Compression ratio vs Porting

[273]

NO!

If having more airflow hurts power it's because more fuel wasn't added with it. Too much airflow is like too much oral sex... A great problem to have that none of us are likely to experience.

Remember, an engine is an air pump. Fuel + air go in, torque comes out. Nothing more, nothing less.

More air flow whether from headers, heads, cam, intake etc.. The carb will automatically add more fuel might need to be setup so not to run rich or lean.

Everyone takes things to extremes I'm not saying run W9's on a semi warm/hot 318, I'm talking fully ported 2.02 valve 318 heads or 340/360 or even EQ may or may not lose some bottom end cause of velocity.

 

[318willrun]

flow trumps compression....

 

[Cudafever]

NO!

If having more airflow hurts power it's because more fuel wasn't added with it. Too much airflow is like too much oral sex... A great problem to have that none of us are likely to experience.

Remember, an engine is an air pump. Fuel + air go in, torque comes out. Nothing more, nothing less.

More air flow whether from headers, heads, cam, intake etc.. The carb will automatically add more fuel might need to be setup so not to run rich or lean.

Everyone takes things to extremes I'm not saying run W9's on a semi warm/hot 318, I'm talking fully ported 2.02 valve 318 heads or 340/360 or even EQ may or may not lose some bottom end cause of velocity.

I know this is taking this subject of target a little BUT.......

C130 chief, i have to disagree.


My first sets of head that i ever ported, had more air flow, had the fuel to support it, and became a DOG on bottom end.

although i had a lot more cfm then before, i totally DESTROY the bottom end.

Did it make more Power! YOU BET, by a couple mile per hour at the end of the 1/4.

Did it run faster? NO! A full sec Slower!!! Why? Because even though it would rev 1000 rpm higher now.(6800+) it would not get out of its on way! It was dead for the first 60 to 100 foot of the track..........then...... it took off like i hit it with a shot of nos!

A eng is a air pump..........and so much more then that. I had such bad exh reversion, the the intake manifold was black all the way up to the carb base.

And that was with a 9.4 compression 340 .474/280 MP cam.

Yes more air/fuel will make more power, IF the port is not to large(read air too slow or weak velocity) and the exh doesn't have reversion or exh reverting to the intake.

 

[Abodybomber]

I know this is taking this subject of target a little BUT.......

C130 chief, i have to disagree.


My first sets of head that i ever ported, had more air flow, had the fuel to support it, and became a DOG on bottom end.

although i had a lot more cfm then before, i totally DESTROY the bottom end.

Did it make more Power! YOU BET, by a couple mile per hour at the end of the 1/4.

Did it run faster? NO! A full sec Slower!!! Why? Because even though it would rev 1000 rpm higher now.(6800+) it would not get out of its on way! It was dead for the first 60 to 100 foot of the track..........then...... it took off like i hit it with a shot of nos!

A eng is a air pump..........and so much more then that. I had such bad exh reversion, the the intake manifold was black all the way up to the carb base.

And that was with a 9.4 compression 340 .474/280 MP cam.

Yes more air/fuel will make more power, IF the port is not to large(read air too slow or weak velocity) and the exh doesn't have reversion or exh reverting to the intake.

The key is velocity. The trick is someone, who's done a few combination's & learned the ropes. Sometimes smaller is better. The trick,is learning where.If that doesn't work,there's always nitrous......

 

[C130 Chief]

You are blaming the cylinder heads for the shortcomings of a carburetor and a wet runner intake.

 

[frosty_the_punk]

I really don't believe there's anything you can do to a set of factory iron heads to completely ruin their port velocity, aside from going overboard on the bowls. I'd say any change would be marginal at worst.

The ports on ford 4V heads have huge cross sectional area. probably 60% more than that of a standard J or X head and they still have perfectly acceptable port velocity and make good power temporarily .

 

[RustyRatRod]

I really don't believe there's anything you can do to a set of factory iron heads to completely ruin their port velocity, aside from going overboard on the bowls. I'd say any change would be marginal at worst.

The ports on ford 4V heads have huge cross sectional area. probably 60% more than that of a standard J or X head and they still have perfectly acceptable port velocity and make good power temporarily .

Case and point.

 

[Cudafever]

I really don't believe there's anything you can do to a set of factory iron heads to completely ruin their port velocity, aside from going overboard on the bowls. I'd say any change would be marginal at worst.

The ports on ford 4V heads have huge cross sectional area. probably 60% more than that of a standard J or X head and they still have perfectly acceptable port velocity and make good power temporarily .

No you cant port a SBM to have ports like that Ford 4V head just like you cant port the ford 2V to the 4V side.

Remember, "Port Velocity" has to do with what the heads are bolt on.
Them ford 4V ports are BIG!!! But bolted to a 500 ci eng or a 1000 rpm 351......Them heads may just be to small.

 

[CPMotorworks]

I know this is taking this subject of target a little BUT.......

C130 chief, i have to disagree.


My first sets of head that i ever ported, had more air flow, had the fuel to support it, and became a DOG on bottom end.

although i had a lot more cfm then before, i totally DESTROY the bottom end.

Did it make more Power! YOU BET, by a couple mile per hour at the end of the 1/4.

Did it run faster? NO! A full sec Slower!!! Why? Because even though it would rev 1000 rpm higher now.(6800+) it would not get out of its on way! It was dead for the first 60 to 100 foot of the track..........then...... it took off like i hit it with a shot of nos!

A eng is a air pump..........and so much more then that. I had such bad exh reversion, the the intake manifold was black all the way up to the carb base.

And that was with a 9.4 compression 340 .474/280 MP cam.

Yes more air/fuel will make more power, IF the port is not to large(read air too slow or weak velocity) and the exh doesn't have reversion or exh reverting to the intake.

Bigger isnt always better, the port has to have the correct size and shape for the CI and RPM. You can't correlate the first set of heads you ported with making you go slower. Its about the correct shape,size and combination, and that includes the cam, compression, etc. That's like claiming every engine needs "backpressure" to run right.

 

[Abodybomber]

It's about about management in valve size,port size ,and applied correctly. That takes ,huge amounts of time. Wait until the valve job ....

 

[moper]

NO!

If having more airflow hurts power it's because more fuel wasn't added with it. Too much airflow is like too much oral sex... A great problem to have that none of us are likely to experience.

Remember, an engine is an air pump. Fuel + air go in, torque comes out. Nothing more, nothing less.

I think I have to disagree - but only in the way that's presented Chief. An engine is an air pump, but that pump is based (for this discussion) on atmospheric pressure. A running engine at some rpm and throttle point will begin to help feed itself because of the physics of those pressure differentials and waves. That point is highly individualistic so there's no "always" or way to apply that broadly. But - I think it has to be added to your statement because by going too large in terms of port volume, or to large in terms of camshaft, you can influence that point in a way that negatively afects the power curve of a particular engine. In short - loss of torque and more peakiness in the power curves because the physics isn't helping until a higher rpm. Flow isn't totally dependant on port volume, but it is related. Especially low and mid lift flow which is really what we're talking about. If flow numbers were really something that could be compared or "raced", for a street car we should be "racing" the numbers for .100 - .300 lift.

 

[Cudafever]

Bigger isnt always better, the port has to have the correct size and shape for the CI and RPM. You can't correlate the first set of heads you ported with making you go slower. Its about the correct shape,size and combination, and that includes the cam, compression, etc. That's like claiming every engine needs "backpressure" to run right.
__________________
Pete Graves
Janesville,Wi

Yeah i wish i would have had the money(and smarts) at that time, to change my 2800 stall and 3.91 gears, for a good 4500 converter and 4.56 gears.

I thing it would have run well, even with my bad porting skills.

It was amazing that with the same cam, it pulled 1000 rpm higher.
That exh port was really pulling hard on the intake port above 4000 rpm.(at least that how i justify the capability of more RPM) :burnout:
A custom cam, to help that situation, could of helped out with the hole rpm range.