[chiphead]

Got my PI distributor installed a few weeks ago and been tuning with it. I've got a safe curve that runs pretty well with no signs of detonation. It is pretty slow compared to what I see some of you guys running, so I'm wondering how you sneak up on the optimum timing curve?

400 with 62 heads, 2802 cam, RPM intake, 750DP, 3200 stall, 3.25 gears.
93 E10 fuel, 180 thermostat. Idles at 850 with 13-14" vacuum.

[Verdoro 68]

I started with the standard generated table with 36 total adjusted down from there. I probably tried 15-20 different variations adjusting base and total timing, tweaking vacuum advance and toggling aggressive mode on and off. I let the app fill in the details. It took a few afternoons driving around and tweaking via the app until I felt like I got things in a place where I was happy with the performance. I have no idea if it's right but the engine seems like it. Might still be a little heavy on initial timing.

[Formulas]

What do the numbers in the L/H column represent the 20-101 ? just trying to learn how to read the graph

[steve25]

There are so many factors involved in attaining an optimal rate and curve that it’s really hard to say.

The hard thing to see/ pin down is that the power a motor makes will start to drop down just before knock starts to happen and then of course the level of power really takes a nose dive once a does enter into a knock condition.

I guess what I am trying to say is that without the motor being on a dyno where you can control the acceleration rate your going to be spending a lot of time researching what the motor wants without destroying it in the process.

While you are going thru this set up keep in mind that until the motor comes fully into the Cams power band that lean mixtures take more lead time to burn completely.

[JLMounce]

My approach is to be overly conservative unless as steve25 has stated, you have the ability to utilize a dyno for tuning.

The way this is done with a dyno is typically in zones, or cell by cell to monitor MBT (maximum brake torque). You sweep through a conservative to aggressive timing curve per cell as the dyno stabilizes the rpm and MAP reading. Typically there is a range where spark advance will flatten out the torque produced at that point in time. For a street vehicle on pump gas, you would set your timing at the low end of that plateau for safety.

As steve25 also mentions, engines on pump gas will typically reach spark knock before MBT, so it's important to be listening to the engine (or knock sensors directly if so equipped).

Based on your original post, if the engine is not showing you any signs of being unhappy, like running hot, pinging, surging or bucking, while also providing good throttle response, it's unlikely that you'll be able to legitimately improve on the tune without a dyno.

If, like me, you kind of have a cruise "route" that you always tend to take, drive that section and you can make tiny changes to the timing by watching you MAP readings. adjust timing for lowest MAP/Highest vacuum. But don't make wild changes at a time. 2* increments at a time an monitor. Same thing with your idle. Start with your idle fueling and adjust for lowest MAP. Once that's dialed in, sweep the timing from your initial through your total in increments and adjust idle timing for lowest MAP. Since the car is an auto, I like to do this with the car in gear, because the load will change as the converter acts on the engine in gear.

[JLMounce]

Originally Posted by Formulas

What do the numbers in the L/H column represent the 20-101 ? just trying to learn how to read the graph

Left hand column is MAP (manifold absolute pressure) reading in kPh. Lower MAP is lower load and typically higher vacuum.

It is possible, but unlikely to see values as low as 20 and higher than 100, but most naturally aspirated engines will not produce those types of results. MAP readings above 100 indicate pressure above atmospheric, typically from turbo or supercharging.

To see numbers below 20, you'd have to have an incredibly efficient engine at low rpm. Idle MAP values in the 30's to low 40's for most stock or mildly upgraded camshafts are normal.

Altitude increases MAP values as well. My 465 with a 242/248 on 112 LSA hydraulic roller at 4500 ft of altitude idles right at 50 kPa.

[grivera]

Sub’d - looking forward to playing with mine in the 66 but still a ways.

[chiphead]

I'm mainly concerned with near WOT curve for now. Steady road cruise is fairly close. I get 18" at light throttle on a flat road at 2400.

Basically, could I add 2* of timing to the top 3 rows (near WOT where there is little vacuum) and then pull timing when I got into some pinging?

Current curve pulled 5 degrees below 3000 and added 3 back in above 3400. That seems to work, but the car has lost a bit of oomph 2000-3000. I also richened the carb up, so its not going lean anywhere. Going back to the classic holley metering block/HSAB calibration corrected the fuel delivery.

I know from previous testing with my MSD distributor, that the engine will start to ping at 36* at 3000 with heavy throttle and a lean (low 15s) mixture. Confirmed with pepper on the plugs. So I know 36* at 3000 is an upper bound I should stay away from.

[steve25]

At 3000 rpm when you get the light ping what gear are you in, drive I assume?

[JLMounce]

Originally Posted by chiphead

I'm mainly concerned with near WOT curve for now. Steady road cruise is fairly close. I get 18" at light throttle on a flat road at 2400.

Basically, could I add 2* of timing to the top 3 rows (near WOT where there is little vacuum) and then pull timing when I got into some pinging?

Current curve pulled 5 degrees below 3000 and added 3 back in above 3400. That seems to work, but the car has lost a bit of oomph 2000-3000. I also richened the carb up, so its not going lean anywhere. Going back to the classic holley metering block/HSAB calibration corrected the fuel delivery.

I know from previous testing with my MSD distributor, that the engine will start to ping at 36* at 3000 with heavy throttle and a lean (low 15s) mixture. Confirmed with pepper on the plugs. So I know 36* at 3000 is an upper bound I should stay away from.

Yes you can do that. Same basic tuning technique you would use when adding timing via a mechanical distributor.

Take a stopwatch and make timed runs. Increase timing by 2* and retest. Continue to add timing until the car either doesn’t go faster or goes slower. Then back off 2*

[chiphead]

Wanted to follow up on this.

I went for a 100 mile cruise in 95* heat a few weeks ago to a car show in Georgia.. Car ran really well, no complaints. Engine temps below 50 MPH were right at 180F thermostat. 60-75 MPH, the temp went up to 185-190F. AFR at 70MPH is 12.8-13.2. Sitting in traffic it creeped to 195 but cooled down once I started moving.

I pulled a few plugs after the engine cooled, and I'm seeing a bit of peppering on the insulators. I don't hear any detonation/pinging. The TH400 doesn't like to downshift once it's in Drive. If I'm doing 45, a hard throttle stab to 3/4 throttle will flash the converter to 3600 but it doesn't downshift. So the engine is fairly heavily loaded at moderate RPM.

Looking at my timing curve in the first post, where should I pull timing?

[JLMounce]

Based on the peppering you are seeing on the plugs, my recommendation is to pull 2* out in the entire loaded range from 50kPa to 100kPa. If you have a good idea where you're peak torque is in the RPM range, you can build a trough around that rpm as well, then ramp in a bit more timing later in the rpm range where propensity for ping is less.

Your cruise AFR may be too rich to support the timing you have in it. You may want to pull 2-4 degrees of timing in the cruise range below 40kPa. That may help slightly with highway cooling. Realistically though I'd try to get your cruise AFR leaned out to the upper 13 territory if possible. That would better support the timing you have for the cruise range.

[BB70]

When checking my plugs, I too worry about where I sit with timing. I like to see a tan pepper free porcelin and also look at the ground strap for a heat line- change in color. I like mine to appear in the upper part of the bend of the strap. If its there and no pinging I be happy. Sometimes that pepper look can be carbon getting knocked loose and sitting there abit.

[steve25]

Really the main factor in how much timing a given motor can use is how the cylinder pressure changes as the rpm climbs.

If you assume a close to ideal fuel curve has been found and enough octane is used,then this is how things work out .

At idle ( 700 to 950 rpm ) with a PI set up you can run 50 to 55 degrees and have a superb idle.

Once the rpm gets up to around 1200 to 1500 then the timing needs to drop back down to between 30 to 36 .

Once the motor starts to come on the cam and peak torque starts to be produced the timing will need to retard some, and then start to rise again at the rate the motor can tolerate.

Once the rpm gets to the level of peak hp then the volumetric efficiency is starting to nose dive fast, so at this point to hold onto peak power longer the timing still needs to advance but at a slower rate.

Keep in mind it’s all about how the cylinder pressure changes with rpm.

[chiphead]

Originally Posted by JLMounce

Based on the peppering you are seeing on the plugs, my recommendation is to pull 2* out in the entire loaded range from 50kPa to 100kPa. If you have a good idea where you're peak torque is in the RPM range, you can build a trough around that rpm as well, then ramp in a bit more timing later in the rpm range where propensity for ping is less.

Your cruise AFR may be too rich to support the timing you have in it. You may want to pull 2-4 degrees of timing in the cruise range below 40kPa. That may help slightly with highway cooling. Realistically though I'd try to get your cruise AFR leaned out to the upper 13 territory if possible. That would better support the timing you have for the cruise range.

Thanks, that's really in line with the tuning approach I was going to use. I just wanted some confirmation it was valid. I pulled 1-2 degrees of timing above 50KPA (15" of vacuum and higher load) and pulled 1-4* of timing at lighter loads. I was adding a lot of vacuum timing at 15" of vacuum around 2600-3400 RPM, likely a bit too much.

I went down 1 jet size on the primary of the 4150, from 71 to 70. That should lean the cruise AFR about 7% above 2500 RPM when the mains start.

Where in RPM range does the 2802 cam make peak torque? I'm guessing 3200-3800 RPM in a 400? How much timing should I add back above 4000 RPM? Rev limiter is set at 5700.

[JLMounce]

Originally Posted by chiphead

Thanks, that's really in line with the tuning approach I was going to use. I just wanted some confirmation it was valid. I pulled 1-2 degrees of timing above 50KPA (15" of vacuum and higher load) and pulled 1-4* of timing at lighter loads. I was adding a lot of vacuum timing at 15" of vacuum around 2600-3400 RPM, likely a bit too much.

I went down 1 jet size on the primary of the 4150, from 71 to 70. That should lean the cruise AFR about 7% above 2500 RPM when the mains start.

Where in RPM range does the 2802 cam make peak torque? I'm guessing 3200-3800 RPM in a 400? How much timing should I add back above 4000 RPM? Rev limiter is set at 5700.

I like to move in 2* increments, and that's where I would start. I'd pull that out from 3500-4500 rpm if you think that's where you're peak torque might be. See how it feels. Because your converter flashes around there, you may not even notice it.

[cdrookie]

I just installed mine yesterday, easier than I thought it would be. My combo is a bunch of nice stuff that don’t match up well, so I’m just throwing a band aid on it. This is attempt 1 and something to build off of for now.

Stroked 400-461
87cc 1st gen E heads ported to 330(I think)
Solid roller 260-269 at 50
Custom 950 carb
5 speed manual
4:10 gears and 29-30” tall tires



Sent from my iPhone using Tapatalk

[ta man]

Originally Posted by cdrookie

I just installed mine yesterday, easier than I thought it would be. My combo is a bunch of nice stuff that don’t match up well, so I’m just throwing a band aid on it. This is attempt 1 and something to build off of for now.

Stroked 400-461
87cc 1st gen E heads ported to 330(I think)
Solid roller 260-269 at 50
Custom 950 carb
5 speed manual
4:10 gears and 29-30” tall tires



Sent from my iPhone using Tapatalk

What rpm is your idle? Vacuum advance?

[cdrookie]

Originally Posted by ta man

What rpm is your idle? Vacuum advance?

idle is 830ish
I didn't put any vacuum advance in it yet.