All! First post here, but I've been lurking for about a year and a half and can say that this is an awesome site.

Her is my situation: I am running a 30 over 427. The short block is basically an L-88, the heads are 990's. THe cam is the Crane L-88 bluprint. While the car runs well I've always seemed to think that it was a little down on power. I've done compression tests, leak down test etc... and evrything checked out ok. The other day i decied to check the balencer. I used a top dead center locator to check the factory groove on the balencer. (brought the engine up to near TDC, installed the TDC checker, brough the piston up contated the stop, placed a mark on the dampener, rotated the other direction, and palced a mark on the balancer.) At this point I expected the factory groove would be half way between the two marks. Its not! I placed a mark on the balencer with a marker and tried to time the engine to this mark, no luck, as I get to about 10* adavced from the new mark I get detonation. Thoughts, ideas, suggestions?

you've found tdc on the balancer correctly, now is the timing tab on the timing cover in it's correct location? if so then the piston stop method should also show that location is correct. How far away from zero was the new TDC mark on the balancer? were you using zero for the reference point when you marked the balancer? Maybe the balancer is continually slipping making your new mark not inaccurate. Is the pinging at idle or cruize or under load and at what rpm?

As Bob said, you have found TDC accurately.
I would ask what you are using for fuel if it is truly an L88?
Anything more than 10 degrees initial with an L88 with today's fuels is probably going to cause problems.

Thanks for the responses guys. I knew that I was not doing something correctly. I did not use zero as the reference point. When using zero as the reference point the factory mark on the balancer is dead on.

Mike, I run the car on VP C-12.

You'd probably like it alot more with medium dome SRPs and a smaller cam!

Mike, the long duration of that L88 cam really bleeds things. If he's at 12.2, DCR should be around 8.6-7, if its down around 11.5, the dcr will be around 8.35 is all.

L-71, when's the next time you'll have the car out to a show or cruise? I'd love to hear it!

Originally posted by 427L88:
You'd probably like it alot more with medium dome SRPs and a smaller cam!

Mike, the long duration of that L88 cam really bleeds things. If he's at 12.2, DCR should be around 8.6-7, if its down around 11.5, the dcr will be around 8.35 is all.

L-71, when's the next time you'll have the car out to a show or cruise? I'd love to hear it! =
Gene,
I realize what the L88 cam does in regards to cranking pressure but I have my own opinions about DCR.
While I don't post it much, here are a few thoughts for you to ponder.

First let me say I think that Pat's DCR calculator is an excellent tool when used with a bit of common sense. :D

Now on to my thoughts about DCR & high compression.

With a big cam you will see lower cranking compression but you also have to use a little common sense with the slam a big cam & lower the DCR syndrome :D
It may have low cylinder pressure at cranking & low rpm's but somewhere it is going to start getting efficient & the engine is going to see whatever compression you have.
If the fuel isn't good enough when this happens ugly things can & eventually will happen.

If the plan is to use & lean on your engine with pump gas most of the time I would prefer to limit the static compression with aluminum heads at 10.-10.5 for 91 octane & 10.5-11 for 93 & change the cam accordingly.

You are right in that cranking compression which is part of the DCR is determined from when the intake valve closes.
The higher the static compression the higher the cranking compression will be the sooner you close the intake valve.
This I think we all agree on.

Now there is a lot of other things that will effect cylinder pressure to a certain extent, like Barometric pressure, cam intensity, engine temp, air temp, humidity & probably a lot of other little things I missed as well.

Here's another thought to screw up the works,,
You can build an engine with say 13.0 & overcam the crap out of it & on paper the DCR will tell you it will run on 91 octane.
The problem comes when that engine gets up in the rpm & becomes efficient & starts actually seeing that 13.0. Now that DCR becomes less of an issue as you are starting to keep pressure in the cylinder & with enough load without proper fuel, it will detonate.

The load part is why lighter low gear cars will usually tolerate more compression than a heavier or higher geared car.

It also works the other way.
We do restricted engines you just could not put a load on at low rpm in most cases.
Small cam hi compression deals like 13.5+ with a cam of say 240 or so @ .050 & at low speeds they will detonate themselves to death if you ain't careful but from say 4000 up they will never see that 13.5 compression as the intake is too small to let enough air in to fill the cylinders :(
Is this enough confusion yet??

Anyway, you are only compressing what is in the cylinder from the time the intake valve closes & this can be completely different depending on a number of things but at cranking speed most of them are listed above I think :confused:

Anyway,,, these are just a few of my uneducated thoughts on the merits of DCR in regards to just using when the intake valve closes.

Someone else can pick up the quench, chamber efficiency & timing issues :D