Valve lift vs. port flow and cam selection

[RevTheory]

Would you think that people of Jon's caliber may tend to nonchalantly BS just a bit.

Oh no, not even a little

One thing they may tend to do, however, is forget about the thousand hours of development work on a bench they put into the port years ago that's allowed them to now go by sight and measurements.

[CamKing]

Would you think that people of Jon's caliber may tend to nonchalantly BS just a bit.

Oh no, not even a little

One thing they may tend to do, however, is forget about the thousand hours of development work on a bench they put into the port years ago that's allowed them to now go by sight and measurements.

In either of the quotes given, he doesn't say he doesn't use a flow bench.
In one of the quotes, he's talking about people using a flow bench to try and match the head to the cam, in my 38 years in the cam business, I've never heard of someone porting the head to match the cam. That's 180 degrees, backwards.

[PRH]

The first engine building/machine shop I worked at(1990) didn’t have a flow bench.
There were only a few within reasonable driving distance at that time.
The only porting we did in house was very minor bowl work.
We had a guy who did any real porting, and he had a flow bench(SF-600).

At the time we were building a lot of oval track motors for a variety of different tracks and classes.
No crate motor classes existed here at that time.

All but one of the classes we built motors for had “no porting” head rules.
Occasionally we’d have the head porting guy flow an unported head for us..... but that would have been pretty rare.

We had no trouble coming up with cams for all those different classes...... and what the heads flowed wasn’t usually even part of the conversation.
There were a lot of race wins that came from those cams that were selected without the aid of flow data.

My experience has been that the “application” has way more influence on the cam selection than what the flow numbers would.

I've never heard of someone porting the head to match the cam.

I see it in forums fairly regularly where someone says something like, “I have this cam I want to use......”, and they’re contemplating some new build.
My advice is usually along the lines of, “don’t build a motor around a camshaft”.

[CamKing]

The first engine building/machine shop I worked at(1990) didn’t have a flow bench.
There were only a few within reasonable driving distance at that time.
The only porting we did in house was very minor bowl work.
We had a guy who did any real porting, and he had a flow bench(SF-600).

At the time we were building a lot of oval track motors for a variety of different tracks and classes.
No crate motor classes existed here at that time.

All but one of the classes we built motors for had “no porting” head rules.
Occasionally we’d have the head porting guy flow an unported head for us..... but that would have been pretty rare.

We had no trouble coming up with cams for all those different classes...... and what the heads flowed wasn’t usually even part of the conversation.
There were a lot of race wins that came from those cams that were selected without the aid of flow data.

My experience has been that the “application” has way more influence on the cam selection than what the flow numbers would.

So, what you're saying is, you didn't need a flow bench, for classes where porting wasn't allowed.
I'm assuming these were mostly classes restricted to flat tappet cam, and stock diameter lifters. Maybe even restricted to stock rockers, or stock size springs. Maybe restricted to a 2bbl carb. Probably in the mid .500 lift range.

[CamKing]

My advice is usually along the lines of, “don’t build a motor around a camshaft”.

Agree 100%
You design the cam around the parameters of the engine, and the RPM range you want to run in.

[PRH]

So, what you're saying is, you didn't need a flow bench, for classes where porting wasn't allowed.
I'm assuming these were mostly classes restricted to flat tappet cam, and stock diameter lifters. Maybe even restricted to stock rockers, or stock size springs. Maybe restricted to a 2bbl carb. Probably in the mid .500 lift range.

Two classes allowed roller cams, one flat tappet class allowed bigger lifters.
Initially only the two classes that allowed roller cams allowed roller rockers.
Eventually the one that allowed the bigger lifters opened up to allowing roller rockers.
Breaking/burning up stock rockers was a big battle for many racers.

There were a few different 2bbl classes, some mandated hyd lifters and under .500 lift.

Sure, a flow bench might have helped sort out some valve job angles, and help figure out which heads were the more preferred castings........ but I’m not sure how helpful it would have been in the cam selection for those classes.

In any case...... we didn’t have one....... yet we still had customers regularly winning races.

[CamKing]

Sure, a flow bench might have helped sort out some valve job angles, and help figure out which heads were the more preferred castings........ but I’m not sure how helpful it would have been in the cam selection for those classes.

In the early 90's, we did some testing on a class where you had to run stock heads, no porting, and only a 3 angle valve job.
On the dyno, we found that going from a 1.5 rocker(.510" Lift) to a 1.6 rocker(.544" lift), actually hurt power. We put the heads on the flow bench, and found out the port went turbulent above .500" lift(it actually got real noisy on the bench, when you increased the lift beyond .500"). The head porter played around with different angles on the valve job, until the port was good past .550" lift. it didn't flow any more CFM, it just didn't get turbulent. Went back on the dyno with the same cam, and now the engine responded to the 1.6 rockers. It was probably less then a 10hp gain, but any hp gain in a class as restricted as that, was a big deal.

[Steve.k]

That makes a lot of sense Mike. I think a lot of guys read Jons quote wrong. I believe he uses every option available to him however i think he means if your chasing after every last cfm on bench you maybe getting a little carried away.

[Elroy]

So some talk about determining lift from flow bench numbers seems common agree or disagree. How about determining duration or centerlines/?

[digger]

seems a bit sketchy to me to base lift on where something backs up at 28", given it will almost inevitably back up a bunch sooner on the engine (much higher depression).

[raynorshine]

Would you think that people of Jon's caliber may tend to nonchalantly BS just a bit.

Oh no, not even a little

One thing they may tend to do, however, is forget about the thousand hours of development work on a bench they put into the port years ago that's allowed them to now go by sight and measurements.

In either of the quotes given, he doesn't say he doesn't use a flow bench.
In one of the quotes, he's talking about people using a flow bench to try and match the head to the cam, in my 38 years in the cam business, I've never heard of someone porting the head to match the cam. That's 180 degrees, backwards.

ya never thought of doing it that way...porting a head to match a camshaft??

-is that reverse engineering?

[ClassAct]

seems a bit sketchy to me to base lift on where something backs up at 28", given it will almost inevitably back up a bunch sooner on the engine (much higher depression).

That's what I said but I don't know what I'm talking about.

[GARY C]

The first engine building/machine shop I worked at(1990) didn’t have a flow bench.
There were only a few within reasonable driving distance at that time.
The only porting we did in house was very minor bowl work.
We had a guy who did any real porting, and he had a flow bench(SF-600).

At the time we were building a lot of oval track motors for a variety of different tracks and classes.
No crate motor classes existed here at that time.

All but one of the classes we built motors for had “no porting” head rules.
Occasionally we’d have the head porting guy flow an unported head for us..... but that would have been pretty rare.

We had no trouble coming up with cams for all those different classes...... and what the heads flowed wasn’t usually even part of the conversation.
There were a lot of race wins that came from those cams that were selected without the aid of flow data.

My experience has been that the “application” has way more influence on the cam selection than what the flow numbers would.

I've never heard of someone porting the head to match the cam.

I see it in forums fairly regularly where someone says something like, “I have this cam I want to use......”, and they’re contemplating some new build.
My advice is usually along the lines of, “don’t build a motor around a camshaft”.

So how did you determine the best cam? That is what the OP is asking.

[GARY C]

Oh no, not even a little

One thing they may tend to do, however, is forget about the thousand hours of development work on a bench they put into the port years ago that's allowed them to now go by sight and measurements.

In either of the quotes given, he doesn't say he doesn't use a flow bench.
In one of the quotes, he's talking about people using a flow bench to try and match the head to the cam, in my 38 years in the cam business, I've never heard of someone porting the head to match the cam. That's 180 degrees, backwards.

ya never thought of doing it that way...porting a head to match a camshaft??

-is that reverse engineering?

If the cam you have matches the ci and rpm requirements and you have the head needed how would it be any different then any other starting point where you would design the engine prior to purchasing parts?

[PRH]

So how did you determine the best cam? That is what the OP is asking.

I don’t think someone is going to come up with the “best” cam in one try, unless they’re duplicating an already well sorted out combo.

We’d start with something that made sense for the combo and application...... see how it worked...... and then make changes based on the results.

In my mind....... that’s not really any different than if I did have flow numbers.

What the head flows is usually pretty far down the list in terms of importance for criteria used to select a cam....... at least in my world.

But then, I’m not trying to develop Cup or P/S engines either.

For the typical street/strip, bracket race, weekend oval track racer....... getting every last possible hp isn’t the top priority.
At least, that’s the case with the stuff I’m working on.