What cam is this?

[JohnJL]

I am sure I bought this cam from Delta, but I am finding the intake and exhaust lifts to be different from some posts here. I am trying to diagnose a low idle vacuum condition.

I get valve lifts of intake 0.4153" and 0.0685" at overlap. Exhaust lift 0.3975" and 0.1093" at overlap. I dont have a degree wheel to check the durations accurately. I can't seem to match what I have to what I thought I had (Delta 250s?). My measurements are all valve lift, not lobe heights. I thought that is the standard and would expect those below are lifts not lobe heights?

Some other threads in my research...
Camshaft - https://forum.ih8mud.com/threads/camshaft.214012/page-6

Valve Adjustment with RV Cam Grind

forum.ih8mud.com

How much vacuum are you pulling with your Delta 250S cam?

forum.ih8mud.com

Any help identifying the cam or otherwise? I am getting ~8" of vacuum at idle with lots of efforts checking and rechecking timing, vacuum leaks, AFRs...do I maybe have a Delta KC859? I have emailed them too.

Thanks!

 

[JohnJL]

Interestingly, Porsche tool 202 Z block is perfect for holding FJ40 heads also!

Intake

Exhaust

 

[rkymtnflyfisher]

I'm going to be watching this one. I have a KC grind from Delta in my 2F, stock valve lash. 15-16 in vac.


Runs like a raped ape though.

 

[JohnJL]

I'm going to be watching this one. I have a KC grind from Delta in my 2F, stock valve lash. 15-16 in vac.


Runs like a raped ape though.

THanks for the reply, a few of your threads have been helpful for me along the way. Clearly something is not right if you are getting 15" and I am getting half that (if its is a KC).

 

[rkymtnflyfisher]

THanks for the reply, a few of your threads have been helpful for me along the way. Clearly something is not right if you are getting 15" and I am getting half that (if its is a KC).

I was just reading through the last couple pages of your build thread, I'm definitely interested in what you find here. When I was checking vac on mine I started wondering about the difference in the KC cam and the OEM, if the valves should be adjusted to anything other than spec.

So far I've left mine alone, I should probably contact Delta Cam and ask for so.e info on the KC.

 

[JohnJL]

I called and spoke to Steve at Delta yesterday, he said they only really sell the 250s and the 262, and neither give 7" vacuum as normal. Compression, leakdown all normal...new cam gear on the way...

 

[Mark Jennings]

I’ve attached an image of my cam report from Delta Cam...it’s a 250S. I use this cam in my 68 F engine, I had the original reground by Delta...I haven’t checked vacuum at idle since I assembled but seems to me it was lower than 16”. Like 10 to 13” if I remember correctly. Valves are set to 8 and 14 thousands.

 

[middlecalf]

So I’m really pretty ignorant on a lot of this engine stuff, but I do know that when I get popping on deceleration that I’m running lean so a carb clean usually gets me back to that nice deep throated rumble (in my SBC) when coming down steep hills in low gear and no throttle. Doesn‘t help much I know.

I have to ask, what’s the gain for using a cam that lowers the vacuum? It’s almost a new year, I need to learn something before it’s over .

 

[Mark Jennings]

Cam improvement.....it’s called ‘volumetric efficiency’....more air/fuel in, more burnt hydrocarbons out...more power....

Manifold vacuum is a result of the throttling effect of the carburetor...and valve overlap (intake and exhaust open at the same time)...longer overlap equates to better cylinder flushing (evacuation) at wide open throttle (WOT)....using the exhaust velocity to pull a clean charge of air/fuel mix into the cylinder. At WOT, a perfect engine would have 0.0” vacuum....14.7 lbs of pressure filling the cylinder that is 100% empty of exhaust gasses.....volumetric efficiency = 1.0.

Higher lift cams opens the valves further....more air in, more exhaust out. If we could just increase the lift, you would actually see a higher manifold vacuum....at idle/throttle closed....but then you would need square cam lobes. Since the lifters need to ‘ramp up’ (even roller lifters need a ramp), higher lifts...always increase duration and overlap.

The compromise for all of this improvement at WOT is......loss of vacuum at idle....e.g. lumpy cam = lumpy idle.

And have another beer.....

You other experts need to check me....I’m old...and memory of these things are fading fast....and have anther beer....

 

[1911]

I have to ask, what’s the gain for using a cam that lowers the vacuum? It’s almost a new year, I need to learn something before it’s over .

When you tighten the separation angle of the intake and exhaust lobes on the cam (less of an angle between them), you can both increase the maximum torque of the engine, and move the torque band lower in the rpm range. This is a Good Thing for four-wheeling and for heavy vehicles like RV's/motor homes. But the down side to it is that cylinder pressures increase, cranking compression increases, valve-to-piston clearance decreases, and idle vacuum decreases and hence idle quality suffers.

Cam design in every four-stroke engine is always a compromise; you can't have your cake and eat it too. You can design it to improve low-end torque at the expense of high-end rpm and hp. You can design it for max hp at wide-open throttle, but everything else will suffer. You can choose where you will make torque and hp in a band of rpm (the power band).

 

[Dizzy]

I've been convinced by SAE articles, that some passive EGR is a good thing (politics aside). If you get all the exhaust out of the mix, some of the combustion is just to restore pressure in the cylinder. I realize that there is a limit to this as well, and at WOT you want no exhaust and a full breath of air fuel/mix.

Lower vacuum means a wider window for the proper balance of the carb, resulting in greater throttle response. It probably helps scavenge fuel droplets off of the intake manifold. At lower pressures, the gasoline will 'atomize' easier.

 

[Mark Jennings]

When you tighten the separation angle of the intake and exhaust lobes on the cam (less of an angle between them), you can both increase the maximum torque of the engine, and move the torque band lower in the rpm range. This is a Good Thing for four-wheeling and for heavy vehicles like RV's/motor homes. But the down side to it is that cylinder pressures increase, cranking compression increases, valve-to-piston clearance decreases, and idle vacuum decreases and hence idle quality suffers.

Cam design in every four-stroke engine is always a compromise; you can't have your cake and eat it too. You can design it to improve low-end torque at the expense of high-end rpm and hp. You can design it for max hp at wide-open throttle, but everything else will suffer. You can choose where you will make torque and hp in a band of rpm (the power band).

Ah ha.....lobe centerline angle and lobe displacement angle.....the closer, the lower RPM peak torque...the further...higher RPM peak torque.

Awesome...have another beer

 

[Mark Jennings]

I've been convinced by SAE articles, that some passive EGR is a good thing (politics aside). If you get all the exhaust out of the mix, some of the combustion is just to restore pressure in the cylinder. I realize that there is a limit to this as well, and at WOT you want no exhaust and a full breath of air fuel/mix.

Lower vacuum means a wider window for the proper balance of the carb, resulting in greater throttle response. It probably helps scavenge fuel droplets off of the intake manifold. At lower pressures, the gasoline will 'atomize' easier.

Exhaust gas recirculating....displaces a small amount of the fuel/air mixture...and actually would allow for higher compression without pre-ignition....allowing for a more complete combustion....more energy extracted per pound of fuel burned....water injection same principal...talk to the boys running huge turbo’s and huge boosts...methanol/water injection.

Old school more air in...more air out and atmospheric pressure pushing it through.

Have yet another beer.....

 

[Dizzy]

I don't quite get how an open exhaust valve would be open at the same time as an intake valve without chancing intake backfire, or pre-ignition?

 

[Mark Jennings]

I don't quite get how an open exhaust valve would be open at the same time as an intake valve without chancing intake backfire, or pre-ignition?

As the pistons goes up forcing gases out...there is enough velocity to create a slight negative pressure in the cylinder. So just before the exhaust vale shuts and the piston starts is downward stroke......you open the intake to take adnntage of the slight negative.....and suck a fresh fuel/air mixture in....and even thought you also suck out some of the fresh charge.......you're left with a nice clean fue/air mix to compress and ignight.

If you add headers, this 'scvanging' effect is improved. If you open up the intake (multiple carbeators....tuned intake runner length) it's even more dramatic.

 

[Mark Jennings]

Exhaust gas recirculating....displaces a small amount of the fuel/air mixture...and actually would allow for higher compression without pre-ignition....allowing for a more complete combustion....more energy extracted per pound of fuel burned....water injection same principal...talk to the boys running huge turbo’s and huge boosts...methanol/water injection.

Old school more air in...more air out and atmospheric pressure pushing it through.

Have yet another beer.....

More on EGR..... also by displacing a small amount of combustible fuel/air with non combustible mass, you have to open the throttle more for the same power.....e.g. a more open intake path....theoretically better volumetric efficiency....the big problem is cooling this non combustible mass. You don't want the hot gass igniting the fuel/air mix prior to the spark plug doing it.....

Some of you diesel guys chim in.....I think Diesel EGR coolers plug up regularly.

 

[JohnJL]

I don't quite get how an open exhaust valve would be open at the same time as an intake valve without chancing intake backfire, or pre-ignition?

Momentum of the air coming it, and the low pressure after the exhaust valve. Also it happens very quick. And there is no spark in the chamber that is open on overlap when that event is happening, unless you timing is colossally off.

 

[Dizzy]

Under the hood of my Nissan is a pair of synchronized coils, eight spark plugs, four cylinders measuring at 2.4L, which was competition for the 22R. Two spark plugs in each cylinder netted greater combustion efficiency than one, also, it creates peak pressure sooner in the piston stroke, by having the combustion of one flame-front increase the compression in the environment of the second flame-front. It used unprecedented amounts of reused combustion gas, up to 24% (on some models) by volume. It got better ratings for fuel economy, HP, and torque, than its predecessor motor without the dual spark.

There is only a short pipe for EGR cooling, The system is still clean when I disassembled it, but the EGR valve is subject to rust, internally. The valve is still available, new, OEM.

A little hijack here: I don't know this for certain, but the 4wd version of the Nissan pickup was likely the first marketed in the USA to deviate from a solid-front-axle set-up. It '86 Toyota, and everyone else, followed.

 

[1911]

Under the hood of my Nissan is a pair of synchronized coils, eight spark plugs, four cylinders measuring at 2.4L, which was competition for the 22R. Two spark plugs in each cylinder netted greater combustion efficiency than one, also, it creates peak pressure sooner in the piston stroke, by having the combustion of one flame-front increase the compression in the environment of the second flame-front. It used unprecedented amounts of reused combustion gas, up to 24% (on some models) by volume. It got better ratings for fuel economy, HP, and torque, than its predecessor motor without the dual spark.

This was a well-known and used technique for a little bit of extra hp in old hemi-head engines; drill and tap the head(s) for a second plug on the side opposite to the original spark plug. That, and indexing the spark plugs so that the spark gap faced the intake valve. Seems almost humorous now, but back then it was a lot harder to wring power out of those olds motors. 1 hp per cubic inch used to be an at times seemingly impossible goal.

 

[JohnJL]

Well its a Delta KC cam....no visible indication the timing gear rotated, the insulation seems uniform almost all around except in one spot.

This is a little weird though...#1 exhaust and # 3 exhaust lobes are "pinched" at the lobe apex...