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Discussion Starter · #1 ·
? also how would altitude effect your v.e.? Or is there a software that corrects for altitude?
 

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Discussion Starter · #2 ·
anything? Say I'm trying to figure out octaine to comp ratio at altitude. Speedymopars had given me a formula for that(that I lost when HB took a dump) Anyway , software, book, links?
 

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I have a dyno program but not sure I would trust what it says for octane especially at altitude.

The way I figure it is that I boat at 4000 ft and I figure I loose right at a point of compression. So if you would feel safe building a 10:1 motor at sea level on pump gas you could get away with 11:1 at altitude.

There is probably some science behind all of this that someone can better speak on, but from my experiences I think its close.
 

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I have a dyno program but not sure I would trust what it says for octane especially at altitude.

The way I figure it is that I boat at 4000 ft and I figure I loose right at a point of compression. So if you would feel safe building a 10:1 motor at sea level on pump gas you could get away with 11:1 at altitude.

There is probably some science behind all of this that someone can better speak on, but from my experiences I think its close.

--Altitude sucks :(
 

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Discussion Starter · #7 ·
Thanks B.B.BILL. I've gotta be right on the edge of being able to run pump gas 11.5 to one,and I'm at about 4250 elev.(alum heads) And yes Outlaw, I'm jealous.:)devil
 

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Yep your right on the edge, but and don't go crazy with the timing and it should be ok. I am not sure about you but we can not even get 91 octane, here most everything is only 90.

I ran a 11:1 motor for a couple years on 90 and never had a problem. I tried it on 25% av gas a couple times but never took the time to dial the carb in so it did not really change much (av gas needs more jet). I would think it would be worth trying just to make sure.

It might be the type of thing where you can roll 5 degrees of timing out and run pump gas, or for extra special fun add some av gas and bump the timing back up.

P.S. Most the time if you actually CC everthing you will find you are 1/2 pt lower than the advertised compression ratios.
 

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Discussion Starter · #9 ·
To make a long story short I melted a set of 990's (ping)with this same bottom end,(had to buy 1 piston because it lifted a ring) so I know (think) I can't quite do straight pump. I'm sure part of that(5+7 nuke) was thanks to the single 4 TR I just took off. My brodix cc'd out to only 116 cc's so I'm assuming I'm tighter now than b-4.(never cc'd the 990's). Any way enougph of my life story , Thanks for the input. I'd still like to hear what dyno software peeps are using. BTW would running say 5+7 lean help cause detonation, or just a lot of heat, or both?
 

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I prob tinker with an old copy of Desktop Dyno 2000 more than anyone (one of therse days I'll find the cash to upgrade).

It does nothing for altitude, only assumes you are not having detonation (so no "octane calculations" either).

If you feed it good info, it seems to do a pretty decent job, like all computer things, garbage in = garbage out.
It sure predicts the behavior of my modestly modded 454 very closely to what I see on the lake. I try to get it the best info I can, most importantly being head flow figures.

IMO, most of your meltdown was likely the single-4 on the TR. I have never run one, but from the people on here that have, and have spoken of it, mixture distribution to the 4 corners was a nightmare. The TR manifold really was never designed to have just 1 carb in the middle of it, supposed to have 1 carb throat basically directly above the manifold runner.

A lean mixture in a cyl burns much hotter than a proper mixture, EGT's go way up if you measured them. Also happens to detonate easier under the same heat/pressure loads.

990's are supposedly arround 118cc chambers, figure what you want for production variation, but your 116cc heads (again, figure what you will for variation unless they've been all matched) should pretty much be a wash as far as CR change goes. 1.7% change in volume. Likely that much in variation one to the next (or more).
 

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Discussion Starter · #11 ·
Thanks Smokin SS , re. the software I wasn't sure how to shop 4 one, figured someone on here may help me out. Re. I should have ditched it a year (or more) ago. Thanks Kreg
 

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E-7 Sheepdog (ret)
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Yea, I'm waiting on the trial 'till I can afford to buy it once I'm adicted. lol

I do use their trial version of the Comp Ratio Calculator. Like it very much, very easy to use, easier than that in DD.
 
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