Ignition timing for a SBC with 18 degree heads

[T-flow]

One of the motors we run is very close to Cole's and it's right in line with his timing aswell. We run 406ci 15* at 32 degreee's , some of the other engines with 15* heads, some 360+ ci - 412ci like 31 degree's timing. Any where from 28-34 should be good to start.


T-flow

[FastBuick]

One of the motors we run is very close to Cole's and it's right in line with his timing aswell. We run 406ci 15* at 32 degreee's , some of the other engines with 15* heads, some 360+ ci - 412ci like 31 degree's timing. Any where from 28-34 should be good to start.


T-flow

Thank you for the info. What fuel do you normally run when you dyno these engines? How much does the timing change as you increase the octane?

Thanks

John

[T-flow]

1-3 degree's, just depends on the whole combo.
110-NOS fuel, not sure about the Q16. Just tune as normal, I think you should be fine.


T-flow

[FastBuick]

1-3 degree's, just depends on the whole combo.
110-NOS fuel, not sure about the Q16. Just tune as normal, I think you should be fine.


T-flow

The Q16 has a MON value of 116 and a RON value of 120+ and an average of 116 which should make it burn slower than the 110 NOS I believe. From what I understand the properties of the fuel that protect it from detonation actually make it burn slower or later. Higher octane slower burn or higher heat to make it burn. Also with Q16 you have to use at least 6-8% more fuel because of the oxygenator which also adds some octane numbers.

It seems as though a lot of people can run 32 degrees of timing and have it work best. The problem I have with mine is at 32 degrees it will run good at a track closer to sea level and when the air is cool (maybe 1200' DA). When I run at the track that I'm at now which is 1000' above sea level and a DA of 3500' the engine develops a flat spot at the hit of throttle coming off the footbrake. It feels like the engine is getting pulled down when I try to launch my 3100# car. 60ft times, ET, and my lights suffer. I changed the timing to 36 degrees the same weekend and the flat spot went away, 60 ft times picked up, ET picked up, and my lights went back to normal.

This seemed like a high timing number for this engine and I was trying to figure out why it wants to be there now? Heavy car? The fuel I'm running? Or is it just that the air is so bad and lacking of oxygen that I have to turn the timing up to make up for the lack of oxygen which makes the mixture burn slower?

Thanks
John

[colebalster]

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

Hey John,

Where are you located? I am in Los Angeles, but my dad and and the car are in Scottsdale, AZ. We race mostly at Firebird, Speedworld, Tucson and Las Vegas.

I have Del West Ti valves, retainers and locks with Jesel Pro Series Rockers. We are running a little bigger cam than yours, but less rocker arm. The cam is 285/296@.050 and the lobes are .470" with 112° lobe sep. Right now I have PSI DR1224 springs with 275 lbs seat and 750 lbs open, and they are working good so far. I'm only turing 8200 RPM though. Also, what's you lash set at. Ours is .028"-.030" hot and it seems a little loose. I haven't tested different settings though.

I remember reading a while back about you possibly changing intake manifolds. Did you ever switch, and if so, did you see any gains?

Cole

[FastBuick]

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

Hey John,

Where are you located? I am in Los Angeles, but my dad and and the car are in Scottsdale, AZ. We race mostly at Firebird, Speedworld, Tucson and Las Vegas.

I have Del West Ti valves, retainers and locks with Jesel Pro Series Rockers. We are running a little bigger cam than yours, but less rocker arm. The cam is 285/296@.050 and the lobes are .470" with 112° lobe sep. Right now I have PSI DR1224 springs with 275 lbs seat and 750 lbs open, and they are working good so far. I'm only turing 8200 RPM though. Also, what's you lash set at. Ours is .028"-.030" hot and it seems a little loose. I haven't tested different settings though.

I remember reading a while back about you possibly changing intake manifolds. Did you ever switch, and if so, did you see any gains?

Cole

Hi Cole,

I'm located across the country from you lol. I'm in the northeastern part of Pennsylvania. I run mostly at Numidia Dragway.

You have good stuff in the valvetrain. The one thing I would keep an eye on is the springs and lifters. That spring pressure sounds like it's on the low side for that cam. What spring pressure did the cam manufacturer recommend? I used to have the Manley Nextek 221424 spring which is similar to what you have. I started to have problems with lifters and springs so I changed to the PAC 1356 spring to get more spring pressure and it seemed to remedy the problem. Everything in the valve train seems to be happy and last longer now. I am running more RPM though so you might not have that issue. My valve lash is .020" Int and .022" Ex hot. I have a Comp Cam. Who makes your cam? Some cam manufacturers use more lash. I had an Isky cam that used a lash very close to yours.

I did change the intake. I went from the GM 10185053 that was port matched and very mildly ported for my heads to an Edelbrock Victor Glidden Spyder part# 2858 that I port matched and mildly ported for the same head. Mainly just cleaned up the casting. It was kinda rough out of the box. I gained 1.5 tenths and 3 mph just with that change alone.

John

[colebalster]

My valve lash is .020" Int and .022" Ex hot. I have a Comp Cam. Who makes your cam? Some cam manufacturers use more lash. I had an Isky cam that used a lash very close to yours.

I did change the intake. I went from the GM 10185053 that was port matched and very mildly ported for my heads to an Edelbrock Victor Glidden Spyder part# 2858 that I port matched and mildly ported for the same head. Mainly just cleaned up the casting. It was kinda rough out of the box. I gained 1.5 tenths and 3 mph just with that change alone.

John

I have a COMP cam as well (RX and XCX lobe). They didn't recommend a spring, but the engine builder out here that helped me with the cam suggested the same Nextex springs as well, however I already had a set of Isky 9945 springs that I was running and they lasted 220 passes, then I put the PSI springs in. The lifters (Isky Red Zone non-EZ roll) are original with 250 passes on them and they look good. Just to be safe I am going to send them back to Isky for a rebuild. I think I will try a few different lash settings on the dyno this time around.

I will most likely get the same intake you have, it looks promising for our application. I think my little Wilson/Edelbrock 2955 intake with Wilson 4150 to 4500 adapter is quite small for our motor/RPM. We'll see on the dyno.

Take care,
Cole

[FastBuick]

I have a COMP cam as well (RX and XCX lobe). They didn't recommend a spring, but the engine builder out here that helped me with the cam suggested the same Nextex springs as well, however I already had a set of Isky 9945 springs that I was running and they lasted 220 passes, then I put the PSI springs in. The lifters (Isky Red Zone non-EZ roll) are original with 250 passes on them and they look good. Just to be safe I am going to send them back to Isky for a rebuild. I think I will try a few different lash settings on the dyno this time around.

I will most likely get the same intake you have, it looks promising for our application. I think my little Wilson/Edelbrock 2955 intake with Wilson 4150 to 4500 adapter is quite small for our motor/RPM. We'll see on the dyno.

Take care,
Cole

My cam is an RX XCX also. I called Comp about spring pressure for my cam and they said a minimum of 285# on the seat with titanium valves. You may have to shim those springs to get around 300-320 on the seat. That's what I had with the Nexteks. Is this a totally new combination? What heads are you running?

If you are running a decently sized 18 degree head the Edelbrock 2858 will definitely make more power than the one you have now. The 2955 that you have is even smaller than the GM intake that I had. My GM intake is equivalent to the 2959 Edelbrock. You definitely have enough cubic inch for the big manifold. Also taking off that adapter will help a lot also. I had an adapter on mine for the dominator and I think that was a lot of the restriction too. You will have to put some hours into the 2858 manifold to match it to your heads and get it right but I think it will be worth it for you. It definitely was for me.

John