Exhaust valve not opening soon enough?

 

not all cylinders just one or two Like the corners on a SBF, or diffent motors that have one cylinder that burns hotter than the rest

 

Uneven water flow , on our AMC;s we run lines from the back to the front on the intake to connect the water ports together and it keeps them all within 5-10 degrees now....before was 40 degrees between the water port on the very back to the very front.....ive heard of some chevy guys running a reverse water pump i believe to feed the heads first then the block to help with this...

 

Here's my opinion:

In most cases, especially with a cast intake, single carb, plate kit situation, I think that the center four cylinders are getting a little more fuel than the corners...by the sheer physics of design. Due to that, the burn speed across the chamber/cylinder on the center cylinders is slightly slower than the burn speed at the corners. I think that in a situation where you are creeping timing into a motor to squeeze every bit of e.t. out of it, the corner cylinders become overtimed first and instead of peak cylinder pressure occuring at 15-20* ATDC (where it needs to be), it ends up occuring at maybe 5-10* ATDC...so instead of the pressure having good leverage on the crankshaft...it's pushing down too soon and the energy is wasted making a bunch of heat.

 

I would think LOTS of variables, but especially head port messaging, and bottomline, cylinder compression, causing temp variances. On our 638, as an example, per the data logger EGTs, our #4 & #5 holes are the hottest. So...we take out .5* out of both of those holes via the MSD ICT. This helps balance the holes out, for a more efficient n20 tune.

 

I thought taking timing OUT of a motor would actually make EGT's go higher?

 

It is all about cylinder efficiency and burn rate. In a perfect world, an 800hp would make 100hp per cylinder, but that is not the case. Very few cylinder heads have symetrical ports and no intake, short of a tunnel ram, has equal length and shape runners..................so the problem with "hot" cylinders, is all about burn rate. As I have said many times, it is not that the centers are rich and the corners lean................. lean/rich, has little, if anything to do with it. It is all about cylinder efficiency and burn rate. If a cylinder is more efficient, it has a faster burn rate and requires less timing than the others.

Monte

 

It is all about cylinder efficiency and burn rate. In a perfect world, an 800hp would make 100hp per cylinder, but that is not the case. Very few cylinder heads have symetrical ports and no intake, short of a tunnel ram, has equal length and shape runners..................so the problem with "hot" cylinders, is all about burn rate. As I have said many times, it is not that the centers are rich and the corners lean................. lean/rich, has little, if anything to do with it. It is all about cylinder efficiency and burn rate. If a cylinder is more efficient, it has a faster burn rate and requires less timing than the others.

Monte

Is there an ignition system that will allow you to set the timing for each individual cylinder?

 

Hey Jeremiah...you are right. It seems to me, that is the difficulty with interpreting EGT #s ALONE, which we never do...we look at the plugs as our primary tuning tool, & just reference the EGTs (or 02 A/F). High EGT #s can be from not enough timing advance, causing the fuel to be burned late in the headers...so retarding the timing more which just compound the problem. The solution: plug reading & timeslip comparison. All just my 2 cents from track experiences. Good luck.

 

I just had number one show up hot on my tunnel ram conventional head bbc. I need to cut them and take some pics, but number one had the heat mark at the bend look to it and number three didn't even burn the cad off. Car ran great, but a little confused by the plugs. It was extremely hot, like 185 in the stage beam, could this alter the plug read?

 

In alot of cases when you pick up ET because the coolant was a little warmer is because your tune is on the fat side and heat in the motor helped burn the fuel. Thats just what i've seen in the past but others might have a different opinion.

 

I definetely agree that if the ET drops with increased water temp, you probably have too much fuel. In this case, it was a last ditch qualifier and I stepped on it a touch. Basically ran what I thought it would, maybe .5 MPH short at the 1/8. Tune wasnt a total shot in the dark, so I was pretty confident I had a couple degree cushion for the conditions. Definetely got my attention when I pulled the first plug out and saw what I would consider a perfect heat mark (even though I know there is no such thing). Had me concerned about what I would find in the rest of the motor.

I was running out of plugs, so had autolites in a few holes to at least get a fuel read, but the rest of the NGKs showed little to no heat.

 

Some classes like top sporteman and dragster want the one with traction controll detection.7530T I think.I have never seen anyone look though.

 

I think that was the conversation. devices that have a traction control.
Thanks