Plenums- stock vs Precision vs Hemco vs etc.

[jjvites]

This question is in addition to the TB one. What do you guys think of all the aftermarket Plenums? Are they needed in the 10's or sooner or even at all?
What is the experience of the community?

Thanks,
Marty

 

[Randy Greenoe]

Just like I posted in the other thread the Hemco DID work for me! With JUST the Hemco and 62 throttle bodyI picked up 2/10s I know whats coming but I swear the Hemco worked for me!

 

[PaCemkr86]

i like the mease upper plenum

 

[Cheeseburger]

The Hemco does exactly what the company claims!

 

[TurboGN]

Hemco seemed to direct more air to the center two (3&4) cylinders in my engine. In fact, the number 4 blew to the outside and there was leakage to the lifter valley. Number 3 leaked to the inside and outside. That's unfortunate because numbers 3 & 4 head bolts have to pull "double duty" by providing half the clamping for the numbers 1&5, and 2&6, respectively. I must admit the car ran great but I believe the Precision plenum/PP combo provides the most even flow numbers. I have no dyno/tract comparisons. Since installing the Precision/PP combo the heads have not leaked. The car feels about the same. Not a plug but the Hemco is now for sale.

 

[6GUN]

Took my GN to the dyno a couple years back. At the time it was a stock engined car running low 12's. Made three pulls with the stock plnm. Then pulled the stocker off and bolted on the Hemco. With no other changes ( 20# max boost) the car picked up approx. 20+ HP to the rear wheels. ... Then went to the track. I picked up 2/10's and 2 mph in the 1/4 mile. I'm now running high 10's with the same HEMCO upper plenum. It does work !
The HEMCO was designed correctly from the start. That's why they don't make a power plate for it. No band-aids needed !


87' GN , factory stock longblock, 10.93 @123mph

 

[DavzGN]

The HEMCO was designed correctly from the start. That's why they don't make a power plate for it.

The reason they don't make a power plate is because they can't due to the small opening of the plenum. It distributes air better than any of the other plenums alone. But the others all distribute the air better than the Hemco when they use a Power plate.

The following page shows the variation from average flow of each plenum.
http://www.rjcracing.com/RJC_Buick_...er_Plate/Flow_Comparison/flow_comparison.html
for example if the plenum was flowing 1200CFM, perfect distribution would give 200CFM to each cylinder. It shows the + or - variance from the 200cfm flow. I'm not sure how the percentages Jason shows work because there is no way the stock plenum flows 81% below average in cyl 2 and 60+% above average in the rear cylinders. using the 200cfm example above, would mean only 38CFM is going to cyl 2 and over 320CFM is going to each of the rear cylinders.


HTH
David

 

[S2V6RACER]

The Hemco race plenum is a peice of junk. The airflow distribution problem will cause head gasket problems if you make big power. I threw mine in the garbage can, as I could not bring myself to sell it to anybody.

How many TSM guys are running the Hemco stuff??

just my experience.

 

[Cheeseburger]

Red Armstrong runs a Hemco and they really do work.
I tested mine against the 70mm KB and sold the KB and stayed with the 62mm Hemco.

Real world track testing does not lie!
I did componsate with my VIC at the time to make sure fuel/air to all cylinders were even.