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Impact of higher compression rate.
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Author:  marc426 [ Sun Sep 04, 2005 1:54 pm ]
Post subject:  Impact of higher compression rate.
Hi slanted people! Just thinking about it but... Since i have a tire-burning 170, i'd like to give it a little more boost. But (again)... without increasing my mileage too much! I live in France and we don't need floods to get 5€/gallons (about 6$ i guess), you do the maths! :D
I was thinking about increasing the compression rate since we got slightly higher octane rate here and a typical engine in europe will run 9 - 10:1 compression (and motorbikes going 11:1 but you know that) without a problem. Will i get a real increase in torque or is it just worthless?
By the way, what mileage should i expect of my dart'68 2dr HT?
If any of you have ideas to gain a few torque without going 4bl clifford intake, it would be very nice to share it.
Thanks again for your help

Marc
Author:  SlantSixDan [ Sun Sep 04, 2005 2:32 pm ]
Post subject: 
I don't think you get higher octane gasoline in France. Remember, North American octane ratings are lower not because the fuel is of lower octane, but because the rating system is different. Your 91 = our 87, your 95 = our 89, your 98 = our 91.
Author:  argentina-slantsixer [ Sun Sep 04, 2005 2:44 pm ]
Post subject: 
Quote:
I don't think you get higher octane gasoline in France. Remember, North American octane ratings are lower not because the fuel is of lower octane, but because the rating system is different. Your 91 = our 87, your 95 = our 89, your 98 = our 91.
that happens with argentinian octane rating sistem too? boomer!
Author:  marc426 [ Sun Sep 04, 2005 3:04 pm ]
Post subject: 
I'll get some 100LL plane fuel then! :D
Still, can i increase the CR with the higher octane rates (compared to the old days, ok! :lol: )
Author:  SlantSixDan [ Sun Sep 04, 2005 3:16 pm ]
Post subject: 
Check your information carefully. European Common Market octane rates are generally lower than they used to be, not higher. The Slant-6's combustion chamber is fairly primitive, and tends towards ping/knock/preignition easily, unfortunately, so the degree to which you can successfully run higher compression in a street-driven non-race car is quite limited. Also, before you do this, work the maths: High-test petrol costs more than low-test petrol, so the relatively small fuel economy / performance benefit you can get may not be worth it.
Author:  ceej [ Sun Sep 04, 2005 8:52 pm ]
Post subject: 
If you decide to run 100 low lead, you may need to re-jet and/or fiddle with your float level as well. The density of aircraft fuel is different than pump gas. You will tend to go rich.

When I couldn't get auto fuel for my 2 stroke aircraft engine, like flying into an airport in the middle of nowhere, I found my burn rate went way up with avgas. It cut my range down noticeably. Had it explained to me by my Dad, an A&P graduated from Spartan back when they trained on big Radials.

The reason you hear of people burning up engines with avgas is; it puts the A/F ratio into the rich side of the scale. That's where most of the "seat of the pants" power increase comes from. Some engines, that have been built up already, are on the ragged edge of their cooling capacity. More power output makes more heat and we have trouble brewing.
People successfully use avgas in car engines, but watch that temperature, and eyeball the plugs. If you're paying six bucks for auto fuel, I'd wonder what Avgas costs with road tax tacked on...?
Probably be money ahead to rework the combustion chambers and get rid of hot spots, then burn pump gas.

CJ
Author:  SlantSixDan [ Mon Sep 05, 2005 8:19 am ]
Post subject: 
Quote:
If you decide to run 100 low lead, you may need to re-jet and/or fiddle with your float level as well.
And carry your lawyer's phone number with you. They've really been tightening up enforcement on sales and use of airplane fuel in cars lately, in both the US and Canada.
Author:  slantzilla [ Mon Sep 05, 2005 11:16 am ]
Post subject: 
The reality is that just increasing compression by itself will not do a whole lot, at least not enough to make it worth the cost on a 170.

Stay away from a Clifford intake on an otherwise stock 170. It will kill so much low end that you will be tempted to slit your wrists. :shock:

A stock 170 will realistically get 21-22 mpg in a decent state of tune. :D
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