Max recommended Comp for staright LPG 351 clevo? - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars
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post #1 of 3 (permalink) Old 02-20-08, 11:12 PM Thread Starter
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Max recommended Comp for staright LPG 351 clevo?

I'm looking to rebuild my cleveland shortly, 351 C6 83 Bronco 3.5 9". I'm going to dump the petrol and go straight gas through an impco 425.

What is the max compression I'll get away with for a daily driver? I'm looking at 2v closed chamber heads and hoping / expecting compression around 10.5 -11. Am I going to get away with that, and expect a decent life out of the motor?
I have the original electronic ignition set up at the moment, and may go a newer version if i have to. Any suggestions on that front?
Cam is unknown at the moment, maybe the Competition cam #255DEH or 265DEH.
I'll never run it past 5500rpm, infact lucky to go past 4500rpm.

Running down ideas and suggestions at the moment


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post #2 of 3 (permalink) Old 02-21-08, 07:28 PM
351 XE on LPG
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Location: Perth, Western Australia
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Re: Max recommended Comp for staright LPG 351 clevo?

Gidday Wet Ones

The 2V CC heads work very well, and the C/R you’ve suggested will be right in the ball park.

LPG mixes range from 100% propane to a 50/50 mix of butane/propane and I’ve never had any detonation problems. Make sure your cooling system is spot on and try for a steady 160ºC.

The stock electronic dissy will be fine, but be sure to have it recurved to suit gas, (total advance in before 2500-2600 RPM). I also fitted a set of decent leads (ICE) to combat cross-fire issues. Have a look at your engine running in the dark. It can be a real eye-opener.

I note that your diff is running 3.5 gears. What is the height of your tyres?

Here is a little calculator I put together for determining revs at cruise, and desired red line peaks.

Click here to download my Calculator v2

I had a similar combo and was very happy with the result. I took a lot of time choosing a cam profile and ended up with an old Cam Dynamics profile, part number 972227 (now badged under the Crane - Blue Racer logo). It had heaps of torque and maxed out about 4500 – 5000 which suits the limit of the 425.
(on page 17)

Here’s a bit of dribble that you might find useful . . .

LPG Compression
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post #3 of 3 (permalink) Old 02-21-08, 10:28 PM
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Re: Max recommended Comp for staright LPG 351 clevo?

propane loves lots of compression, and lots of advance
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