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Discussion Starter #1
So I just started getting my old cat back on the road after many years and I'm doing my best to remember all the things I did to the car 20 years ago.

Anyhow I just converted the brakes from manual to power and it turns out the motor is only pulling about 8" vacuum at idle and about 12" at 2k RPM. Power booster is basically not functioning with such low vacuum. Once I saw those numbers I remembered that's the way it was when I built it. Doh! Its hell getting old.

Well I have 2 questions. First, do you all think I can pull more vacuum based on the engine specs (I'll give them in a moment) and second, any recommendations on a 12v vacuum pump that some of you with high overlap cams might be using.

Here's the car as it sits now:

3.90 limited slip in 9" w/ 31 spline axles
small block c6 / e4od first gear / shift kit
2800 stall converter

351w bored .030 over
69 cast iron heads with extensive porting polishing and fitted with 2.02 / 1.60 valves
Torker II single plane
Eddy 750 cfm carb
msd 6t / blaster 2 coil / duraspark dizzy
Flat top cast pistons 11.5 compression
Comp cams 280h installed straight up
- Lobe separation (degrees): 110
- Intake Centerline (degrees): 106
- Valve Lash: Hydraulic
- Duration: Intake 280/Exhaust 280
- Duration @ .050" Lift: Intake 230/Exhaust 230
- Valve Lift: Intake 0.512/Exhaust 0.512
- Lobe Lift: Intake 0.32/Exhaust 0.32

Comp cams 1.6 roller tip rockers
1 5/8" full length headers

Timing is 13 initial 33 total. All in by 2500 rpm.

Don't rough me too hard on those heads, 20 years ago it was the hot set up :) Oh and the only other thing I've done is spray brake cleaner around the intake to make sure there were no leaks and adjust the idle mixture screws a bit. That got me from 5" to 8" of vacuum. The motor is making great power, long strip of rubber in front of the house at the moment :)

Any help would be greatly appreciated!
Charles
 

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Vacuum pumps are pretty obnoxious....... how about adding in a vac storage can first and see how you get by with that? I have one of these on mine and it helps quit a bit:https://www.summitracing.com/parts/cca-5200?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-comp-cams&gclid=Cj0KEQjwv467BRCbkMvs5O3kioUBEiQAGDZHL5ZB9noJoJ5TGnLDzO9GSCbTXYG9FmP3oNBywZWy7SsaAqBg8P8HAQ

If you go the pump route - I'd try and locate it in something to quiet it down.... or pad the noise somehow. I had one that drove me insane(r) lol!
 

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Discussion Starter #3
Thanks Bad69cat! Yea I heard those pumps were pretty loud. Here's a thought, I was thinking of getting one of those electric motor conversions for the headlight covers. Mine has a leak in the small canister between the lights when the lights are on. Has anyone ever used the factory installed vacuum canister under the driver fender as storage for the brake booster rather than the headlight covers? A couple check valves and in theory it could work.
 

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It won't have the volume you need due to the small hose size. You have the same problem that I had with the Tool. I tried the $400 vacuum pump and hated it. One question, what torque converter are you running? A torque converter with the wrong stall speed for the camshaft can kill a couple inches of vacuum.
 

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Discussion Starter #5
It won't have the volume you need due to the small hose size. You have the same problem that I had with the Tool. I tried the $400 vacuum pump and hated it. One question, what torque converter are you running? A torque converter with the wrong stall speed for the camshaft can kill a couple inches of vacuum.
Right now there's a 2800 stall converter and C6 which is a what my tranny guy recommended. I think it's just a big stick, I changed the timing a little to 16 initial 36 total and it went up just a little. Next chance I get I'm going to play around with full manifold vacuum rather than ported to the dizzy and see if that helps a little more.

Also pulling the 750 eddy off and replacing with my trusty old Holley 4150. I noticed the throttle plates are binding a little in the Edelbrock. I might have a little leak around the throttle shaft bushings.
 

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also I would plug off all other vacuum accessories (in case of leaks ) and make sure your PCV valve is working correctly ...
 

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Discussion Starter #7
I'll do that, thanks ndtorque!

I got my old Holley out and started taking it apart for cleaning. What a mess! It sat in a cabinet but with dirt roads around here the road base dust really caked on. Ugh that stuff is like cement...

I am sooo drooling over this:

http://denver.craigslist.org/pts/5607818104.html

only 30 cfm more than whats on there now but my gut is telling me it's too big :)
 

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That's gonna be to much carb...... my cam is about the same and my 750 is probably to big. See what shakes out after you try a few things with your current set up. I think you can gain some with a little tweaking and testing.... my stall is 2800 but now that I have the AOD in there is not a good match. It was better on launches with the FMX.
 

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I have a very very similar build and have 11-12" at idle. I think you should be able to get more with tuning.
The only differences in mine, I have 10 to 1 compression and installed the cam 4 degrees advanced. Dual plane intake. My timing is 16 degrees initial with 38 total.
 

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Discussion Starter #10
Thanks for the input maxmerc. Sounds about right, my cam is installed straight up so your getting a little vacuum boost on me there. Oh and I live in CO at about 4k ft above sea level which probably accounts for the rest of it. Even with the rebuilt Holley the best I can do is 10" @ 1k rpm. Drops to about 8" at 800 rpm where I have idle set though. She's running better than ever so I think that's all she's got to give.
 

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I think you might need a cam change or else you will have to go to hydraboost. I didn't notice the 106* cam centerline before, that will for sure kill vacuum. You need 110* LCL and maybe drop to 270 advertised duration to get the vacuum where it needs to be for power brakes.


The size of the carburetor won't affect the vacuum signal, and a 750 is a bit big for your engine, but since you own it I would not buy a different carburetor. A 650 CFM carburetor might give slightly better response, but it won't change the problem with power brakes.




Thanks for the input maxmerc. Sounds about right, my cam is installed straight up so your getting a little vacuum boost on me there. Oh and I live in CO at about 4k ft above sea level which probably accounts for the rest of it. Even with the rebuilt Holley the best I can do is 10" @ 1k rpm. Drops to about 8" at 800 rpm where I have idle set though. She's running better than ever so I think that's all she's got to give.
 

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This may be to late but I have a more radical setup than your and I get the vacuum I need by using Rhodes lifters. I ground camshafts for 18 years so I ground my own but the close love centers and overlap with the large @50 duration decrease your vacuum. Rhodes lifters bleed down to lower your lift and duration at idle to increase your vacuum and mellow out your idle Once you get on it the lifters pump up and you get the full effect of your wild cam. They work great in my Eliminator. Hope I'm not to late to help.
 

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I istalled an "UP32" from Volkswagen/Hella - cheap, small, quiet and very effective - even without an additional reservoir perfekt power brakes.

Mike
 
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