Air Gap RPM divider
12-09-2012, 01:46 PM
#1
Air Gap RPM divider
Made this today from a 1" billet Holley spacer. I'll let you know how it works in the spring. I was able to get a good idle at 800 rpm with my cam, 468 intake 488 exhaust lift. intake duration 254@.050 exhaust 266@.050 110 center. Holley 650 double pumper. I was able to back down the idle screw a bit and then open the idle mixture screws a bit more. idles great at 800-850. 
12-09-2012, 02:09 PM
#2
Team Owner
Member Since: Oct 2004
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St. Jude Donor '05
Firm believer in keeping a DP functioning like a DP.
Glad it works for you
12-09-2012, 03:29 PM
#3
Race Director
Not sure what you are trying to do here but it looks like you are trying to fill in the space that was cut down on the RPM Air Gap, if so you can just buy an RPM intake. The purpose of the cut down divider was so the Air Gap works like a dual plane but also lets you rev it to the moon.
I did a back to back test on an RPM Air Gap and Vic Jr and the Air Gap was neck and neck with the Vic Jr ( no the Vic Jr didn't make less torque it actually made a bit more than the RPM Air Gap across the board) .
Where the Vic Jr takes over is over 6000RPM and even then you are only talking 5 HP or less, but you see them at the race track for this reason that 5 HP represents a lower ET. I would not screw with the Air Gap because as far as I am concerned it is the best dual plane manifold out there.
You did a good job, but I really can't see the point, maybe I an missing something here but I don't read books or listen to whatever anyone has to say in a bar, I go out and do it and see with my own eyes. If you were having trouble with the idle is certainly wasn't the cut down divider
I did a back to back test on an RPM Air Gap and Vic Jr and the Air Gap was neck and neck with the Vic Jr ( no the Vic Jr didn't make less torque it actually made a bit more than the RPM Air Gap across the board) .
Where the Vic Jr takes over is over 6000RPM and even then you are only talking 5 HP or less, but you see them at the race track for this reason that 5 HP represents a lower ET. I would not screw with the Air Gap because as far as I am concerned it is the best dual plane manifold out there.
You did a good job, but I really can't see the point, maybe I an missing something here but I don't read books or listen to whatever anyone has to say in a bar, I go out and do it and see with my own eyes. If you were having trouble with the idle is certainly wasn't the cut down divider
12-09-2012, 04:43 PM
#4
Race Director
Most know how a vacuum leak can cause stalling and a poor driving car. That huge leak between the 2 planes does the same thing with a larger cam. Very important to avoid vacuum leaks. Shame on edelbrock for calling the air gap a street part. it is NOT.
So, kudos to the OP for taming a big cam for street use! The power band will be VERY wide!
nice job!
Done on a milling machine?
So, kudos to the OP for taming a big cam for street use! The power band will be VERY wide!
nice job! Done on a milling machine?
Last edited by Matt Gruber; 12-09-2012 at 05:09 PM.
12-09-2012, 04:46 PM
#5
Burning Brakes
Nice work! Beejay did a similar mod and his low end torque and mileage improved.Can you make another one? I'll purchase it from you.I don't have the equipment to make one of those.I like your design it is just a drop in and leaves the manifold untouched.
12-09-2012, 05:43 PM
#6
Not sure what you are trying to do here but it looks like you are trying to fill in the space that was cut down on the RPM Air Gap, if so you can just buy an RPM intake. The purpose of the cut down divider was so the Air Gap works like a dual plane but also lets you rev it to the moon.
I did a back to back test on an RPM Air Gap and Vic Jr and the Air Gap was neck and neck with the Vic Jr ( no the Vic Jr didn't make less torque it actually made a bit more than the RPM Air Gap across the board) .
Where the Vic Jr takes over is over 6000RPM and even then you are only talking 5 HP or less, but you see them at the race track for this reason that 5 HP represents a lower ET. I would not screw with the Air Gap because as far as I am concerned it is the best dual plane manifold out there.
You did a good job, but I really can't see the point, maybe I an missing something here but I don't read books or listen to whatever anyone has to say in a bar, I go out and do it and see with my own eyes. If you were having trouble with the idle is certainly wasn't the cut down divider
I did a back to back test on an RPM Air Gap and Vic Jr and the Air Gap was neck and neck with the Vic Jr ( no the Vic Jr didn't make less torque it actually made a bit more than the RPM Air Gap across the board) .
Where the Vic Jr takes over is over 6000RPM and even then you are only talking 5 HP or less, but you see them at the race track for this reason that 5 HP represents a lower ET. I would not screw with the Air Gap because as far as I am concerned it is the best dual plane manifold out there.
You did a good job, but I really can't see the point, maybe I an missing something here but I don't read books or listen to whatever anyone has to say in a bar, I go out and do it and see with my own eyes. If you were having trouble with the idle is certainly wasn't the cut down divider
12-09-2012, 05:44 PM
#7
Most know how a vacuum leak can cause stalling and a poor driving car. That huge leak between the 2 planes does the same thing with a larger cam. Very important to avoid vacuum leaks. Shame on edelbrock for calling the air gap a street part. it is NOT.
So, kudos to the OP for taming a big cam for street use! The power band will be VERY wide! nice job!
Done on a milling machine?
So, kudos to the OP for taming a big cam for street use! The power band will be VERY wide!
nice job! Done on a milling machine?
12-09-2012, 06:46 PM
#9
Le Mans Master
I've had experimenting with this very idea on my list for a while, but haven't had the funds to follow thru. Do keep us posted.
FYI, the opening between upper and lower plenums is meant to improve top-end.
FYI, the opening between upper and lower plenums is meant to improve top-end.
12-09-2012, 11:43 PM
#10
Burning Brakes
Not sure what you are trying to do here but it looks like you are trying to fill in the space that was cut down on the RPM Air Gap, if so you can just buy an RPM intake. The purpose of the cut down divider was so the Air Gap works like a dual plane but also lets you rev it to the moon.
I did a back to back test on an RPM Air Gap and Vic Jr and the Air Gap was neck and neck with the Vic Jr ( no the Vic Jr didn't make less torque it actually made a bit more than the RPM Air Gap across the board) .
Where the Vic Jr takes over is over 6000RPM and even then you are only talking 5 HP or less, but you see them at the race track for this reason that 5 HP represents a lower ET. I would not screw with the Air Gap because as far as I am concerned it is the best dual plane manifold out there.
You did a good job, but I really can't see the point, maybe I an missing something here but I don't read books or listen to whatever anyone has to say in a bar, I go out and do it and see with my own eyes. If you were having trouble with the idle is certainly wasn't the cut down divider
I did a back to back test on an RPM Air Gap and Vic Jr and the Air Gap was neck and neck with the Vic Jr ( no the Vic Jr didn't make less torque it actually made a bit more than the RPM Air Gap across the board) .
Where the Vic Jr takes over is over 6000RPM and even then you are only talking 5 HP or less, but you see them at the race track for this reason that 5 HP represents a lower ET. I would not screw with the Air Gap because as far as I am concerned it is the best dual plane manifold out there.
You did a good job, but I really can't see the point, maybe I an missing something here but I don't read books or listen to whatever anyone has to say in a bar, I go out and do it and see with my own eyes. If you were having trouble with the idle is certainly wasn't the cut down divider
12-10-2012, 10:35 AM
#11
Race Director
Made this today from a 1" billet Holley spacer. I'll let you know how it works in the spring. I was able to get a good idle at 800 rpm with my cam, 468 intake 488 exhaust lift. intake duration 254@.050 exhaust 266@.050 110 center. Holley 650 double pumper. I was able to back down the idle screw a bit and then open the idle mixture screws a bit more. idles great at 800-850.
Any more info on it, seat to seat duration? Brand?
Any other changes, heads? headers?
What rear is in it?
Thanks! i'm keeping notes on dual planes fully divided.
12-10-2012, 12:11 PM
#12
Fell free to pm me for more info..
Last edited by 77C34SPD; 12-10-2012 at 12:19 PM.
12-10-2012, 05:15 PM
#13
I am not interested in making these to sell. This is just an experiment to see if I get any added benifits. This is simple to make,you just need to account for the compressed gasket thickness to be sure the divider doesnt bottom out on the intake. The top can be what ever you have room for. Mine was .300 because of my air cleaner needed to fit with the stock hood. Any questions,just pm me. And yes I know they make a full divider air gap, I just did not like the spreadbore design plenum.
Last edited by 77C34SPD; 12-10-2012 at 05:28 PM.
12-10-2012, 06:20 PM
#14
Race Director
Here are some old chassis dyno's from my 355ci SportsmanII heads, comp cams 270H hydraulic flat tappet, 10:1 compression and a 750 Holley DP. This was 10 years ago when some of these things like 200cc intake ports and mechanical secondaries were considered to be crazy to run on the street. I love to prove them wrong, I put every part that wasn't supposed to work on the street and came out with a real nice easy to drive engine with lots of power.
I did the same test on my 406ci to 6500RPM and it shows about the same thing, the HP drops off earlier with the RPM Air Gap but both intakes are great and you wouldn't know which one you had on there if didn't open the hood. I will try and find them but I lost a lot of pictures many moons ago when my PC crashed but like I said basically the same thing only the Vic Jr holds on a little longer at the higher RPM's
Funny thing is there was no changes other than the intake and the the single plane made more torque, I just love old wives tales
This was 2002-3 and this one is the RPM Air Gap just came out
This is the Vic Jr, notice all the torque the single plane is losing
12-10-2012, 10:36 PM
#15
Burning Brakes
Thanks for posting that. Nice bread and butter street build. I would have expected it to strongly favor the duel plane. Over 4000 the SP is a no brainer.
12-11-2012, 06:55 AM
#16
Race Director
Kudos to motorhead for not reading that advice to keep CR under 10:1 with iron heads!
Since we both used the same cam, i'd say his great results are from the 64cc heads making 10:1. I was talked out of them, said to be too much compression. I expect this is the reason he was happy with the SP.
SO now look at the OP's combo. LOW CR and a cam with LOTS more overlap than the 270H! He needs the fully divided DP to keep what little CR he has, making some power.
Since we both used the same cam, i'd say his great results are from the 64cc heads making 10:1. I was talked out of them, said to be too much compression. I expect this is the reason he was happy with the SP.
SO now look at the OP's combo. LOW CR and a cam with LOTS more overlap than the 270H! He needs the fully divided DP to keep what little CR he has, making some power.
12-11-2012, 07:43 AM
#17
I actually am running 58cc aluminum heads with 210 runner with this set up. The bottom end is stock L48 except for cloyes true roller timing chain and new oil pump. Rod and mains looked like new.
12-11-2012, 08:14 AM
#18
Race Director
Stock as in dish pistons, and not bored out and not decked? That would be ~9-9.6:1.
Much better than stock ~8:1.
I was about to nominate it for worst combo of the year
Good thing it is off that list!
Much better than stock ~8:1.
I was about to nominate it for worst combo of the year
Good thing it is off that list!
Last edited by Matt Gruber; 12-11-2012 at 08:20 AM.
12-11-2012, 11:33 AM
#20
Another note Matt: pulls just over 20# vacuum at idle (800-850 rpm) with the divider in place. I just got this tester today (its a high quality unit) so I cannot tell what it was before.