head porting, camshaft, other super-bad-fightin' stuff

[joegebff]

Seems to me the center line axis of the cam would have to remain the center line. So any material ground off would result in a loss of lift, no matter where it was removed from.

I might be wrong.

I need to see one of Gene's graphs to be sure.

Go get some limes....

[Markadeck]

Interesting thread. Makes me wish I were 40 years younger. But, if you grind off some of the bottom of the cam and change the rocker ratio you're going to get more lift and valve open timing. I fooled with and spent big bucks on gasoline race engines and know zero about flowing diesel heads, but gassers sure benefit from it. You're saying if someone is going to polish and port diesel heads do not even bother with the intake ports?

[strokin_it7.3]

I could do this much better on a dry erase board. Very crude, watch out!

In the pic, the cam on the left, has the dotted line where it would be if it was a constant base circle cam, with no lift. Above it, you can see the lobe where it makes a lift (to measure lift on a cam, if the lobe is pointing perfectly vertical, take the mic's and measure the horizontal measurement, which is base circle to base circle. Then turn it 90*, and measure the base circle to top of the lobe, subtract the first measurement and you have total lift). On the right, the expert machinist has carefully milled away the area shaded in yellow. So when you go to measure the first measurement, the BC stays the same, however when you take the measurement again, the cam lift is going to be exactly as much more as what you just cut off the base circle of the cam. Now do you see where this can add lift? This is ONLY to add valve lift, and not to change timing or duration. (well, duration in a way, but how about lobe seperation)

Damn, This is my twelve-thousandth post. I was hoping to make that one over in the off topic section!

[joegebff]

But the cam itself is still supported by circles in the cam bearings that have not been altered. My pea brain tells me that the expert job of precision grinding that you just did will only allow the valve to close even further, so to speak.

I'm not saying you are wrong. I'm not even saying that you are mistaken. I'm just saying I don't see it.

Congrats on 12K.

I do appreciate the effort on the sketch.

[Izzy351]

It increases the total "swing" between the top of the lobe and the opposite side. You have to visualize it rolling the push rod...

[ron's power stroke]

quoted from Dave Lott

Injectors, Big oil. GT42R or bigger, Big DIIC, DI tuning, headers, camshaft, port work, DI fuel system
13,500-16,500.00
600+ on a single turbo
800+on NOS
Not sure on twins but will soon find out.
__________________
David Lott
No purpose no happiness, know purpose know happiness
Snow White ------> www.DieselInnovations.com

[strokin_it7.3]

No the cam still resides in the same bearing journals. However the amount you cut off the base circle, you add to the pushrod, so you do not overextend the hydraulic lifters. Sorry, but i do know, that i am right on this one.

[Markadeck]

Originally Posted by joegebff

But the cam itself is still supported by circles in the cam bearings that have not been altered. My pea brain tells me that the expert job of precision grinding that you just did will only allow the valve to close even further, so to speak.

I'm not saying you are wrong. I'm not even saying that you are mistaken. I'm just saying I don't see it.

Congrats on 12K.

I do appreciate the effort on the sketch.

Me neither, but due to my old age I can remember something we called 3/4 race cams. These were simply OEM camshafts that were modified by talented machinists in plain old machine shops. Now it's evolved into a full fledged custom camshaft industry.

[Markadeck]

Originally Posted by strokin_it7.3

No the cam still resides in the same bearing journals. However the amount you cut off the base circle, you add to the pushrod, so you do not overextend the hydraulic lifters. Sorry, but i do know, that i am right on this one.

Or rocker ratio? The cams I was referring to for the most part in my above post were in relation to flathead engines. So, no pushrods or rocker arms. But they were probably used in the overhead valve engines too, but in high school I was a Ford man even then.

[Markadeck]

I remember in my Pontiac powered street racing days a little known trick I was using that I did my best to keep secret was this. Pontiac OEM rockers were all 1.5 lift, a cute little trick was to replace the exhaust only with 1.65 and don't tell even your best friend you did it. It was an instant super low budget camshaft replacement that no one but you knew about.....Cute, huh?

[piotrsko]

Originally Posted by Markadeck

I remember in my Pontiac powered street racing days a little known trick I was using that I did my best to keep secret was this. Pontiac OEM rockers were all 1.5 lift, a cute little trick was to replace the exhaust only with 1.65 and don't tell even your best friend you did it. It was an instant super low budget camshaft replacement that no one but you knew about.....Cute, huh?

Same thing in V-dubs from the same era, only we used chebbie rockers with bushings but then you started breaking valve springs..........

The Only reason there isn't a lot of porting/head work done: We FORCE the air in with a blower. No driveability issues, no lope. Not enough HP, add more blower which is faster cheaper easier. the exhaust side is a problem since you may end up with a dilution effect because of poor scavenging.

[YellerMax]

Kris is correct, cams can be (and commonly are) reground to increase lift and duration. I have sent two cams off to be reground before. Just takes longer pushrods to make up for the smaller base circle

With regards to porting, Kris, thanks for the explanation: to make make sure I'm on the right page, we increase airflow via PRESSURE from the turbo, rather than VOLUME from port-matching. This doesn't work in gasoline motors because the SHAPE of the induction matters because it is a fuel/air mixture and pressure gradients, turns, etc... affect fuel atomization. For a diesel, air is air, and the ONLY thing that matters is how much air makes it into the cylinder, whether is is by having an efficient method into the cylinder or by having it pressurized before it gets there.

This satisfies my question with regards to the INTAKE side, but not the EXHAUST side. In fact, I would think a diesel would doubly benefit from exhaust work: let me explain.

First, once combustion has taken place, a diesel and a gasser work EXACTLY the same. Power stroke, valve opens, exhaust stroke. With a higher operating compression, it backpressure is going to cause much more parasitic loss on a diesel. As the piston moves up to push the exhaust out, ANY pressure is going to fight the piston and cause drag on the motor--this is basic physics, the exhaust is trying to push OUT, and if it cannot efficiently get out the exhaust port, it is going to try to make its space bigger by pushing the piston down the OPPOSITE direction than we want it to go.

Second: turbocharger. The more efficiently we can get our exhaust gas to the turbo, the more FREE power we can get by spooling that bad boy up.

My notion here is that intake work will do NO good unless your turbo has reached maximum efficiency and you CANNOT generate any more pressure, which is a moot point because the engine would fail long before you reached that point. But I think a diesel COULD benefit, much more than a gasoline motor even, from improving PRE-TURBO exhaust flow with a better camshaft and/or valvetrain, exhaust porting, etc...

What do y'all think? make sense?

[Markadeck]

Originally Posted by piotrsko

Same thing in V-dubs from the same era, only we used chebbie rockers with bushings but then you started breaking valve springs..........

The Only reason there isn't a lot of porting/head work done: We FORCE the air in with a blower. No driveability issues, no lope. Not enough HP, add more blower which is faster cheaper easier. the exhaust side is a problem since you may end up with a dilution effect because of poor scavenging.

If I were to list the valve train stuff I used to break, you'd wonder why I still fool with anything related to high performance. I used to snap the valves right off at the head from my radical cams I ended up running. You can only imagine what that does to whichever cylinder it happens in. I finally went to Ti valves at 1000 bucks for 16, back in the early '80's, I would not even want to price them today. But it can go on my tombstone, He croaked with nothing, but he had fun..........LOL....... I once broke my forged crank into 3 pieces at launch (6500 rpm) you know the damn engine kept on running until I shut it down. Course it was seized from that point on. I then borrowed a friends high dollar motor to race the next weekend while mine was in Cincinnati getting redone by the premier Pontiac man of the period, and I'll be damned if I didn't blow his up too.

[monsterbaby]

It's a known fact that any supercharged engine can and does benifit from exhaust port work and it doesn't matter what type of fuel you run or who's engine it is every single one has some benefit to having the exhaust side worked on. A turbo charged engine even more then a mechanical blower setup but either one does. Reason is yes on the intake side you are forcing it in with the supercharger but on the exhaust side it exits the motor the same was NA engine does with the exception of on a turbo engine you also have the added restriction of the turbo itself. it's not as free of HP as everyone thinks it is, I believe it was Banks that did a dyno test (not sure if it was on a diesel or gas but doesn't matter for this discussion) but took an engine without a turbo on it, ran it on the dyno then put a turbo in the exhaust without actually pushing the boost into the engine (so you aren't getting the benefit of it but you can see the lose) without having the numbers directly in front of me it IIRC it was a 3 or 4% loss in power just having to push the exhaust through that turbo making boost, maybe not much but it's loss non the less. Now if just spinning that turbo is costing a few percentage points in power how much is poor casting and restrictive ports costing? I have heard of at least one person actually taking the PSD exhaust manifolds and having them extruded honed and having dyno proven increase in power just doing that alone with no other changes.

[YellerMax]

I've actually been thinking about that... extrude honing is a vastly untouched, affordable performance option for the average car nut. Nothing to worry about making new parts fit either. I'm convinced this stuff needs to be explored more, and when (gulp) I blow my motor up I'm going to totally rework the heads to prove it has benefit