I'm planning an engine build. I'm not going to get into specifics, but it will be an FE, and it will be used as a street mileage type motor that still makes good power. The fuel is E85, but I do not want this to turn into a discussion about the viability of E85, fuel system problems, or the like. Leave that for the alternative fuel forum.

Now then, what would be a safe dynamic compression ratio for 105 octane, in a quench headed FE? The chart from that Vizard article I have been quoting seems to indicate 10.5 or 11 to 1. Obviously, the static compression ratio will be above that. Of course, some important parts of that article have recently been called into question, and that's why I'm asking here.

 

Rusty, I'm thinking you could do at least 11 to 1 dynamic. Does Vizard's chart take into account the latent heat of vapourization as well as the octane ? My belief is that the 105 R+M/2 E85 could stand more heat from compression than 105 gasoline could. DF

 

Isnt Ethenol at the pump in Iowa? I remeber it being an option when I lived there, my father ran it in his 66 f-100 all the time.

 

What got this all started was a newspaper article stating there is an E85 station planned for the Cedar Falls area, and that the cost would be 20 to 50 cents cheaper than regular gasoline.

My thinking on the octane was this:
In order to determine the octane rating of a fuel, they run it in a test motor. The research octane is run at 600 rpm, and the motor octane is run at 900 rpm. They use known test fuels to calibrate the machine. So my thinking was that 105 octane = 105 octane, no matter what the fuel is, since it's run in an actual variable compression test engine when they determine the octane rating. I thought that if the latent heat of vaporization was a factor, it would have shown up in the octane testing.

Unless I'm way off and the rating system is different for E85?

I'm also looking at custom domed pistons. Ross wants about $815 for a set. Anyone know of a better deal?

 

BE CAREFUL:

Dynamic compression vs static or 'normal compression'. I'm building a 400 for propane and when researching found that most race engines do not go over 9:1 Dynamic due to heat. A 15:1 engine with a Huge cam- like nascar etc will yield somewhere around 9:1. More and engine durability is questionable.

I'm not saying this is gospel but close to it. I ended up with 10.5:1 Static and 8.7 or so dynamic...still getting it together.

 

This is true, but consider this. Alcohol has a high latent heat of vaporization, which will make things very cold before being combusted, taking a lot of heat with it. Also, it's energy content is low compared to gasoline and even propane. These two factors should lower the amount of heat transferred to the engine. Propane is a very different animal.

Also, I'm running about 8.7:1 dynamic in my 390. It runs on 89 octane pump gas without pinging or overheating. It's also a street driven motor.

I think it'll be fine. We're not talking about a dragster or a Na$car motor here. Ultimately, compression and combustion pressure will be controlled by my right foot. 15 seconds of WOT at a time, max, and not very often. Kind of hard for heat to build up in that time. If I was bent on destruction and floored it all the time, sure, I might be able to blow it up. But the way I drive, it'll live a long and useful life.

 

I'd sure like to know the quench and timing dynamics that allow you to burn 89 on 8.7 dynamic- never heard of that being done- and I'm not opposed to learning a bit. Hadn't considered the evaporation of alcohol as a cooler. My reference to na$car was only to emphasize the heat and durability thing.

I'm not sure how the propane will respond- no one talks about dynamic compression and thats doubly true with propane builds so I'm riding on what I can find and apply as I go. Could be i can go higher as well but not willing to risk it.

 

There's another guy here that runs 9.0:1 dynamic in a 428, with regular pump gas. I think this quench thing has a lot more benefits than it's commonly given credit for. That's one of the reasons I like the FE by the way, no open chamber heads.

My particular motor is running .032" quench distance, with stock FE C7AE-A iron heads. That's cutting it a little close I know, but I've kept it under 5500rpm and all is fine. I dont need to run a lot of timing either. I'd have to get out the timing light for specifics, but base timing is 10 BTDC, with the "less" mechanical advance position in the distributor. I'd have to go take it apart and look to see where I set it. Also running vacuum advance. Adding timing doesn't seem to add power either, so it's fine where it is.

Edit: What you might be able to with that propane is set the timing to where it makes the best power. I think you'll be well below the threshold of where it would ping.

Re-edit: I'm not sure how true this is, but I've heard of people running Methanol in their drag cars, where the engine is colder at the end of the run than it was at the start!

Re-re-edit: That cant be true. They must have been measuring the intake manifold temperature.

 

didn't know the FE had that advantage. I've always had a soft spot for the 390- have one out back tarped over thats a factory 4v- also have an opportunity to buy 3 '76 trucks for $500- ones a highboy with motor probs and flatbed and other two have body parts and one a dcent 360- thinking it over.

I've been so shocked about the 400 that i thought was a dog that i've left the fe for now. I just might have to build an fe for propane and see what it does - with all that quench i could run up the dcr until heat makes me stop.