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| Low Vacuum https://slantsix.org/forum/viewtopic.php?t=16650 |
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| Author: | Bill460 [ Mon Mar 20, 2006 10:47 am ] |
| Post subject: | Low Vacuum |
I installed a performance cam from Clifford along with Intake manifold (Holley 390) & headers,. rebuilt head, engine has 19,000 orig miles (1965) Cylinders had 145 PSI. Mopar performance distributer. Problem with low Vacuum at idle & really not a lot of power. I've rechecked CAM & rebuilt carb. only 12" of HG at idle. Motor will not pull 5600 lb truck up a hill at highway speed (4.11 gears) Clifford says I should get a Mallory distributer ($300.00+) Is this motor too small for a 1965 Boyertown bodied ambluance? Thanks in advance, I'm run out of ideas. |
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| Author: | SlantSixDan [ Mon Mar 20, 2006 11:31 am ] |
| Post subject: | Re: Low Vacuum |
Quote: I installed a performance cam from Clifford along with Intake manifold (Holley 390) & headers,. rebuilt head, engine has 19,000 orig miles (1965) Cylinders had 145 PSI. Mopar performance distributer.
Welcome to the board. Problem with low Vacuum at idle & really not a lot of power. I've rechecked CAM & rebuilt carb. only 12" of HG at idle. Motor will not pull 5600 lb truck up a hill at highway speed (4.11 gears) Clifford says I should get a Mallory distributer ($300.00+) Is this motor too small for a 1965 Boyertown bodied ambluance? Thanks in advance, I'm run out of ideas. A couple things occur to me. Looking at the setup you put together, it's really not set up for the low-end torque you need to haul that truck around. Clifford is known for this kind of "one size fits all" behaviour: Doesn't matter what it is you need, they'll sell you what they tell you you want. You don't mention the specs of this "performance cam" they sold you, but low vacuum at idle + no low end torque tells me it's probably a high-RPM cam very unsuitable for your application. Same goes for the headers and 4bbl, which aren't really the best tools for the job of making gobs of torque, and the MP distributor has a very unsuitable mechanical advance curve for that task (all the mechanical advance gets dumped in immediately off idle, which makes bigtime ping problems, which means you have to set the base timing way retarded, which worsens the low-RPM torque problem and the low-vacuum-at-idle problem.). Clifford's proposed "solution" is also typical of their moneygrubbing behaviour: After they sell you the wrong parts the first time, and you call back to say it's not working the way you want it to work, they propose to sell you another batch of wrong parts. You do not need a Mallory distributor! The MP distributor can be recurved with only slightly more difficulty than any other slant-6 distributor (the minor extra difficulty lies in finding suitable springs, since the MP dist comes with only one far-too-lightweight spring). The stock exhaust manifold or a set of Dutra Duals would be much more conducive to truck-duty low-end grunt, than the headers will ever be. The 4bbl carb, especially that one, is kind of like a bad hangover: You embrace the idea that it needs to go away long before it actually goes away. There are a lot of different parts and build techniques that can be applied to a slant-6 and the vehicle it's in to optimize for any particular task (getting down the dragstrip in a hurry in a lightweight car, hauling a heavy truck up a mountain, or anything in between). There isn't a one-size-fits-all solution; the build really has to be approached with a view to the eventual service the engine will see. If I were starting with a stock slant-6 truck (and I wish I were; mine's got a 318), and I wanted more muscle without a complete engine teardown and rebuild, my recipe would look something like this: •2bbl carb (Carter BBD or Stromberg WW) or twin 1bbl carbs, ducted air cleaner •Carefully-recurved Chrysler electronic distributor driving a GM HEI module •Dutra Duals with a 2" pipe off each, rest of exhaust system to taste, or, stock exhaust manifold with carefully-thought-out 2¼" headpipe, rest of exhaust system to taste •MP244 camshaft installed slightly advanced from straight-up If I had enough money and time in the budget, the first thing I'd add to the above would be a good cylinder head rework with hard seats, bronze guides; valves, ports and pockets lightly cleaned up to remove airflow obstructions. If I had more money and more time, and/or if the block warranted it, I'd bore it as large as I dared and/or do the long-rod conversion for added torque. From that point on, the remaining questions become minor (which spark plugs to use, what's the optimal transmission/rear gear/tire size setup, etc. None of the above is as sexy when you open the hood as Clifford's pile of expensive and inappropriate chrome and aluminum, but...there it is. |
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