Max 32° mech. adv. for low cr engine: confirmed

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BigBlockMopar
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Max 32° mech. adv. for low cr engine: confirmed

Post by BigBlockMopar » Tue Aug 29, 2017 5:12 pm

Had my Dodge Dart on the dyno yesterday and I can confirm the 'ballpark' rule of 28-32 degrees of max. mechanical advance seems legit.
The low cr 318ci engine maxed at 32° degrees advance at 2750rpm.

Fun thing to notice was, that it liked timing to be pulled back from 32° to 30°, from 3000 to 4000rpm.

Another thing that got painfully obvious, was that a too large exhaust diameter can cost more power than one might think if the engine doesn't need it.
https://www.bigblockmopar.com
'73 Dodge Dart - 318ci - IMPCO E vaporizer / 425 mixer - A518-OD trans - 3.55 gears - 225/50/17" tires.


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storm
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Re: Max 32° mech. adv. for low cr engine: confirmed

Post by storm » Wed Aug 30, 2017 1:05 am

BigBlockMopar wrote:Had my Dodge Dart on the dyno yesterday and I can confirm the 'ballpark' rule of 28-32 degrees of max. mechanical advance seems legit.
The low cr 318ci engine maxed at 32° degrees advance at 2750rpm.
and the higher the compression the lower the required timing would be as well.
BigBlockMopar wrote:Fun thing to notice was, that it liked timing to be pulled back from 32° to 30°, from 3000 to 4000rpm.
Does this correspond to the engines torque peak?
BigBlockMopar wrote:Another thing that got painfully obvious, was that a too large exhaust diameter can cost more power than one might think if the engine doesn't need it.
Yep to large an exhaust slows down the exhaust flow which impacts negatively on exhaust extraction from the cylinder during valve overlap. Take a look at PipeMax if you want to fiddle with your exhaust.
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Re: Max 32° mech. adv. for low cr engine: confirmed

Post by BigBlockMopar » Wed Aug 30, 2017 4:11 am

I knew the exhaust would be too large for this engine, but didn't expect that much loss.

I'm still waiting for the dynorun sheets but the timing pullback was confirmed on backtoback runs.

My timing table was unchanged from when I entered the dyno, expect for the change in timing above 3000rpm.
https://www.bigblockmopar.com
'73 Dodge Dart - 318ci - IMPCO E vaporizer / 425 mixer - A518-OD trans - 3.55 gears - 225/50/17" tires.

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Re: Max 32° mech. adv. for low cr engine: confirmed

Post by Steptoe » Wed Aug 30, 2017 4:06 pm

Fun thing to notice was, that it liked timing to be pulled back from 32° to 30°, from 3000 to 4000rpm
This is where the cam starts to work.. higher rpms and the overlap/ duration and cylinder pressure tend to increase a few lbs at this point.

The dyno has AFR and knock readings etc? Dyno guys tend to just look at power curves, rather than on std street cars whats happening at cruise , low load pms.
Its very interesting to see numbers at what the car is doing 95% of the time and time the VA to that.

Yes exhaust does have huge effect, not just at WoT but cruise loads also... that back pressure can tend to prevent scavenging of fuel out of the combustion chamber before the exhaust closes.. also length size primaries on headers tuned to the rpms the car works at most of the time.
Hence why Chevy truck , cast , rams horns performed far better over headers, right thru rpm and load ranges.. even after changing primary lengths...same exhaust system.
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Re: Max 32° mech. adv. for low cr engine: confirmed

Post by BigBlockMopar » Wed Aug 30, 2017 4:56 pm

The dyno had it own O2-sensor.
During the 2nd and later runs, AFR was around low 12s (Gasoline scale).
My own car's AFR-gauge craps out after 10minutes of driving time these days. Most likely the O2-sensor is failing.

First runs where made with 32 degrees. Then tried 34 degrees, then 28 & 30 degrees. All made less power.

I'm trying to gather up all the info and fab it into easy viewable files.
I've got videoclips of the runs, chassisdyno-run graphs, but also got dynorun-logs from my digital MegaSquirt ECU, showing RPM, vacuum, ignition advance and some more info.


Image

Image
https://www.bigblockmopar.com
'73 Dodge Dart - 318ci - IMPCO E vaporizer / 425 mixer - A518-OD trans - 3.55 gears - 225/50/17" tires.

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Re: Max 32° mech. adv. for low cr engine: confirmed

Post by BigBlockMopar » Wed Aug 30, 2017 6:36 pm

I've put some more indept info on my site for those interested: https://www.bigblockmopar.nl/2017/08/do ... dynoday-3/
https://www.bigblockmopar.com
'73 Dodge Dart - 318ci - IMPCO E vaporizer / 425 mixer - A518-OD trans - 3.55 gears - 225/50/17" tires.

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Re: Max 32° mech. adv. for low cr engine: confirmed

Post by storm » Wed Aug 30, 2017 8:25 pm

Could you clarify if previous dyno runs were done on a hub dyno like the latest one was please. If it wasn't that will have an effect on hp numbers. Roller dynos will always have some slippage, it can't be helped. Hub dynos have no slippage at all.

Your blog post says the cam is bog stock if that's true then the rpm range for the cam would be approximately idle to 3000 rpm. It will breath higher to 4500 rpm and not struggle but the torque will be low rpm. You'll need a bigger cam to get more hp but it should be a torque beast for its size with a stock cam.

The dyno room's cooling fan may also have an effect on your hp and torque numbers. From what I can see in the pictures the fan's shroud could well be helping to force air into the intake tubing, more air=more power. Id be interested to know the fans speed rating equivalent and see a run without it giving an advantage.

I've just subscribed to your YT channel :D
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Re: Max 32° mech. adv. for low cr engine: confirmed

Post by BigBlockMopar » Thu Aug 31, 2017 5:05 am

Previous dyno runs were made on the same dyno-hubs and shop.
The shop itself has moved a mile from its location but other than that its setup is the same.

I don't think the dynoroom is airconditioned. It just has fresh air fans.
https://www.bigblockmopar.com
'73 Dodge Dart - 318ci - IMPCO E vaporizer / 425 mixer - A518-OD trans - 3.55 gears - 225/50/17" tires.

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Re: Max 32° mech. adv. for low cr engine: confirmed

Post by storm » Thu Aug 31, 2017 5:53 am

I wasn't suggesting the dyno room was air conditioned. I was suggesting the fan, and associated ducting, that is used to keep the radiator cool is forcing air into the intake pipe.

I just finished watching 1973 Dodge Dart - Dynoday Revisited 2016 on youtube and your maximum torque peaked at approximately 2800 rpm. All things considered you are making pretty good hp from the old girl.
Fuel flow requirements calculations viewtopic.php?f=5&t=1638

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Re: Max 32° mech. adv. for low cr engine: confirmed

Post by BigBlockMopar » Thu Aug 31, 2017 2:37 pm

The dyno-operator had issues with the transmission kickdown 'kicking' in when starting a run.
I readjusted the throttle linkage to the transmission a large way but it still wanted to kickdown to a lower gear. Didn't want to loosen the linkage any further in fear of lowering oil pressure in the transmission too much to cause slippage.
I advised the operator to either start at a higher rpm or try and feather a bit into the run and focus on HP more.
So the current maximum torque-rpms are a bit variable.

We decided to do the runs in 2nd gear, instead of 3rd gear during the previous sessions.
https://www.bigblockmopar.com
'73 Dodge Dart - 318ci - IMPCO E vaporizer / 425 mixer - A518-OD trans - 3.55 gears - 225/50/17" tires.

BigBlockMopar
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Re: Max 32° mech. adv. for low cr engine: confirmed

Post by BigBlockMopar » Thu Aug 31, 2017 7:06 pm

Here's the last dyno-run we made, after I changed back the max. advance from 34 to 32° @ 2750rpm again, and have it drop to 30° from 3000 and higher.

Image

Same run as shown in TunerStudio, the tuningsoftware of MegaSquirt.
You can play back the run as it happened, seeing exactly what happened in detail;

Image


Ignition advance table shown in 3D;

Image

With max. power dyno-runs, one only uses the top row of the timing table, which relates to mechanical timing curve in a distributor.
https://www.bigblockmopar.com
'73 Dodge Dart - 318ci - IMPCO E vaporizer / 425 mixer - A518-OD trans - 3.55 gears - 225/50/17" tires.

BigBlockMopar
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Re: Max 32° mech. adv. for low cr engine: confirmed

Post by BigBlockMopar » Mon Sep 04, 2017 1:47 pm

I've combined various videos taken during the dynoruns and dyno-charts into one videoclip;

https://www.youtube.com/watch?v=bNkscmjhi-A
https://www.bigblockmopar.com
'73 Dodge Dart - 318ci - IMPCO E vaporizer / 425 mixer - A518-OD trans - 3.55 gears - 225/50/17" tires.

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