Alcohol compression ratio question

[racergeo]

  I am thinking of running alcohol with mechanical FI on an engine I'm building for BV. I have heard of some high compression ratios being run by the World of Outlaw cars (on the order of 16 to 1) and Frank parks (Jr Fuel dragster 6.70@ 195) told me 17 to 1. What are the high and low parameters you would run and why. I have always believed the benefit of running alcohol was the ability to run high comp. and that was what gave you any power gain over race gas. Your thoughts. thanks George

[Anvil*]

For good breathing motorcycle engines and 60's era Fords I tend to start around 15:1, but what RPM and what engine makes a world of difference. For SCCA racing an MGB can run 15:1 on gas as the long cam and lack of breathing doesn't allow for a full charge, so the dynamic or effective compression is quiet a bit lower (it does add a limitation of not applying full throttle at a lower RPM range or it will detonate). This is more a long winded way to say it depends. More cam, strong parts, higher RPM, weaker breathing, and a forgiving combustion chamber allows for more compression (and not to forget water injection). There is also a trade-off where the piston dome really messes with the combustion flame-front.

If you add a bit more information someone here may be familiar with your engine / vehicle combination.

[Dynoroom]

A couple of things to think about....

Sprint cars lift after <3 seconds.

Jr. fuel drag racers are running in the 6's with not real heating in the system.

And at Bonneville you are WOT for 5 miles. if running 200 mph you'll be at WOT for 15 seconds for the timed mile and if you are running 300 mph that will be 12 seconds, not to mention the time it takes to get to that last mile.

One last thing, todays racing gas has an octane rating that compairs with alky. if I were running in the fuel class I'd have a bit of that nitro in the tank with the alky.

YMMV

[racergeo]

  Michael, So your not in favor of that much compression, but you didn't answer my question, how much? By the way when I raced sprint cars if you would have lifted off the thottle in three seconds you would have been lapped ever thee laps. They run wide open all the way around the track.

[jimmy six]

You can go to websites and find true compression ratios by putting in your cam timing and find it's not what you think it is. Silvolite is a good one. Don't believe anyone advertised CR; do your own calculations using your chamber and piston.
From my experience Aug usually has corrected altitude of over 7000 feet and October has the altitude in the 4's and sometimes lower...The choice is yours..................Good Luck

[Dynoroom]

  Michael, So your not in favor of that much compression, but you didn't answer my question, how much? By the way when I raced sprint cars if you would have lifted off the thottle in three seconds you would have been lapped ever thee laps. They run wide open all the way around the track.

Actually I run as much compression as I think I can get away with. I've run 15.5 on gas at Bonneville with no issues. I was just giving you something to think about when compairing different racing types, nothing more.
As for the sprint cars... good on you I thought they still "breathed" the engine from time to time i nthe turns. Must of been a winged car, I was thinking real sprint cars.........
OK KIDDING!!!

[racergeo]

   Michael, I actually agree with you. I went to the last race at the old Ascot Speedway in SoCal. It was a wingless sprint race.Jimmy Sills and that era. Anyway I saw a few of them snap roll all the way down the back stretch. Never even thought about driving one after that,. Lot of guys been killed in those things. Our local 3/8 clay track has 360ci sprints running in the 12's. No lifting. Jimmy Six I understand dynamic compression ratio and the effect of cam timing and overlap, but I am asking about static compression ratio. NASCAR was running 17 to 1 with endurance engines until they mandated a 14 to 1 max a few years ago.

[Dynoroom]

  Michael, I actually agree with you. I went to the last race at the old Ascot Speedway in SoCal. It was a wingless sprint race.Jimmy Sills and that era. Anyway I saw a few of them snap roll all the way down the back stretch. Never even thought about driving one after that,. Lot of guys been killed in those things. Our local 3/8 clay track has 360ci sprints running in the 12's. No lifting. Jimmy Six I understand dynamic compression ratio and the effect of cam timing and overlap, but I am asking about static compression ratio. NASCAR was running 17 to 1 with endurance engines until they mandated a 14 to 1 max a few years ago.

I think Nascar mandated 12:1 and according to my sources they were pushing towards 16:1 but I really don't know.....  

[racergeo]

  Michael you are right . The SB2 parts I bought on EBay yielded a lot of compression probably cause they are a mismatch. My 42cc heads probably would have been with a dish pistons instead of the flat tops I won for 10c on the $. I also have a few extra cubes as a result of stroke and bore mismatch. Back on topic, how much compression on alky guys. From personal experience if possible. By the way I have a friend that was a NASCAR crew chief and he keeps in touch with his old mates and they keep him up to speed on what goes on. He claims the top teams are making over 900hp. Not bad for so low a compression.

[Dean Los Angeles]

Compression makes horsepower on any fuel.

Methanol makes more power by providing more heat.
Gasoline at 20,943 BTU’s/lb at 14.7:1 air/fuel ratio by mass equals 0.068 lbs of fuel/lb of air or 1415 BTU’s/lb of air.
Methanol at 9,770 BTU’s/lb at 6.4 air/fuel ratio by mass equals 1527 BTU’s/lb of air. About 22% more bang.
Nitromethane at 5,160 BTU’s/lb at 1.7:1 air/fuel ratio by mass equals 3035 BTU’s/lb of air.

[jdincau]

Interesting referance material

http://www.turbofast.com.au/racefuel.html

YRMV

[jl222]

Interesting referance material

http://www.turbofast.com.au/racefuel.html

YRMV

 Thanks for the link

    JL222

[hotrod]

And to round out the energy per pound of air vs fuel types:
Keep in mind that the specific energy produced per pound of fuel is not exact, and depending on the source you will get the value computed using the higher heating value or the lower heating value.

http://www.afdc.energy.gov/afdc/pdfs/fueltable.pdf


Using the lower heating values you get:
Typical gasoline Thermal energy 18,676 BTU/lb Gasoline Max power rich    12.5:1 = 1494 BTU/lb
Typical gasoline Thermal energy 18,676 BTU/lb Gasoline Max power lean    13.23:1 = 1411.6 BTU/lb
Typical E85 Thermal energy 12648 BTU/lb rich max power fuel air mixture 6.48:1 = 1951.8 BTU/lb
Typical E85 Thermal energy 12648 BTU/lb lean max power fuel air mixture 7.38:1 = 1713.8 BTU/lb
Typical ethanol Thermal energy 11,585 BTU/lb 9.00:1 stoich fuel air mixture = 1287 BTU/lb
Typical methanol Thermal energy 8,637 BTU/lb  6.45:1 stoich fuel air mixture = 1339  BTU/lb
Typical methanol Thermal energy 8,637 BTU/lb 5.00:1 max power rich fuel air mixture = 1727.4 BTU/lb

I am estimating the max power rich fuel air mixture for methanol from various sources, if anyone knows their true AFR on methanol for max power that would help.

As you can see due to the heat contribution of gasoline mixed with ethanol in E85 it is equal to slightly superior in energy release potential compared to methanol.

Larry

[interested bystander]

Generally accepted A/F ratio for max power with alcohol is 5 to 6 to one.

(Maybe too broad a spread? I dunno.

That's by weight!

[The wonderful One]

The streamliner with a 430" Rodeck SB is at 16.5. Add 5% of the yellow stuff to compensate for the 5K feet between sea level and  B-Ville and you should be back at sea lavel HP. Trust me this is safe. We ran at Ascot for seven years (CRA champions two years, Davis / Wirth racing) and had no problem with a Rodeck at 16.0. on alcohol. I ran 15.0 on 92% in Jr. fuel in the 1966 with 60 degrees lead. Best ET 9.87 at 200 even with a 310 CI cast iron SB and cast iron heads. Looking back I think it would have been better to run 50 degrees. Not because it would be easier on the engine but I think it would have gone faster. Be brave. The Wonderful One