Freiburger, DCR, and testing.....

[JeffMcKC]

Re: Freiburger, DCR, and testing.....

I have no Idea why you would be using AvGas, that stuff stinks for making power. It has a lot of stuff in it that has nothing to do with making power on the ground.

[BlackoutSteve]

Re: Freiburger, DCR, and testing.....

Funny you should say...
I used 100/130Av while dyno-ing my engine, and George said to try his VP110 stuff.
Well, The power went down slightly and the knock sensor went up slightly even though the Av's specific weight was less as well.
Surprised both of us.

I am aware that the 100/130 ratings are not Research or Motor numbers, but what ever this stuff's R/M numbers are, they must be good enough.

[Eric68]

Re: Freiburger, DCR, and testing.....

Tell ya what Steve, post up your cam specs and static compression ratio and I'll use my "bench racing" DCR calculator to give you a good idea what octane you really need . . . your specs have to be measured, accurate specs though. I'll also take a pretty good stab at what your cranking compression (pressure) is. You can check my prediction of cranking pressure with a gauge and use whatever octane gas I recommend and see if it pings . . .

I need bore, stroke, cam timing both adv and .050 duration numbers + LSA and ICL. See if I am close and then form opinions about whether DCR calculators are worth the trouble or not ;)

[BlackoutSteve]

Re: Freiburger, DCR, and testing.....

Static c/r 12:1
4.00" X 4.28" bore X stroke.
Rod length is 6.136"
Cam is Crane's 138101 http://www.cranecams.com/?show=brows...01&lvl=2&prt=5
The LSA I'm pretty sure is 112°, but the ILC, I'm not sure of off-hand.

I reckon I was able to calculate my required octane reasonably accurately to about 100 (R+M)/2 through blending with pump gas.
I know my cranking compression, but will wait for your guess first.

Also, I will be doing away with AvGas as I have bought a Snow water injection kit. It will be interesting to see if it supports what I have.

Don't get me wrong. I think DCRs are able to assume an octane tolerance through trial and error and comparison. What I strongly disagree with, is their prediction of the actual dynamic c/r in an operating engine. ;)

[Eric68]

Re: Freiburger, DCR, and testing.....

OK, Steve, here you go.

Assuming your static compression ratio is exactly 12.0:1 and your density altitude is 1000' I'm going to say that your cranking PSI will be right about 213 PSI. Using Advertised duration, your DCR is 9.0:1. (if you installed it dot to dot, it is on a 109* ICL)

Now, knowing that your BBC is using an open chamber head (I believe you are) and that you need a decent sized dome piston to achieve 12.0:1 static compression, I know that you will need a fair amount of ignition advance to make max power (I'm guessing 42-44* total advance). Because of the need for a lot of timing advance and your high DCR I would say that you cannot run on 92-93 octane R+M/2 pump gas that we have here in the states. You might squeak by with it if cruising, but I would not race on it. Now if you had a more compact chamber that needed less timing (like a modern chamber SBC) you might just get by with pump 92-93 premium.

Bottom line, I believe that you need 96-98 octane (R+M/2) fuel.

[joe_rocket45]

Re: Freiburger, DCR, and testing.....

[BlackoutSteve]

Re: Freiburger, DCR, and testing.....

All that sounds pretty close. The c/r is 12.03:1, so basically, it's right on 12:1.
The chambers are "open" but are small compared to typical open chambers. They are 112cc.
The pistons have a 36cc dome that is about 0.500" high from memory too.
The cranking pressure is 220-225psi. A little more than your prediction.
The cam is installed "straight up". I dialed it in with a wheel and cam card.

At the track, the car continued to make mph until 40° total. 42° slowed the car, but this was with the previous camshaft, -not that I expect much difference between the two. Who knows, maybe it wanted more fuel to use the 42°..? We didn't get that far.

The 96-98 octane sounds close too. Probably better than I originally suggested
My mix was 33% AvGas (which I was told to be about 104) with 92 pump. This is all using the (R+M)/2 method. (92+92+104)/3=96, so that's good.
There is also a small reaction that you get when you mix high octane unleaded and with leaded, which apparently gives about a point. I read this and Shell confirmed it when I called too.

[Eric68]

Re: Freiburger, DCR, and testing.....

Yep, looks like we're in the ball park. So if you had not actually built your engine yet and used just the specs and the calculator, you would at least have an idea what to expect. You could play with cams and compression ratios too to either bring the cylinder pressure down enough to run pump gas or go the other way adding compression and cam for a race gas build.

BTW. Happy New Year guys! Did anyone else enjoy the Orange Bowl (Capital One Bowl) Michigan / Florida game as much as I did? That was better than the Rose Bowl! Especially since the Wolverines won!

[ls7gto]

Re: Freiburger, DCR, and testing.....

BTW. Happy New Year guys! Did anyone else enjoy the Orange Bowl (Capital One Bowl) Michigan / Florida game as much as I did? That was better than the Rose Bowl! Especially since the Wolverines won!

Eric, that was a great game, I drive by Henne's high school everyday, and worked with his cousin. It tough being a BIG BLUE fan in this penn state area.
Now back to the subject, this has been very inforitive and comfusing.

[Saltfever]

Re: Freiburger, DCR, and testing.....

(snip . . .) It's a percentage: 8 divided by 1. The pressure at peak compression will be 80% greater than it is when the intake closes (I'm simplifying other factors out of the picture for clarity, of course). That does not change according to density or pressure in the cylinder at the start of the process (when the intake closes). The number of air and fuel molecules in the cylinder is fixed at that point, and the ratio of compression or percentage of compression will not change.

Geeze, I turn my back on this thread for one day and you guys add two pages! I feel left out ;D

I believe that would be either 8x or 800%, but not .80, David. But we know what you mean. ;)

[Saltfever]

Re: Freiburger, DCR, and testing.....

Wow! Somehow we got 7pgs of dcr debate on a new forum! And everyone is arguing again but not really disagreeing.

Not an argument, it has been a great discussion! Contrary to some other blogs, the people on here are intelligent, sophisticated, and forward thinking! Oops! Leave Keith Turk out of that last comment! ;) Happy new year gentlemen.

[BlackoutSteve]

Re: Freiburger, DCR, and testing.....

Amen brother.. ;)

Now, let's boogie! http://www.youtube.com/watch?v=v0BCQAFWNiA :D

[Barry_R]

Re: Freiburger, DCR, and testing.....

I've been reading along with some interest. I'll admit that I never bought into the mis-named DCR deal. Way too many uncounted variables - OK for directional info I guess, but not an "end all" by any stretch.

I don't pay much attention to cranking compression either ever since my 428 CJ engine in the bad old days came up with scary low numbers - like 130 - and still tossed my 3600+ pound tank into the 11s on pump junk.

My current EMC FE Ford made 661HP on 91 octane at 429 cubes, 10.5:1, flat tappet solid, single 4, N/A, etc. That darn motor has more tricks than a Holiday Inn magician - none of which show up on DCR. Maybe I can find more - its never been on a computer yet

[JeffMcKC]

Re: Freiburger, DCR, and testing.....

Just because it low does not mean it wont run, but it might run better LOL

[Freiburger]

Re: Freiburger, DCR, and testing.....

Eric's demo shows me up rather nicely, though I wish I'd had a chance to give a wild-ass guess on the spec beforehand cuz I think I would have been about as close.

Interesting that the other calculator gives an entirely different answer.