[Guest]

I am rebuilding the 289 as u read, the mechanic wants to drop the comp down to under 9 so it won't ping on standard unleaded. In Australia its octane rating is 91-93. You can get a higher rating around 96 for more cash at the bowser.
How do you go in America with the unleaded situation, do you drop the comp ratio or run standard compression and just add enhancers to the fuel?

 

[Opentracker]

A rule of thumb here is anything under 10-1 compression will work
with our 92 octane. 10-1 will work with aluminum heads or steel heads
with a quench chamber.

 

[adamg69]

This gets tougher than you would think. It isn't so muchas the compression ratio but the final pressure of the air/fuel mixture and things like hot-spots in the combustion chamber that determine whether you're going to get a ping or not. I have something like 11:1 compression and got rid of the ping using cooler than stock spark plugs and a little octane booster with 93 octane gas/petrol. It would have been wiser to aim for something in the 10.5:1 kind of range to get away easily on the 93 octane. Also the ignition timing will have to be adjusted for the octane/compression.
There is some good info on th subject at:
http://www.badasscars.com/techtips.html
How does your mechanic say he is going to get to the sub 9:1 compression ratio? Are you planning on new heads? Is he talking dished pistons? I don't know much about the 289 and the heads available but if it was me I'd be aiming at aroun 10.5:1 max, 10:1 min and then play it by ear on the timing and use the 93 octane gas you can get regularly. Also, if yu are using heads that didn't have hardened valve seats now is your chance to get them installed, just a little security against the unleaded.

69 Sportsroof, 351C, 4spd toploader, Restomod BOSS 429 clone - the one and only (?) 1969 BOSS 351

http://home.swbell.net/boss351/mustang/boss1.jpg
http://stangnet.cardomain.com/user/adamg69

 

[Guest]

Go 10:1. Also aluminum heads dissipate heat better, so you can run higher compression, like 10.5:1!!

65 coupe 302
(rebuilding a 351W)

 

[Guest]

Thanx for the input. He wants to put in dished pistons and claims that if it is set up right on a dyno I won't notice a big difference. I have to admit that it is more a cruiser than a racer. Geez it gets flamin' hairy doing the "ton" (100mph) when to front starts to float! But I don't want to be left with a car that goes like a tired snail either.

 

[AussieMustang]

chello, another aussie . Great!
I posted a roll call for Aussies on this forum a few days back .I see you have just registed today .
Your in STEAK&KIDNEY I guess .
How about finding the "Aussie roll call "post and give the rest of locals some info
Thanks
$

If in doubt give it a clout
If at first you don't succeed , find a bigger hammer
http://albums.photopoint.com/j/view?u=1584152&a=12055089&p=43600042.jpg<P ID="edit"><FONT SIZE=-1>Edited by AussieMustang on 03/29/01 06:12 AM (server time).</FONT></P>

 

[Guest]

Chello... Larry here in Sydney. You have and have not a problem !!! It all depends on how often or when you use your 'stang. If it is a daily driver then of coarse fuel is a concideration. If, on the other hand, you only drive your mustang infrequently or on weekends etc. why worry about filling up with super ( lead replacement fuel) as it is called now ?...the low miles you will be travelling won't matter so much. This is the situation we have with our '66 convert - Not used every day, only every now and then. We just pay the extra ..and drive..and loving it..!!! Ok, on the other side if driven all the time like my '76 302C ute -I run LPG to save a lot of money on fuel.
having said that your engine guy, is right, you will not notice much difference in the comp. ratio -' just cruise -in ' does'nt need a ' knife - edge' performance modification.
BTW... for our american friends- aluminium heads here in aussie are not really an option. the cost is waaaaay out of line if the exchange rate is put into perspective. At the moment our dollar is trading at about 48.80c for each american dollar...!!!! So if AFR ..for example run about $700-$1000...US... you have to DOUBLE that for aussie dollars PLUS... FREIGHT..!!!! Aluminium heads are few and far between here down under. I do not know anyone running them !!!! Also windsor motors are fine.. but all the performance guys run clevelands... we have had them here from '71 thru to about '84...plenty of performance equip. availble..
just my 4 cents worth ( exchange rate inflation..!..)

Larry.......