Advantages of advancing the cam on a street engine?

[groberts101]

Thanks for the input, sounds like I'm on the right course then. I edited my post on you to add this
"On the intake I'm focusing on 3 areas, blending the seat to bowl, narrowing the guide boss to a vane, and taking .100" out at the pushrod pinch because I think stock it gets flow separation."
I could tell there was a lot of swirl action, even the beak in the chamber that shrouds the intake, which I'm grinding to match 45deg seat.
It makes sense to a degree, they were making a truck head with mpg in mind.
Maybe I'll post pics

Eric

The tiny narrow ass pinch speed doesn't cause separation at that juncture, at least as far as I've ever seen with a pitot or bench results going from stock to around 282cfm @28", but that WAAYYY too fast floor speed created by it just hamstrings the SSR further on down the line.. was what I was getting at with my above comment.

Basically, settle down the upstream speeds and you'll have an easier time getting the SSR flow separation under control was the main point. Otherwise you'r left bandaiding the SSR because of that too narrow pinched floor width. You can really only gain so much width in the pinch without going to an offset rocker/pushrod setup so you'll need to get the roof up as high as possible and then push the common walls on either side of the divider as hard as possible. There is no water in the first couple inches so you can go deep on both sides/ports until there's barely any divider left. If you use the OEM improved metal gasket(aluminum IIRC, that divider can easily be whittled down to around .080" without worry for losing the gasket during torquedown or over longer term heat cycling. You can go even narrower than that if longevity is not a key concern too. Think my last set went downwards of around .060" and still sealed up with the modified gasket just fine. Good luck with it.

[E.Roy]

Thanks for the input, sounds like I'm on the right course then. I edited my post on you to add this
"On the intake I'm focusing on 3 areas, blending the seat to bowl, narrowing the guide boss to a vane, and taking .100" out at the pushrod pinch because I think stock it gets flow separation."
I could tell there was a lot of swirl action, even the beak in the chamber that shrouds the intake, which I'm grinding to match 45deg seat.
It makes sense to a degree, they were making a truck head with mpg in mind.
Maybe I'll post pics

Eric

The tiny narrow ass pinch speed doesn't cause separation at that juncture, at least as far as I've ever seen with a pitot or bench results going from stock to around 282cfm @28", but that WAAYYY too fast floor speed created by it just hamstrings the SSR further on down the line.. was what I was getting at with my above comment.

Basically, settle down the upstream speeds and you'll have an easier time getting the SSR flow separation under control was the main point. Otherwise you'r left bandaiding the SSR because of that too narrow pinched floor width. You can really only gain so much width in the pinch without going to an offset rocker/pushrod setup so you'll need to get the roof up as high as possible and then push the common walls on either side of the divider as hard as possible. There is no water in the first couple inches so you can go deep on both sides/ports until there's barely any divider left. If you use the OEM improved metal gasket(aluminum IIRC, that divider can easily be whittled down to around .080" without worry for losing the gasket during torquedown or over longer term heat cycling. You can go even narrower than that if longevity is not a key concern too. Think my last set went downwards of around .060" and still sealed up with the modified gasket just fine. Good luck with it.

Thanks for all the pointers. I meant that the pushrod pinch causes flow separation off the ssr after the pushrod, they put kicker ramps in top and bottom corners on the pushrod side, and that is a small radius around the pushrod for the air to follow at higher rpm.
What cfm did you get with your heads at .5" lift?
Oh and does filling the rocker stud divot help?

Thanks, Eric

[groberts101]

Thanks for all the pointers. I meant that the pushrod pinch causes flow separation off the ssr after the pushrod, they put kicker ramps in top and bottom corners on the pushrod side, and that is a small radius around the pushrod for the air to follow at higher rpm.
What cfm did you get with your heads at .5" lift?
Oh and does filling the rocker stud divot help?

Thanks, Eric

Had to dig them up, I keep almost everything but finding it is the harder part. It was... 8mm LS valves 2"/1.55" flowing 248/219 @.500".. with no exhaust pipe on 4" bore. Kept flowing up to .700" where we stopped the testing. Swirl was 1310rpm which was actually better than I had remembered.

Keep in mind that bigger numbers are possible but that particular head was done specifically towards reduced swirl and the PR pinch was not fully maxed out. In fact, it was actually straightened with putty to mimic a traditional straight up vertical wall entry SBC port rather than the canted style entry of the Vortec design. Not gasket matched on the PR pinch side either since all that does is make a larger dead space and puts you right back towards a pronounced hump from which you started out with. Basically end up having a bigger port entry with similar hump intrusion even though the pinch was made wider. About the only time I match that side of the gasket is if the intake runners exit turn into the heads entry can be improved upon by doing it. Hope that helps.

[randy331]

What cfm did you get with your heads at .5" lift?

You were saying you wanted to make peak TQ at 3500 rpm, that means it will make peak HP at 5000-5500 rpm.

How much cfm do need for that ?

Cfm demand is pretty low on 355 cubes at 5000 rpm.

Randy

[E.Roy]

Had to dig them up, I keep almost everything but finding it is the harder part. It was... 8mm LS valves 2"/1.55" flowing 248/219 @.500".. with no exhaust pipe on 4" bore. Kept flowing up to .700" where we stopped the testing. Swirl was 1310rpm which was actually better than I had remembered.

Keep in mind that bigger numbers are possible but that particular head was done specifically towards reduced swirl and the PR pinch was not fully maxed out. In fact, it was actually straightened with putty to mimic a traditional straight up vertical wall entry SBC port rather than the canted style entry of the Vortec design. Not gasket matched on the PR pinch side either since all that does is make a larger dead space and puts you right back towards a pronounced hump from which you started out with. Basically end up having a bigger port entry with similar hump intrusion even though the pinch was made wider. About the only time I match that side of the gasket is if the intake runners exit turn into the heads entry can be improved upon by doing it. Hope that helps.

Nice, that's pretty much what I'm hoping for, around 250cfm at .5". I have purposely not touched the intake inlet opening at the gasket, the port mold helped me see and so did measuring the Edelbrock 2716 EPS intake, which is narrower than the vortec port at the gasket.

Randy, I'm trying to make it easier for the exhaust pulse suction to get the intake port up to velocity, so I'm streamlining intake port and trying to reduce turbulence, swirl and tumble, taking out the GM manipulation features. Laminar flow is my aim and hoping to max port performance in 3,500-4,000 range . I'm barely if at all increasing cross section area between pushrod and valve guide vane.

Pointers and theory welcome
Thanks
Eric

[GARY C]

Low rpm tq, 12.5 or better compression with electronic controlled water meth system.

[groberts101]

Low rpm tq, 12.5 or better compression with electronic controlled water meth system.

Fully agree. I do think it could also be done with a smaller dome though. Maybe 11.25'ish:1 and running a map based tune on an msd programmable box would allow 93 octane. E85 blends would be closer towards 12:1. Full e85 could stand much more too.

I'd also lean towards a 1.5" primary size or maybe stepped to a 1.625" even if resulting in slight port mismatch. Smaller collector too or even a slip on merge with tiny 2" choke wouldn't hurt either. Need to get up on the pipe quicker if at all possible.

[E.Roy]

Moderate compression up to 10.5:1 is part of the plan.
My budget limited plan is using the stock pistons, so I will need to have heads milled near .030 and use a beaded steel .015 gasket (12cc dish .025 in the hole)

I agree on headers, maybe find a tri-y like the Doug Thorley used by the Creason team or get 1 5/8 full length and possibly extending primary tubes into a nice merge

I'll try to post pics of port work and the port mold I made

[randy331]

Randy, I'm trying to make it easier for the exhaust pulse suction to get the intake port up to velocity

How do you go about achieving that ?

How do you know your ex system has a "ex pulse suction" ?

How do you know you have done what it takes to "get the intake port up to velocity" ?

Is it always an advantage to "get the intake up to velocity" ?

Is it possible to get the intake port up to too much velocity ?

Just wondering how the goals are defined ?????

Randy

[E.Roy]

Randy, I'm trying to make it easier for the exhaust pulse suction to get the intake port up to velocity

How do you go about achieving that ?

How do you know your ex system has a "ex pulse suction" ?

How do you know you have done what it takes to "get the intake port up to velocity" ?

Is it always an advantage to "get the intake up to velocity" ?

Is it possible to get the intake port up to too much velocity ?

Just wondering how the goals are defined ?????

Randy

How do you go about achieving that ?
I'll admit its theory based on observation and basic principles of pressure and flow. I've done exhaust port mods to keep the exhaust flowing as it is almost closed, by smoothing the exhaust seat to chamber angles and removing the burr there. I also made a smoother rounder path where intake and exhaust port are adjacent. For intake, the stock seat ridge being ported to a larger diameter (more area means more force) and now having a smooth transition should help apply more negative pressure to the intake port in less time. Then smoothing what I feel are features limiting velocity are straightened out.

How do you know your ex system has a "ex pulse suction" ?
I'm pretty confident there will be one with headers

How do you know you have done what it takes to "get the intake port up to velocity" ?
I dont know exactly, but it isn't hard to copy off LS3 or high performance heads

Is it always an advantage to "get the intake up to velocity" ?
I dont know if always, but after reading engine scientists say it, I'll consider it a safe bet on my application especially to get higher performance at a lower rpm than most care about

Is it possible to get the intake port up to too much velocity ?
After reading, I feel the answer is no for my engine combo, since the events are happening dozens of times per second

After this is all assembled, I do hope to measure the total performance of the setup on a chassis dyno. If you think my theories are wrong can please give reasons.

[randy331]

The post was just to spur some thought and discussion.

Keep in mind, that flow path works both ways.
If you make it easy for the intake to flow to the ex, the ex can just as easily flow to the intake.
Things aren't a nice steady flow in one direction in a engine.

I've seen some engines with ex soot up in the intake port, and others nice and clean.

At low rpm there is lots of time for things we don't want to happen, to happen.

Randy

[GARY C]

The post was just to spur some thought and discussion.

Keep in mind, that flow path works both ways.
If you make it easy for the intake to flow to the ex, the ex can just as easily flow to the intake.
Things aren't a nice steady flow in one direction in a engine.

I've seen some engines with ex soot up in the intake port, and others nice and clean.

At low rpm there is lots of time for things we don't want to happen, to happen.

Randy

My thought is valve timing.

[E.Roy]

The post was just to spur some thought and discussion.

Keep in mind, that flow path works both ways.
If you make it easy for the intake to flow to the ex, the ex can just as easily flow to the intake.
Things aren't a nice steady flow in one direction in a engine.

I've seen some engines with ex soot up in the intake port, and others nice and clean.

At low rpm there is lots of time for things we don't want to happen, to happen.

Randy

Yeah, I understand that basically things are constantly changing in an engine. Being that I'll be running a mild to moderate cam, likely with duration maxing out around 230 @ .50, overlap will not be in race cam territory even with a tighter LSA. Also I'm willing to accept a loss in off idle performance from the porting job to hopefully make it perform stronger at 3,500 on to 6,000.

Eric