[quote=94vettelover2;1572380402][quote=Weav's Vet;1572367250]All righty then, something I've never heard of!!!!! This might explain a lot. I guess maybe I'll have to pull that intake back off to have a look see. This engine has always had a crappy idle like a vacuum leak somewhere. Maybe this is why! Thanks!!!!!

Is this a fairly common problem? I did wash the intake down with kerosene and brake cleaner when I had it off. Perhaps I did loosen the sealant up.

 

Here is a pic. I am still trying to find my before and afters with Comp Cams

Comp Cams on my LT1

Factory GM

 

Okay, mine look a lot like the Combination Motorsports guide plates. Where did you find the GM plates? They're nice an straight.

 

Is this enough to hurt anything or cause vibration?

 

The part number is on the picture, GM part number 14041051. Dealership, or any reputeable parts counter that sells AC Delco/GM stuff.

 

Thats not real bad, but I have OCD. Its all about the details and proper geometry. Others may have a different opinion.

 

Well of coarse I missed it.

I called locally and a Performance dealer. No such number. Are you sure it's correct?

 

Let me look it up as it is/was a common thread on another forum. I thought I posted over here.
Here it is
14011051
http://www.gmpartsdirect.com

 

Can anyone say how common of a problem this is? Of all the threads about vacuum leaks I don't recall ever seeing it. Maybe I just missed it.

Is it worth taking off the intake to check?

 

Okay, so there's a difference between the lifters, right? I mean, they (LS7 and GMPP) have different part numbers, are of a different design, right?

There are posts saying that if you go to GM for replacement lifters what you'll get are LS7s, that they are the "replacement" for LT1 lifters. I also read that the LT1 lifters are no longer available. Is this just more "bad" information?

My thoughts on "lifters were holding their pressure" is a valve spring issue. Too much valve spring pressure over-comes the lifters' spring, collasping it. I suspect the excessive spring pressure also forces oil out of the lifter; sort of in a reverse flow.

Check me on this:

As the valve spring begins to compress, higher and higher pressures are applied to the rocker, pushrod and lifter. That pressure is working directly against the camshaft lobe throught the rocker, pushrod and lifter. All the while this is happening, the oil pump is appling pressure to the oil entering the little hole in the body of the lifter.

So we've got pressures working in different directions; effectively against each other.

At some point, the valve springs' pressure can over-come the oil pressure AND the lifters' internal mechanism. At that point, the lifter plunger begins to collapse.

Now, wouldn't that cause the lifter to no longer be able to follow the cam lobe? Would that result in a LASH condition, where the lifter bounces on and off the cam lobe, as opposed to a PRELOAD condition where the lifters remain in constant contact with the lobe?

If that's what's happening, there'd be noise generated which could/would be interpreted as knock - then we'd have timing retard.

Could that be why AFR sells a spring preload kit that maintains spring pressure on the lifters WITHOUT having to resort to higher pressure valve springs?

Just trying to wrap my mind around this issue. Since something's definitely going south in the 4500 rpm range and there HAS to be a cause.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 MY 2010!!!

 

Thank you very much........
I've asked several times about the lifters not holding pressure. It was said the OE lifters were good to 7K. I've said they act like they are loosening up after running it for a while. In others words some of them start ticking after I set the preload and button everything back up. LE said to run a thicker oil like in the 50wt range. I didn't want to do that. So now once again I'm back to this knock retard issue. Hopefully the LT4 module and the Teflon tape I put on the sensors today will take care of it. I still have this possible lifter problem or is it a problem if the above fixes the knock retard if there was knock retard.......mercy

Thanks again Jake for all of your brain storming!

 

Here are the lifters I ordered.

http://www.summitracing.com/parts/NAL-12371042/

 

7K!? I wonder. AirFlow Research says HR valve train instability kicks in at not much over 6K. If you check out their website I believe there's a write-up on that.

No matter though, since what you're experiencing is well below either of those. My thinking is that since your jaggedness is beginning as such a relatively low RPM, something REALLY significant is happening.

As I wrote before, if it was kicking in at the top of the band I could more easily see it happening, but IN THE MID-RANGE??!!

How about checking with SKI on CF; drop him a line. I believe he and his Dad are on top of a lot of this stuff. He may be able to point you in the right direction if he doesn't know, himself.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

 

You did the right thing. Although factory lifters have a great track record, I think the combination of age and higher than typical spring pressures makes swapping them out a positive step..

 

I've had my doubts about them all along Pete. I'll order some LS7 lifters. I can check the intake casting screws at the same time.

 

I havent been around here in a while. These are the LS7 lifters I am using. They are the only ones GM carries now for the LT1. I also measured the pushrod length with a checker. I know I've asked several times before but.. Was the car ever datalogged? That is the very first thing I would have done. I hope you get this fixed soon. Probably something as simple as a bad opti.

 

I have a spare Lt-1 intake manifold in my basement.I checked the number of casting screws/plugs-there are 5.If I knew how to upload pictures,I would take a picture of the bottom of intake & pictures of my corvette that I have in my phone & post them here.Wouldn't be bad idea to reseal those plugs anyway

 

Much appreciated!

I just ordered new lifters so I'll reseal them when I replace them.

 

Wow, this has got to be the most information I've ever seen in one thread anywhere. It could be a sticky someday!! I feel for you Weav, I wish I had more input to help you out. I had about a two week delay at the end of my build because it took me that long to figure out I had too much preload and the valves were never shutting. But mine was bad enough it wouldn't even run, just spit fire and unburned fuel out the headers. Yours actually starts and runs, so probably not the same problem.

Anyway, just wanted to offer what little info I can. My dual valve springs are rated at 165@1.8, 385 @1.2. I cheated the install height to 1.81 to get the seat pressure down to right about 150 closed, about 350@~1.27 open. This is still considerably more spring than Comp Cams calls for with the 503 cam, but they seem to get the job done. And on stock 17 year old lifters. I haven't run it on a dyno yet, hopefully I don't have the same problem you do. It doesn't feel like anything's wrong with it, it pulls very hard all the way to the rev limiter at 6400, and runs the times I hoped it would. Hmm, I'm curious though. It'll probably be April before I get to the dyno, so hopefully you've figured it out by then. Wonder if it would show up on a data log? I also don't have the same knock module you do (it's a 92), and I believe mine has been almost completely tuned out.

One other thing that stands out, you said there was a puff of smoke from one side before the build. Now the cylinder pressure is lower on one side than the other, and then there is that post earlier suggesting one side of the engine isn't acting the same as the other. Not sure where to go from there, but maybe a lead for Jake and Pete to flush out? Or maybe a bunny trail to take their attention off the real problem....

Allright, I'll get out of the way again and quit distracting the guys who really know what they're doing. Best of luck, there are a lot of us pulling for you even if we don't all fill the thread with non-helpful posts to say it.

 

Thanks for the info and support reoch! Whatever is going on will come out it's just being stubborn. I watched a youtube video of your car and it sounds great! Hopefully I can get this problem squared away and I'll have similar results.

So here's where I am.........
Everything is back on underneath the car so no more creeper time to speak of. Everything is on the front of the engine except for some wiring and radiator hose, serpentine belt, that sort of thing. I found some NITB GM guide plates on another forum so the intake is coming off to replace the TFS guide plates with the GM's, new LS7 lifters going in, recheck push rod length (it's probably going to be 7.1 which I happen to have). Reseal casting screws on the bottom of the intake. Install LT4 knock module. Put everything back together and hope for the best. I'll give the data logging software another shot when I get it fired back up. If I have missed something in all of this tearing back apart I have no idea of what it is. It has been a bitch redoing it all but now I know what isn't the problem..........hopefully It'll be a few days before it all gets here but I'll be back!

Once again I want to thank all who have helped me with this! I couldn't have done it without you!