Question about my Dynamic number

Looking for some advice from the masters in here ;)

Ok I ran my combo and it's coming in at 9.79:1 for the DCR. Will I be able to pull off the switch down too pump gas... 93 octane?. I picked up a water injection system and will be adding this to the package. My next thoughts are about wot timing and how much to start with. On motor I'm thinking 30 degrees and on hose 22 degrees on a 200 hit.
I'm thinking of opening up the coolant bleed pipe assembley to a -6 line assembly in place of the tiny factory stuff used. I'm doing this in hopes of adding a little more coolant flow in the heads.

Thoughts and advice welcomed :)

Is this with a solid roller or a hyd roller?

9.8:1 DCR is really high Hawk! How did you get at that combo?

Bret

Spoke with a few people (including the makers of Evans coolant) about the bleed line myself with the same interest.

I was told that line is for essentially preventing vapor pockets & enlarging it would reduce coolant flow downward through the block by bypassing it back to the rad, reducing potential cooling insted of improving it. Flow would go in the front of the head & out the back instead of through the block.

This is opposite of the added coolant lines on a conventional SBC where this is an improvement.

Spoke with a few people (including the makers of Evans coolant) about the bleed line myself with the same interest.

I was told that line is for essentially preventing vapor pockets & enlarging it would reduce coolant flow downward through the block by bypassing it back to the rad, reducing potential cooling insted of improving it. Flow would go in the front of the head & out the back instead of through the block.

This is opposite of the added coolant lines on a conventional SBC where this is an improvement.

Wow, thats interesting. I opened up the passage and put the larger line on my old combo with the thought of having more flow being better.

I thought the exact same thing & by chance this came up in conversation.
After thinking it out, it makes sense.

I used to modify old SBC's with external lines back to the 'stat housing from the top & bottom centers of the heads...... Brodix heads even comes with tapped holes ready to install them. This modification on an LT1 seemed a natural, until further thought proved otherwise.

Is this with a solid roller or a hyd roller?

9.8:1 DCR is really high Hawk! How did you get at that combo?

Bret

I used my info on the dcr calculator at smokeumup.com and it gave me the number. Here's a screen print of it www.hotrodhawk.com/dcr.htm
Could this be incorrect?
The cams a hyd roller

My actual cranking compression on a guage is 190 . The motor temp was around
120 when I took the readings.

Thank you Lonnie for that info on the coolant line, I'll steer clear of the bigger line mod.

Jeff, Which head gaskets are you running?

Hawk,

Your using the intake valve closing at at .050", you have to use the actual closing point of the valve and it will give you the right DCR.

What's your static compression, cubes, rod length and intake lobe/specs?

Bret

My bad Ken the cometics I'm using are 4.040 bore/ .040 thick.
That will bring the number down alittle.

Bret
Static compression 12.9,355 cubes, 6" rod length and Comp #3317s intake lobe @ 112.

Hawk,

That works out to a 8.72:1 DCR

Try 81 for the closing event on your calculator and you should get close to that.

Bret

Thank you Bret :)
..so would you say she's safe for 92 octane with the above total timing?
I'm about ready for "tires to pavement" this coming weekend and looking forward to some much needed HP under the right foot :D

Thank you Bret :)
..so would you say she's safe for 92 octane with the above total timing?
I'm about ready for "tires to pavement" this coming weekend and looking forward to some much needed HP under the right foot :D

30 degs total is pretty light so I would say you should be safe with that. If that's with the LT1 ECU then who knows what the timing really is, but if that's with a distributor or aftermarket ECU then you could start there and creep up on it. If you have any issues with knock it will be below TQ peak, but at the top end it's probably not going to happen.

Bret

THANKS Bret for your time :bigbigsmile:

Not a problem Hawk, I want to see how that puppy does this year.

Bret

If that's with the LT1 ECU then who knows what the timing really is, but if that's with a distributor or aftermarket ECU then you could start there and creep up on it.Bret


whats the deal with the LT1 ECU?

Lord look over me as I train wreck my own thread ;)...

If you set total wot timing to lets say 24 degrees and there is no knock detected while in a pass it will add timing till burst knock is detected then it pulls it back down till knock activity has stoped. The timing control of the factory LT1 ECM is closed loop and with the opti's Hi-res signal it makes it all happen. Bret have you tried zeroing the data in the Minimum spark advance table. It seems that this is where the additional timing comes from at least in my testing/log files from wot testing.

Man I'm not the guy to ask about that thing. Those ECU's are not my favorite thing. A good Big Stuff, DFI or FAST always seems like the way to go with me. They are made to be user friendly, don't have a rev limit etc..... Hell a carb and a MSD Pro Billet Digial looks like a better way to go to me.

The thing I never get is you set the timing on the tables and then pull out a timing light and read it or even data log it and it doesn't correlate, WTF is that all about?

Bret

Thank GM for that ;) Jim and I mapped it out. I think Hawk is on to the right tables. it is RPM based. I hav enot looked in a While I just always know the curve so i punch in the numbers as needed ;)

damn, i have never even heard of that before!

Bret have you tried zeroing the data in the Minimum spark advance table. It seems that this is where the additional timing comes from at least in my testing/log files from wot testing.
This being on your '94, so you are referring to an OBD I pcm correct? Is this also a trait of an OBD II LTx pcm?

I've not toy'd with a obd2 just obd1 stuff but I'd still think it would apply. On a OBD1 the table is named Minn spk advance and from zero RPM too 4000 RPM the data is set at zero advance then from 4400 rpm to the upper limit it's set at 10 degrees on a factory tune. Think of this table is a "adder" table to the base timing table[s] named "load vrs advance". If no burst activity is picked up by the Knock sensor it will add additional timing up too the value entered in minn adv. The rate of the advance is based off of the data in the attack vrs RPM and decay vrs RPM tables for retard.

...oh my head ;)

TRy setting min advance too zero in all fields on hose/boost tunes.