[Mike S]

I had a 10.0 race this weekend. Had a tuff time slowing car to go 10.0's. I had a bye run during eliminations so I took 4 degrees of timing out to slow it down. So went from 38 to 34. I lost 12mph in the 1/8 and slowed up .67 in the 1/8. Can't go by 1/4 mile since I was on the brakes all day.
38 degree 60' 1.380
1/8 6.297 / 108.31
34 degree 60' 1.471
1/8 6.975 / 96.30
back to 38 60' 1.393
1/8 6.326 / 108.06

I did not think 4 degrees of timing would take away that much hp. It felt very flat. Is this a normal result?
I have 12-1 comp with e-heads and using VP c12.

PS. I qualified last. Took out no. 1 first round. I was on the brakes hard all day. Had my best run in the finale .002 light and ran 10.003 to his .007 light and 10.010 take the win.

[ponjohn]

Way to go Mike.

[Half-Inch Stud]

....still looking for someone to post a HP vs Total advance plot.

[cosgrove]

Winners keep getting better all day. Nice final round!

[dammen8]

I was just on the dyno and found out that 6 degrees was worth 66hp on my combo... this was with highports.. not sure if that helps.

Chad

[steve25]

As you Hone in on fine tuning your combo and especially once you hit the 12 to 1 compression point, then a 2 degree timing change SHOUD make for a surprising change in power, as should a 1 degree change in the closing point of the Intake valve by means of degreeing!

Next on the list would be valve lash, and yes this all assumes that the fuel curve is kept in check.

Nothing boils my water faster than reading a post that someone made a Manifold change to supposedly make a A/B comparison either at the track or on the Dyno and the same Carb was used without even seing if there was a need for a jetting change!


Sorry for getting a tad off subject here!

[CraigG.]

What combo mike?

[CraigG.]

A very interesting question - Tom V and other more expert members?

[Mike S]

It's a 455 .040 with flat top pistons. E-heads with 72 cc chambers flow 330 at .700., Victor intake with 1050 holley. Cam is solid roller 282/286 .650/.652 lift. 2" headers into 3.5 x pipe and mufflers. TH400 with brake, 8" convertor stalls about 4900. 4.10 gears in a 12 bolt with stock suspension. Weight 3200 with no ballest.
I found, it likes 40 degrees timing but I keep it at 38 just to be safe. A lot of people think 40 is to much so I turn it back a tad.
Also found it likes to be a tad lean at 13.1 af.
Also found it runs better on VP C12 than VP 110.

This past race I had 140lbs of ballest and had a tuff time slowing it to 10.00. I was hitting the brakes at the mph cone to run 10.00/124. This weekend the car was hooking like it never did, that was part of the problem. Had my best 60' ever Saturday with a 1.33.

[Tom Vaught]

Originally Posted by CraigG.

A very interesting question - Tom V and other more expert members?

People get greedy with timing, especially boost guys.
If you start the process a bit late you do not get the maximum pressure in the cylinder (pushing on the piston/crank) vs the optimum crank angle for turning the crankshaft.

If you start the process too early then you are actually doing more work compressing the charge that you need to do and you also run out of 'push" on the piston before you reach the optimum angle on the crank.

So the data posted make sense as that engine combination would really like 40 degrees but when you take 6 degrees out you are now at 34 degrees and the combustion pressure is pushing a lot less on the piston/crankshaft vs where the ideal point should be.

You typically don't hurt stuff like you do with too much timing but you lose power quickly with less than ideal timing.

Tom V.

[p4msi1]

Deadly runs, man!

[steve25]

The higher a motor is in compression , the faster the peak cylinder pressure goes away as the piston descends the bore.

Having the needed dead on timing to max things out is way more a narrow thing on a motor above 11 to 1 comp then a motor with with less then 11 to 1!

This is why guys with motors of 9.6 or less never find more then a 12hp gain in power over even a 4 degree range unless they have there Cam closing the Intake valve right where it needs to be, and are not over scavenging the motor by means of there Cam and Exh system combo.

[CraigG.]

Thank you steve25 and you guys.

I also wonder what effects the type of fuel has on the rate of burning (over-simplification) and timing - e.g. VP C12, VP 110, Unleaded 93 and E85?

Thanks again, Craig

[steve25]

Any more octane then what your motor needs to not detonate at full throttle and normal engine temps will only serve to cost you power.
That being said long motor life comes from running the motor 3 to 5% detuned from max, be it by means of octane, timing or both!

[johnta1]

I found, it likes 40 degrees timing but I keep it at 38 just to be safe. A lot of people think 40 is to much so I turn it back a tad.

Don't think your engine cares what other people think?



It definitely told you what it thought of the 34º?


Your engine alone is what matters.

I'd try 42º and see what it does.



Retarded timing is a real killer on an engine.
(especially if the AFR is off or octane of fuel is off)

[slowbird]

Originally Posted by CraigG.

Thank you steve25 and you guys.

I also wonder what effects the type of fuel has on the rate of burning (over-simplification) and timing - e.g. VP C12, VP 110, Unleaded 93 and E85?

Thanks again, Craig

Fuel does play a roll in timing, depending on what fuel im running my timing is anywhere from 28-32.

I think 100hp from 4° is very extreme, unless you detenating the engine then you could see 100hp.

[CraigG.]

Mike, I have a combo similar to yours except for the bigger cam and I use E85 - so very interested in the thread. Have you used e85 and any experience with differences in timing over gasoline - perhaps it's own thread?

If anyone has more sources of information on the timing - fuel - horsepower question, please advise.
Thanks again, Craig

[Torment]

Also keep in mind this 'back to back' was not on an engine dyno in a controlled environment, it was in a car on a track. The reduced power at peak torque, for example, may cause the converter to act tighter reducing RPM and power to the tire. Average power to the tire during the run is what the MPH is telling you. On an engine dyno maybe that 4 degrees isn't 100hp, but the net effect of the combination of parts in the chassis is what you saw.

[Tom Vaught]

Originally Posted by Torment

Also keep in mind this 'back to back' was not on an engine dyno in a controlled environment, it was in a car on a track. The reduced power at peak torque, for example, may cause the converter to act tighter reducing RPM and power to the tire. Average power to the tire during the run is what the MPH is telling you. On an engine dyno maybe that 4 degrees isn't 100hp, but the net effect of the combination of parts in the chassis is what you saw.

Very True.

Without Kistler Cylinder Pressure Sensors installed in the head to read the actual combustion pressures you are really guessing about the sum of the effects going on at the track.
Several have made posts with some of the valid reasons why the engine was down on power.

The actual PUSH on the piston and how efficiently it pushes and for how long is totally based on the combustion event, the flame speed, and when it happens (starts and finishes).

Tom V.