Blown7
Now I think we are getting somewhere. Are those numbers accurate?
If I had to pick a cam for a engine, slightly warmed it would be this Engle cam
5056-H K-56HYD .538"
.538" 272¬?
272¬? .336"
.336" 224¬?
224¬? 110¬? $160.00
New .904" Lifter profile for midrange torque, slightly rough idle 9.0 to 1 compression power from 1500-5500 RPM
with 9.1 pistons, timed straight up.
http://207.178.130.99/catalog/search_results.php
Jeff
82Waggy
Yes, you got something wrong. You added 15 degrees to the actual intake valve closing point, not the closing point at .050 which is usually wrong anyway.
1980_Cj7
Man, this stuff has my head spinning faster than the camshafts we're talking about. I was hoping maybe somebody out there has a warmed up 401 that runs on pump gas and could tell us what they used. All this theory is fine, but until you fire it up and step on the gas, it is still all just theory. There's nothing like actual results and experience.
Don't take this the wrong way. I'm not saying you guys don't know what you are talking about. It's obvious you do, but most of the engines you are building are for a different purpose, and way more sophisticated, than what we are trying to accomplish. I'm also smart...smart enuff to know there's no way I'm going to become an engine designer or camshaft expert overnight.
82Waggy
It's not just theory. Most of it is good sound practice. You want to reduce the potential for detonation; run a quench distance beteen .040 - .050, polish the chambers, and keep dynamic compression reasonable.
The tools have been shown to you so that you can work this out for your circumstance.
You want to prevent piston scuffing; ensure a round bore and proper wall clearance.
All of the above applies to any engine. The rest is up to you.
Goose
See CJ-7.. this is where all that foolin around with calculators in school leads.. (sorry guys.. :wink: )
If you want an old school opinion..you have already decked the block a bit and had the heads milled right?..well then you have bumped the compression some, and probably (in spite of all the theory to the contrary..) are going to get into detonation issues if you go much past 10.5 to 1.. so heres my humble opinion. take this block to another machinist tell them what went on, have them clean those bores up and get a set of pistons for it.. just maintain a conservative .009 or a little more clearance and go.. (at this point you have to realize that no matter how many guys shake thier heads at thier charts and theorys.. ) the facts are you have had mechanical contact between two moving pieces of machinery..(pistons/walls) so A. the clearances were too tight and B. if those pistons you had in there are going to require a 15 minute warm up cycle to stop this do you want to bother with it..?? just a humble "old school" it has worked for me opinion
Soo Listen to the Goose 'Make dem holes round and loose'...sheesh sorry had a Jesse Jackson moment there.
Goose
oh and by the way..I in no way mean to denigrate the opinions of those learned ones here who actually understand all the stuff they have put out here trying to help..When I get ready to build a full on BIG power engine..I'll be talking to them..until then just reading all that I felt 'sorta like a Chimp looking at the space shuttle.. :oops:
1980_Cj7
Goose, I agree on the solution to our piston scuffing. What I'm trying to decide now is what new pistons to buy, and whether to stick with this cam or get a different one, in order to be able to run pump gas.
Sounds like you're saying get stock CR pistons, the way you mentioned that with what's already been done, the CR will already be a little higher.
You're saying keep it under 10.5:1. Others are saying we need to be under 8:1. Then there's the static and dynamic deal. I'm starting to look like that chimp, ha, ha.
That's why I'm saying I just wish I knew someone who had one something like what we're trying to end up with together and running, tried and true, so we could just play copy cat. We can't afford to screw up again. Heck, we can't even afford the first screw up.
And I too am not putting down the guys on here who understand this stuff and have been working so hard to help us. In fact, I'm jealous, but for now it's still over my head. I'm learning a lot though. Thanks again for the help everybody.
82Waggy
Perhaps the assumptions given were wrong? Aside from fixing your piston scuffing problem I thought you wanted to run as much compression as possible that would live on pump gas, and that you were building a motor for your Jeep which suggests bottom end torque is the goal - the commonly accepted static cr limit for pump gas with iron heads is about 9.25:1 and you need to ensure that the intake valve does not close to early so as to shoot dynamic compression above 8:1.
Quench and chamber surface are everything when it comes to controlling potential detonation.
Nothing special about what has been suggested. You can use the calculator to do the math or do what others have done that arrived at the same end, such as the use of KB 354 pistons with proper bore clearance and open the heads up to about 62-65CC's with an .045 thick head gasket - should put you right in the ballpark for compression and quench.
Here's what my 401 spec'd after machining:
Bore = 4.205 (.040 over)
Deck = 9.201 (.007 removed from deck)
Reconditioned Rod Length = 5.855
Reconditioned Crank Stroke = 3.675
KB Piston Compression height = 1.510
Piston Dish CC = 28
Head Gasket Bore = 4.275
Head Gasket Thicknesws = .045
Piston to Deck Clearance = -.002 (Above Deck_
Resulting Quench distance = .043
Chamber CC = 65
Intake Closing deg = 60
Static CR = 9.13
Dynamic CR = 7.57
Your final machining may vary slightly so use the calculator to see what you got, but it should be close as I had to mill off .007 deck height to clean and square the block - yours was probably milled less in which case you won't have to open up the head chambers as much as I did to keep compression in check and a few thousandths piston height either way won't make a whole lot of difference.
Not much else to say.
AMX69PHATTY
It sounds like high Dynamic Compression may have been part of the problem.
This is a result of the intake valve closing angle of the Clevite Cam.
The Clevite Camshaft has an Intake Closing angle of only 34 degrees @ .050.
To lower the Dynamic Compression you need a different Camshaft.
The SilvoLite page calculator suggest getting a different camshaft with an
Intake Valve closing angle of a minimum of 45 degrees ABDC @ .050 Lift.
Remeber, on the SilvoLite calculator 15* has been added to the cam value at .050 lift.
The more this angle is greater than 45* on the CAM, not in the Silvolite Calculator,
60* or more in the Calculator, the lower the Dynamic Compression will be.
Using nominal values, looks like Ross and KB pistons give about the same static compression.
If the Rods are a little shorter, by .003, this will lower Compression.
If the Deck and/or Heads have been milled, this will raise compression.
My 365 motor, 0.000 deck, dished cast pistons, had 9.53:1 Static CR and 7.93:1 Dynamic CR,
was always ran on pump premium gas, and had no Detonation problems.
The cam in this motor had an Intake closing angle of 45 degrees ABDC.
:t:
ROSS Forged Pistons
KB354 Pistons
82Waggy
Perhaps an explanation of the difference between static and dynamic compression ratios is in order.
Static compression ratio assumes that the piston compresses the intake charge from zero degrees BDC to zero degrees TDC - the full length of the stroke - this does not actually happen because the intake valve is not closed until some point after the piston has passed through zero degrees BDC. Because of this there is some backfeeding through the intake valve that is relieving compression until the valve has closed fully. It is the point of crank rotation at which the intake valve is fully closed, measured in degrees After Bottom Dead Center, that compression can actually begin and this is what is reffered to as Dynamic Compression.
As you can see it is the Dynamic Compression Ratio that actually controls cylinder pressure. Therefore, it is important to choose a cam that is compatible with the static compression ratio of the pistons so as to not build too much cylinder pressure.
Many will recall the muscle cars of the late sixty's/early seventy's that claimed compression ratios of as much as 12:1. Even my 69 Javelin 390 has a static ratio of 10.25:1, but these engines used large duration cams with late intake valve closing points to limit dynamic compression ratio in order to run on the premium leaded pump gas available in the day - they would have a tough time on todays lower octane unleaded fuels.
Low compression engines are a different story. Many aftermarket cams are designed to help build cylinder pressure by closing the intake valve earlier than stock in order to build additional power. Combine one of these cams with higher compression pistons and you will likely exceed usable limits, as has been shown earlier in this thread.
1980_Cj7
82Waggy wroteYes, you got something wrong. You added 15 degrees to the actual intake valve closing point, not the closing point at .050 which is usually wrong anyway.
So when I'm using the Silvolite calculator, I should be using cam specs based on .050 events, right? So since the cam specs that AMX69Phatty posted for our Clevite cam say the intake valve closes at 34* ABC at .050" lift, I should use 34 + 15 or 49*, right?
Sounds like the stock cam specs aren't at .050 because of how AMX69Phatty deducted to get an assumed .050 event.
82Waggy
CJ7, You are correct. It should be the closing event degrees at .050 plus 15 - or 49 as you have indicated.
Your cam card should specify when the intake valve closes. Another way to determine when the valve closes is to take 1/2 Advertised Duration Plus the intake Lobe Centerline angle minus 180 degrees to come up with the closing angle After Bottom Dead Center. In this case you would not add the 15 degrees when using the calculator.
Note that adding 15 to the .050 closing event on any cam is a guess. The actual closing event may be more or less degrees away from the .050 event.
AMX69PHATTY
1980_Cj7, yes, for your Clevite Cam I used 34* + 15* = 49*
in the SilvoLite Calculator and it gave a Dynamic Compression of 8.63:1
with the Ross pistons you have, and a Static compression of 9.7:1
When I changed the value in the SilvoLite Calculator to 60 degrees,
which assumes a cam with a .050 Intake closing spec of 45 degrees ABDC
and then add the 15 degrees to that SilvoLite says to, and use 60 degrees
in their calculator, I then got a Dynamic Compression of 8.0:1 thereabouts.
And this was with the same Ross pistons and Static CR of 9.7:1
The KB 354 pistons come out more or less the same as the Ross units
because the KB's are a little taller but have a larger dish volume.
I'm amazed with all of this cause my 365 Motor had no detonation problems.
Per the SilvoLite calculator it had 9.53:1 Static and 7.93:1 Dynamic Compression,
and when I just checked, the cam had an Intake closing angle of 45 degrees ABDC @ .050 lift !
I did not do that on purpose when the 365 was built, but it looks like I was just dumb lucky :?
WOW ! I'm amazed ..... :shock:
So it sounds like if you find another cam with an Intake closing angle
of 45 degrees or more ABDC @ .050 Lift you could be good to go with the parts you had.
Of course open up the bores on the pistons for more clearance.
It looks like the Clevite Cam was designed to create more Dynamic Compression
in a motor that was stock or built with LOW Static Compression.
Over the counter aftermarket replacement 401 cast pistons are for 8.5:1,
but your motor already had HIGH Static Compression with the Ross Pistons,
and therein is where the problem llies, ....... it seems ( escape clause :wink: )
Blown7
AMX69PHATTY wrote1980_Cj7,
but your motor already had HIGH Static Compression with the Ross Pistons,
and therein is where the problem llies, ....... it seems ( escape clause :wink: )
You don't need a escape clause because that was the major problem , and I will go so far to speculate that the cam was timed wrong ,and if it was installed in the retarded position it probably had even higher dynamic compression then the calculator shows.
Jeff
82Waggy
You meant advancing the cam would close the intake valve earlier.
Here is an interesting article on cam selection - probably more than you want to know. http://www.compcams.com/Community/Articles/
Scroll down to the article titled "Be The Camshaft Expert".
I'm going with a custom grind from Crower for my 401, similar to their part number 45241, http://www.crower.com . This cam has an actual intake closing point of approximately 65 degress ABDC and would work well with a static compression ratio in the 9.5:1 range.
1980_Cj7
We have a brand new Comp Cams camshaft sitting here (not the one that is currently in the engine). Here's the specs on it. Just when I thought I was getting a handle on some of this stuff, now I'm seeing new things like "valve timing at .006" and "cam installed at 106 intake clearance" and "duration at .006 tappet lift". What does that mean, and would this cam be any better? I'm thinking not. Seems like a little too much lift and duration, and the intake closes only 6* latter than the one we have in now (if that .006 is the right value to be looking at).
I was going to run the calculator, but I'm uncertain of some of the terms and what values I should use.
Camshaft Specification Table
Part Number 10-210-4
Engine 1966-1979 American Motors Co.
290ci-401ci
8cyl.
Grind Number A 292H-10
Description
--------------------------------------------------------------------------------
Intake Exhaust
Valve Adjustment 0 0
Gross Valve Lift 0.518 0.518
Duration At 0.006 Tappet Lift 292 292
--------------------------------------------------------------------------------
Valve Timing At 0.006
Open Close
Intake 40 72
Exhaust 80 32
--------------------------------------------------------------------------------
These Specs Are For The Cam Installed At 106 Intake CL
Intake Exhaust
Duration At 0.05 244 244
Lobe Lift 0.3235 0.3235
Lobe Separation 110
--------------------------------------------------------------------------------
Recommended Valve Springs 986-16
82Waggy
Way too much duration for what you are trying to do- you would have no bottom end power.
Read the article I listed above. It will clear up a lot of the questions you have on cam specs.
CL = Centerline, not clearance
The intake valve closing point is 72 deg ABDC
.006 refers to tappet lift and is used for the duration spec here because hydraulic lifters spring about that much before the valve begins to move.
AMX69PHATTY
Not sure if this cam would work for you or not. :-|
Cam suppliers list working rpm ranges, but any one given cam
listed for an AMC also says it's for anything from a 290 to a 401, 111!!!
so since yours is a 401 I would think the power band would be lower.
Do you have a Cloyes True Roller Timing Chain with the 4* Advance & Retard Keyways ?
If so, you could install this cam 4* Retarded, giving a 44* Intake closing @ .050 Lift.
Although Retarding the Cam does shift the power band RPM range upward.
It does have less duration, 228* IN / 235* EX @ .050, than the Crower.
It may be a little "radical", but putting it in a 401 would "tone it down" a little.
I think you can order a cam ground to whatever specs you want from any supplier.
They pretty much don't grind an AMC Cam until they get an order for one anyway.
Maybe try calling Crane, Crower, Iskerdian, Lunati, or whoever you prefer and ask'em.
:t:
Cam Suppliers give their specs in at least 2 different ways.
One is called "adverised" duration, which is usually at .004-.006 lift.
The other duration spec which is kinda "standardized" is at .050 lift.
The area on the cam lobes between these two durations is called the "ramp".
This is the area where the valve is opening and closing on the valve seat in the cylinder head.
During this time between .004 and .050 valve lift air flow is negligble.
The .050 lift is used as a standard so a person can compare one cam to another.
Cause if one suppliers specs are at .002 and anothers at .008 one can't compare'em.
fuzz401
that cam is close to what I have
Grind Number A 292H-10
1980_Cj7
82Waggy wrote
Read the article I listed above. It will clear up a lot of the questions you have on cam specs.
Yes, I glanced at the article, but just didn't get chance to read it yet. Looks like a really good article with lots of great supporting illustrations. I'm looking forward to studying it. Thanks for the link.
