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That looks good to me. My table was close to that on Chevron 94 @15 psi. I had no detonation. I've since turned things up a bunch and spraying water/meth
One thing your table doesn't do is take into account rpm vs boost very well. For example, you shouldn't have a constant 15* timing across the whole rpm range @11psi.
I understand you probably aren't making nearly as much cylinder pressure as others, but advanced timing with low rpm and boost is how you bend rods and lift heads. Managing cylinder pressure is critical.
I would shoot to back it down a degree or two with every 1000rpm less. You're likely ok at 15.8* timing and 11psi at 6000rpm, but I would reduce that timing number to something like 13* at peak torque, and less as rpm drops more. You wont lose much power with this method, and if you want more just add another pound of boost. Boost is safer than timing.
Thanks for the reply. I think I was struggling with this issue a little bit...and it makes sense. The cam likes timing at idle and cruise but I need to slope off the low rpm side of the timing curve at higher boost pressures.
Right. So for example my '67 cruises with a lot of timing but it tapers off as the car gets into boost. I forget my exact cruise timing but it's upper 30's or low 40s, and then I'm at a max of 15 timing at max boost.
You want to ramp it up from idle into vacuum/cruise then ramp down as boost/rpm increases. Smooth the transitions etc. Don't be afraid to try things out but go in steps and save each revision as a different file name that way if something isn't quiet right you can jump right back into the previous
Wow, ok, so I can raise and flatten the low vac, high rpm area of the curve, I'll work toward that. My cam at idle needs 23-24. Struggled to turnover below 20 degrees. I rolled over the low rpm, high boost area of the curve, feel better about it now. The 7665 turbo comes on quick, so there is more exposure/stress on the low rpm/high boost area of the curve. Thanks.
Wow, ok, so I can raise and flatten the low vac, high rpm area of the curve, I'll work toward that. My cam at idle needs 23-24. Struggled to turnover below 20 degrees. I rolled over the low rpm, high boost area of the curve, feel better about it now. The 7665 turbo comes on quick, so there is more exposure/stress on the low rpm/high boost area of the curve. Thanks.
rolled over low rpm/high boost area of curve
NP. Every engine will be different like if I tried to use 22-23* at idle my idle would be close to 2000 rpm
One thing your table doesn't do is take into account rpm vs boost very well. For example, you shouldn't have a constant 15* timing across the whole rpm range @11psi.
I understand you probably aren't making nearly as much cylinder pressure as others, but advanced timing with low rpm and boost is how you bend rods and lift heads. Managing cylinder pressure is critical.
I would shoot to back it down a degree or two with every 1000rpm less. You're likely ok at 15.8* timing and 11psi at 6000rpm, but I would reduce that timing number to something like 13* at peak torque, and less as rpm drops more. You wont lose much power with this method, and if you want more just add another pound of boost. Boost is safer than timing.
I agree with this. It'll work as long as the number chosen is the most conservative. But at high RPM you can certainly add a little timing back in above peak torque.
Its possible my timing at idle comes down when I increase the cruise section of the curve (higher rpm/low vac), since the tangential cells affect each other. I still have some small issues around idle that can improve. I'll work toward this and report back.
Update spark curve. Followed advice here: added idle and cruise timing in the high rpm, low vac areas. Sloped off the low rpm, high boost areas. I think everything improved across the board. Pulls hard, gets into boost quick, and my idle issues have improved. When I quickly blip the throttle, it was almost stalling. Not perfect, but now snappier and rev happy. I'll have to run more logs but I observed no knock. The learn asking for way more fuel now, which is great.
So my tuner has said to me a few times that turbo combos need more idle and cruise timing because they burn "lazy" compared to NA combos. The sign that idle/cruise timing needs to increase (I'm paraphrasing here) is higher than idle temps. Now there is a lot to managing coolant temps, more than just timing, but it's in the mix. Btw he originally started me out at 13 timing and I've increased it to 15 with my SBE. Once we swap to the build engine (with Summit Pro LS forged rotating assembly) and the TFS 220 heads, I'll look into running more timing at WOT but will pull plugs to verify that the engine is happy. I wouldn't anticipate the increase in timing will be more than running say 19-20 degrees though, we'll see.
So my tuner has said to me a few times that turbo combos need more idle and cruise timing because they burn "lazy" compared to NA combos. The sign that idle/cruise timing needs to increase (I'm paraphrasing here) is higher than idle temps. Now there is a lot to managing coolant temps, more than just timing, but it's in the mix. Btw he originally started me out at 13 timing and I've increased it to 15 with my SBE. Once we swap to the build engine (with Summit Pro LS forged rotating assembly) and the TFS 220 heads, I'll look into running more timing at WOT but will pull plugs to verify that the engine is happy. I wouldn't anticipate the increase in timing will be more than running say 19-20 degrees though, we'll see.
That's interesting because when I got my car up and running, built iron block 370 Billy LSA heads, I was at 13 degrees at idle and it seemed like temps rose quickly and they just stayed up there. Now I'm sitting around 17 degrees at idle and to me it seems like temps don't rise as quickly and they kinda plateau afterwards give or take a few degrees. That's more or less the sweet spot for me and if I go to say 20 degrees then my idle will sit artificially high. Currently at WOT I'm at 11 degrees spraying 2000cc of water meth
Im still struggling with idle, but maybe I should leave it alone. Im at 950 and would like to be 800 rpm. With the latest tune, i tried to drop the timing and it started like crap and idle was worse. Blipping throttle stalls, etc. So 23-24 seems ideal in my situation.
Im still struggling with idle, but maybe I should leave it alone. Im at 950 and would like to be 800 rpm. With the latest tune, i tried to drop the timing and it started like crap and idle was worse. Blipping throttle stalls, etc. So 23-24 seems ideal in my situation.
Have you just tried turning the idle speed down in the software?? Still seems like that's a lot of timing for idle
I agree with you, it does seem high. My idle is set to 700. I'll spend some more time understanding the idle and startup areas. I could never get the engine to turn over cleanly until I turned the timing up.
Last edited by 68steiny; Jan 12, 2025 at 08:38 AM.
So my tuner has said to me a few times that turbo combos need more idle and cruise timing because they burn "lazy" compared to NA combos. The sign that idle/cruise timing needs to increase (I'm paraphrasing here) is higher than idle temps. Now there is a lot to managing coolant temps, more than just timing, but it's in the mix. Btw he originally started me out at 13 timing and I've increased it to 15 with my SBE. Once we swap to the build engine (with Summit Pro LS forged rotating assembly) and the TFS 220 heads, I'll look into running more timing at WOT but will pull plugs to verify that the engine is happy. I wouldn't anticipate the increase in timing will be more than running say 19-20 degrees though, we'll see.
Yes thats where im at 13-15, but i need to double check once again as I believe the engine is 1* advanced from where the holley is at.
5.3. stg 2 s480 850 idle rpm. Hopefully before weeks end Ill recheck.
I only asked because of where Ive seen alot of tunes especially the Sloppy version all in the 22* range.
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Term X timing table sanity check 
