I like that little lip you leave at the upper/lower plenum transition.

I don’t know if it helps or not, but I like the idea of it.

I believe I saw some pics and posts from that guy on FBBO. I'll have to look around to see if I can find any of his intake manifold pics.

Thanks for the kind words about the garage!

if you find a link to the guys 451 build can you post a link?

if you find a link to the guys 451 build can you post a link?

like you, i'm working on finishing up a garage...then planning to get to work on my slightly ratty 67 coronet. Not looking to do a FAST build but probably 70's street racer style (to an extent), might build a 451 for it so i'm always looking at those builds.

That guy is me.

Basically, the 4 runners that have the sharpest turn coming out of the plenum flow the least...... the “inner” runners.
3,5,4,6.
I’d have to dig out my notes since I did that testing quite a while ago, but that’s how I remember it.
Not really much difference between upper and lower.

That’s tested as bolted to a ported head, and comparing how much flow is lost with the manifold in place(and it loses a bunch).

The overall best one I’ve tested was extensively modified by Jim Sieler for his Dart.
His motor was a very high effort build with several pretty high dollar parts in it....... and it made quite good power on the dyno.
He never quite got the car sorted out well enough to use all the power he had.
I’m sure if he would have stuck with it, there would have been some very low 11-sec ET’s...... and maybe even a “10” at MIR on a killer day.

He’s also a fun guy to have around at the track....... wish he was still playing in those classes.


It’s roadrunner2’s motor, in his car.

Edit: this is why it’s best not to go by memory.......
On a mildly reworked 301, all the ports lost about 20-21% compared to the head by itself(about 50cfm).
It looks like the % of loss is within about 1% for all runners, on one that has what I would consider a “normal” amount of rework.
At that level of rework, on a head that flows solidly over 280cfm, its about an 18cfm improvement avg for all 8 runners over the untouched manifold.

Jim’s intake averaged 13cfm better than the one with the “normal” rework, although some of his ports flowed over 30cfm better than the same runner on the one with normal porting.
What brought the average down was there were two runners that showed minimal improvement at all over the stock intake.
Runners #1 and #7.

To put it in perspective, the 8cyl flow average for the head with a radius plate was 286.7cfm.

The intake was tested bolted to the head with all ports blocked off except the one being tested, and a Holley 1000cfm 4150 carb mounted to the carb pad.

The 8cyl flow average for the stock manifold was 212.8cfm.

The 8cyl flow average for the normally ported manifold was 230.7cfm.

The 8cyl flow average for an ootb Performer RPM was 250.6cfm.

If Jim could have picked up #1 and #7 about 15cfm..... the 8cyl flow average would have been right there with the RPM.

Some of the runners on a cleaned up Victor only lost a few cfm compared to the head with the radius plate.

Basically, the 4 runners that have the sharpest turn coming out of the plenum flow the least...... the “inner” runners.
3,5,4,6.
I’d have to dig out my notes since I did that testing quite a while ago, but that’s how I remember it.
Not really much difference between upper and lower.

That’s tested as bolted to a ported head, and comparing how much flow is lost with the manifold in place(and it loses a bunch).

The overall best one I’ve tested was extensively modified by Jim Sieler for his Dart.
His motor was a very high effort build with several pretty high dollar parts in it....... and it made quite good power on the dyno.
He never quite got the car sorted out well enough to use all the power he had.
I’m sure if he would have stuck with it, there would have been some very low 11-sec ET’s...... and maybe even a “10” at MIR on a killer day.

He’s also a fun guy to have around at the track....... wish he was still playing in those classes.


It’s roadrunner2’s motor, in his car.

Edit: this is why it’s best not to go by memory.......
On a mildly reworked 301, all the ports lost about 20-21% compared to the head by itself(about 50cfm).
It looks like the % of loss is within about 1% for all runners, on one that has what I would consider a “normal” amount of rework.
At that level of rework, on a head that flows solidly over 280cfm, its about an 18cfm improvement avg for all 8 runners over the untouched manifold.

Jim’s intake averaged 13cfm better than the one with the “normal” rework, although some of his ports flowed over 30cfm better than the same runner on the one with normal porting.
What brought the average down was there were two runners that showed minimal improvement at all over the stock intake.
Runners #1 and #7.

To put it in perspective, the 8cyl flow average for the head with a radius plate was 286.7cfm.

The intake was tested bolted to the head with all ports blocked off except the one being tested, and a Holley 1000cfm 4150 carb mounted to the carb pad.

The 8cyl flow average for the stock manifold was 212.8cfm.

The 8cyl flow average for the normally ported manifold was 230.7cfm.

The 8cyl flow average for an ootb Performer RPM was 250.6cfm.

If Jim could have picked up #1 and #7 about 15cfm..... the 8cyl flow average would have been right there with the RPM.

Some of the runners on a cleaned up Victor only lost a few cfm compared to the head with the radius plate.

I don’t really like porting intake manifolds, so I don’t do much of it.

One thing I found interesting when testing manifolds is that they “usually” result in some amount of loss in flow from the head, when attached....... even when they are capable of flowing way more than the head they’re attached to.

Years ago I was messing with some std port Indy SR heads. I got them to flow in the 340 range, and was testing some manifolds on them.
An M1 single plane with very minimal plenum deburring and a gasket match would flow a little over 300cfm when attached to the head.
Or rather, the head would flow a little over 300 with the manifold attached.

So, we know the intake is good for over 300....... and yet when you bolt it to an unported 906 head that only flows in the 230’s...... the head still loses flow.

On those 286cfm 906’s in my previous post, that same M1 intake that was passing 300+ cfm when on the SR’s, knocked the 8cyl avg down to 263cfm.

Basically, the 4 runners that have the sharpest turn coming out of the plenum flow the least...... the “inner” runners.
3,5,4,6.
I’d have to dig out my notes since I did that testing quite a while ago, but that’s how I remember it.
Not really much difference between upper and lower.

That’s tested as bolted to a ported head, and comparing how much flow is lost with the manifold in place(and it loses a bunch).

The overall best one I’ve tested was extensively modified by Jim Sieler for his Dart.
His motor was a very high effort build with several pretty high dollar parts in it....... and it made quite good power on the dyno.
He never quite got the car sorted out well enough to use all the power he had.
I’m sure if he would have stuck with it, there would have been some very low 11-sec ET’s...... and maybe even a “10” at MIR on a killer day.

He’s also a fun guy to have around at the track....... wish he was still playing in those classes.


It’s roadrunner2’s motor, in his car.

Edit: this is why it’s best not to go by memory.......
On a mildly reworked 301, all the ports lost about 20-21% compared to the head by itself(about 50cfm).
It looks like the % of loss is within about 1% for all runners, on one that has what I would consider a “normal” amount of rework.
At that level of rework, on a head that flows solidly over 280cfm, its about an 18cfm improvement avg for all 8 runners over the untouched manifold.

Jim’s intake averaged 13cfm better than the one with the “normal” rework, although some of his ports flowed over 30cfm better than the same runner on the one with normal porting.
What brought the average down was there were two runners that showed minimal improvement at all over the stock intake.
Runners #1 and #7.

To put it in perspective, the 8cyl flow average for the head with a radius plate was 286.7cfm.

The intake was tested bolted to the head with all ports blocked off except the one being tested, and a Holley 1000cfm 4150 carb mounted to the carb pad.

The 8cyl flow average for the stock manifold was 212.8cfm.

The 8cyl flow average for the normally ported manifold was 230.7cfm.

The 8cyl flow average for an ootb Performer RPM was 250.6cfm.

If Jim could have picked up #1 and #7 about 15cfm..... the 8cyl flow average would have been right there with the RPM.

Some of the runners on a cleaned up Victor only lost a few cfm compared to the head with the radius plate.