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Topic Review (Newest First)
07-01-2005 03:35 PM
GoneNova/406 i have a 406,10.5 c.r. and wanted to be able to use 87-89 octane because i figure it will get worse before it gets better so i built another 406 with 9.4 c.r. 64 cc combution chamber and a magnum 280 comp cams 1.6 rockers at 512/512 lift and am running 87 octane.runs great if this helps.i think you should increase your c.r. some to about 9-1. to run that cam.you may just have to try it.
06-30-2005 10:34 PM
h8louzn
Quote:
Originally Posted by lluciano77
He put a bigger turbo on then the original. It was running low 11s.
Wow, Can't belive what I see.
We are talking about compression ratio not times!
06-29-2005 08:24 AM
454C10 Here is a site that gives turbo eclipse specs: http://dsm.misterdeedub.com/1gvs2g.html

7.8:1 cr for 90 to 94 turbo eclipse
8.5:1 cr for 95 to 99 turbo eclipse
06-28-2005 04:53 PM
lluciano77
Quote:
Originally Posted by Rick WI
Your not going to run 11:1 with a turbo on 91 pump gas with any kind of reasonable tuneup. I'm not even going to bother debating that point.


He put a bigger turbo on then the original. It was running low 11s.
06-28-2005 10:59 AM
killerformula there's always somebody who claims they run 12:1 on 87 octane. This could be for any number of reasons, but the fact of the matter is that its really hard to get a motor to perform on any kind of street gas with iron heads and more than 10:1 compression, and few people have luck with it. Some of the things in terms of stories you folks are going to run into are the following: new motors or EFI cars. Different ball game, different conversation completely. Folks running aluminum heads. You're talking about one less point of compression due to heat sinking, you really can't parallel the two. You'll also run into people who say "its an 11:1 motor" or "12:1" who have no exact measurements to prove it.

There's a lot of stories this way and that in hotrodding, don't believe all the hype, 99.9% of motors adhere to the rule of thumb, which is 10:1 for iron and 11:1 for aluminum on street gas.

K
06-28-2005 08:01 AM
baddbob camshaft duration also factors in big time, cranking compression is a great indicator of what fuel can be compatible. Burn rate also.
06-28-2005 07:53 AM
454C10 That is exactly my point. Can't compare new high tech engines to old school american V8's. Even late 80's engnes have more engine tech than those old 60's designed V8's.

10.3 or 10.5 is about the same thing. However, printed in black and white, Road and track claims 10.5:1 cr. Maybe R&T got it wrong.
06-28-2005 07:42 AM
brainsboy It has 10.3 not 10.5 and it only has that because it uses a new method called direct injection, where the fuel injector is located in the combustion chamber to keep it cool, along with aluminum heads and with an Extremely low boost level, makes it possible
06-28-2005 07:31 AM
454C10 double post???
06-28-2005 07:25 AM
454C10 Each engine design has it's own octane requirement. Comparing the compression ratios of late model, high tech engines to an old school V8 is not going to work.

Furthermore, old style V8's need a bunch of ignition advance to make power. Slow flame travel over a big piston needs a bunch of timing advance.

Old BBC's typically need over 40 degrees of timing to make max power! This makes them very prone to detonate. Even a semi-high tech vortec 350 has enough modern design in it's combustion chamber ("fast burn heads") to only require 32-34 degrees advance. Plus their "smaller" diameter pistons need less timing advance because it requires less time for the flame to travel across a smaller piston. Therefore a sbc with late model heads (vortec or aftermarket) can run a lot more cr as compared to a BBC.

Due to more engine tech, it is becoming common to turbo charge high compression engines. The new Audi A3 2.0T uses 10.5:1 cr with it's turbo engine! (Road and Track, July 2005, pp 74-79). However, when determining the max cr of an engine with a low octane fuel, it is important to compare apples to apples. So, an old school 400 Ford needs lower compression than most, especially if used with a mild cam in a heavy car with a low numeric gear.
06-27-2005 11:59 PM
GoneNova/406 i just put a 9.4,406 together and it uses a comp cams magnum 280 with 1.6 rockers and i am using 87 so far.
06-27-2005 11:58 PM
h8louzn
Quote:
Originally Posted by lluciano77
How about my friend's Eclipse? It ran 11:1 stock with a turbo charger. He put a bigger aftermarket turbo on it and it runs fine with 91 octane.
Your friend does not have a stock eclipse with 11:1.
No matter what he tells you.
They have around 8:1.
06-27-2005 11:45 PM
Rick WI Your not going to run 11:1 with a turbo on 91 pump gas with any kind of reasonable tuneup. I'm not even going to bother debating that point.
06-27-2005 11:25 PM
lluciano77 How about my friend's Eclipse? It ran 11:1 stock with a turbo charger. He put a bigger aftermarket turbo on it and it runs fine with 91 octane.
06-27-2005 11:19 AM
Rick WI I suspect there is a limit to the amout of timing the computer can pull out. This is not unlike what will happen on say an LT1 motor that is run on 87, in addition to a large decrease in performance overall.
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