[KARGUY]

Which is the leanest cylinder while using the performer RPM intake ?

Thanks Karguy

[KARGUY]

Any dyno guys out there, Cliff R ?

[silver68]

I too am interested in this subject, as I am switching to an RPM very soon. There doesn't seem to be as much R&D info on the part of racers in the pontiac community as one might think (at least not given away for free on forums Haha).

[KARGUY]

Seems to me I read somewhere that lean cylinders can cause spun rod bearings in certain set ups. Maybe cylinder 7 or 8 ?

Any info is appreciated.

Karguy

[69FIREBIRD76MM]

Isn't that inportant when you're running boost or nitrous? I assumed if you are running a performer rpm is not for a full race motor. Why worried about it. This is just my assumption. And I am not an expert.

[steve25]

Are trouble shooting a issue that has already happened to your motor KARGUY?

That Manifold is pretty darn good in terms of fuel distribution and being that it's a duel plane if any cylinders are lean it will be the ones that feed off the short depth Plenum and then the ones that have the longest runners may be fatter running.

None of the consecutive firing cylinders on this Manifold are feed off the same Plenum so having them make the latter firing ones lean as can happen in a single plane type can not happen.
If you cut open the Plenum divider as some do then all bets are off in terms of fuel distribution atleast at part throttle !

[JSPONT]

I think the issue was with the performer not the rpm.

[Elarson]

A few miscellaneous comments:

Malcolm McKellar told me that Pontiac factory testing showed the distribution was more equal on a dual-plane than on a single plane manifold.

Distribution will change dramatically under acceleration vs. sitting on a dyno. Acceleration causes the fuel in the plenum to favor the rear cylinders.

Spun rod bearings are generally caused by an installation without enough crush and/or insufficient oil. Lean cylinder won't do it, unless you're so lean that you're just hammering it with detonation and actually beat the bearing loose. Mild detonation won't do it if the bearing fit is correct.

Eric

[KARGUY]

Steve25

No, I do not have any problem with spun rod bearings. I just want to prevent that in the future. I read about this issue some where on this forum and wanted to see if any body had actual A/F data.

Thanks

Karguy

[steve25]

A lean running cylinder will not pound out Rod bearings in and of itself !, think about it with some logic, if the non lean cylinders are making more power from having a correct mixture and are in turn being worked harder , then why would a cylinder making less power spin a bearing ?

The temp on a lean running cylinder will go up and make other issues take place , and a cylinder firing at the wrong time, but with the right mixture can make for issues , but I think your barking up the wrong tree, as either Manifold the performer or the rpm version should serve you fine if the Carb on top is working well!

[Steve C.]

Performer RPM runner lengths (inches)
R1 5.75
R3 6.25
R5 6.75
R7 6.75
R2 6.50
R4 6.00
R6 6.00
R8 6.25

Average length 6.28

Performer RPM runner volumes (cc)
R1 255
R3 250
R5 240
R7 290
R2 265
R4 280
R6 285
R8 230
Average runner volume 262

Plenum Volume (cc)
Vol 667
Vol 733
Total plenum volume 1400


.

[PAUL K]

^^^ that's a lot of information! ^^^

[Steve C.]

I posted it because of this statement.....

"...if any cylinders are lean it will be the ones that feed off the short depth Plenum and then the ones that have the longest runners may be fatter running."


.

[KARGUY]

Steve C.

Thanks for posting the runner length and volume. Do you have any flow data as well?

Thanks for everybody that responded.

KG

[Steve C.]

My engine builder has flow tested my different cylinder heads but we have never tested intakes. I know both Jim Hand and Rocky Rotella have tested intakes on flow benches. High Performance Pontiac magazine published some of Rocky's results in a associated article.
Jim Hand told me years ago that a stock intake will flow about 91.5 to 92 percent of a head at 250 cfm and the Performer RPM will flow about 93.5 percent. I have specifics but in short Rocky stated the RPM intake flows about 2 percent more than an average unmodified iron intake. This was his testing on a stock 5C head that flowed as average of 208 cfm at .500" lift and a stock SD-455 head that flowed an average of 237 cfm at .550" lift. Note his Performer RPM was box stock and not modified other than removing the water X-over.
In addition he measured a QJ carb with those intakes. His Holley HP950 and Cliff-modified QJ each reduced flow by about another 5 percent. If the QJ is stock, the reduction can be as much as 7 percent depending on the angle of the secondary air valves.

As for my personal use I have a Performer RPM intake that is modified inside and the ports are about 2.300" tall to match all my various cylinder heads that I've used. Many years ago on a 412 combo it supported 560 hp, later on a 462 combo it supported 580 hp and on my current 505 I tried it and on the dyno it was at it's limit as far as I was concerned. It made only 615 hp with the Performer RPM intake. My 505 ended up with a Victor intake with the carb flange cut down 0.650" for hood clearance and the horsepower improved to 640 hp. Later I changed from a Crower solid roller to a Ultradyne MSP solid roller with 3 degrees less duration , along with a few other minor changes, and we picked up another 20 hp. For my specific use the Victor intake rocks.

And a fwiw, on a previous 462 pump gas combo I dyno tested a Victor intake and at peak torque rpm it made 595.1 ft.lbs. torque. With the Performer RPM at peak torque rpm it made 589.1 ft.lbs torque. So at upper rpm's the Victor intake does fine in producing good torque numbers. The Victor intake is no dog in producing torque under the right circumstances. That said, at a lower rpm the Performer RPM intake made more torque, 491 ft.lbs at 3500 rpm vs 487 ft.lbs on the Victor intake at 3500 rpm. Although not measured on our dyno the Performer RPM would produce more torque even lower. But with torque numbers like this despite what some will suggest the Victor is a fine street intake. Rant over

.

[tom s]

A little off topic but maybe informative.When. I built my 366 NASCAR RA V engine I only had a single plane intake to drive with.On the dyno the engine made great HP for a real 9.5 pump gas engine.I put it in the car and it sucked with street driving with my OD 5 speed.Sean at SMI really worked hard to get it drive able.We ended up with a 3310 Holley.At 2000 on the highway it was at about 17-1 AFRs no mater what we did.I finally found a factory dual plane intake and without ANY carb change the AFRs fell to high 14s to low 15 at 2000.tom

[Cliff R]

The Performer RPM intake has at least one somewhat restrictive runner, but without going out and looking I can't remember which one it is?

We had a customer who ran one on a pretty high HP 455 and kept spinning the rod bearing on that cylinder, his engine was making around 735hp.

After the second time this happened he switched to a single plane intake and never had any further issues with rod bearings.

When you look closely at the RPM intake and look into the runners it's pretty easy to see which runner is pinched off by the runner case over it. I even tried porting one in that area once to open it up some and remove the restriction and broke right thru into the runner above it.......Cliff

[steve25]

A lesser flowing runner and a lean running cylinder do not go hand in hand in every instance!

In a duel plane Manifold making very high levels of HP it's the velocity difference between the long and short runners and the shallow Plenum not damping the reversion pluses as well as the deeper side does.
Combine this with the fact the the shorter runners need to have better line of sight with the back side of the intake valve and now you have fuel distribution issues !

[KARGUY]

Cliff R,

Do you happen to recall which cylinder spun the rod bearing twice?

Thanks

[slowbird]

Originally Posted by Cliff R

The Performer RPM intake has at least one somewhat restrictive runner, but without going out and looking I can't remember which one it is?

We had a customer who ran one on a pretty high HP 455 and kept spinning the rod bearing on that cylinder, his engine was making around 735hp.

After the second time this happened he switched to a single plane intake and never had any further issues with rod bearings.

When you look closely at the RPM intake and look into the runners it's pretty easy to see which runner is pinched off by the runner case over it. I even tried porting one in that area once to open it up some and remove the restriction and broke right thru into the runner above it.......Cliff

I would think you would here the detonation if it was bad enough to pound a bearing into spinning. Maybe there were other issues???