Bill/APEX Motorsports
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- Nov 6, 2000
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(I decided to start a new thread, as it was--ahem--going astray.)
The following quote is from Ben Treynor:
"Compression ratio unknown; compression test went from 165 to 195-200, which is about 10:1 per APEX. Car runs geat on CA pump gas, no detectable detonation during dyno runs (and we were listening for it!)"
We did, indeed, check the compression on Ben's Hennessey-modified cylinder heads. First of all, let me say that 165psi, which is what we usually see on stock heads, is pretty low for the supposed 9.6:1 compression ratio. 9:1 5.0 Mustangs are typically 160psi, and 9.85:1 DOHC Cobras are between 195-210psi, really consistently. It seems to us that the ratio from Dodge is overstated. No worries, though, as the cars make every bit of their stated hp.
Therefore, it leads us to believe that the Hennessey heads are around 9.8-10:1. Again, that doesn't worry me, as they made the impressive hp numbers that John promises. He said they took off .050" from the deck surface to increase the compression ratio. The supplied pushrods were too long, so, using our adjustable pushrod length checker, we determined the correct length and procured new pushrods so the T&D rocker tip resided on the proper portion of the valve tip. (John had no problem crediting Ben for the pushrods once he receives them.)
So, it appears to us that the stock compression ratio might not be 9.6:1. Oh well. Ever hear of the '99 Mustang Cobra debacle? That cost Ford millions of dollars because the Cobras were about 20hp shy of their "new" rating of 320hp. At least Dodge's hp numbers are on the money, and Hennessey's products again performed exactly as stated.
The following quote is from Ben Treynor:
"Compression ratio unknown; compression test went from 165 to 195-200, which is about 10:1 per APEX. Car runs geat on CA pump gas, no detectable detonation during dyno runs (and we were listening for it!)"
We did, indeed, check the compression on Ben's Hennessey-modified cylinder heads. First of all, let me say that 165psi, which is what we usually see on stock heads, is pretty low for the supposed 9.6:1 compression ratio. 9:1 5.0 Mustangs are typically 160psi, and 9.85:1 DOHC Cobras are between 195-210psi, really consistently. It seems to us that the ratio from Dodge is overstated. No worries, though, as the cars make every bit of their stated hp.
Therefore, it leads us to believe that the Hennessey heads are around 9.8-10:1. Again, that doesn't worry me, as they made the impressive hp numbers that John promises. He said they took off .050" from the deck surface to increase the compression ratio. The supplied pushrods were too long, so, using our adjustable pushrod length checker, we determined the correct length and procured new pushrods so the T&D rocker tip resided on the proper portion of the valve tip. (John had no problem crediting Ben for the pushrods once he receives them.)
So, it appears to us that the stock compression ratio might not be 9.6:1. Oh well. Ever hear of the '99 Mustang Cobra debacle? That cost Ford millions of dollars because the Cobras were about 20hp shy of their "new" rating of 320hp. At least Dodge's hp numbers are on the money, and Hennessey's products again performed exactly as stated.