Easy solution for D1's and cruise bucking
 

I had a car recently that got a D1 on his H/C car.We installed the kit and there was some real bad bucking at cruise.Found out the MA was getting too much air(not enough bypass).After figuring it out I ordered another 1 1/2 bypass valve assembly from ATI.
We installed this on the pass side up pipe midway up the radiator by drilling the pipe,welding a 1 1/2 fitting then installing the valve and pointing it at the ground under the radiator.The vacuum was Tee'd off the other valve.
The car drives perfect now.No bucking at all,start up is great..

Figured I'd pass this on ;)

you can just up the MAF numbers up to 6Khz also and get rid of 99.9% of the weirdness with an ATI. If you look the MAF numbers in that range are lower then a stock car and that drops the PW way too far at idle and part throttle and when the car pulls fuel to drop the ltrims the car just dies. It doesnt make sense since you would think the numbers would be higher since there is a lot of air moving there with the ATI but with the throttle blade closes/almost closed it must get some kind of reversion thing happening. C5 MAFs are ~a foot away from the TB and they dont seem to have that problem..

More bypass is the proper, although more expensive, way to do it though..

:cheers: good stuff you guys

I also had to add a second bypass valve. I was getting too much turbulence without it.

Been over a week and still great..
Yes,you can play with the MAF table but that isn't really a permanent fix..This is actually cheaper than what I've read of people going with $500+ valves..
I've got a few E-mails about how to do this,hopefully next weekend I'll take some pics so people have an idea on how it goes together,really simple when you see it.

Michael, hows your car runnin'. Good I hope. :drive:

Which Mike you talking too in here, Im a mike too :cheers:

Not sure what you mean by the MAF table changes not being permanent, its not something will be learned out with the ltrims - on the contrary - it makes the ltrim numbers very consistant across the board. It just takes a little time to do it. I have 4 ATI cars running around that idle/drive like stock and no one has complained.

Only problem is if you pulley up a bunch it will change things a bit, I do think having more bypass is the right way to do it (or move the MAF away from the TB/change to a draw through) but its hard to get any easier then LS1edit :)

Sorry, Boost@4500 is the Mike I'm refering to.

I was finding that MAF readings were way too unconsistant and varied too much each time light load was put on it,meaning significant A/F changes while cruising.Yes it can be tuned it with some time put into it.I chose to get rid of turbulance by the 2nd valve..

Or, if you want to get fancy just disable the MAF for the lower RPMs. Mine doesn't kick in until ~1800+ RPMs. Works pretty well with the supercharger strapped on. I don't have any bucking issues at least with the S/C and my cam.

curious to see your guys cam specs I run a large cam with the blower

Good point..Anyone else running 230+ duration?

I'm running a Hot Cam (218/227 @ 50 .525" / .525" 112 LSA) and I'm experiencing really bad bucking at cruise. Hope to get something done soon to alleviate the problem.

Edit: Running a D1-SC @ 5psi

The car is running pretty good. I just put a 9" in it last week so I'm very anxious to get back to the track and see how she runs.

Interesting, what I did was compare some stock engine MAF logs and played with the MAF numbers (below 6khz only) until I got the g/s very close to stock. That eliminated all the idle and part throttle, mostly cell 4, weirdness.

bypass valve is the right way to go, i would love to see some pics of it, if you get any taken

Ryan

How do you go about disabling the MAF for an rpm range like that? :secret:

Lord. I'm running the same cam as you know and I don't have any bucking effect. I am running a aftermarket BOV though. I wonder if that would have any effect.

Clint

Clint -- I posted my dyno graph on LS1.com a few weeks ago and you said that my HP numbers were low as well. (467hp/483tq) Hopefully I can get this thing straightened out soon. But I do believe the problems are different. Hopefully, adding an extra surge valve or an aftermarket BOV will fix my part-throttle issues. Then I'll stick it back on the dyno and try and figure out what is going on with my top-end. I was running Denso Iridium plugs @ 0.042 when the car was on the dyno, but have since switched to NGK TR6s @ 0.035. Hoping that it's something simple, like the spark was being blown out. :eyes:

Dyno graph in case anyone else wants to see it: http://www.outerworld.ws/dyno/1.jpg