I would have the thing tuned long before I would take a down step and swap the cam to a stock whimpy cam and risk a cam going flat, then you'll be out a lot more.
CK5
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Thinking of doing the unthinkable... *Rotor to cap gap. Normal?*
- Thread starter y5mgisi
- Start date
There is also the option of spending the $150. on what you need to burn your own chip? Lots of places to learn! If you really don't need the vehicle to drive daily right now just take some time to get equiptment and spend some time in the learning curve. I have spent my whole life being a gearhead and have formal training (4 class's a year instead of one in high school and one year at Lincoln Tech) but went another route for carreer. Got into EFI when I bought the first Chevy truck that came with TBI in 1987. A short bed 2wd GMC 5.7L. Got into doing conversions with this system to other carbed cars of all makes about ten years ago. I enjoy doing them and electronically tuning more then the wrenching now that I am 51 with 3 back surgeries.
Look in the EFI section. Dave has a write up on How To!
Actually he's right, that's a good idea. Learn how to tune it yourself if it's not that expensive.
y5mgisi
1 ton status
Damn you guys and your voice of reason!
y5mgisi
1 ton status
Thats true too. So i dunno. I guess maybe i should advance the cam still and do the tuning? Just forget about the junkyard cam?
I don't tell anybody what they should do, but if it was me I would start by advancing the cam to see about building more cylinder pressure (vacuum in the lower rpm ranges) first.
It can also tell other things, such as if it hardly makes any difference in cylinder pressure, something else mechanically is wrong.
A cam is something you never want to re-use. But through NAPA (Melling) you can get an inexpensive new replacement cam if you must replace the cam.
For your situation- looking for good idle quality, good performance in the lower rpm range, it can't hurt to advance the cam and see what changes it made. Then I would set inital timing (distributor) around 4-6 degrees advance, and see if you can't get 18-20" of vacuum.
From there, you could still tune away with a new chip, etc., to get it running even better, especially above 1,800 rpms. But thats your choice.
It can also tell other things, such as if it hardly makes any difference in cylinder pressure, something else mechanically is wrong.
A cam is something you never want to re-use. But through NAPA (Melling) you can get an inexpensive new replacement cam if you must replace the cam.
For your situation- looking for good idle quality, good performance in the lower rpm range, it can't hurt to advance the cam and see what changes it made. Then I would set inital timing (distributor) around 4-6 degrees advance, and see if you can't get 18-20" of vacuum.
From there, you could still tune away with a new chip, etc., to get it running even better, especially above 1,800 rpms. But thats your choice.
y5mgisi
1 ton status
That is probably the best way to go about it huh?
The one fact I do know, is that no amount of tuning will cure low cylinder pressure. You need another 20#'s plus to be able to build good vacuum at idle / above idle.
But I will say your engine situation is quite unique, so I make no guarantees over the internet. I do hope you get it solved, or closer to being completely solved.
But I will say your engine situation is quite unique, so I make no guarantees over the internet. I do hope you get it solved, or closer to being completely solved.
y5mgisi
1 ton status
Well hell. I guess its not too much trouble just to advance the cam some. So maybe i will still do that and then also tune regardless.
y5mgisi
1 ton status
So im thinking these guys to advance the cam if my crank gear doesnt have the multiple keyways on it.
http://www.summitracing.com/parts/CCA-4760/
http://www.summitracing.com/parts/CCA-4760/
What is your vacuum, I went back a couple pages and still didn'y see it? Why are you so set on advancing the cam? You already know your cam is straight up didn't you just put a new chain set on there? The cam will be cut 4 degrees advanced from the factory most likely. You have an aftermarket cam, vacuum is not going to be stock anymore, and it doesn't have to be perfectly stock. Have you done a leak down test? Compression test? I would do a leak down test, and compression. If both those are good then tune the thing. If they are bad then you can find what your problem is. Good luck.
If your going to learn to tune why take the engine apart? I'm telling you that cam can be tuned. If you can't then it may have been keyed off a few degrees. I use a cam degree wheel and check cams whenever I install them and 9 times out of 10 they are within a 1/2 degree. Tenth time is usually bad, way off and I return the cam.
y5mgisi
1 ton status
Folken, the new chain was on the blazer. This problem is with my 90 suburban. My vacuum at a warm idle is around 15in.hg or so. That's with the timing advance as far as it will let me. Mix that with my low cylinder pressure (compression?) And it makes me think that advancing the cam could do me some good. Little back ground about the motor, it was a rebuilt short block that I got from a guy that died(ya I know) so i couldn't ask him anything about it. I just measured the bore and stroke and found that it was a mid 70s 350. Now here is where my memories get fuzzy. I THINK I re used whatever timing set he had on there and I THINK it was a roller setup with the 3 key ways. I guess my low vacuum/cylinder pressure is making me suspect that there is some retardedness going on somewhere in the cam or chain. The other thing is this cam is supposed to make really good vacuum or at least that's my impression. I do want to tune it and i still will. It just seems like I have more issues then just a slightly out of tune situation.
y5mgisi
1 ton status
Eagle, as far as taking the engine apart I think I have decided to not do the cam swap. But to just pull the water pump, balancer, and timing cover to advance the cam It's not really to huge of a deal. So I'm still considering doing that so far.
Yeah but it may not need advance! Get a degree wheel and find out where it really is.
If you can get 15 inches of vacuum there's not need to do that ethier. That's where all those spec cams are and it's tunable.
If you can get 15 inches of vacuum there's not need to do that ethier. That's where all those spec cams are and it's tunable.
y5mgisi
1 ton status
Ok i got a guy that say he has a degree wheel i can borrow. Not sure when i will get it but i am ordering my stuff next check.
y5mgisi
1 ton status
Been reading up so much on chip burning that my head just might explode. In fact I read so much about it that i actually had a tough time sleeping last night. Woke up several times thinking bin, data, tunerpro, adx, xdf, data logging, ve tables one and two, spark advance tables, highway mode, Google, etc! It's pretty intense.
I warn people! 
Then once you realize 80% of that **** in a chip does not and should not be touched you'll be better.
Then once you realize 80% of that **** in a chip does not and should not be touched you'll be better.
y5mgisi
1 ton status
Yea i just spent a while comparing the 7747 performance bin to the stock bin and noticed that only the pertinent ones have been messed with. Now, if i could just figure out how to make my laptop listen to my truck we would be set!
