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Wisconsin Engines

VG4D LP compression ratio


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Old 10-27-2016, 08:33:53 PM
hogman2002 hogman2002 is offline
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Default VG4D LP compression ratio

Can anyone tell me what the compression ratio of a VG4D with LP heads is?
The reason I ask is I have a gas VG4D in a New Holland skid steer with a cracked head. I found a complete VG4D on craigslist for a decent price($250) and planned on using it for parts. But after pulling the head off I realized it has LP heads.
So can I switch out both heads to the LP ones and run 87 octane gas without causing problems?
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Old 10-28-2016, 01:01:28 AM
K-Tron K-Tron is offline
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Default Re: VG4D LP compression ratio

Im not sure if Wisconsin ever published a compression ratio for any of their air cooled engines. I have heard your run of the mill Wisconsin engine runs at just 5.5:1 compression, but thats just word of mouth. I have been meaning to calculate the compression ratio of one of my stock VP4's and compare it to that of the "hot" VP4 I built with custom head gasket/shaved block and shaved head. I do know that Wisconsin offered a different cylinder head for "high altitude" use, but again I have no compression ratio figure to go by. I would think that the compression is a few points higher on the LP heads to burn the lower octane fuel more efficiently. Can you post a picture of the heads that you have? Im curious where your head cracked. I've never seen that happen before. There is no coolant to cause a temperature differential to cause a head to crack. If someone else does not chime in, I would expect that you could run both LP heads as long as the cylinders are clean and you have good 0.062" thick stamped steel head gaskets. I will double check my books to see if I can find any numbers.

Chris

---------- Post added at 01:01:28 AM ---------- Previous post was at 12:08:34 AM ----------

I have a pretty extensive library of Wisconsin Engine manuals and the only compression ratio I could find was that of a stock V461-D (7.1:1). Unfortunately that is an overhead valve engine and likely runs a higher compression than a standard L-Head VG4D. I have a brochure on "high altitude" cylinder heads, and they can be furnished on all models when ordering new, with exception of the ACN, AEH and AENL as they came factory with high altitude cylinder heads. My LPG gas brochure specifies a different cylinder head is used. I wish it gave more specifications... Chris
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Old 10-28-2016, 11:26:34 AM
hogman2002 hogman2002 is offline
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Default Re: VG4D LP compression ratio

Here's a pic of the cracked head. The crack was my fault for not keeping the cylinder and head fins clean.

I non scientifically measured the combustion chamber of the two heads by filling them with water using a 35cc syringe. Came up with 133 cc on the gas head and 112cc on the LP head. After plugging the numbers into an online compression ratio calculator I came up with LP cr of 6.4:1 and a gas cr of 5.7:1. With the LP heads I should be able to safely run 87 octane gas, right?
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Old 10-28-2016, 02:24:02 PM
K-Tron K-Tron is offline
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Default Re: VG4D LP compression ratio

I am very surprised the head cracked like that. I supposed it could be welded back up, you would have to drill the ends of the crack and then go from there. Based on the compression ratio calculations you performed, it will probably be safe to run LP heads on an otherwise ordinary Wisconsin engine. I have run numerous Wisconsin engines on 91 non ethanol pump gas with shaved heads without any issue. Once all of the cooling shrouds are cleaned out, try it out and report back.

Chris
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