[footjoy]

I know the large valve heads rule. If you have two identical castings one with the big valves and one with small valves, at what point do the big valve heads make more horsepower is it at 1000 rpm or 2000, or 4500? I am just curious. if it is 3500 or more how much would a everyday cruiser benefit?

Thanks

[slowbird]

Just my opinion but everywhere everytime if setup up right

[67gtospud]

There’s a lot of variables but, theoretically if you put the same heads on the same engine with the only difference being one has big valves vs small valves, the big valve head should outperform throughout the entire rpm range since more air can be moved than the small valve heads.

[footjoy]

Originally Posted by 67gtospud

There’s a lot of variables but, theoretically if you put the same heads on the same engine with the only difference being one has big valves vs small valves, the big valve head should outperform throughout the entire rpm range since more air can be moved than the small valve heads.

Ok that was probably a stupid question.

Thanks

[Scott Roberts]

Originally Posted by footjoy

Ok that was probably a stupid question.

Thanks

Not really.. a small valve can be torquey in the lower rpm. The smaller valve can produce higher velocities in that range in general terms so youre question itself isn't stupid

[b-man]

Moved to Street forum, the engine in question is for a street cruiser.

I honestly doubt you’d see any difference between the big and small valve heads on your Tri-Power street 400 with the 068 or similar cam you’re planning on using.

Keep in mind that all Tri-Power engines had small valve heads and none of them were slouches.

[Steve C.]

http://www.wallaceracing.com/hp-valve-size.php

http://www.wallaceracing.com/intake_valve.php


.

[65sport]

Originally Posted by Steve C.

http://www.wallaceracing.com/hp-valve-size.php

http://www.wallaceracing.com/intake_valve.php


.

Do you know what "FPS" means as an input on valve size ?

[slowbird]

Originally Posted by 65sport

Do you know what "FPS" means as an input on valve size ?

Feet per second

[Cliff R]

Folks underestimate the potential of the small valve heads and still seek out big valve versions.

In many cases a small valve head will be a better bargain, and you can always put big valves in them anyhow.

Years ago we had a 455 short block ready to finish but the custom CNC ported KRE heads and roller cam coming with them were not going to make it in time to get the engine finished and in the car for the Norwalk race.

I reached under the work bench and grabbed up a set of 1969 #46 small valve heads. Did a quick seat and valve grind on them, better springs and screw in studs. Went to the parts room and grabbed up an older Crower flat hydraulic cam and finished the engine and got it installed in time to make the race.

The car was an 1981 Firebird, TH350, Continental converter and 4.10 gears with pretty tall DOT's. Right off the trailer it ran high 11's in the heat of August and it was pretty hot that year. I wasn't expecting much more than low to mid-12's out of it to be perfectly honest. You just never know with these things......FWIW......Cliff

[footjoy]

I built a 400 with #15 heads I had the heads redone I put screw in studs larger springs and all the other correct stuff. It was the first pontiac motor I played with it had good response but I missed something in the build. Maybe bad tune wrong cam, carb. My choices were not good ones. I didn't have the heads ccd before hand and found out after I took motor back apart the heads were 90 cc combustion chamber. Which gave me 8.6 compression and I was hoping for 9:1
I didn't do my home work.
I think I will put these 15s on the shelf I tried to sell them online but all I got was stupid comments on small valve heads.
But I think these heads would work great on a 455 or a 400 with the right parts.

Thanks Greg

[steve25]

There's no carved in stone answer to that question as it by enlarge depends on how many cid the motor is and how it's Camed.

Some factors are right off the bat the small valve 1968 and up heads are down to 148.5 CCs of Intake port volume from the standard 154 to 156 CC size of the big valve heads, this kicks up the port velocity.

This fact right there brings down the torque and hp peak rpm of the small valve heads by 5% as compared to the big valve heads.
This makes them a great pick for the 326 motors and grocery getter 350 motors with 2.73 rear gears.

On bigger cid motors you can go 5% bigger in Cam duration if you want without having a low speed Torque drop off.

Any way you look at it though if your not with your back up against the wall when running these small valve heads of having too much compression then if your rebuilding them with new valve and need to do a valve job anyway then there's no doubt that installing the bigger valve sizes ( both Intake and Exh in most cases) is very worth more power.

Do a search in this section for what I posted about reworking 2 years ago, search under " The plus side of cheap small valve heads"

[Cliff R]

Following that logic one could simply up the cam duration by 5 percent to pick up the lost airflow using smaller valve heads.

I know on the engine mentioned above we used a pretty "hefty" cam in it, 308/314, 248/256 @ .050" on a 108LSA. Idled like chit, stinky, but "BRUTAL" mid-range power. It was more or less just a parts engine filled with what we had readily available at the time to make time constraints.

It eventually did get it's custom CNC ported KRE heads and a custom ground solid roller cam which put it solidly into the high 10's. Also interesting is that the new combination doesn't "feel" as strong as the old one if you were evaluating the performance by "the seat of your pants". It's smooth/broad/flat power curve just pulls really hard like a big locomotive and lacks the explosive mid-range power it had with the iron heads and flat tappet cam combination even though it obviously puts considerably more power to the pavement at full throttle thru the 1/4 mile........Cliff

[Skip Fix]

Correct numbers or not the 70 455 with small valve #15s was only 10 HP off the the 70 455 with #64 big valve heads, not sure if there was also a cam difference or not.

[geeteeohguy]

Originally Posted by Skip Fix

Correct numbers or not the 70 455 with small valve #15s was only 10 HP off the the 70 455 with #64 big valve heads, not sure if there was also a cam difference or not.

I have been running these exact heads on my '67 400 in my GTO ragtop for the past 10-12 years. With an 068 cam, stock q-jet, TH400 and 2.56 gears, it's a great economical high speed low rpm road car. The only thing I did was add screw in studs. Not as strong as it used to be with the 3.36 gear and 670 heads, but it runs on pump gas, which the stock combo wouldn't.

[steve25]

Totally true Cliff!

[steve25]

The 70 455 with 64 heads would have had the 068 Cam, the 1968 400 2bbl casting 15 head I can't say without looking it up, but for sure it would not have had the 068 Cam, maybe at best the 066 Cam if ordered in the GTO with that option, or if not that then the standard 2 bbl Cam of the day.

[Slick]

FWIW,

I had a totally stock, but well tuned 1970 Bonneville with the #15 head 455. 3.23 Safe-T-Track and turbo 400 (naturally), ~29" tall tires (P255/70R15 Radial T/As).

It was very fast for what it was. 13.90s at 97. My original 70 T/A RAIII, 3.31 Safe-T-Track, T400 ran 14.31 at 99.8. Runs at Capitol and Budds Creek.

Of course the T/A spun through all of first, the Bonneville was glued.

P cam in Bonneville (i.e. 067).

Bottom line: in mild form small valve heads can run!

Stuart

[SD455DJ]

Originally Posted by Slick

FWIW,

I had a totally stock, but well tuned 1970 Bonneville with the #15 head 455. 3.23 Safe-T-Track and turbo 400 (naturally), ~29" tall tires (P255/70R15 Radial T/As).

It was very fast for what it was. 13.90s at 97. My original 70 T/A RAIII, 3.31 Safe-T-Track, T400 ran 14.31 at 99.8. Runs at Capitol and Budds Creek.

Of course the T/A spun through all of first, the Bonneville was glued.

P cam in Bonneville (i.e. 067).

Bottom line: in mild form small valve heads can run!

Stuart

I totally agree with Stuart (Slick), Skip, and Cliff. These engines are sleepers and don't need large valves when the engine is fairly stock. Here is the dyno sheet of my '70 YH 455 360 hp stock rebuild motor with the original small valve #15 heads, a Summit 2802 cam and stock log manifolds. The compression was just a smidge under 10.0 to 1.

I believe it could have cracked 400 hp with more cam, but I was happy with the 390 hp/512 tq it made. I also believe it would have made 420 hp/525 tq with stock #64 large valve heads throughout the pull range.

Dennis

[PDC]

Originally Posted by SD455DJ

I totally agree with Stuart (Slick), Skip, and Cliff. These engines are sleepers and don't need large valves when the engine is fairly stock. Here is the dyno sheet of my '70 YH 455 360 hp stock rebuild motor with the original small valve #15 heads, a Summit 2802 cam and stock log manifolds. The compression was just a smidge under 10.0 to 1.

I believe it could have cracked 400 hp with more cam, but I was happy with the 390 hp/512 tq it made. I also believe it would have made 420 hp/525 tq with stock #64 large valve heads throughout the pull range.

Dennis

With all the big-displacement roller-cammed fuel-injected dream-builds these days, it’s important to remember how much fun you can have with a flat tappet carbureted engine that churns out power like this.