Yellow Bullet Forums banner

1 - 20 of 114 Posts

·
Registered
Joined
·
4,181 Posts
Discussion Starter #1
Maybe we can have a discussion on timing and what makes some motors want more or less of it.

IMO:
-Spark plug location
-Chamber design & Shape
-Chamber size


I also wonder how much cam events effect this?

Quench?


Lets see where this goes.
 

·
Registered
Joined
·
803 Posts
Maybe we can have a discussion on timing and what makes some motors want more or less of it.

IMO:
-Spark plug location
-Chamber design & Shape
-Chamber size


I also wonder how much cam events effect this?

Quench?


Lets see where this goes.
Don't forget piston shape, fuel type/octane/atomization, air density/quality/altitude, RPM, rod length, and so on just to name a few more.
 

·
Registered
Joined
·
4,181 Posts
Discussion Starter #6
In general, less. I agree, there might be a bunch of things that contribute. Maybe we should break it down a little.

What things will have a major effect on timing? (Within the design, components and Variance)

What would make it less or more sensitive to timing?
 

·
Registered
Joined
·
1,013 Posts
In general, less. I agree, there might be a bunch of things that contribute. Maybe we should break it down a little.

What things will have a major effect on timing? (Within the design, components and Variance)

What would make it less or more sensitive to timing?
In my eyes two things mainly control it

Piston design has a huge part in it. A flat top would require less timing than a domed piston. The flame front has to travel over a dome thus slowing the flame front down. As where a flat top would have a faster burn due to nothing slowing it down.

Chamber shape and valve angle would be another big area to look at. A 9 degree head would need less timing than a 23 degree head.

To me this is why you see a large dome and a big chamber in most nitrous motors and a flat top and a smaller chamber in most N/A motors. A flat top and. A shallow chamber is more efficient.
 

·
Registered
Joined
·
4,181 Posts
Discussion Starter #8
I agree with some of this for sure.
But I have ran a few 15*, 18* and the older -12 Brodix heads(15*) liked more timing than my other 15* or 18* stuff.
IMO The spark plug location had the biggest effect. As the chambers were very close to the same in size and shape. Even with the same exact piston(we used the same short block).

This is where I would like to talk about some different thing's and see if we can come to a good conclusion to what and why.
 

·
Registered
Joined
·
1,013 Posts
I agree with some of this for sure.
But I have ran a few 15*, 18* and the older -12 Brodix heads(15*) liked more timing than my other 15* or 18* stuff.
IMO The spark plug location had the biggest effect. As the chambers were very close to the same in size and shape. Even with the same exact piston(we used the same short block).

This is where I would like to talk about some different thing's and see if we can come to a good conclusion to what and why.
Would it be safe to safe to say a more central plug location would offer more even burn in turn being a faster burn?
 

·
Registered
Joined
·
401 Posts
When i first started with my A-460 headed engine 5 years ago it liked 32-34 degrees timing. 4.3 stroke, 4.440 bore 15-1 compression on C-14+ 930hp. Next change went to methanol, some head work and new pistons and camshaft. Similar compression but a little flatter dome. 28 degrees timing and 1000 hp. Next i went back to gas had more headwork done same valve sizes just port and chamber work and titanium valves put in and changed to 4.15 stroke 4.5 bore. Took a mold of the head and had diamond make a piston max compression 17-1+ it needed 36 degrees timing 1060 hp. Had more headwork with larger intake valves installed, new camshaft, lost a tiny bit of compression, got rid of that ugly spark plug hole in the pistion, smaller valve reliefs and flatter piston. 34 degrees timing 1117 hp on C-16 1172 on Q-16 I wish i new what it was that made it happy with 28 degrees 3 years ago. I have made the head more efficient payed alot of attention to flame travel and require more timing. Timing is the same on Q-16 and C-16. I was hoping to get timing in the 30-32 range with my piston change but failed.
 

·
Registered
Joined
·
836 Posts
I'm ready for some explanations. I have a 15* victor headed sbf . It made peak power at 31 degrees. The old guys keep busting on me about the timing they ran back in the day. They think I'm crazy and should turn it up. I have some understanding of why but this is perfect I can't wait to read this to the dinisoars .
 

·
Registered
Joined
·
7,238 Posts
I'm ready for some explanations. I have a 15* victor headed sbf . It made peak power at 31 degrees. The old guys keep busting on me about the timing they ran back in the day. They think I'm crazy and should turn it up. I have some understanding of why but this is perfect I can't wait to read this to the dinisoars .
As a dinosaur...if you really got your act together, 26 is a good number.
 

·
Registered
Joined
·
796 Posts
Rod length play a part, Longer rod more time spent at or near TDC? Also,, I just came off dyno with my SBF, curious as why with timing above 32* it made more average power, but crankcase vacuum suffered. I understand ring seal was compromised, if making power what causes that?
 

·
Registered
Joined
·
4,181 Posts
Discussion Starter #16
When i first started with my A-460 headed engine 5 years ago it liked 32-34 degrees timing. 4.3 stroke, 4.440 bore 15-1 compression on C-14+ 930hp. Next change went to methanol, some head work and new pistons and camshaft. Similar compression but a little flatter dome. 28 degrees timing and 1000 hp. Next i went back to gas had more headwork done same valve sizes just port and chamber work and titanium valves put in and changed to 4.15 stroke 4.5 bore. Took a mold of the head and had diamond make a piston max compression 17-1+ it needed 36 degrees timing 1060 hp. Had more headwork with larger intake valves installed, new camshaft, lost a tiny bit of compression, got rid of that ugly spark plug hole in the pistion, smaller valve reliefs and flatter piston. 34 degrees timing 1117 hp on C-16 1172 on Q-16 I wish i new what it was that made it happy with 28 degrees 3 years ago. I have made the head more efficient payed alot of attention to flame travel and require more timing. Timing is the same on Q-16 and C-16. I was hoping to get timing in the 30-32 range with my piston change but failed.

This very good and right up with what Im talking about, kinda.
"What caused this"

Were the cam's the same in this build?
What all was done to the combustion chambers?
What type of quench did you have?
 

·
Registered
Joined
·
4,181 Posts
Discussion Starter #17
For the guy's that have had a bunch of stuff on dyno's. And run a bunch of the same head on different combo's or just big changes in cams. Does the cranking compression have effect on timing?

I see how there can be a relationship between cam timing events, as this controls cylinder pressure and effective explosion.

Is timing controlled by these events in relationship to crank position?

How important is timing in relationship to power?
 

·
Registered
Joined
·
796 Posts
I changed the cam only, more lift, more duration, wider LSA(only because I can't remember all events for both cams), and more overlap. I put IVC as close to the first cam as I could, trying to keep cylinder pressure up. Total timing was same, made the same flat tq curve, rev'd higher, made more hp, didn't fall flat after peak.
 

·
Registered
Joined
·
401 Posts
This very good and right up with what Im talking about, kinda.
"What caused this"

Were the cam's the same in this build?
What all was done to the combustion chambers?
What type of quench did you have?
This engine has had 4 different cams in the last 5 years. It did however have the same cam when it required 28 and 36 degrees timing. It got a cam change mid season when i hurt a piston. Had new valve guides installed and a fresh valve job. The valves got countersunk too deep and the guides pertruded to deep in the intake runner, killing alot of flow. My head guy was swamped so i went to the guy who had time. Put it back together and it required the same 36 degrees of timing but gained tiny bit of power with cam change. When i changed from the 4.3 to the 4.15 stroke i changed rod length from 6.660 to 6.800. That is a large difference in piston speed and at the same time put a crazy dome on the piston. The heads are older A-460 heads so the chambers did get a bit of a workover. Improved the swirl around the intake valve to not wash out the plug and send the charge right out the exhaust. Looks alot like the newer heads in design but a smaller chamber. I think its 76 cc right now ( changed a few times but biggest change done right before it ran 28 degrees timing.)
 

·
Registered
Joined
·
836 Posts
As a dinosaur...if you really got your act together, 26 is a good number.
Yeah there's so much to learn. I'm sure the dinosaur's... know why I'm running less timing, they just want me to figure out why. 26 degrees huh , well I'm too tired to wrap my brain around it right now but it's now on my list of why and how come.
 
1 - 20 of 114 Posts
Top