on this build?

 

post

 

Actually yes..

I'll have to take more pictures soon but I found that tuning this blower setup with TBI using the speed density calculations was pretty tough. Possibly the way manifold pressure/vacuum is created with the blower has something to do with it, or how the injectors fire above the blower, but I decided to try something else...

I sourced a New take-off MAF sensor from a GT500 (2007-ish) and had a maf flange welded to my "cold air" tube. Installed and wired the maf, reconfigured the tune for MAF rather than Speed Density, sourced a GT500 MAF Transfer Function, and went to town. Same ECU, Same TBI, pretty much everything the same. This setup resembles how all the newer fords place a MAF sensor before the blower.

For one thing, tuning is much simpler now. The sensor tells the ECU exactly how much air mass is moving into the engine so it can match the incoming air with a proper amount of fuel, based on what your AFR reference table shows. This eliminated the complex speed density calculations. I have a MAT correction table that keeps the AFR even across all Air Temps, which was simple to populate by adjusting as the engine warmed. The car now doesn't stall, doesn't hesitate, revs cleaner, drives better, etc. I still have some "trimming" to do since the transfer function wasn't developed for this intake tube but it was pretty close from the start and the Auto-Tune function in Tunerstudio does this trimming for me, based on my reference AFR table. I also have closed-loop fueling to help keep things in line.

Now, if I ever want to change the AFR table in the future (maybe get more aggressive up top or better cruise economy), I just change the values in the AFR table and the fueling will automatically be correct. If it was speed density, I'd have to readjust the fuel table to achieve that new AFR.

Very unique combination of parts used in this build. I'm really picky with tuning and driveability and this change was pretty relieving.

 

Thanks for the update. I have a brainstorming question for you. Here's the plan. 420" Windsor, Holley Hi-Ram Intake, 6-71 Blower, Twin Holley 4bbl TBI. Until boost comes in fuel is fed by injectors in the throttle bodies. Boost comes in and the 8 lower injectors begin flowing . Now my question concerns adding a MAF sensor. Using something that looks like a mailbox on top of the throttle bodies then mounting the MAF on the front. I know the placement wouldn't be ideal put I've read on some rock crawler sites of mounting the MAF sensor directly in front of the throttle body. What are your thoughts?

 

Very interesting idea, though I have to ask the point of the throttle body injection when you're using port injection anyway. Just get big injectors in the ports and reduce the complexity of tuning. The MAF in the scoop is probably going to give you headaches when modeling a transfer function for something so large and uniquely shaped, with such a harsh flow path. Flow across a MAF sensor needs to be as laminar as possible and a scoop atop two throttle bodies will be anything but smooth. I'd try speed density tuning on that setup before installing the maf. you may have pretty good luck, especially if port injecting fuel.

As an update to the thread: I just took the car for a tuning session and it's running great, very crisp, power is great, tires are dying. The car has a high speed vibration at the trans/driveline so I believe my driveshaft is out of balance. I'll be removing it and taking it to get looked at or rebuilt. Looking forward to getting this thing on the road for some car meets and racing!

 

From what information I've found about the od style roots blower it requires fuel flow over the rotors for cooling. I know all the newer stuff runs dry. Thanks for your thoughts o the subject.

 

I read about that too, and I thought I read something about Teflon stripped vs non-stripped rotors with fuel over them. one of them needed it and one of them didn't. My manifold didn't have any room for port injectors but if you end up with a blower that doesn't need fuel over top, I'd just run port injection alone. If you need fuel in the blower, I'd probably do primarily port injection with 1 or 2 injectors up top just to spray the rotor pack.

Start a thread up when you get your build goin!

 

So what are the odds the balancer could be bent and not the crank?

I noticed my crank pulley wobbling and it looks like the balancer also wobbles (the inner section), though it almost looks like the crank itself is rotating true in between the balancer and timing cover. I was about to convert the setup to a cog belt and noticed it, now I'm worried the motor is trash.

 

Yes factory crappy crank with a bunch of belt tension so I wouldn't be surprised if it was trashed but it's odd to me that the center section is also wobbly. I'd have to rent a balancer puller to check it.

 

Dammit you know your sh*t man. I am impressed bud. Who are you? A retired mechanic? with 40+ years of experience you are trying to remember or what? I see a lot of stupid comments and posts in a lot of different forums but you are always on point. Hat's off to you vinces427bb