SpeedTalk Store - Opinion Columns

Ignition timing for a SBC with 18 degree heads

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Ignition timing for a SBC with 18 degree heads

Postby FastBuick » Tue May 31, 2011 11:05 am

I was wondering if anyone has done some dyno testing on a SBC with 18 degree heads and Q16? I was wondering what ignition timing seemed to work the best? Just looking for a range to start in and fine tune from there. Any help is greatly appreciated. Thank you
FastBuick
Pro
Pro
 
Posts: 444
Joined: Fri Nov 12, 2010 9:39 am
Location: Pennsylvania

Re: Ignition timing for a SBC with 18 degree heads

Postby Rick360 » Tue May 31, 2011 11:17 am

What Bore/Stroke? What rpm range? What size dome and compression? These things all affect best timing.

Rick
Rick360
Expert
Expert
 
Posts: 666
Joined: Sun Oct 03, 2004 8:55 pm
Location: Missouri

Re: Ignition timing for a SBC with 18 degree heads

Postby FastBuick » Tue May 31, 2011 11:31 am

Rick360 wrote:What Bore/Stroke? What rpm range? What size dome and compression? These things all affect best timing.

Rick

Drag Race engine
4.190 bore with a 3.625 stroke
Converter stalls at 7000 RPM
Shift at 9000 and goes through the traps at 9200. RPM falls to 7800 after the shift in a powerglide. I footbrake the car on the starting line to a 3800 leave RPM.
15.5:1 Compression with a .125" dome custom JE piston.
FastBuick
Pro
Pro
 
Posts: 444
Joined: Fri Nov 12, 2010 9:39 am
Location: Pennsylvania

Re: Ignition timing for a SBC with 18 degree heads

Postby colebalster » Tue May 31, 2011 2:55 pm

Here's my combo using VP C12 fuel. We tried 28-32 degrees on the dyno and it likes 31 degrees the best. The 108 octane is a little low for this motor and ROM though. We have since switched to C14, but did not play with timing any before it got hurt (unrelated).

4.130" bore
3.750" stroke
.125" Dome
14.5:1 compression
780 Peak Power at 7700 RPM
285/296 @ .050"
.752"/.730" lift


Cole
colebalster
Pro
Pro
 
Posts: 317
Joined: Tue Nov 03, 2009 4:08 pm
Location: Simi Valley

Re: Ignition timing for a SBC with 18 degree heads

Postby FastBuick » Tue May 31, 2011 3:48 pm

colebalster wrote:Here's my combo using VP C12 fuel. We tried 28-32 degrees on the dyno and it likes 31 degrees the best. The 108 octane is a little low for this motor and ROM though. We have since switched to C14, but did not play with timing any before it got hurt (unrelated).

4.130" bore
3.750" stroke
.125" Dome
14.5:1 compression
780 Peak Power at 7700 RPM
285/296 @ .050"
.752"/.730" lift


Cole

Thanks for the info Cole. I would be curious to see if you need more timing for the higher octane fuel. If I understand the theory right higher octane fuels are actually harder to light based on their properties to resist detonation. If you end up dynoing with C14 or other high octane fuels would you be able to let me know what information on the timing you find?

I only have on track testing information. I tried 32 degrees and it worked well in the good air but when the weather got hot and humid I lost a lot of bottom end and throttle response. It actually developed a bog off the line. Changed timing to 36 degrees and the bog went away throttle response was back and the car picked up et in the heat.

Thanks again

John
Last edited by FastBuick on Tue May 31, 2011 3:53 pm, edited 1 time in total.
FastBuick
Pro
Pro
 
Posts: 444
Joined: Fri Nov 12, 2010 9:39 am
Location: Pennsylvania

Re: Ignition timing for a SBC with 18 degree heads

Postby dfree383 » Tue May 31, 2011 3:51 pm

36 sounds like an awful lot of timing, did you try tuning the carb?
User avatar
dfree383
Guru
Guru
 
Posts: 2175
Joined: Fri Feb 01, 2008 7:01 pm
Location: The Sand Box

Re: Ignition timing for a SBC with 18 degree heads

Postby John W » Tue May 31, 2011 3:54 pm

My 440 liked 32° on the dyno. 4.185 x 4.0, 14.9:1 (flat-top), q16, pk hp @7700rpm.
Image
Image
User avatar
John W
Member
Member
 
Posts: 135
Joined: Mon May 02, 2005 1:22 pm
Location: Spring, TX

Re: Ignition timing for a SBC with 18 degree heads

Postby FastBuick » Tue May 31, 2011 4:10 pm

dfree383 wrote:36 sounds like an awful lot of timing, did you try tuning the carb?

Yes I did try tuning the carb and nothing seemed to help it. It isn't like a fuel stumble though. You can barely hear it. It's just very quick. Runs the rest of the track great. Feels almost like a miss or at least a late fire. I have run the carb that way for a while. The only thing that has changed is the timing. I used to run 36 degrees but turned it back because I thought it might be hurting the head gaskets. I found out that lack of water in the middle of the head was the problem. Got them crossdrilled and problem went away.

I also thought that 36 was too high for this head which is why I still worry. I thought 28-32 would be the range. Maybe the bad air requires such a high timing number? We were running in 3500' DA when the problem occurred.
FastBuick
Pro
Pro
 
Posts: 444
Joined: Fri Nov 12, 2010 9:39 am
Location: Pennsylvania

Re: Ignition timing for a SBC with 18 degree heads

Postby FastBuick » Tue May 31, 2011 4:15 pm

John W wrote:My 440 liked 32° on the dyno. 4.185 x 4.0, 14.9:1 (flat-top), q16, pk hp @7700rpm.

Thanks for the info. I wonder how much the piston top affects it? Dome vs. Flat top. I do get very good flame travel across the piston though.

I like your car. Great wheel stand! And it's great to see it was done with a Small Block.
FastBuick
Pro
Pro
 
Posts: 444
Joined: Fri Nov 12, 2010 9:39 am
Location: Pennsylvania

Re: Ignition timing for a SBC with 18 degree heads

Postby Rick360 » Tue May 31, 2011 4:46 pm

I raced/dynoed a 360ci 18º (4.060x3.48). 15:1 domes 52cc chamber. Peak power at 8000. It wanted 37º with C14+. I saw dyno sheets of a Patterson 306ci 18º that wanted 40º.

More stroke & ci or more dome = More timing
Less stroke & ci or less dome = less timing.

I am not sure how Q16 affects timing or burn.

I think 34 would be a good place to start.

Rick
Rick360
Expert
Expert
 
Posts: 666
Joined: Sun Oct 03, 2004 8:55 pm
Location: Missouri

Re: Ignition timing for a SBC with 18 degree heads

Postby colebalster » Tue May 31, 2011 4:54 pm

FastBuick wrote:
1) I would be curious to see if you need more timing for the higher octane fuel. If I understand the theory right higher octane fuels are actually harder to light based on their properties to resist detonation.

2) If you end up dynoing with C14 or other high octane fuels would you be able to let me know what information on the timing you find?


Thanks again

John


John,

1) For the limited knowledge of fuels that I have, I was told the the higher octane had a slower burn rate vs. lower octane. Therefore, you had to run more timing to light the mix sooner so peak pressure in the cylinder would occur at the correct moment.

2) I am still working on the rebuild, and won't have the motor back together for a little while yet. But, when I do I will be on the dyno and I'll run a few different setups to see what happens.

P.S. - I like the power/RPM you're turning with your motor. I can't afford the valve spring budget to turn that many RPMs. I am hoping to get our car dialed in as well as yours when we're done with this motor build. We are changing from a 4800 converter launched on a foot brake to a 6800 converter and adding a trans brake. It should wake things up a little bit.


Good luck,
Cole
colebalster
Pro
Pro
 
Posts: 317
Joined: Tue Nov 03, 2009 4:08 pm
Location: Simi Valley

Re: Ignition timing for a SBC with 18 degree heads

Postby bigjoe1 » Tue May 31, 2011 5:46 pm

When I ran a 900 Hp Pro Stock truck motor ( 358 cubes ) it was best at 29 degrees- very little differance from 28 to 32 degrees, maybe 5 to 10 HP


JOE SHERMAN RACING
bigjoe1
Show Guest
Show Guest
 
Posts: 5175
Joined: Thu Aug 24, 2006 7:16 pm
Location: santa ana calif-92703

Re: Ignition timing for a SBC with 18 degree heads

Postby FastBuick » Tue May 31, 2011 6:20 pm

Rick360 wrote:I raced/dynoed a 360ci 18º (4.060x3.48). 15:1 domes 52cc chamber. Peak power at 8000. It wanted 37º with C14+. I saw dyno sheets of a Patterson 306ci 18º that wanted 40º.

More stroke & ci or more dome = More timing
Less stroke & ci or less dome = less timing.

I am not sure how Q16 affects timing or burn.

I think 34 would be a good place to start.

Rick

Thanks Rick. That makes me feel better knowing that those combinations used that much. It seems as though my combo wants to be in the 36-40 range now. The 360 ci that you dynoed has some of the same characteristics with the exception of the cubic inch. My heads have 53 cc chambers. I believe the C14+ and Q16 have similar properties but the Q16 has slightly more octane and an oxygenator.

I will most likely start at 34 and go up and see where it stops making gains.

Thank you very much for the info.

John
FastBuick
Pro
Pro
 
Posts: 444
Joined: Fri Nov 12, 2010 9:39 am
Location: Pennsylvania

Re: Ignition timing for a SBC with 18 degree heads

Postby FastBuick » Tue May 31, 2011 6:32 pm

Cole,
Your theory on the fuel octane is the same as what I believe to be true so I would hope we're not both wrong lol.

Actually with the right valve train parts the springs will last. The major key is to keep things light. Titanium valves, lightweight rocker arms, and lightweight retainers and locks. Also enough spring pressure also makes a big difference. 400 lbs. on the seat and 1100 lbs open 1.500" springs. The last set of springs had 250 runs when I took them out. They were still good. I only changed them because of the amount of runs.

You'll get yours dialed in. That sounds like a good combo. Let me know how you make out. If you need any help I'd be happy to help.

Thanks

John
FastBuick
Pro
Pro
 
Posts: 444
Joined: Fri Nov 12, 2010 9:39 am
Location: Pennsylvania

Re: Ignition timing for a SBC with 18 degree heads

Postby FastBuick » Tue May 31, 2011 6:40 pm

bigjoe1 wrote:When I ran a 900 Hp Pro Stock truck motor ( 358 cubes ) it was best at 29 degrees- very little differance from 28 to 32 degrees, maybe 5 to 10 HP


JOE SHERMAN RACING

Thank you for the response. The Pro Stock truck engines use the 10 or 11 degree valve angle heads right? That along with the smaller, if any at all, domes should contribute to the low timing number?

It's good to know that there is at least a 4 degree window to hit the right timing where it stays the same or very close.

Thank you

John
FastBuick
Pro
Pro
 
Posts: 444
Joined: Fri Nov 12, 2010 9:39 am
Location: Pennsylvania

Next

Return to Engine Tech

Who is online

Users browsing this forum: brandonu, john kimble, John Wallace, mag2555, redsmokin57, stepside and 13 guests