[25stevem]

Please folks also keep in mind that in terms of making a hp goal in a street motor, or for sure a street strip type motors while running a good flowing aftermarket out of the box heads or very well ported iron heads your lift at the valve needs to be .100” for every 100 hp your looking to make.

In terms of the cam and down the road adding higher ratio rockers you need to consider this.

If your cam was very close to having the needed amount of overlap for your CID, and that the correct placement of that overlap is taking place, then when you add on higher ratio rockers you will find that to make the most of that ratio swap that the cam now needs to be retarded.

This is why barring some mechanical issue when some guys add 1.65 rocker or higher, little to no improvement in power is seen.

To detail this even more if you find a reduction in power by such a swap then that’s telling you that your cam pick is very off in the first place, or it’s just not degreed in right to start with.

[Formulajones]

Originally Posted by 25stevem

You can’t compare minimum port area between a SBC and a Pontiac by comparing there port volume because a SBC head has a intake runner that’s over a inch longer then a Pontiac.
It’s a long way from being apples to apples!

If your running any of the common aftermarket streetable heads on your motor and your not running at least .525” lift then your leaving power ( TQ and HP ) that you payed and maybe waited dearly for on the table big time.

It’s really that simple.

Especially with the stroke of a 455 that is air starved at any rpm above 2400!

It’s all about the higher level of average gas speed ramming the cylinders harder.

First, I was never arguing the fact that valve lift was or wasn't important. And I agree a 455 is air starved with any of the conventional aftermarket head offerings. That's my point.

My argument was a simple one, Making statements an engine is going to be soggy or have poor street manors just based off "what some consider" the head flowing too much air is not correct. That's not the whole picture. My comparison to SBC port size is more than fair enough for the sake of this discussion.

Just trying to keep things simple for others reading without going into complicated discussions. And the statement of too much head flow hurts performance now has others thinking their "out of the box" Eddy heads or Kauffman heads are too big for their 455's. That couldn't be further from the truth.

[tom s]

I have never found a head with "too" much flo is a cause for soggy low end.I have found what intake you put on the heads can effect it.Pulling a dual plane intake from a perfectly driving 455 and putting on a single plane can effect the off idle performance.JMHO,Tom

[25stevem]

It’s not about too much flow, it’s about too much flow produced by means of unnecessary port area for the average rpm range the motor needs to live in.

On the other side of the coin, too much flow for too small a port area will have the car performing like a rocket from just off idle, but once the Hp peak is reached the Hp will nose over very fast.

[Steve C.]

"You can't make a Pontiac head big enough. You can make it wrong, but not too big."

Ken Crocie


https://www.motortrend.com/how-to/hr...pontiac-heads/


.

[64speed]

Originally Posted by Formulajones

First of all, highly doubtful. Frankly you would need to know the cross section area of the head before making such a statement. Flow really isn't the whole picture.

Given the fact that the cross section area of the intake ports of conventional Pontiac Kauffman and Edlebrock heads are on the small side, very close to what would be considered decent for a small block chevy, and they are sitting on a much larger 455 with a 4.210 crank, you would have a really hard time hurting any drivability or low speed performance.

Second of all, you've already had this engine running before with those heads and you commented many times on how powerful it was. Ask yourself, but I think you know the answer.

In a nut shell, I wouldn't even worry about it

Yes I have had this engine running before but it was with a much more radical cam. My main concern of course is drivability because I drive this car almost everyday except snow. I have driven in rain etc. Up until the lifter bore of the other block failed I had put 3800 miles on it in 4 months.

[flat-bill]

Is 750 cfm enough for this setup? I certainly am no expert. Just asking.

[NeighborsComplaint]

It will run fine. The car is not going to be a slouch even with the 1.52 rockers and should have huge midrange power. You really can't mess up a 455 with big ports. The fact that you are using an RPM will help the intake velocity too. If you swap to 1.65 rockers down the road, you'll get some gains that won't be that noticeable until you're in the upper-mid to high RPM register where you hardly spend any time anyway.

[Jay S]

I kind of doubt bigger rockers will be necessary either, but it will leave some power untapped. The cam that Crower sells as the 60919 right now does not need Rhoad’s lifters in a 10:1 455. I imagine the engine builder spent quite a bit of time and effort sorting thru 3 sets of lifter to get a good set. Sounds like your stuck with what you have there. Drivability is going to be fine with the 60919.


I can think of quite a few before and after performance engine dyno pull examples where a bigger port volume and flow was used, and was the only change. Those engines usually make more power at the start of dyno pulls, less peak tq, then more top end power. Pretty much no change in part throttle response. I think it is because at low speeds the air flow follows the port floor on the bigger ports more than the small ports. The end result is the bigger port makes the engine’s cam act like it has less overlap and gains some low end power. It makes less peak TQ against the smaller port because the smaller port has more velocity there. Then once the velocity is high enough the extra air flow of big port overtakes the smaller ports.

[64speed]

Neighborscomplaint and I had a conversation about this via DM and he was very helpful. No I am not stuck with the cam, that’s why I was asking, I have a great machinist but ultimately no builder, he is I and I is he LOL. As far as degreeing the cam I have never done that so it will be installed “straight up”. I had damn near 600hp with my old combo and while awesome to drive it was just too much. My wife didn’t want to drive it and even at a 60 mph roll if you downshifted and punched it it would just smoke the hell out of the tires. I am saving those cam specs for a strictly fun car. I drive this one.

[25stevem]

Your making a mistake once again by just stuffing the cam back in dot to dot , that being your assuming the Cam was ground right in the first place, which it may not have been.
Your also assuming your chosen Cam and Crank gears are made right .

[64speed]

Ok so I called Wayne and he is gonna do whats necessary and degree the cam for cheaper than I can buy the tools so thats done.

[25stevem]

Very good decision!

[grivera]

Definitely the right decision- btw, degreeing a cam is not difficult if you have the skills to build the engine.

[blueghoast]

Your motor will have exellent throttle reponse with that cam and the
325 cfm flow, It will problly peak a little early like around 5000 rpm's.
And the drive ability will be fine also. I've also never line hone a block
just for going to studded mains. haven't had a problem yet and these
are 600+ pump gas motors that I drive daily. JMO

GT