Thread: 1.5 inches of vacuum

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How can I get that much more vacuum out of my motor. I have a built 454 motor. its a 454 bored .030 over. a xe268 cam and 781 heads with stock size valves and rocker ratio., I don't remember the dome on the piston but it makes it about 10.25 compression ratio. I mud drag with this setup. I have to pull 15 inches at 800 rpm. I'm pulling 13.5 they let me race but it needs pull more vacuum. I've tried adjusting my 4 idle adjustment screws. I'm running my intial timing at 10 degrees. Somebody needs to set me straight on total timing I think I should be checked at about 3000 rpm. Any advice is appreciated. Thanks

Replace the lifters with Rhoads units....
http://www.rhoadslifters.com/

BBC timing.

With no vacuum advance mechanism 12 degrees advance at idle, 36 max all in at 3000 rpm. With vacuum advance 8 degrees initial (with it unplugged).

Kitz

I would like to go with those rhodes lifters but I don't want to put a new cam in. Too much work. I have the vacuum advance plugged and have the intial at 10 degrees. I don't know what its at 3000 rpm I need to check that. It already turns over pretty hard when its warm. I don't know if will start good at 12 degrees. I have a new battery but maybe my starter is getting a weak or hot. Do you think this will help my vacuum. What do you guys think. The reason I picked this cam is because of the build off of Comp Cams website. [URL="http://www.compcams.com/Community/Articles/Details.asp?ID=1108284073" It shows in there build that it pulls 15.7 inches of vacuum I'm getting about 2 inches less of vacuum.

Its a lot of work but some combinations run better with the cam set advanced or retarded from standard. A mechanic at the local performance shop told me he bought a healthy 305 (just overhauled) very right because the owner had tried everything and the engine was a slug so he replaced it. The vacuum test showed very low for a healthy engine. The mechanic cam-timed it and found a lot of power and healthy vacuum. There are several ways to do this but he ran cold compression checks on several cylinders, then moved the cam forward and back tooth by tooth on the timing chain to maximize the compression readings.
The other method is to use a degree wheel on the crank and a dial indicator on the rocker arm to dial it in but I don't know the details.

Doubleclutch has a point. I believe if you advance the cam timing 2-4* it will reduce reversion and lower the tq curve at the expense of the top end. This ought to give you plenthy more vac...

Definitely try the spark lead first.

-Chris

You can use the same cam with the new lifters , you just have to break the cam in again like a new one to use the rhodes lifters.....just pull the intake.
Moving the cam one tooth on the timing chain will not hurt either.

So I tried with the intial timing at 12 degrees didn't help with the vacuum do think I should go some more. I checked it at 3000 rpm its only about 28 degrees shouldn't it be more than that. Also it wouldn't turnover very good so tommorow I'm going to put a new starter in it. It also seems the left side exhaust seems way more raspier almost annoying compared with the right side. I have upright headers it just seems ones different sounding than the other. I just have pretty much stock ignition except a mallory hei replacement distibutor.

What if ain't using my vacuum advance, I never have, don't really know the reason. Should I try it. I just figured at wide open throttle the vacuum drops to 0 so vacuum advance really wouldn't help. But should I just hook it up and run it up to 3000 and see what I have. Thanks

Just another thought, should I try to go with a better ignition, right now its just all stock hei ignition. I've read if your running race gas that you should have a little better ignition. Maybe that would clean up my idle a little bit and help through out my rpm band. Also would elavation change my vacuum, say about 2000 feet higher.