[DeTomaso] Compression Ratio Question
Mad Dog Antenucci
teampantera at yahoo.com
Fri Sep 21 21:31:05 EDT 2007
Garth,
Are you on Hillary's campaign committee?
You need to be ;-]>
Dawg
Garth Rodericks <garth_rodericks at yahoo.com> wrote:
Whoa doggie! Let me run back to the firehouse and get my flame suit.
First of all concerning the Alu heads, I was quoting (or perhaps misquoting) a post from one
of the EXPURTS on this list (or the PI board) who reported that the "closed chamber
Cleveland heads" had less tendency to cause pinging than some (I forgot which) aluminum
heads due to the combustion chamber design - this is from memory (or apparent lack of -
gotta see if I can find that old post). Yeah, it seems counter-intuitive. But then again,
experience probably makes you a better racer than all the boy-racer slackers on this board
(myself included) who have read more about racing technique than you, but haven't tried it.
Anyway, the material of the heads was not the point of my post. My point was that Art could
build a durable high horsepower low compression engine that he could run on pump gas with
less worry about pre-ignition or detonation failure than a high compression engine running on
the same crummy pump gas.
And you're right. Lots of things contribute to detonation - Chamber design (shape, size,
geometry, plug location), compression ratio, engine timing, mixture temperature, cylinder
pressure and fuel octane rating. Too much spark advance ignites the burn too soon so that it
increases the pressure too greatly and the end gas spontaneously combusts. Backing off
the spark timing will stop the detonation. The octane rating of the fuel is its ability to resist
detonation. A fuel can have a variety of additives or have higher octane quality. For instance,
alcohol as fuel has a much better octane rating just because it cools the mixture
significantly due to the extra amount of liquid being used. If you use fuel with a lower octane
rating than what the engine's compression ratio and spark advance demand, then detonation
could result and eventually cause a failure.
In a nutshell, high compression and crummy gas make for the perfect storm, one that will
undoubtedly be encountered driving hard around LA and through the desert to Vegas
on local pump gas.
But, we're talking Panteras here! So, to each his own! Do what you want and what you
think is best. We all have opinions about the best approach. Art is collecting as much info
and opinion as he can to make the best decision for himself.
.--"-. / " : (o"""| / ,- `-._| ,'-" `,-' /--.( / . \ > ) : |\ .\ T `.\ ` Y : \ !.
Flame suit on!
Mad Dog Antenucci <teampantera at yahoo.com> wrote:
Garth wrote;
"Aluminum heads usually increase the likelyhood of deonation so forget a high compression engine"............
Wooooooooooooooooooooot?! I know you said your advise wasn't worth 2-cents but I disagree with you buddy. ;-]>
Didn't Bob's engine break?! ;-]>
Detonation can be caused by allot of issues including going too LEAN, incorrect timing blah-blah....and maybe I misunderstood DR. DAN on this point but if you are running alum heads my understanding is all things being equal and you are runnng a healthy cam with lots of duration like Art is planning you should be able to GAIN a point on compression or go from 10:1 to 11:1 but I could be wrong....my 302B heads are 11:1 or 11.4:1.....OKAY DAN wotta say?
Dawg
Garth Rodericks <garth_rodericks at yahoo.com> wrote:
Art,
Your 377 stroker was running 10:1 compression with iron, closed chamber heads, and you
believe detonation killed it. Was the aforementioned CR before or after the additional .020
was milled off the heads?
You want...
- 408 stroker Cleveland built with CHI 3V aluminum heads
- Max HP
- Durability - I don't want to blow up any more engines due to detonation.
- Plenty of compression ratio, 11 or 11.5:1
- MSD knock sensor this time around
My 2-cents, and that's about all it's worth...
You're throwing your money away building a high compression engine. This engine will fail in
short order the way you want to drive it. Also, aluminum heads usually increase the
liklihood of detonation. So, forget high compression. The knock sensor and in-car timing
adjustments are merely band aids for the high CR and pump gas. And you WILL NOT get
max HP when you dial it back.
Build a high HP low compression engine that will be durable and reliable on pump gas. Bob
Benson's Pantera has a 411 Windsor Dart block, Brodix heads, Scat crank, steel rods, etc.
and makes 550-600 HP with a CR less than 10:1 (I think it was 9.8:1, but I don't recall for
sure - Bob?)
The point is you can make BIG power with a durable low compression engine and pump gas.
Here's a 9.2:1 CR 2V Cleveland that makes 520 HP on unleaded pump gas:
http://www.kostecki.com.au/articles/art_of_power.html
I think this engine will be much better suited to the way you want to drive your car and will
far outlast your proposed build.
Keep us posted!
Garth
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Mad Dawg Antenucci
Team Pantera Racing
The 1st & still the only vintage race team in open road racing
www.teampanteraracing.com
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Mad Dawg Antenucci
Team Pantera Racing
The 1st & still the only vintage race team in open road racing
www.teampanteraracing.com
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