I was wondering if anyone could tell me if the cam i have in my truck is worth keeping in it, because so far i am not impressed with it. It is the lunati 61601, .535\.540 duration 256/262 1000 to 5500 rpms.

the motor 460
bored 30 over
flat top pistons
d3ve heads
hedman elite headers
scorpion roller rockers
weiend stealth intake
edelbrock 750 cfm carb
cloyes double roller with straight up timing

the problem is it sparkknocks no matter what the ignition timing is at while pulling a trailor without an octane booster. I also had more power with the old cam ( I do not remember specs on). If anyone has any suggestions please let me know thanks.

 

Do you know what your deck height is at? And how thick are the head gaskets? If you have .060 or more piston to head clearance it can make for a detonation prone motor.

 

It should be the stock deck height. The head gasket is .40 i think.

I never had this problem before the cam change.

 

The pistons could be too far in the hole, if it wasn't checked who knows for sure ? Was the cam degreed in ? Are you just turning the dizzy back or have you taken/limited some of the centrifugal advance without moving the initial advance ?

 

If i remember correctly the pistons were at the very top of the bores. The cam was not degreed so for sure i dont know if it is completly straight up, that is one of the thing I am going to do here shortly. how do you limit the centrifugal advance? As of right now I have the base timing at 6* as that is the only way I can maintain 60 mph, I have had it at every degree from 3 to 20. Is there any reason why this cam would do this and the old cam would not. The old cam was .484/.510 duration 204/214 112*lobe separation.

 

I'd look at two things, first check position the cam is installed. Buy or borrow a degree wheel to do this. It could be advanced more than you realize, straight up might not really be straight up. The other is that your old cam could have longer advertised duration, that would make the cylinder pressure lower cause the intake valve would close later in the stroke, lowering the dynamic CR.

If your timing set has adjustments, I'd reset the cam a notch or two retarded from wherever it's at currently. If that doesn't work then get a custom cam ground. I paid about $240 for a custom cam and lifter kit for my 460. PM me if you want the cam grinders info.

 

It's hard to see the difference between .020 or .030 down and a true zero deck without measuring. If your .020" down and you used a .050 head gasket then your quench distance would be .070", and thats bad for detonation resistance. But your old cam could have masked it with more low lift duration.

 

Your initial timing depending on the fuel you run should be around 10 to 12 and you need to keep it in that range. You'll need to adjust the centrifugal advance from there. If you are using the stock dist. there are 2 slots in there that limit it and it probably is in the long slot. You will have to take it apart and see what you have, the slots are marked, numbered for degrees. If the slots don't work out I weld one back and carefully grind it in till I get it right for the motor, trial and error. For the springs, if you have another dist around rob the light spring out of it and ditch the heavy spring in your dist for the light one to get started. I always run 2 light springs. Just running one has never worked for me.
When pistons are down in the bores too far, depending on the head you are using it can cause detonation. It should always be checked and corrected if needed by milling the block. IMO if it's more than .020 in the hole I'd mill the block to get it close to zero.
If you are sure you put the timing chain in the zero slot and it is a good quality chain and gears then I'd try to work it out with the dist before tearing into the motor.

 

"Do you know what your deck height is at? And how thick are the head gaskets? If you have .060 or more piston to head clearance it can make for a detonation prone motor."

Can someone explain this to me. I am having trouble understanding why this is true. I keep visualizing the piston/head/chamer shape and given that there is going to be an open volume in there, and assuming the pressures are relatively equal in the volume, I fail to understand how the clearance around the edges of the piston would matter. What is it about this small area that makes the engine prone to detonation?

Also, does it matter what shape the piston is, eg flat top, domed, dished? Is one shape more/less prone to detonation than another given the same compression ratios?

 

How could raising the compression with the pistons with the stock rods make my quench distance more?
Also My timing set has three key ways 4* advance, straight up, and 4* retard. Do you think I should get a different timing set? Man I hope I dont have to pull the motor apart that would suck.

 

Flat tops set at .030 down will have more compression than big dish pistons at zero deck. And different pistons have different compression heights, 1.752 to 1.772 are both common compression heights for 460 pistons. So short flattops will have more compression than tall dish pistons, and possibly be way more prone to detonation.

Also, don't trust the timing marks on the timing set and the machining on the cam to be perfectly accurate. If the timing set has a 2 degree error and the cam has a 2 degree error and both errors are on the advance side of the tolerance you could be an extra 4 degrees advanced. The only way to know for sure is to put a degree wheel on the crank and check it. I've heard guys talk about a 6-7 degree error stack.

Your problem pinging problem sounds like an overly advanced cam, maybe combined with poor quench. That's why I'd check it with a degree wheel if I was you. Summit has degree wheel sets for about $85, or a wheel alone for $30 or so if you already have a dial indicator setup.

 

The KB site is crappy to see, I highlight the text to make it readable, but here is a great article explaining quench:
United Engine & Machine Co. Incorporated

and another good write up by Scott Johnston and Paul Kane, orginally posted at 460Ford:

"There is more power than just raising the compression by using quench. Here is a quote from Scott Johnson and Paul Kane on the subject of the importance of quench and engine performance. In all the engine builds, this is factored in.

“Quench is the distance between the flat portion of the cylinder head deck and the top of the piston. The early BBF's set the piston about .010" below deck at TDC. Combined with a head gasket of about .040" thick this made for a quench distance of about .050". The later 460's set the piston even further below deck at TDC to further reduce static C/R with a resulting quench distance of some.065" which is really marginal.

The reason quench is important? As the piston approaches TDC the air fuel mixture in that area is violently forced into the chamber proper and serves to: rehomogenize the mixture in the chamber and cool the chamber resulting in greater detonation tolerance for a given static compression ratio. The name is derived from the fact that the small crevice area there serves to quench the flame front.

A quench distance greater than .060" loses much of the effectiveness of the design. I set most of my combos at Deck height for higher RPM use and about set the piston about .005" out of the hole for lower RPM use. Tight quench makes more torque for a given static C/R plain and simple. 7 to 10 pound feet for every .010" you close the quench distance is nothing to sneeze at.

Remember that at speed the piston and con rod stretch and the actual running distance is even closer. The higher the rpm window of operation the greater the amount of stretch. The trick is to have the piston almost kissing the head at max RPM so that the violent shock wave imparts a lot of additional mixture motion in the chamber when the flame front is in its early stages. Tight quench combos have faster mean flame front rates than non quench combos and need less ignition timing to make best power.

This is the reason I avoid using Sealed-Power pistons, or any piston for that matter, that has a short compression height which leaves the piston sometimes as much as .035" down the hole at TDC in the later blocks.”

“Just want to add that the quench area of the combustion chamber must be tight clearanced enough (as outlined above) so that the negligible air/fuel mixture does not ignite in this area.

When the quench distance is inadequate/too far open, the air/fuel mixture ignites in this area....hence, NO QUENCH.”

 

One more thing: verify you distributor advance is working right and not stuck advanced, and make sure your harmonic balancer hasnt slipped giving you inaccurate readings. Heck, you might check your timing light against a known good unit also..

 

I know the distributor advance is working, It will advance up to 56* i think, what would be a good max advance or is it just trial and error?
The harmonic balancer was new when the motor was built, but how can u tell if it has slipped?
Also kind of worried about having speed pro pistons in it now.

 

I've been thinking that you changed the cam only, is that correct or are you dealing with tuning a complete rebuilt motor?