Supercharger, Timing? Vacuum port?

[2Loose]

Been doing some searches to answers to these questions, no can find!
OK, my 55 chevy gasser project is coming along, the motor (a 67 Olds 425 with a Hampton 6/71) is assembled, 8:1cr, mild blower cam, 113 deg lobe sep., alum heads, bottom end bolted up solid with a full girdle, pair of mighty Demon 650's off of another blown motor (a chevy), MSD ignition system with blower timing retard, MSD billet dist. with vacuum advance.....

So, questions:

1. The Don Hampton intake is an old Offy dual 4-bbl intake with the center gutted and the blower mount flange tigged on (beautiful welding job...), and no ports are available for vacuum/boost reference, do I just drill holes anywhere I want to reference the signal? Am looking at the rear of the vertical portion of the intake under the blower plate just in front of the distributor, and am thinking three 1/4" pipe thread holes....

2. The distributor has a vacuum advance, as I want to primerily drive this on the street, I think it would be good to keep the vacuum advance and not lock it out, need some opinion there....

But still need to know, hook the vacuum advance up to the port I will drill under the blower???

3. Have a vacuum/boost tube to run to the MSD boost retard function, I assume that will be the same (or next door) port as the timing advance for the distributor?

4. The Demon carbs are set up for a blower app, and need a vacuum reference (I think, need to verify that, anyone jump in here....) for those carbs, so am thinking one more port under the blower????

5. Have a blower boost/vacuum gage in the dash, so I think another port for that tube in the same location under the blower???

My first blower build, so looking for someone who has been there to tell me what not to do wrong!

Am real near to putting this motor in the car and hooking up the wires, then cranking and observing the rush I will get!!!

Aloha,
"2Loose" Willy
Maui

 

[mathd]

Hi,

For the intake, are you 100% sure there is no port for the intake signal?, if they where covered with weld?
If i where to drill/tap this port i do it where it was from the factory. Now if there is no port from the factory... I check on similar intake models where they are from the factory.. Otherwise, i will retain myself from giving an advice on where to drill/tap the port because i dont want to give a bad advice.

1.For the intake vacuum signal, you need only one port usually(i am using T fitting that come with the vacuum/boost gauge.).
http://www.egauges.com/pdf/AutoMeter/100v.pdf
For the hole/tap size.
My intake is drilled for 1/8 NPT fitting with a 3/16 hose (maby because i have a small blower) but i am using these fitting:
http://espimages.biz/2386/I/179/16/90.JPG for referencing the carb and the boost gauge to the intake.

2.For the vacuum advance, usually it has to be referenced to the intake but i dont run vacuum advance with my supercharged setup so its best that someone confirm this one.

3&5. I do think that yes you can use the same port instead to drill many holes in the intake, but check the MSD instruction for the boost/retard unit just to make sure.

4.I dont know for the Demons models.. But with the holley carb, they usually are referenced to the intake(mine is) OR sometime there is no powervalve(and bigger main jets to compensate) so no need to reference the carb IN THAT CASE and thats for holleys.

Nice webpage you got there..

 

[2Loose]

Looked that manifold over very closely, no existing vacuum ports that I can find. Am thinking of drilling/tapping in that vertical portion behind the water neck in front, or in front of the distributor in back....

Here's a LINK to a web page with some more closeups of the intake manifold...

Have had some advice from another source who has run some blower motors and he advised using two ports if available for the two carbs, and that the Demons for blower apps do require remote vacuum sensing from the manifold under the blower.

He also advised locking out the distributor for initial startup and setting the advance conservatively. And set the MSD boost retard to the full 3 deg/lb boost for initial startup. I also have the MSD dash timing adjustment, so I can dial that up or back, am thinking now of setting the initial timing about 24 deg with the advance control set in the middle, which will give me about 6 deg plus or minus from the 24 initial setting.

Later if I want to play with some mechanical advance curves (different springs/advance stops) I can do that, but am thinking to just leave it locked out for now.

It would be easier for me to drill several manifold vacuum ports and plug them now while the motor is out of the car, then they are available if later I want to use them.

But still researching this and learning more about it.
Aloha,
Willy

 

[Indycars]

Followed your link which took me to another link that said.......

So when the rust got so bad I had to finally retire the old gal, I kept the 425 and the turbo 400, complete with a switch pitch "hi-lo" stall converter, all nice stuff.....

2Loose,
A torque converter with a switch.....how does that work? How much does it change the stall speed.
http://2loose.chevytalk.org/olds425one.html

Sounds like having your cake and eating it to, perfect for the street hot rod !

 

[mathd]

Ok, you are dealing with a custom made intake/blower adapter. I can't help for that(where to drill&tap).

Yes, its best to drill and tap before the engine is in the car. You want to do that work with the intake removed from the engine and well cleaned so no metal debrist get inside the engine.

 

[2Loose]

.........A torque converter with a switch.....how does that work? How much does it change the stall speed......

In those big cruiser gunboats GM produced for Buick/Olds/Caddy back in the 60's there was a "kickdown switch" somewhere on the throttle system that activated the switch-pitch converter and picked up the rpm as much as a thousand! These were on th400's and big blocks, it was in my 67 Olds Delta 88 4dr hardtop behind my 425, it was a beach cruiser here on Maui for my family of six for many years!!! The switch-pitch converter actually changes the angle of the converter blades to change the stall speed, pretty tricky, but guess they stopped making them 'cause they were pretty spendy to make.

I just saw an article about those switch-pitch converters making a comeback in one or two of my hot rod oriented mags (I get 6 each month), ah yeah, here they are:
http://www.bdub.net/tranny/TwoTimer-Car ... 7-text.pdf
http://www.bdub.net/tranny/DualPurposeT ... g-text.pdf

And, here's some more reading material for you that just popped up from a google search....
http://www.buickperformance.com/switchpitch.htm
http://www.pontiacstreetperformance.com ... sting.html
http://gmcmotorhome.info/SWITCH.html

Willy

 

[2Loose]

.........Yes, its best to drill and tap before the engine is in the car. You want to do that work with the intake removed from the engine and well cleaned so no metal debris get inside the engine.

I can handle that, rags inside the intake, grease on the drill bit and tap, a friend manning the shop vac near the inside of the hole being drilled, lots of ways to keep it clean, been there, done that, for many, many years....

But for this one, as the motor is still on the stand, I just pulled off the blower, and will flip the motor upside down so all the drill waste and tap waste falls out on the floor, and vacuum the inside of the intake manifold thoroughly before flipping it back upright. My point of drill and tap is the vertical section (side of the plenum) between the manifold passages and the blower mounting flange, looks like the best spot to me. Will be drilling 2 in front and 2 in back and plug the unused ones, will post some pix....

Willy