before/after 383 dyno results

[randy331]

My suspicion is that those individuals who are putting together the pushrod v8 engines that make the most hp/ci......... are not focused on how to improve the low lift flow in their cylinder head program.

This is spot on the money.

X2

Randy

[MadBill]

To continue the topic drift just a little further, here's a theoretical case where reducing low lift flow with no other changes could help a previously cam-optimized engine:

A friend of mine has a number of BBC-based four cam Batten engines. The older editions have cam duration specs which closely match ones optimized in the Dynomation program. The intake cams in later ones have ~ 0.150" more lift (predicted by DM to give substantially more power) and almost 20° more duration. The rationale for the excess was that with the limiting factor of the bucket diameter, trying to add a lot of lift but no duration leads to dunce cap-shaped lobes with disastrously small contact areas. In testing it was found that the excess duration cost less power than the higher lift added.

In such a circumstance, reduced low lift flow would almost certainly be a plus.

[Stan Weiss]

For the vast majority of engines that have physical limitations on lifter diameter, journal diameter, etc, how do you just "cam it right" for improved low lift flow ?

How do you keep the time/area up top if you just keep improving low lift flow and taking duration out to compensate?
Lift becomes a limit as duration goes down.

The problem is, we are always confronted with the choice of best compromise. The valves don't have unlimited motion. We are always confined by the architecture of the engine, class rules, budget, etc.
The best cam for a certain application isn't a perfect cam, it's just the best compromises.

There are other reasons steeper seats are used than the flow we see on a bench.

So far the thread has been for the most part very civil even though there has been disagreement on ideas,...as it should be.
For the few that think this thread had some sinister motive to go down a certain path and have nothing to contribute,... read other threads and stay out.

Randy

A couple of answers are increased rocker arm ratio and asymmetrical cam lobe design.

Stan

PS - I have never used one but I believe the Jones Inverse Radius Roller cam might also be an answer.

[gruntguru]

Want to decrease low lift flow? Easy, just pocket the valves into the head.

[BradH]

The problem is, we are always confronted with the choice of best compromise. The valves don't have unlimited motion. We are always confined by the architecture of the engine, class rules, budget, etc. ...

There are other reasons steeper seats are used than the flow we see on a bench.

I've used the phrase "optimize the compromise" recently for this reason, especially when it comes to street/strip combinations like my own.

Were you expecting the 50* seats with your porting to have increased the flow across almost the entire lift range? It seems like most flow tests of steeper seat angles show losses at low(er) lifts, so I wasn't expecting the results you got.

Definitely looking forward to seeing what results your updates make.

[LoganD]

For the vast majority of engines that have physical limitations on lifter diameter, journal diameter, etc, how do you just "cam it right" for improved low lift flow ?

How do you keep the time/area up top if you just keep improving low lift flow and taking duration out to compensate?
Lift becomes a limit as duration goes down.

The problem is, we are always confronted with the choice of best compromise. The valves don't have unlimited motion. We are always confined by the architecture of the engine, class rules, budget, etc.
The best cam for a certain application isn't a perfect cam, it's just the best compromises.

There are other reasons steeper seats are used than the flow we see on a bench.

So far the thread has been for the most part very civil even though there has been disagreement on ideas,...as it should be.
For the few that think this thread had some sinister motive to go down a certain path and have nothing to contribute,... read other threads and stay out.

Randy

Well, stop playing with engines that have crap valvetrains! That's in jest, but it's obvious that there's always limitations that prevent "ideal" scenarios. My problem with making a blanket statement along the lines of "too much low lift flow is bad for power" is that it's wrong. On a very specific engine application it could prove true due to other factors outside of flow such as combustion quality, valvetrain limitations, etc. That's not the fault of the increased flow itself, it's the fault of the specifics of the combination.

If low lift flow is bad, then why do 4-valve heads make so much more power?

[Orr89rocz]

2 intake valves are better than 1

[Carnut1]

2 intake valves are better than 1

2 vs. 4.jpg

Some DV art to add to conversation.

[randy331]

Were you expecting the 50* seats with your porting to have increased the flow across almost the entire lift range? It seems like most flow tests of steeper seat angles show losses at low(er) lifts, so I wasn't expecting the results you got.

It's not surprising given the valve job they had when I got them.
It really was a horrible valve job. Big edges around the top cuts in the chamber etc.
A better 45* and or cleaning up around the horrible one they had would have made them flow more under .300, then you'd see a more normal change going to 50* seats. But I don't bother flowing them in stages of porting.

Randy

[CGT]

Were you expecting the 50* seats with your porting to have increased the flow across almost the entire lift range? It seems like most flow tests of steeper seat angles show losses at low(er) lifts, so I wasn't expecting the results you got.

It's not surprising given the valve job they had when I got them.
It really was a horrible valve job. Big edges around the top cuts in the chamber etc.
A better 45* and or cleaning up around the horrible one they had would have made them flow more under .300, then you'd see a more normal change going to 50* seats. But I don't bother flowing them in stages of porting.

Randy

I was just running your flows through Rick's Curtain area program, very pronounced increase in window DC at all lifts.

[ClassAct]

Want to decrease low lift flow? Easy, just pocket the valves into the head.

That's why I pointed out earlier that you have to reduce low lift flow correctly. Just screwing shit up to reduce flow anywhere is always a bad idea.

[BradH]

...

Take the Chrysler stage 6 head. What a piece of shit that thing is. Period. To make them work, you do many things that are considered wrong. They will make power, but the flow numbers never look like they should. In fact, if I see what I consider big numbers for that head, I know it's wrong. Fixing it will certainly reduce flow across the bench. But they will always be quicker in the car, and if you pay attention you'll see the BSFC numbers are better.

...

As in, "Take my Stage VI head... please!" (spoken w/ a Rodney Dangerfield impression)?

The MP Stage VI head(s) could be a whole thread on its own, except I suspect there's probably only a handful of people on SpeedTalk who have used and/or worked on them... and even those folks might not want to bring up the subject due to bad memories.

[gmrocket]

For the vast majority of engines that have physical limitations on lifter diameter, journal diameter, etc, how do you just "cam it right" for improved low lift flow ?

How do you keep the time/area up top if you just keep improving low lift flow and taking duration out to compensate?
Lift becomes a limit as duration goes down.

The problem is, we are always confronted with the choice of best compromise. The valves don't have unlimited motion. We are always confined by the architecture of the engine, class rules, budget, etc.
The best cam for a certain application isn't a perfect cam, it's just the best compromises.

There are other reasons steeper seats are used than the flow we see on a bench.

So far the thread has been for the most part very civil even though there has been disagreement on ideas,...as it should be.
For the few that think this thread had some sinister motive to go down a certain path and have nothing to contribute,... read other threads and stay out.

Randy

Well, stop playing with engines that have crap valvetrains! That's in jest, but it's obvious that there's always limitations that prevent "ideal" scenarios. My problem with making a blanket statement along the lines of "too much low lift flow is bad for power" is that it's wrong. On a very specific engine application it could prove true due to other factors outside of flow such as combustion quality, valvetrain limitations, etc. That's not the fault of the increased flow itself, it's the fault of the specifics of the combination.

If low lift flow is bad, then why do 4-valve heads make so much more power?

You have a problem with blanket statements?

Yet you said low lift flow is always good..

Let's see one of your engine builds that proves it? A before and after would be good

[digger]

If low lift flow is bad, then why do 4-valve heads make so much more power?

A 2v head probably makes more power if both are done to meet the piston demand the engine requires ie same flow at peak valve lift

[paulzig]

I was just running your flows through Rick's Curtain area program, very pronounced increase in window DC at all lifts.

How many extra flows would you need with a 45° seat to equal or better the window DC of the 50° seat at all lift points?