Installed new cam and lifters. Having a low vacuum issue. I min datalog to look at.

[06blackgto]

Hi guys. If anybody could figure this out I would really appreciate it. I had a ls7 lifter basket collapse on me about a month ago. So I put in a new set of johnson link bar 2116LSR lifters. The cam is cut on the exact same specs as my old one. Only diff. is the new cam is a cam motions cam on softer lobes for better valvetrain control. The old cam was cut by lunati which has alittle harsher lobes. the cam is a 219/232 .625 .599 109lsa Nothing too radical besides the lsa. I notice that my vacuum is down quite abit. before at idle in park it would hang around 13.3 and in gear foot on brake it would be around 8.8 in hg.
Now at idle in park it's in the low 10's and foot brake in gear it's in the mid 6's. Having alittle hot startup issue, but I have been adding more air at the temps and I believe that is helping that part out. I just for the life of me can't figure out why my vacuum is down. Unless I have timing off one tooth, but the car seems to run great and sounds great. I haven't taken over 3500 rpm's yet. just babying it getting the street tuning down. I know I need to lean it out alittle bit more at idle. And there are no vacuum leaks anywhere. Thanks for any help. I tried upping idle timing 4 to 5 degrees it didn't help.

[06blackgto]

If anybody could just look it over for a sec I would appreciate it. I just spent the day taking the timing cover off and it's lined up dot to dot. Car seems to be running great besides alittle hot start issue that Im working on. and the cam is on a 109+0 . so dot to dot should be right on the money.

[GHuggins]

I'd solely be guessing or even grasping at straws here, but just a few thoughts.... Did you check cam degreeing, pushrod length or is it somehow even remotely possible that with this cam not being the radical "on / off" lobe profile that it's somehow just all around flowing air differently knocking the engine vacuum off some?

If the tune hasn't changed between cams, it must be either a mechanical difference in the motor or a vacuum leak from an improper oil seal?

[06blackgto]

Thanks Ghuggins. yeah i haven't changed anything in the tune. I did go on a wot run tonight just to 6200rpm's. It pulled strong and smooth. I did get the heads ported on the exhaust side and new btr .660 valvesprings since mine had 35k miles on them. One other weird thing was my oil pressure is now down about 5psi at idle and mid throttle.
I'll pick up a vacuum canister and see if that helps. maybe the new johnson short travel slow leak down link bar lifters are doing better then my ls7 lifters. Maybe they were bleeding down too quickly and throwing the old cam off it's lift and duration. I do have .050 preload on my new lifters. They like .025-.035 preload. but I didnt think the extra .015 preload would hurt. I don't have a degree wheel so didn't check it. I measured pr length. and needed longer ones with the link bar lifters. 7.550 compared to my old 7.400 pr's.

[jpb1972]

Did you ever figure out your issue?

[steve-0]

Hi guys. If anybody could figure this out I would really appreciate it. I had a ls7 lifter basket collapse on me about a month ago. So I put in a new set of johnson link bar 2116LSR lifters. The cam is cut on the exact same specs as my old one. Only diff. is the new cam is a cam motions cam on softer lobes for better valvetrain control. The old cam was cut by lunati which has alittle harsher lobes. the cam is a 219/232 .625 .599 109lsa Nothing too radical besides the lsa. I notice that my vacuum is down quite abit. before at idle in park it would hang around 13.3 and in gear foot on brake it would be around 8.8 in hg.
Now at idle in park it's in the low 10's and foot brake in gear it's in the mid 6's. Having alittle hot startup issue, but I have been adding more air at the temps and I believe that is helping that part out. I just for the life of me can't figure out why my vacuum is down. Unless I have timing off one tooth, but the car seems to run great and sounds great. I haven't taken over 3500 rpm's yet. just babying it getting the street tuning down. I know I need to lean it out alittle bit more at idle. And there are no vacuum leaks anywhere. Thanks for any help. I tried upping idle timing 4 to 5 degrees it didn't help.

lol you are ruining 109 lsa cam . sure you gonna loos all the vacuum, im running 112lsa cam and my vac. 8 iH , at idle , also im running electric brake vacuum pump ,

[10SecSleeper]

It's gonna have less vacuum. Your logged MaP looks typical for the mods.

Start over with the tune, From the base file. Don't get your hand into everything. Find out what each thing is actually changing.

[ABADZL1]

It's gonna have less vacuum. Your logged MaP looks typical for the mods.

Start over with the tune, From the base file. Don't get your hand into everything. Find out what each thing is actually changing.

Do you realize this thread is over a year ago?