max comp on reg gas poll

[unclematty]

I was running 10:1 pistons, and heads that are shaved .015 on 87 octane and I did it for a long time, also the base timing is 8 degrees btdc, and at WOT I get 33-36 degrees advance, and all this from an old 521 cid caddy motor, and only a hint of predet on initial throttle opening, this thing will really move a 6000+ lb blazer w/ 39.5s and 4.10s. I don't remember what kind of duration or lift I have from the cam but I do remember it is for towing.

that being said 10:1 works for me, but I kinda know what I'm after and what to listen for.

 

[big_truxx]

old 521 cid caddy motor

that a bored or stroked or something 500?

 

[big_truxx]

build it with iron heads, run a 7.5:1 dynamic compression ratio, and 87 octane and be happy with it.

without knowing what dynamic compression is i cannot fully understand. however that would be great for yer grandma's grocerie getter, not for anything I would own.

 

[davesanrn]

pump gas

cam is the key, particulalry overlap.

 

[big_truxx]

it still seems like the easiest way to do it is to build the engine then see what it likes for gas lol

 

[sled_dog]

without knowing what dynamic compression is i cannot fully understand. however that would be great for yer grandma's grocerie getter, not for anything I would own.

learn what dynamic compression is. Just search the internet for articles and read them. 7.5:1 isn't as low as it sounds when stated in Dynamic.

 

[Mad-Dog]

say what,.........how do you know what the dynamic CR is at a given RPM before the motor is built ?

 

[big_truxx]

I seriously will research when i have the energy. but aso i will prolly build an engine to what i want it to do then decide what kinda fuel it would need to run

 

[beater_k20]

mad dog, cam timing doesnt change with RPM. at least mine never did.

 

[thor]

Mad dog, not trying to pick a fight this time .... Here is a good discription of dcr, I'm too lazy to cut and paste... DCR

 

[Mad-Dog]

You're right ,variable valve timing would be a unwanted by-product of a loose timing chain.

 

[Mad-Dog]

No problem Thor, sometimes i need to be stuffed back into the sock drawer...........
BTW that is a great link......thanx...!
Here is a DCR calculator for your pleasure.....

http://www.kb-silvolite.com/calc.php?action=comp

I am at a loss to know what the Intake closing point (degrees) ABDC @ .050" lift + 15 degrees is on my cam because i can't find the cam card, but i am guesstimating that it's very close to the advertised duration figure which is 274....i added 15 degrees to this and came up with a 7.9:1 dynamic compression ratio.........not sure what this means exactly but i am studying this dynamic thing as we speak so i will get back with ya later.
Chow 4 now

 

[LongIslander26]

What CR?

The altitude you live at has alot to do with it as well. I live at 6000' above sea level, we can run a goodly amount more compression here with a more aggressive timing curve on regular gas than folks would be able to get away with in say, Phoenix (1000' ASL). Just across the State line in New Mexico, regular gas is 85 octane, and my Jimmy with 9.1:1 CR loves it, which tells me I can probably run my CR even higher with no pinging. Food for thought when a rebuild comes around. Cam specs have alot to do with it too.

 

[beater_k20]

congrats on reviving a dead post 5 months to the day after it died.

 

[muddybuddy]

damn, i thought this was a new thread, i dont really look at dates.

i think there should be a indicator that displays who revives dead threads

 

[POWERMAD]

Posted 07-25-2005, 09:54 By longislander26

Must be a glitch in the system

 

[beater_k20]

no, it kicks it to the top every time someone votes. sombody found the old thread, voted on it, then it kicked it to the top, and people have been voting on the poll constantly.

is big_truxx even around anymore?