I now have a 91 HO engine. Getting ready to drop into a 93 f150. I'm going to port the heads and intake, and put in the crane 2020 cam. The one thing that I haven't heard from the guys that have installed them into trucks is. What type fuel is ran in them? What octane? If my numbers are correct the HO engine has 10.75 compression.

 

A lot of that will depend on your cam. I can run 14:1 compression on 89 octane pump gas without a problem but it all depends on how much cam overlap you have, i don't have any experiance with that cam but i'm thinking you can run 89 octane with 36 degrees total timing advance on that motor. I would also be interested to hear what everyone else is running though.

-Jon

 

1. HO motor is the same as the truck one (minus the different cam) except for the few years when there were factory installed forged pistons, this ended in 1992.

2. 10.75:1 compression is way, way off base. They're appx 9:1, depending on headgasket thickness, if the block has been machined, heads milled, etc.

3. Compression has nothing to do with cam overlap making you choose fuel as I learned. Overlap only creates idle vac (or lack thereof on large cams, thus unburned fuel). Ignition timing also has a LARGE factor in fuel used. Very high compression = very high cylinder pressure = far more heat generated (think diesel motor) = more chance to detonate prior to the correct time in the ignition sequence.



Hope that clears up a few things.

 

Yes it does. Thanks

 

Static compression ratio doesn't have much to do with the dynamic compression and cylinder pressure of the engine when its running. A cam with a lot of overlap will have lower cylinder pressure than a cam with less overlap. Thats why high duration cams idle rough, the valves are hanging open so long at low rpm that the engine is misfiring because it can't build compression. We are running 800 horsepower engines on 93 octane fuel. Timing does have a big influence but we usually run 36 degrees and retard it 6 degrees for every 100 horsepower shot of nitrous.

-Jon

 

None of that matters with a 2020. It's a high lift, low duration cam with a high LSA. It's intended to give massive amounts of midrange at the expense of high end HP.

 

Well nearly two points of compression is a big difference to me on a build up, not sure about you. This will effect many things you may/may not want to do in the future. I'm well aware large cams idle poor due to the over fueling at low RPM, perhaps you didn't read what I typed...

800hp on 93 is attainable in a boosted FI or large nitrous shot but you'd be maybe into the 20-22° total timing area with that, not streetable on nitrous unless you had a device pull timing automatically and not able to drive without spendy staging devices or progressive controllers as you'd induce massive wheel spin. Not something that sounds interesting to me. FI is more easily setup via tuning, FMUs are for ones just getting into it.

What I'm getting at is... don't tell someone a 13.5:1 motor with a 234/238 (292/296) .540/.550 112LSA cam on 87 pump fuel is going to run well. It's powerband is totally off for normal use in a truck and a very radical combo for anything streetbound.

 

I wasn't manking any reference to it being suited for a truck application, or being easy to drive on the street, i was just making the point that if you wanted to run an engine like that it can be done on pump gas.

-Jon

 

You want to use the lowest octane you can without detonation. Put a couple bucks worth of 87 in the tank, and see if it pings under load. If it does, try a few bucks worth of 89 and see if it pings under load. If it does, try 91, etc. When it no longer pings under load, you've found the best octane gas for your application.