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The Terminator
Engine/Tuning
Self Tuning With SCT Pro Racer
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<blockquote data-quote="03cobra#2" data-source="post: 16443270" data-attributes="member: 52057"><p>Update, finally some progress in the right direction.</p><p></p><p> First thing I did was start the car let it warm up and see where my vac is at idle. At 875 rpm or so it's at 11-12in of vac. Boost bypass is fully open and not fluttering. I even tried to close it while the engine was running and couldn't. So plenty of vac at idle to keep the bypass open. No problem there. </p><p> </p><p> Next I took the car for a spin watching my boost / vac gauge the whole time. What I noticed is light part throttle acceleration 1500-2000 rpm when the gauge is showing vac and approaches 0 you get the surge and the wideband shows a temporary lean spike. I believe that's the boost bypass snapping shut at the last second right before boost (0 on the gauge) and a rush of air going in the engine causing the lean spike. With such a big blower and pullied for 26lbs it does not take much pedal effort at all to get right into boost, like 15 TP counts on my log. </p><p> </p><p> My thought is if there is more spring pressure in the bypass valve it can close at say 4-6in of vac instead of 1-2in hopefully closing before any boost builds up. So my solution was to install a spring on the arm of the boost bypass to help pull it closed sooner. My thinking is that during part throttle low rpm acceleration the bypass will start to close at say 3-4in instead of 1-2in hopefully smoothing out the transition.</p><p></p><p> I went to home depot bought a variety pack of springs and picked one out that I felt was right. Installed it on the arm of the bypass valve and attached the other end to the fuel rail bracket. In essence giving the bypass more tension in the closed position.</p><p></p><p> Started up the car and let it warm up and idle at 875 or so rpm with about 11i-12in of vac. Checked the bypass and it was locked open, could not close it with my finger. So still more than enough vac to keep it open at idle. Blipped the throttle and it closed. Took the car for a spin and did notice the surge was decreased... Definetly better. The surge I noticed on my boost / vac gauge is happening sooner meaning the bypass is closing sooner... so the spring I put on there is working as intended. Vac to boost transitions at 2000 rpm and up is smoothed out and finally I feel like I'm heading in the right direction with this hiccup.</p><p></p><p> Low speed drivability and idle is good to go. I will probably hunt around for a stronger spring and put it on there in hopes to cure the problem all together. Doing research it's a common problem. Whipple even came out with a fix (putting orafice in vac line to solenoid for some guys). I'm not sure if it's the cams, the fact it's pullied for 26 lbs or what but at least I know what's going on and have improved things. At this point I'm happy with how it drives, and look forward to enjoying the car now and getting some more dyno numbers now that I can get my iats lower with ice.</p><p></p><p>Don't mean to ramble but I figure someone will run into this. [ATTACH=full]1648112[/ATTACH]</p><p></p><p>Sent from my Pixel 2 XL using Tapatalk</p></blockquote><p></p>
[QUOTE="03cobra#2, post: 16443270, member: 52057"] Update, finally some progress in the right direction. First thing I did was start the car let it warm up and see where my vac is at idle. At 875 rpm or so it's at 11-12in of vac. Boost bypass is fully open and not fluttering. I even tried to close it while the engine was running and couldn't. So plenty of vac at idle to keep the bypass open. No problem there. Next I took the car for a spin watching my boost / vac gauge the whole time. What I noticed is light part throttle acceleration 1500-2000 rpm when the gauge is showing vac and approaches 0 you get the surge and the wideband shows a temporary lean spike. I believe that's the boost bypass snapping shut at the last second right before boost (0 on the gauge) and a rush of air going in the engine causing the lean spike. With such a big blower and pullied for 26lbs it does not take much pedal effort at all to get right into boost, like 15 TP counts on my log. My thought is if there is more spring pressure in the bypass valve it can close at say 4-6in of vac instead of 1-2in hopefully closing before any boost builds up. So my solution was to install a spring on the arm of the boost bypass to help pull it closed sooner. My thinking is that during part throttle low rpm acceleration the bypass will start to close at say 3-4in instead of 1-2in hopefully smoothing out the transition. I went to home depot bought a variety pack of springs and picked one out that I felt was right. Installed it on the arm of the bypass valve and attached the other end to the fuel rail bracket. In essence giving the bypass more tension in the closed position. Started up the car and let it warm up and idle at 875 or so rpm with about 11i-12in of vac. Checked the bypass and it was locked open, could not close it with my finger. So still more than enough vac to keep it open at idle. Blipped the throttle and it closed. Took the car for a spin and did notice the surge was decreased... Definetly better. The surge I noticed on my boost / vac gauge is happening sooner meaning the bypass is closing sooner... so the spring I put on there is working as intended. Vac to boost transitions at 2000 rpm and up is smoothed out and finally I feel like I'm heading in the right direction with this hiccup. Low speed drivability and idle is good to go. I will probably hunt around for a stronger spring and put it on there in hopes to cure the problem all together. Doing research it's a common problem. Whipple even came out with a fix (putting orafice in vac line to solenoid for some guys). I'm not sure if it's the cams, the fact it's pullied for 26 lbs or what but at least I know what's going on and have improved things. At this point I'm happy with how it drives, and look forward to enjoying the car now and getting some more dyno numbers now that I can get my iats lower with ice. Don't mean to ramble but I figure someone will run into this. [ATTACH=full]1648112[/ATTACH] Sent from my Pixel 2 XL using Tapatalk [/QUOTE]
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