Would you consider this vacuum normal?
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From: Central PA. - - My AR15 identifies as a muzzleloader
I believe in the Beer Fairy
Would you consider this vacuum normal?
As of a few weeks ago I've got a motor in my car which I bought used and I'm attempting to tune it. Tonight I checked and found that at idle (800rpms) I've got vacuum hovering in the 9-10" range. The cam in it is a TSP Torquer V2 112LSA. It's got 9 deg of overlap, and it's a 234/236 durations.
Would you consider 9" of vacuum too little, or is that to be expected with 9 degrees of overlap? At higher RPMs and off throttle, I'd say it peaks at around 17-18 inches. Briefly of course.
I read online where people talk about 15" on a cammed LS1, but have yet to see someone say they've been down this low. Getting this thing to idle agreeably is quite a challenge. It wasn't too bad before I adjusted the VE table, but now that I have that right, too many other idle parameters need work and I'm not thrilled with the variations from morning cold starts to afternoon warm running idle.
Would you consider 9" of vacuum too little, or is that to be expected with 9 degrees of overlap? At higher RPMs and off throttle, I'd say it peaks at around 17-18 inches. Briefly of course.
I read online where people talk about 15" on a cammed LS1, but have yet to see someone say they've been down this low. Getting this thing to idle agreeably is quite a challenge. It wasn't too bad before I adjusted the VE table, but now that I have that right, too many other idle parameters need work and I'm not thrilled with the variations from morning cold starts to afternoon warm running idle.
Thread Starter
Team Owner
Joined: Jul 2012
Posts: 34,479
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From: Central PA. - - My AR15 identifies as a muzzleloader
I believe in the Beer Fairy
There are times where the tuning gets a bit old. Howtos do not seem particularly helpful. Just followed one on idle tuning and idle is worse than ever. So yea, that could be better. But the gains in other areas keep me going.
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Team Owner
Joined: Jul 2012
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From: Central PA. - - My AR15 identifies as a muzzleloader
I believe in the Beer Fairy
I want to say I don't have a vac leak, but I just don't think I'm getting enough out of this car. Yea, the tune has a little to do with it and that's not perfect by any means. But for it to be this low I'm not sure where to look. I already put on new intake gaskets. Replaced the entire PCV setup, I know the HVAC has no leaks, and beyond that, unless the valves/cylinders themselves are the issue, I'm lost. Oil looks very clean so I don't think there is an issue with the cylinders. The engine wasn't 'new' so leakdown was a little inconsistent, but not too bad. I probably have numbers on that here somewhere. I'd hate to go tearing the motor back down to chase vacuum, but that might be what ends up happening this winter.
(edit) I should have mentioned, lifts are .600 so in every spec mine is milder than yours.
Last edited by K-Spaz; Oct 13, 2016 at 08:43 AM.
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I had a similar cam and my vacuum was about like yours. I had about 12" at 950 rpms.
There has been and continues to be a lot of confusion about pushrod length and lifter preload. It might be time well spent to pop one valve cover and see just what you have.
Do you know what lifters were installed. One of the roller lifters Comp sells requires a preload of only 2 (two) thousandths. There's so little room for the lifter to accept more preload that setting it up with the normal 50-80 thousandths has you running like you're on solid lifters with way too much preload.
As for idle stability, I agree that the information you'll see out there can give you a really bad rash on the bumm. If you want to go Speed Density, not so bad, because the 02 sensors are out of the mix. On the other hand, if you want the oem configuration, you've got reversion hitting the MAF, slow 02 sensors if you have headers, and a VE table that just doesn't want to see what the MAF sees. I was able to get mine to behave somewhat and most people would probably have been satisfied, but I was not, so after far too many hours trying to decipher the interactions, I took mine to a pro and now both my cars come off idle and back very nearly like a stocker.
Since you have HPT, there are some reputable people that will do remote tuning with you. You can be stubborn like me, and battle with it on your own out of disbelief that it can be too complicated to crack, or pay a few bucks to let someone that knows what they're doing fix it for you and go have fun driving your car.
I finally threw up the white flag and have no regrets that I did. My only regret is that I didn't do it farrrrrr sooner.
There has been and continues to be a lot of confusion about pushrod length and lifter preload. It might be time well spent to pop one valve cover and see just what you have.
Do you know what lifters were installed. One of the roller lifters Comp sells requires a preload of only 2 (two) thousandths. There's so little room for the lifter to accept more preload that setting it up with the normal 50-80 thousandths has you running like you're on solid lifters with way too much preload.
As for idle stability, I agree that the information you'll see out there can give you a really bad rash on the bumm. If you want to go Speed Density, not so bad, because the 02 sensors are out of the mix. On the other hand, if you want the oem configuration, you've got reversion hitting the MAF, slow 02 sensors if you have headers, and a VE table that just doesn't want to see what the MAF sees. I was able to get mine to behave somewhat and most people would probably have been satisfied, but I was not, so after far too many hours trying to decipher the interactions, I took mine to a pro and now both my cars come off idle and back very nearly like a stocker.
Since you have HPT, there are some reputable people that will do remote tuning with you. You can be stubborn like me, and battle with it on your own out of disbelief that it can be too complicated to crack, or pay a few bucks to let someone that knows what they're doing fix it for you and go have fun driving your car.
I finally threw up the white flag and have no regrets that I did. My only regret is that I didn't do it farrrrrr sooner.
Thread Starter
Team Owner
Joined: Jul 2012
Posts: 34,479
Likes: 532
From: Central PA. - - My AR15 identifies as a muzzleloader
I believe in the Beer Fairy
I had a similar cam and my vacuum was about like yours. I had about 12" at 950 rpms.
There has been and continues to be a lot of confusion about pushrod length and lifter preload. It might be time well spent to pop one valve cover and see just what you have.
Do you know what lifters were installed. One of the roller lifters Comp sells requires a preload of only 2 (two) thousandths. There's so little room for the lifter to accept more preload that setting it up with the normal 50-80 thousandths has you running like you're on solid lifters with way too much preload.
As for idle stability, I agree that the information you'll see out there can give you a really bad rash on the bumm. If you want to go Speed Density, not so bad, because the 02 sensors are out of the mix. On the other hand, if you want the oem configuration, you've got reversion hitting the MAF, slow 02 sensors if you have headers, and a VE table that just doesn't want to see what the MAF sees. I was able to get mine to behave somewhat and most people would probably have been satisfied, but I was not, so after far too many hours trying to decipher the interactions, I took mine to a pro and now both my cars come off idle and back very nearly like a stocker.
Since you have HPT, there are some reputable people that will do remote tuning with you. You can be stubborn like me, and battle with it on your own out of disbelief that it can be too complicated to crack, or pay a few bucks to let someone that knows what they're doing fix it for you and go have fun driving your car.
I finally threw up the white flag and have no regrets that I did. My only regret is that I didn't do it farrrrrr sooner.
There has been and continues to be a lot of confusion about pushrod length and lifter preload. It might be time well spent to pop one valve cover and see just what you have.
Do you know what lifters were installed. One of the roller lifters Comp sells requires a preload of only 2 (two) thousandths. There's so little room for the lifter to accept more preload that setting it up with the normal 50-80 thousandths has you running like you're on solid lifters with way too much preload.
As for idle stability, I agree that the information you'll see out there can give you a really bad rash on the bumm. If you want to go Speed Density, not so bad, because the 02 sensors are out of the mix. On the other hand, if you want the oem configuration, you've got reversion hitting the MAF, slow 02 sensors if you have headers, and a VE table that just doesn't want to see what the MAF sees. I was able to get mine to behave somewhat and most people would probably have been satisfied, but I was not, so after far too many hours trying to decipher the interactions, I took mine to a pro and now both my cars come off idle and back very nearly like a stocker.
Since you have HPT, there are some reputable people that will do remote tuning with you. You can be stubborn like me, and battle with it on your own out of disbelief that it can be too complicated to crack, or pay a few bucks to let someone that knows what they're doing fix it for you and go have fun driving your car.
I finally threw up the white flag and have no regrets that I did. My only regret is that I didn't do it farrrrrr sooner.
Well, with it being wintertime I'll probably beat my head against the wall a while yet. There's no tuner I know of within 3 hours of here so I'll probably mess with it some more. It seems to be running better today, and idles nice (more or less). It isn't perfect but it's drivable. I need to move on from the idle and get the top end and higher rpm timing right now. I didn't want to move on before I investigated the vacuum thing. If that was unduly low, I was going to look into that before attempting to go further. I just didn't think there was a vacuum leak (other than the valve overlap)I imagine if I was to have the block bored, put in new pistons and rings, get the heads redone, I could probably get a lot more. But I don't intend to do that, at least not for a while anyway.
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