Engine runs like crap........

[ACME A12]

Pulled the other head off and I see the same marks on the pistons. Now I must decide what to do. Does anyone think that the #8 pressure issue would be caused by the valves maybe not being totally closed? I have half a notion to put it back together and try to run it with adjustable rockers......what do you guys think/

Per the Comp website that cam is a pretty aggressive hydraulic unit and requires a fairly low rear gear, etc. to properly function. Two questions before I answer yours:

1) Is your set-up (gearing, carburetion, exhaust, etc.) truly complementary of this camshaft? Looks like a basically stock engine with a big hydraulic bumpstick to me...

2) Is this the type of camshaft that you want to run?

Your move.

:jester:
Ray

 

[Hoosier Bird]

My new one is even bigger. I have everything to put it together except bottom end. I was going to order stroker kit but economy put me on a tight budget. Everything I have is good to go with that cam.......except..........If I figured my compression correctly it is only 7.75......ouch......flat top pistons are down in the hole .100, 906 heads 76cc 4.280 bore X 3.380 Stroke........:brickwall: :brickwall: :brickwall: So now I'm thinking I should get a smaller cam and run it till my budget changes.......

 

[ACME A12]

My new one is even bigger. I have everything to put it together except bottom end. I was going to order stroker kit but economy put me on a tight budget. Everything I have is good to go with that cam.......except..........If I figured my compression correctly it is only 7.75......ouch......flat top pistons are down in the hole .100, 906 heads 76cc 4.280 bore X 3.380 Stroke........:brickwall: :brickwall: :brickwall: So now I'm thinking I should get a smaller cam and run it till my budget changes.......

OUCH. That's a blower motor compression ratio - but I don't see any polished GMC Huffer sitting on top of that intake...

You've got to do something about the valve to piston clearance issue and that's just too much cam for that small amount of CR. TIme to go cam shopping. JMHO. :cents:

:jester:
ACME
Former "over-cammer" of everything; REFORMED...

 

[ACME A12]

I looked in page after page of previous threads but couldn't find it anywhere; what kind of rear gear have you got in that thing?

Ray

 

[george68hemirr]

Re: Hot Naked Chick........

I was about to say if the heads have been milled alot the stems are to long for a rocker shaft style rocker!

i saw that too....they do look long...and i did say that before about the heads could be milled too much

 

[george68hemirr]

My new one is even bigger. I have everything to put it together except bottom end. I was going to order stroker kit but economy put me on a tight budget. Everything I have is good to go with that cam.......except..........If I figured my compression correctly it is only 7.75......ouch......flat top pistons are down in the hole .100, 906 heads 76cc 4.280 bore X 3.380 Stroke........:brickwall: :brickwall: :brickwall: So now I'm thinking I should get a smaller cam and run it till my budget changes.......

since you have the whole top off.....you may as well pull the motor and be done with it,,,,rings,rod bearings,main bearings,cam bearings...etc.....what could all that cost....then you know what you have and it will run sweet!!!

 

[69hemibeep]

7.775:1 is just asking for turbos

 

[mac]

low compression, valves hitting pistons, and a huge cam.....that just sounds like a 3 part problem. :cents:

 

[69hemibeep]

low compression, valves hitting pistons, and a huge cam.....that just sounds like a 3 part problem. :cents:

Mac, I think the low compression motor is a different one.

 

[mac]

low compression, valves hitting pistons, and a huge cam.....that just sounds like a 3 part problem. :cents:

Mac, I think the low compression motor is a different one.

what did i miss??? :huh:

 

[mcmopar]

low compression, valves hitting pistons, and a huge cam.....that just sounds like a 3 part problem. :cents:

Ditto. Too much cam for the compression and mechanical problems as well. Not a good mix. If your pistons are that far down in the hole and your valves are still tickling the pistons you definitely need to make some serious changes.

 

[ACME A12]

low compression, valves hitting pistons, and a huge cam.....that just sounds like a 3 part problem. :cents:

Mac, I think the low compression motor is a different one.

what did i miss??? :huh:

Nothing. Same engine. Bob was into the Coronas again...
The "new one" that Gary was referring to was the cam that he intended to install in the 496" stroker that got put on the back burner...IF I AM UNDERSTANDING CORRECTLY...

Gary, in calculating the CR, what values are you using:
as the compressed head gasket thickness?
as the head gasket bore diameter?
as the piston dome volume? (zero, since it's a flat top?)

May not make a huge difference, but when I punched this into the Little Orphan Annie Secret Decoder (guessing all of the above) I came up with a slightly higher ratio...

Ray

 

[Hoosier Bird]

I looked in page after page of previous threads but couldn't find it anywhere; what kind of rear gear have you got in that thing?

Ray

I've never checked but from the way it reacts even with the crappy engine, I think 3:91. If not I was going to put one in it.

 

[Hoosier Bird]

The "new one" that Gary was referring to was the cam that he intended to install in he 496" stroker that got put on the back burner...IF I AM UNDERSTANDING CORRECTLY...

Gary, in calculating the CR, what values are you using:
as the compressed head gasket thickness?
as the head gasket bore diameter?
as the piston dome volume? (zero, since it's a flat top?)

May not make a huge difference, but when I punched this into the Little Orphan Annie Secret Decoder (guessing all of the above) I came up with a slightly higher ratio...

Ray

I'll post my calculation but this may take a few minutes ..........and yes you were understanding the new cam correctly. :brickwall:

 

[ACME A12]

[quote="ACME A12":17lpgoq2]I looked in page after page of previous threads but couldn't find it anywhere; what kind of rear gear have you got in that thing?

Ray

I've never checked but from the way it reacts even with the crappy engine, I think 3:91. If not I was going to put one in it.[/quote:17lpgoq2]

That's good if you end up keeping this camshaft and sorting everything out. 3.91 is exactly what Comp recommends...

 

[Hoosier Bird]

I've got a stock block with pistons in it that I just measured and with the stock pistons they are only down in the hole .008. Give me one scenario that makes sense to have the piston down that far....... :brickwall:

 

[Hoosier Bird]

383 Engine
Bore: 4.250+.03
Stroke: 3.375
Deck: .090
Heads: 906: 76cc
Head Gasket: Steel type: .020
Piston Clearance: .006 Guessing
Distance to Compression ring from top of piston: .337

Bore and Stroke give you: 795.7cc
Deck: 21.139cc
Head: 76cc
Head Gasket: 4.703cc
Clearance to top ring: .163cc

Deck + Head + Head Gasket + Clearance to top ring= 102.005cc+Bore and Stroke=(Total 897.705cc)
897.705 / 102.005 = 8.800:1 CR

If I have made any mistakes please tell me or I'm ripping this engine apart this weekend. :brickwall:

 

[ACME A12]

Now that looks more like what I came up with...and I cheated using the following:

http://www.csgnetwork.com/compcalc.html

Using your previous piston deck clearance number of .100" this yielded about 8.6 to 1. The change to .090" yields about 8.85 to 1 - VERY close to your 8.8 to 1 calculation...

But it seems like you still have too much cam for this combo - you're down a little on CR, no headers, Comp says use a 750 - 800 CFM carburetor and an adjustable valvetrain, but more importantly you've got valves contacting pistons. If you plan to stay with the 292H this issue still has to be remedied - so at best it turns out that the cam is out of phase and you correct that through degreeing it, and maybe you pick up some additional measure of correction by adopting the adjustable valvetrain, but you still may be looking at flycutting the pistons (and they're already .090" down in the hole...) or replacing them. You'll definitely have to get out the clay and check it once you address all of the above. Might be easier just to take a step or two back as far as the cam goes and have something that is seemingly more compatible with your current engine combo until the green comes in and you build your 496"... :cents:

Ray

 

[69hemibeep]

My new one is even bigger. I have everything to put it together except bottom end. I was going to order stroker kit but economy put me on a tight budget. Everything I have is good to go with that cam.......except..........If I figured my compression correctly it is only 7.75......ouch......flat top pistons are down in the hole .100, 906 heads 76cc 4.280 bore X 3.380 Stroke........:brickwall: :brickwall: :brickwall: So now I'm thinking I should get a smaller cam and run it till my budget changes.......

No Coronas last night. Does this quote not sound like a new engine?

 

[Hoosier Bird]

For now I'm thinking downsizing the cam would make the most sense. Least I can drive it this summer........at least it's not as bad as I thought last night... :crazy: