John Deere a cam duration

[42jda]

How much is too much, and how much is too little for a 4 to 4.5 speed limit application, with some good lugging power in a 9.25 by 6.25 motor running stock rpms?

 

[Ole Johnny]

From experience of many years of drag racing I have learned that if you want low end torque, you dont want overlap (rumpedy rump) Since the engine is only gona see about 1200 RPM maximum, nearer to 0 overlap is better and as for valve lift, there is NEVEDR too much as long as it dont loose compression via overlap.
You hear the 6 cylinder motors running big cams to make higher RPM but for a JD go LOW OVERLAP

 

[Lynerd]

41jda I use 205 @ .050 and 108 degrees LC and .390 lift set at 107 degrees intake CL on 36 A with 5.875 and 8.375. This is stock duration for exhaust and 20 more degrees for intake. Motor your size I would go 208 to 210 degrees and could open up gap a few thousands would take some timing out if it was too much. Lynn

 

[Josh Blackburn]

I have a cam design your looking for. If interested to know more give me a call 9893775366.

 

[BushogPapa]

JD didn't have any overlap in the A, but did in the "B" and 720 D..Hummmm....figure THAT out...!!
The 620/630 seems to have the same lack of Overlap as the "A" and will pull like a FOOL..go Figure..!!

Ron..

 

[buickanddeere]

Don't worry about it.
Tell your cam grinder what displacement and heads/induction system is on the engine. Then ask your cam grinder what compression ratio and cam cam grind HE recommends for the highest octane fuel you are will to purchase.

 

[Ole Johnny]

Exactly. Overlap kills compression so at a slow RPM with no overlap, you get all the bang possible.

 

[north puller]

Really??? As a general rule, to produce more low end torque you decrease the lobe seperation, which will increase overlap if duration is kept the same. You also advance cam timing for low end lug.

Most tractor grinds decrease lobe seperation, increase duration a small amount, and increase lift a decent amount.

I'm not saying that he is the best, but if you call Sonny Daniels at Bullet Cams, you will be more educated by the end of the discussion.

 

[macandmall]

I have a "41 B I rebuilt in 2007. I had it bored .090 over, aluminum pistons from hinrich"s, rebuilt the head with new valves and guides, shaved .100 off the head, and had custom built from Algona regrind the cam with their "puller grind". They remove material from the back side of the lobe, then grind the top flatter, which increases duration. The left hand exhaust valve timing is opening 1" before the timing mark. This engine does not have much low end lugging power. It feels and sounds good at high rpm, but only dynos 26. It really falls on it"s face when it gets lugged down, so it doesn"t perform well on the track. I do have bigger tires on it too, old style 12-38"s which doesn"t help, the taller tires "gear it up". Custom built claims it should still have good low end power, but it doesn"t. I thought it would be hard to crank by hand with the aluminum pistons and .100 off the head, but it isn"t too hard to crank it with the petcocks closed. Here are some pics of the cam before I installed it.

 

[macandmall]

I have a '41 B I rebuilt in 2007. I had it bored .090 over, aluminum pistons from hinrich's, rebuilt the head with new valves and guides, shaved .100 off the head, and had custom built from Algona regrind the cam with their "puller grind". They remove material from the back side of the lobe, then grind the top flatter, which increases duration. The left hand exhaust valve timing is opening 1" before the timing mark. This engine does not have much low end lugging power. It feels and sounds good at high rpm, but only dynos 26. It really falls on it's face when it gets lugged down, so it doesn't perform well on the track. I do have bigger tires on it too, old style 12-38's which doesn't help, the taller tires "gear it up". Custom built claims it should still have good low end power, but it doesn't. I thought it would be hard to crank by hand with the aluminum pistons and .100 off the head, but it isn't too hard to crank it with the petcocks closed.

 

[buickanddeere]

What is the actual mechanical compression ratio? What is the cranking psi? Advance the cam one gear tooth and try it again, sounds like it's retarded.

 

[Curious one]

I agree with B&D that the cam timing is off. Did you degree the cam to the intake lobe centerline specified by the cam grinder? I've only had one out of the 8-10 custom grind cams that were timed correctly using the timing marks on the cam gear. You'll need a degree wheel and someone that knows how to use it if you don't know how it's done. Mike

 

[macandmall]

I've got some homework to do, get the specs for the cam, check compression, but it is probably around 7 to 1
Scott

 

[macandmall]

I decided to take it apart anyway. I found that the cam timing was retarded. Intake center of lobe was at 110, now is 96. The exhaust valve was closing after the piston passed tdc, more than an inch down the bore, and the intake begins to open just as the exhaust closed. I advanced the cam 1 tooth, and now the exhaust closes right at tdc. The exhaust now begins to open before the piston reaches bdc, at least an inch to go in the bore, and the intake closes after the piston begins to move up the bore. I put it on my neighbors dyno today. I gained 5 hp after tuning it on the dyno today, it started at 20 today.It is still only making 25-26 hp, but it will lug a lot better. I noticed that right away when I drove it down the road. Starting from a stop in 6th gear is a breeze now. Before the adjustment, it was difficult to get going in 6th. Our local pull is Tuesday night, I am sure it will do better than it has in the past.
Here it is pulling in 3500#. My Son recorded it on my phone, not very good quality video. It spun out at 255', right where most of the others stopped. The winner was an Oliver 70, went 263'. I'm very happy with the power now.
http://www.youtube.com/watch?v=DZ_1jAGU4t8&feature=youtu.be
Scott

 

[buickanddeere]

Good to hear you are on the right track and she's running better.
Given the duration and compression ratio, the combustion chamber pressure should be higher.
If the mechanical ratio was brought up to 9 or 10 to 1 , you would be startled at the increased power.
It's all about combustion chamber pressure. Not cam duration, not mechanical compression ratio, nor rpms but............. A balanced combination of all three.