Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - DCR Calculation
Thread: DCR Calculation
View Single Post
  #23 (permalink)  
Old 01-18-2013, 01:56 PM
1Gary's Avatar
1Gary 1Gary is offline
Registered User

Last journal entry: 383 dyno sym
Last photo:
Join Date: Oct 2010
Location: Roch,NY
Age: 69
Posts: 1,572
Wiki Edits: 0

Thanks: 201
Thanked 157 Times in 143 Posts
Originally Posted by F-BIRD'88 View Post

Your cr counds out the 11.48:1 but I have reservations on some of the stuff.
Like how you got valve to piston clearance with a tiny single valve relief of 1 cc.
Some of it seems od to me..

Any idea on the fuel specs beyond "98 octane" rated.

Here , our fuel is rated as a average of the two different bench tests.
R and M... Motor octane is always lower and emulates a engine more accorratly under load in the car.

We do have a 98 octane R+M/2 pump gas here at some limited gas stations.
Sunoco GT-98. It generally is good for a 11.5 to 12.5:1cr engine if the tune and conditions are good. It is not readily available.
Here we also have a 100 R+M/2 octane unleaded sold at very limited locations some stations.
Delta Sonic---- it is Sunoco GT-100 sold as "CAM2" Its good stuff.

Our 94 octane premimum is quite good. I cannot tell you the absolute cr limit.
Some people get in trouble around 10.00:1 some have better luck with a bit more cr up to around 11:1. Beyond that it is real hit and miss. Depending on daily conditions and tune up.

many many stations in the US in particular sell very inconsistant fuel quality and octane. Many epople have touble even at les than a 10:1 ratio their local pump premimum gas. Especially in the Mid West states.

I do know that your fuel is rated differently than ours. And that generally the European fuel and oil quality standards are higher
than North America.

Having been there done that... I always warn people to take all this DCR stuff with a grain of salt when planning a engine build for pump gas for true street driven use.

Had a friend here that bought into the DCR stuff hook line and sinker and even after ignoring my warning and explaination of the hows and whys,,, destroyed two perfectly good 350's @ 10.70:1 cr. What happended was exactly what I predicted would happen. We rebuilt them with 9.8:1 and all was good..

I built on a t 12.65:1 with plenty of cam etc etc.. it went fine for a while on 94 with conservative (reduced) timing, but really liked and wanted 110 unleaded.
Came unglued on me one day when I forgot to reduce the timing for 94 pump gas use. Never heard a thing.
Broke a ring land. But it was fun. ( On this one I knew perfectly well that the 94 octane fuel was not going to be enough for this engine so no surprise) Like said it really liked and need the 110 octane unleaded. Went like a raped ape....

I suggest you tread lightly on it with pump gas. (watch the water and engine air inlet temperature)
stay off the throttle or reduce the timing a bit if when conditions are not optimum.
As the engine ages the octane requirement will go up. (carbon buildup- oil consumption, deposits in the combustion chamber)

Do you have any way to detect detonation @ WOT? "engine ears" or a knock detector?
I built my own amplified "engine ears" for under $50. Unfortulatly on that day I smoked that 350 I did not have my "ears" on.
Now I am reading your words,so let me see if I got this right.You have blown up three engines because of poor parts choices ignoring DCR's in one of them and trying to use the DCR formula in two of them which is a band-aid repair.The concept of the use of DCR's formulas is to formulate a build in advance of purchasing those parts not afterwards.Then because of poor driver feel not knowing a engine at the top end is leaning over on the top end,you suggesting a devise"engine ears" to detect the mystic of detonation which if DCR's where properly applied in the first place would have been on a bucket list checked off so as not to be a problem.

I am going to suggest this "old school" thinking doesn't work and I came from that time period.When the gas changed it was a game changer.That that type of thinking needed to change with it and no less the use of DCR formulas is in no small was a huge part of moving forward.Not backwards.

I am for the record suggesting with a admitted history of three damaged engines because of poor execution of the DCR's formulas is enough proof that if applied correctly wouldn't have happened.

I am also saying for the record that a DCR of no more than 8.5 is disheartening to me as well.It does sound low,doesn't it??. But it is what is. And we all have to learn to accept it or end up paying for the consequences.
Reply With Quote
The Following User Says Thank You to 1Gary For This Useful Post:
GunnerTHB (01-18-2013)