Thinking about a new cam - help please
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Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
Yup you did, your azz backwards.
Advancing cam increases dynamic compression and low end torque, retarding cam for more top end power with a loss of low end.
Advancing cam more than 4 degrees off spec can cause detonation problems as well a power loss. Try different cam timing combinations on a Dyno Sim program you'll be surprised one degree can make a difference on a properly built performance engine.
Advancing cam increases dynamic compression and low end torque, retarding cam for more top end power with a loss of low end.
Advancing cam more than 4 degrees off spec can cause detonation problems as well a power loss. Try different cam timing combinations on a Dyno Sim program you'll be surprised one degree can make a difference on a properly built performance engine.
Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
If your dynamic compressions that high due to just the advanced cam your not going to run not alone start. Sounds like starter heat soak.
Granted ring gap will be tighter with less leak down your splitting hairs that only a leak down test will reveal.
Granted ring gap will be tighter with less leak down your splitting hairs that only a leak down test will reveal.
Thread Starter
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Senior User
Joined: Apr 2007
Posts: 375
Likes: 0
From: Glenwood, IA
I can retard the timing a bit and I dont have the slow start. It isnt the heat with the starter. It has to do with the heat and the timing. It is that I have it advanced that much. I am going to retard it a little bit. It just seems to run harder where it is at.
Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
Seems we have a crossfire three way conversation here, I replied about the cam to crank relationship 390 posted.
You will run harder at low end with more ignition advance to a point before your bucking plus detonation not alone hard starting problems. FE's like a lot of initial and total advance, tells ya something doesn't it about a wedge vs a more efficient combustion chamber design?
You will run harder at low end with more ignition advance to a point before your bucking plus detonation not alone hard starting problems. FE's like a lot of initial and total advance, tells ya something doesn't it about a wedge vs a more efficient combustion chamber design?
Last edited by "Beemer Nut"; Aug 25, 2007 at 11:01 PM.
Fleet Mechanic
Joined: Aug 2007
Posts: 1,828
Likes: 253
From: Piney Woods of East Texas
I run through first and secound and shift into third about 30' from the end.
Fleet Mechanic
Joined: Aug 2007
Posts: 1,828
Likes: 253
From: Piney Woods of East Texas
Yes drags are different than Pulls, my mistake. Speed is what get you through the mud faster.
Have you run any of the compression tests?
From what all that has been discussed, the pistons swap would be the greatest gain.
You may be able to boost compressions by only changing the pistons and transferring the rings to the new pistons. But you would have to examine the cylinder walls closely at the top. The higher compression may position the rings higher in the cylinders. I would probably be tempting to re-hone the walls and install new rings. I generally buy over size rings and custom fit my rings. Or move to the newer zero tension rings.
Have you run any of the compression tests?
From what all that has been discussed, the pistons swap would be the greatest gain.
You may be able to boost compressions by only changing the pistons and transferring the rings to the new pistons. But you would have to examine the cylinder walls closely at the top. The higher compression may position the rings higher in the cylinders. I would probably be tempting to re-hone the walls and install new rings. I generally buy over size rings and custom fit my rings. Or move to the newer zero tension rings.
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Thread Starter
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Senior User
Joined: Apr 2007
Posts: 375
Likes: 0
From: Glenwood, IA
The engine only has about 1500 miles on it. So ring wear shouldnt be an issue. When I had the machine work done, I told the machine shop that I wanted 10:1 to 9.5:1. When I wicked it up he had milled the tops of my pistons to bring the compression down to 9:1. And yes I was PISSED!!
He was on a kick about not being able to run on pump gas. I told him that I would run the premium. Damn chevy lovers!! I think he just wanted to give the chevys a chance.
He was on a kick about not being able to run on pump gas. I told him that I would run the premium. Damn chevy lovers!! I think he just wanted to give the chevys a chance.
Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
The hp loss by a half piont isn't that much, I would of been pisssed and made then replace the buckets. This is the reason why I do my own work as I trust no one and why I own a lathe, Bridgeport mill, Tig and Mig.
Fleet Mechanic
Joined: Aug 2007
Posts: 1,828
Likes: 253
From: Piney Woods of East Texas
Have your rings seated yet with 1500 mi? Oil consumption stopped?
There may be some cam timing changes that may help. Would be easier than changing the cam. You should talk to the mfg of the cam for those changes.
As for cam, we have determine that you may not have clearance for a higher lift. A roller cam open and close quicker than a hyd/flat tappet cam. As far as a which one, I haven't a clue. They have your hands tied with the stock class.
There may be some cam timing changes that may help. Would be easier than changing the cam. You should talk to the mfg of the cam for those changes.
As for cam, we have determine that you may not have clearance for a higher lift. A roller cam open and close quicker than a hyd/flat tappet cam. As far as a which one, I haven't a clue. They have your hands tied with the stock class.
Cross-Country
Joined: Jul 2007
Posts: 79
Likes: 1
Originally Posted by 428HIGHBOY
I sure wish I had all those toys. So now that we are off of the compression topic, how about the cam? What can I do to get a fair amount of power and keep my 17" of vacuum?
Duration and lobe separation are the 2 things to watch for if you are trying to hold the same vacuume numbers. the lower the lobe separation angle, the more overlap you will have and the less vaccume at an idle. The same with increasing the duration. Lift is mostly free.
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Senior User
Joined: Apr 2007
Posts: 375
Likes: 0
From: Glenwood, IA
So now I have 110 deg seperation. If I was going to go with roller I could have a highrer lift and longer seperation with the same duration and have the same vacuum as long as the duation stays the same??