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Hi,
Another question as we prepare for the Trans Am. What maximum compression ratio will USA and Canadian fuels support, assuming we use the highest octane fuels available?
I think the highest I've noticed in CO is 89: do the octane numbers increase as you approach sea level? Will 89 in CO support a 10.5:1 compression, or more? The maximum altitude we expect to see on the rally is 8500ft.
Also, we'll be almost certainly using 2 x 45DCOE Webers. Will I need to rejet for the higher altitudes if the carbs have been set up at, say, 3000ft?
Regards
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JohnH, Sydney, Australia
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Corvette! Doing it in America's very own sportscar sounds like a dream.
What have you got for a motor? Is the 123 a new model? The first one only had stock and LPG curves in it making it fairly useless.
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69 142S Overdrive + 69 164S Manual
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I should say that have no connection to 123 because this sounds a bit like an ad! But I'm very pleased with it. The one you describe had no appeal to me but they now have a programmable 123. You plug it into a laptop and use their software to put your wanted advance curve using about 10 engine speeds. It was pretty simple.
You can put in 2 different curves and switch between them by putting (or not) 12v to one of the leads. Dead easy. Now you can play with ignition curves on the dyno. I haven't done it yet but I'm planning to soon.
I put one in my 142 a couple of months ago and did a nav rally here in NSW. That put about 1000kms on it and no complaints whatsoever.
I got mine from a bloke I know in the UK when I was there in May but the Australian agent does have them. I couldn't find them on his website, but I emailed him and he did. So I bought a second one to go in the rally car when we put it back together for the Trans Am - although the Corvette idea is more than tempting!!
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JohnH, Sydney, Australia
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I forgot to say that the curves have a user determined rev limiter. Handy. It seems to work quite smoothly. After I wrote, I ggogled their Dutch website and came up with this: http://www.123ignition.nl/id/50.html
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JohnH, Sydney, Australia
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I had a locked distributor with an Allison conversion on my beast. The dyno operator, a friend of mine would say to me, you built it, you reach in an rotate the dizzy. He'd sit in the car and load it to 4500. It made the same torque at 4000 to 5000 and peak power was 6000 to 6500 on my stock rod motor. 27° on a brew of leaded and hioctane unleaded waay back then. 34° on toluene mixed in. I would have liked 20° @ idle for easy cold starting, but it wasn't hard to put up with.
You can turn 8750rpms with a stock distributor and a set of XU-1 points. My mentor who taught me how to port and how to build cheaply did it all the time.
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69 142S Overdrive + 69 164S Manual
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While you're in Canada, you can get 94 octane at most PetroCanada gas stations. I run this in my 142 with excellent results.
Rob
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91 octane should not be a problem here in CO. One trick, find gas stations near lakes or reservoirs. Boat folks like higher octane, it seems.
But I seriously don't think you'll have any problems. You can always tweak timing in 2 mins if you get pre-combustion happening. A cool thermostat might help with that when climbing hills.
As for the Webers... yeah, you ain't gonna want to re-jet those just for a quick jaunt over the hills. I bought DCOE40s for my car off ebay.. they came from California, LA area, so presumably were jetted for that area. I bolted them on and ain't touched 'em since. It runs fine at 5000-9000 feet. Runs great, actually. And I'm pretty sure I'm running a good bit more 10.5 comp.
Avoid cheapo gas stations, go with the brand names. Conoco, Phillips 66, etc. in this area. 91 octane should be easy to find. For some reason, the usual here is 85, 87, or 91.
Basically, don't worry about it. If you anticipate a leg in your journey that takes you from high altitude to low in a day, make sure your tank is low when you arrive at a location that offers higher octane.
Do you know what your CO route is? We (I speak for myself and other good folks I've met) are here for you in this area if a problem comes up...
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-Matt I ♥ my ♂
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Hi Matt,
Thanks for the offer of help (if needed!). Unfortunately we don't come as far south as Colorado. That's a shame because I usually spend winters there and have friends there, apart form any BB contacts. The event spends a couple of days in northern Wyoming, but that's about as close as we get.
Here's a link to the route:
http://www.endurorally.com/pages/trans-america-2015-rally-route-outline
Regards
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JohnH, Sydney, Australia
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Great route! Looks like you'll be going over Teton Pass in Wyoming. Likely your highest elevation at 8400 and change. No big deal. You'll be just fine.
Compared to some of the other (wonderful) vehicles registered.. yes, you'll be just fine :)
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-Matt I ♥ my ♂
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What are you using for fuel in Aus? Canada & USA use a different method to measure, I think their 87 is our 91(Phil?)
Altitude is very significant, 3000ft is nearly worth a jet change, 8500 absolutely!
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69 142S Overdrive + 69 164S Manual
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Hi Paul,
I did know about the different methods because I spend a bit of time in the US. The effective difference between what we in Australia use (RON) and what the US uses (RON + MON)/2 is about 5 points. We're higher. My engine is currently tuned to get away with running on 91 (in Australia) which means I could get away with about 86, at lower altitudes, in the US.
In reality I use 98 here and it certainly feels better. I'm currently running 9.3:1 static compression but plan to raise it to 10.5. Then I'll certainly need to run 98 (or 93 in the US). Plus carry some octane booster. I've a got a programmable 123 distributor in the car, so I can set one of the ignition curves to retard the timing a bit if we get pinging. It's switchable on the fly.
As a side note, having seen the costs of shipping the car to the US - for some reason significantly higher than shipping it back - I'm thinking about buying a car in the US to do the event. I've always wanted a 70-72 Corvette... I've got garaging in Colorado so it actually is a possibility.
Regards
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JohnH, Sydney, Australia
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I have a stock B20E converted to carbs and have no trouble running it on 92 R+M/2 octane here at sea level. That's nominally a 10.5:1 CR engine, although as actually built by Volvo it's a bit lower.
The Apple Farmer Panamericana race car I built some years back had close to 11:1 CR and it was fine with 92 octane Pemco gas in Mexico, but that had a lot more valve overlap than a stock E engine.
Note that there are rapidly decreasing returns in power from raising compression. There's a lot more gain in going from 9:1 to 10:1 than there is in going from 10:1 to 11:1, and not just because it's a bit less change in percentage in the latter case. It's not a linear function.
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For long distance rallying do you think that you really need to up the c.r. as far as 10.5? High compression isn't everything, and won't give you a big jump in power unless the rest of the engine spec can do it justice. A few HP less is a good swap for less fussy octane management and possible reliability compromises. For rallying I think I'd take a bit of extra torque over a few ponies at max revs. IMO of course.
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The New World countries use AKI, which is (RON+MON)/2. The rest of the world uses RON, a higher number.
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My back feels better when I sit in a Volvo seat
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posted by
someone claiming to be Blackjackmc
on
Mon Aug 18 17:58 CST 2014 [ RELATED]
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A side note on compression and fuel. I purchased Mazda CX5 1 month ago, 13.1 comp direct injection 2.5 litre, runs on 91 or E10. Exhaust is 4 x2 dual pipes with very long runners, the theory being very little chance of hot exhaust getting back in the combustion to create knock. The piston has small well in centre of head where fuel is injected. Got some stuff with no sign of ping. Love technology.
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I live in the flatlands of the Midwest, at 1100 ft above sea level. I have made numerous trips to Colorado and other high plains areas - up to the top of Pike's Peak several times (14,100 ft), all without re-jetting carbs. My normal length of stay was 5-8 days.
I use 87-89 octane at home and premium in the mountains. I seldom got piston ping, except on very hot days (100F +). But, what happens at about 4,000ft and higher is oxygen starvation. Full throttle produces nothing at lower rpms, going out to pass on a 2 lane road is an adventure in patience - think VW beetle! Even with my 1998 V70 R, when the rpm wasn't high enough to let the turbo spool, giving it more gas meant going slower.
You will find 89 octane to be good with your compression ratio.
I would only re-jet if I were moving there. Remember, you need more air and less gas.
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My back feels better when I sit in a Volvo seat
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SU's & CD Strombergs are fairly good at correcting themselves, K-Jet is good too. D-Jet does to some degree, all of which haveno CPU! Fixed choke carbs need jetting changes.
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69 142S Overdrive + 69 164S Manual
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These engines will run at higher altitudes, just not like they do at sea level. I agree, if I were to move to Colorado Springs, I would have the jets changed and suffer poor mileage at lower altitudes.
These folks are just 'passing through' and can live with sluggish response for a week or two. If they were to race their cars on a track, the a re-jet would be needed.
My carb'd VW, BMW 2002, and BMW R90S were all driven to the top of pikes peak. The only problem I had was the prop shaft boot on the bike expanded to almost bursting point. It went down as I rode down the mountain.
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My back feels better when I sit in a Volvo seat
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Octane numbers will go up at lower elevations, typically to 92 at sea level. What compression that will support depends on cam selection, but I can run a stock B20E (nominally 10.5:1 and a D cam) without problems, although it requires some care in tuning.
Yes, you will want to change the jetting when there are large changes in elevation.
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