| rustedorrotting | -- 06-14-2022 @ 9:11 PM |
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I have a unique problem. The rebuilt 41 v8 i purchased off from an engine stand years ago has 175# compression per cyl and i can't seem to get more than 13 inches of vacuum. I made my living as a mechanic and this smells of a cam and maybe it's been stroked. Any suggestions?
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| TomO | -- 06-15-2022 @ 8:21 AM |
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Most modified cam shafts were marked on the distributor drive. Look for a stamp or engraving on the face. Tom
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| 40 Coupe | -- 06-17-2022 @ 4:04 AM |
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Wow the compression is out of sight! usually about 90# on an original stock engine. I would agree with your suspensions.
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| carcrazy | -- 06-17-2022 @ 12:46 PM |
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That high compression could be due to extreme amounts of carbon and/or lead build up in the combustion chambers. Are the vacuum readings steady at idle? What is the altitude of your location? If your altitude is 6,000 ft. above sea level a vacuum reading of 13" Hg is about right.
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| 37RAGTOPMAN | -- 06-23-2022 @ 7:56 AM |
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did you you try a differnt compression testers to campare, ? low vacuum sounds like a modified cam shaft, also try another vacuum gauge, does the engine idle and at what speed, my 2 cents 37 Ragtopman
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| rustedorrotting | -- 07-13-2022 @ 8:51 AM |
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I bought this engine about 1990. I wasn't looking for an engine but i did want the dress up parts. At that time Aluminum heads and 3x2 manifold was about 750$. I was buying a repairable cab from this man when he asked if i needed an engine. It was on an engine stand wrapped in plastic and he told me it had been rebuilt about 15 tears earlier. I paid 650 for the engine. I have taken off the Weiand heads that it came with and replaced them with used Offy heads. I have hand lapped the valves and adjusted the lifters, so no carbon buildup The cam has no identifying marks behind the crab style distributor. While getting it to run I went back to basics and did a comp test 175# per cylinder! Also couldn't get more than about 13 inches of vacuum. I live in Michigan, so no high altitude involved. I have 3 two's on it but only the primary is active. The secondary' have both fuel and air blocked off. By the best I can figure I have a 41 engine.
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| carcrazy | -- 07-13-2022 @ 10:47 AM |
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Your low vacuum may be due to massive leaks at the manifold or the mounting surface for it. The manifold mounting surface may be warped enough to prevent a good seal. Do you have a stock intake manifold to mount on the engine to see if it corrects the vacuum issue? If so, it would be a good idea to install it with a new gasket to see what happens.
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| TomO | -- 07-13-2022 @ 10:56 AM |
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13" vacuum could be because of the camshaft grind. You have several unknowns that will have to be resolved before you can determine why you have 13" of vacuum. What is the camshaft grind, what is the compression ratio of the heads and the bore and stroke of the engine. IMHO if the engine runs the way that you want it to, just drive it. You will not get a smooth idle with a modified cam and with those compression readings, you might have to run high octane fuel. You might find better opinions on the HAMB, the posters on the board are more familiar with modified engine that the people on this Forum. https://www.jalopyjournal.com/forum/ Tom
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