top fuel cam timing
- Thread starter flapjack
- Start date
Nitrohelper
Nitro Member
They have been consistent over the years in the area of 300 degrees duration at .050 -- the lift has increased with better valve springs...
Most of the experimentation has been with the firing orders - both the 4/7 and 2/3 swaps...
Larry jr.
Nitro Member
You forgot dual pattern lift and lobe centers, also it is many times a pushrod length or rocker arm that is used to really dial it in.
Nitrohelper
Nitro Member
Not hardly - the open & closed cam timing today is relatively the same as the Engle KB 425 that was run in the '70s - just a lot more lift...
We ran 114 & 116 lobe centers in the '60s, and I ran a staggered lift cam in 1973...
We've been running staggered rockers since the '80s...
Larry jr.
Nitro Member
My daily driver has 114 lc's and .643 int and .678 exaust the duration is 316. Isky did it for me, I also have one in My Camaro that Donnie Johansen ground that is 112 lc's .533 int and .557 exaust 279 deg duration.
Push rods and rocker arm changes are whats up these days.
The cylinder swap cams are to designed to lessen crank deflection under the huge load nitro motors produce, and to allow the engine to rev quicker and run smoother at high RPM.
What would you run right now if building an 8000+ HP fuel motor, that is the question, not what We ran back in the Iron Men in Wooden Ships eara.
Larry jr.
Nitro Member
Dual pattern cams have longer exaust duration than single pattern cams, the dual pattern cam will make more torque in the top end with a head that has a more restriced exaust port, like the old iron heads or even the early aluminum race heads.
The new high flowing billit stuff like single pattern cams to make more torque at top end of the run.
Have you ever seen a dragster with headers glowing cherry red? that is caused because the cam has more exaust duration degrees than it needs and it burning raw fuel out the pipes, the use of the longer exaust duration is an attempt to to overcome bad flow characteristics of the exaust port and increase port velocity on the intake side, but the effect is a fat running condition that cannot be overcome by tunning the fuel / timing curve.
Last edited:
Larry jr.
Nitro Member
This is about lobe center, what does it do,why is it important?
Lobe center is a routine, a method of fine tuning the timing of a cam, so the intake valve closes at a particular point.
The intake valve closing point is the most important valve event in the engine.
The reason? Inertia, The intake charge's momentum keeps it flowing into the cylinder despite the piston's upward movement after the intake stroke.
Delaying the intake valve's closing to take advantage of this phenomenom increases cylinder filling and thus Power. Thats a good thing.
Its kind of tricky to know just how long is enough. If the valve is held open to long the fuel charge momentum dies, gases back up up in the port suck mixture out of the cyilinder causing a loss of horse power.
If the intake valve closes to early we have limited how full the cylinder gets and horse power is lost. Either way the motor loses horse power.
The ideal thing is to close the intake valve at the precise millisecond the mixture loses its momentum and stops before it reverses direction,this is the whole point of degreeing cams, it is that this will put the cam in the correct position to make this all happen.
The reason we use the lobe center method is simple, Ramps. All cams have ramps, Acceleration ramps that gather up the clearences in the valve train before the valve is shot off its seat, and decereration ramps that cushion the shock of the valves closing. The problem is these ramps move the valve so slowly that determining when the valve has opened or closed is very difficult.Because of this, engine builders developed a method ignoring the ramp when measuring valve movment.
The ramp isn't there to move the valves anyway its sole purpose is to babysit the valve train Engine builders don't look at the valves movment until the valve has moved enough and is clear of the ramp That area is called is the checking height.
The problem is all ramps are not the same size, on a push rod motor the cam has huge ramps, because of the need to cushion the valve train components during open and closing.
Ramps on OHC motors are smaller because there fewer parts to deal with and not as much cushioning needed.
All motors are different they pretty much have they're own ramp and checking height, they can range fron .020 to .050 and it would be impossible to compare them as different checking heights give to very different timing conditions.
So measuring cam timing independent of engine design is what lobe centers are . Still using a checking height the lobe center approach indexes the cam on anaverage of its opening and closing points, its Center not one of those points. because no matter what the staring and stoping points the center of the cam will aways be the same.
Now with that being said, it is Not the Physical center that is being sought, its the Mathmatical Center, or the average of the cams opening and closing points. In some cams both points are the same but not in most.
So Lobe centers serve three purposes.
First, to time the intake valve at the critical closing point to make maximum horse power.
Second, it is an arbitrator in the world of high performance tuning it get everyone on the same page when talking cams, and valve timing.
Third, It gives bench racers something to talk about and sound knowledgable around the pits.
Lobe center is a routine, a method of fine tuning the timing of a cam, so the intake valve closes at a particular point.
The intake valve closing point is the most important valve event in the engine.
The reason? Inertia, The intake charge's momentum keeps it flowing into the cylinder despite the piston's upward movement after the intake stroke.
Delaying the intake valve's closing to take advantage of this phenomenom increases cylinder filling and thus Power. Thats a good thing.
Its kind of tricky to know just how long is enough. If the valve is held open to long the fuel charge momentum dies, gases back up up in the port suck mixture out of the cyilinder causing a loss of horse power.
If the intake valve closes to early we have limited how full the cylinder gets and horse power is lost. Either way the motor loses horse power.
The ideal thing is to close the intake valve at the precise millisecond the mixture loses its momentum and stops before it reverses direction,this is the whole point of degreeing cams, it is that this will put the cam in the correct position to make this all happen.
The reason we use the lobe center method is simple, Ramps. All cams have ramps, Acceleration ramps that gather up the clearences in the valve train before the valve is shot off its seat, and decereration ramps that cushion the shock of the valves closing. The problem is these ramps move the valve so slowly that determining when the valve has opened or closed is very difficult.Because of this, engine builders developed a method ignoring the ramp when measuring valve movment.
The ramp isn't there to move the valves anyway its sole purpose is to babysit the valve train Engine builders don't look at the valves movment until the valve has moved enough and is clear of the ramp That area is called is the checking height.
The problem is all ramps are not the same size, on a push rod motor the cam has huge ramps, because of the need to cushion the valve train components during open and closing.
Ramps on OHC motors are smaller because there fewer parts to deal with and not as much cushioning needed.
All motors are different they pretty much have they're own ramp and checking height, they can range fron .020 to .050 and it would be impossible to compare them as different checking heights give to very different timing conditions.
So measuring cam timing independent of engine design is what lobe centers are . Still using a checking height the lobe center approach indexes the cam on anaverage of its opening and closing points, its Center not one of those points. because no matter what the staring and stoping points the center of the cam will aways be the same.
Now with that being said, it is Not the Physical center that is being sought, its the Mathmatical Center, or the average of the cams opening and closing points. In some cams both points are the same but not in most.
So Lobe centers serve three purposes.
First, to time the intake valve at the critical closing point to make maximum horse power.
Second, it is an arbitrator in the world of high performance tuning it get everyone on the same page when talking cams, and valve timing.
Third, It gives bench racers something to talk about and sound knowledgable around the pits.
Last edited:
flapjack
Nitro Member
- Thread starter
- #11
If I am getting this straight, cam profiles could be one of the areas in which teams could invest some time to eek out more performance, and have it fly under the radar of the NHRA's performance enhancement ban (where they are banning blower mods and what not). Or is it truly dried up?
Larry jr.
Nitro Member
Big fuel motors are in the upper 116-118 range. pro stock stay in the range of 104- 108 because they are geared different with trans and just make less power.
The combination of cylinder head port/runner design and lobe center is where all the horse power is in big fuel racing.
The combination of cylinder head port/runner design and lobe center is where all the horse power is in big fuel racing.
Larry jr.
Nitro Member
It would appear that way.
Nitrohelper
Nitro Member
The "425 cam" was run on either 108 or 110 lobe centers back in the day -
now it's also ground on 112 ,114, or 116 C/Ls -
we have a 116 in one of the fuel altered guys that I help...
The original 425 timing at .050
INT-EXH
298-298
39 79
79 39
110 -110
110 C/L
78 overlap
.425 - .425 = lift at cam
1.57 - 1.52 = ratios
.667 - .646 = total lift
Current cam in a 3.75 - 325+ car
300-302
37 86
83 36
113 -115
114 C/L
73 overlap
.485 - .485
1.70 - 1.60
.824 - .776
The big change is a lot more lift & exhaust timing due to much better valve springs and bigger rollers with stronger rocker arms...
Because the engines go to 8300rpm at the hit, the bottom end torque isn't needed so now the lobe centers are opened up...
The intake has a little more timing ,but the big change is the exhaust opening and,
then an earlier closing to reduce the overlap to help boost manifold pressure...
During the early '80s we found that the early exhaust openings (80+) were better for performance,
but the valve train opening against the cylinder pressure was the weak link ...
Last edited:
Larry jr.
Nitro Member
Funny what We found in the 80's was the cams breaking off against the hydrualic pressuse created in the cylinder when a hole was dropped, jacking the heads off the block. This was because of the volume of fuel that went into the motor the cams were just not strong enough to handle the stress, thus the cam being the weak link.
Made many sacrifices to the aluminum gods during the early liquid tunning age. Burnt a few to the ground too.
Made many sacrifices to the aluminum gods during the early liquid tunning age. Burnt a few to the ground too.
Last edited:
Cymon Sez
Nitro Member
Didnt even notice the "tech section" of this site until the new layout. 
We still make this cam for some of the nostalgia cars out there as well as some newer stuff for current Top Fuel teams.
Steve
Engle Racing Cams
We still make this cam for some of the nostalgia cars out there as well as some newer stuff for current Top Fuel teams.
Steve
Engle Racing Cams
Post more please.
This is much better then the other crap.
Thanks in Advance!
Similar threads
