[DeTomaso] Compression Ratio Question

[Garth Rodericks]

Ok, let's see if I got my flame suite on now.
   
   
  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.
   
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  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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