Classic example of too much exhaust for (street) engine?

[BigBlockMopar]

Dyno-output is DIN corrected.
The Dyno's AFR reading are on the 'normal' gasoline (14.7=Lambda 1) 'scale', but Propane is stoich at 15.5:1 AFR.

We didn't play with fuel settings at the dyno after the 2nd run.
The first run was lean, I adjusted the 'Power-adjustment' on the Propane carb '2 turns' richer and we kinda left it there, also because it was now at the same level as last year's runs. I personally think, afterwards, it could have be a tad richer perhaps.

We did play with max. timing but power went down when deviated from 32° max.
Above 3000rpm it turned out to improve the powercurve a bit when advance was backed down to 30°. Was fun to see this actually proven on a dyno.

The exhaust change didn't make much of a seat of the pants improvement, to my surprise.

I will also try some ignition changes.
Currently I'm using a MSD Blaster SS e-core coil.
I have also have a MSD TFI coil to try, and a bunch of stock e-core and canister coils.
The ignition is relay powered, so it gets full battery power (which is rather high in the car, approaching 14.9 - 15volts).
For this, dwell settings for the Blaster SS were set to 2.8ms max to prevent auto-firing of the coil.

[stealth]

The lean condition would make sense if your exhaust is flowing better now...I'm thinking richer might find your missing hp...

I hope your not tuning to stoic for best power....

[BigBlockMopar]

No, no tuning for stoich. Stoich is just a chemical number.
I recall having seen max. power for gasoline is usually around 0.80 Lambda or thereabouts?
The engine WOT-mixture was about 0.84 Lambda during the runs if my calculations are correct.

The lean, first dyno-run was because my in-car AFR-sensor is in need of replacement and its values are off. It only became obvious on the dyno.

[MadBill]

<Written before seeing above 3 posts, too much trouble to re-write.>
A few points:
o The chemically-correct (stoichiometric/Lambda/ λ for pure propane is 15.67:1* vs. a typical 14.7:1 for gasoline. (*Many fuels labelled "propane" have significant percentages of various other hydrocarbons which can alter the number; I don't know the situation in your location.)

o As we know, gasoline produces maximum normally aspirated power running rich enough to ensure all the air is used, usually ~12.5-13.5:1. Gaseous fuels like propane however displace a significant percentage of the charge air, accounting for the generally lower power output and the production of max power on leaner mixtures. According to this useful primer: http://www.hotrod.com/articles/wideband-oxygen-sensor/ max power on propane is obtained with ~ 13.2:1 true AFR or 12.5:1 on a gasoline-calibrated meter, but I suspect this is based on a straight conversion from the classical 12.5:1 gasoline number rather than real world results as affected by charge displacement, so you definitely should experiment.

o Many/most wide band O2 gauges are set up to read out AFR based on the assumed 14.7:1 stoichiometric ratio. If the one at your dyno does,the actual pure propane AFR number will be ~6.5% larger

o With the near-zero effective overlap of your stock cam, long tube headers will have a limited effect.

[user-17438]

The link you showed was in the 11are at 4000rpm.

Coolant temp and oil temp can sway a dyno pretty easy also.. I never see much gain when people being me their stock car and put long tubes and louder mufflers on. They are lucky to gain a few hp. Camshaft and pickup torque converters pick rwhp up big.

[Geoff2]

I have been using cams with less exh duration for many years now.

You might find interesting reading on Isky Cam's Tech Tips: Is extra exh duration really necessary....

[BigBlockMopar]

Bill,
I've changed my car's AFR gauge to read Propane AFR. But the dyno's AFR guage is indeed still based on Gasoline AFR (14.7).
Propane in my area is a mix of Butane and Propane, which could vary during winter and summer. Although I've never seen any proof of this.
For this it would probably better to read in Lambda all the time.

MT,
Coolant temp is always steady and fairly low in the engine. Even during the dyno runs. I have MegaSquirt logs showing temps staying low all the time.
Perhaps, a bit more heat in the engine could help make some more power?
I don't have MegaSquirt sampling the oil temps at this time.
I chose the mufflers for their better flow-numbers. Being the Pro-XS (street), they are not loud at all.

The 360 engine that will replace the 318 some time soon will focus on efficiency and mostly producing torque.

[MadBill]

I have been using cams with less exh duration for many years now.

You might find interesting reading on Isky Cam's Tech Tips: Is extra exh duration really necessary....

Are you assuming those specs are at 0.050"? Remember it's a stock 318 c.i. 2 bbl. cam. I think they're probably at 0.006" and would need as much as 50° subtracted to approximate 0.050" numbers...

[BOOT]

Same mufflers? Same shop do both exhaust?

[BigBlockMopar]

Different mufflers. Went from stockish Turbo mufflers to Borla Pro-XS.
Entire different exhaust system.

The earlier exhaust was a cheap & quick custom bent job. Good enough at the time.
The current exhaust system I put together myself from pre-bought parts.

Current exhaust;


Previous;

[MadBill]

It's a good looking system and will surely support hundreds more horsepower than the present output, but can't be doing any harm, provided the AFR is verified/optimized with it.

[user-17438]

Bill,
I've changed my car's AFR gauge to read Propane AFR. But the dyno's AFR guage is indeed still based on Gasoline AFR (14.7).
Propane in my area is a mix of Butane and Propane, which could vary during winter and summer. Although I've never seen any proof of this.
For this it would probably better to read in Lambda all the time..

Or just use 14.7 as stoich and know it should be richer . THE WIDEBAND READS LAMBDA then converts to AFR. They number is just a number. So your stoich would still be 14.7 no matter what fuel you use 1.0 is stoich in lambda

[Belgian1979]

Hi BBMopar,
We talked over at MS forum, so I thought I give you my thoughts.

I used to run the GM type HEI with MSD blaster coil. The spark was really, really weak and lots of misfires. When I went to ms sequential and LS coils, it was a night and day difference.

[BigBlockMopar]

The link you showed was in the 11are at 4000rpm....

This line made me have a look back more closely at the sheets and videos, as I was sure the AFR's were in the low 12s... and shame of me, I found I mixed up a number of things.

The 16°C ambient temps were during the 1st dyno-session I made with the car, in 2013. (Done 3 in total now).
The 2nd Dyno-session had higher temps, 21+°C degrees, much closer to the 3rd Dyno-session's 25-27°C.

Also, the AFR numbers.
It seems the AFR-numbers listed on the dynosheets I got from the 2nd Dyno-sessions, don't match to the numbers in the videos I shot during the runs.
I think the AFR's on the screen in the video were shown in Propane scale, and the dynosheet I got was listed in Gasoline scale.
The last dynosession the AFR was shown in Gasoline scale again.

Something else I noticed comparing the videos of the 3 dyno-sessions,
During the 1st session, the engine made close 74hp @ 2000rpm during loading up against the dyno just before the run.
At the 2nd session, the engine made around 76hp @ 2000rpm during dyno-loading.
At the 3rd session, the engine made 80hp @ 2000rpm when loaded. So there's definitly some improvements made at the lower end.
I think we should have played with mixture a bit more during the session.

Because of this, I adjusted the power-setting on the propane carb a little richer today and my ButtDyno thought it noticed some improvement during a WOT acceleration. But I need to do some more WOTs to rule out wishful thinking.

[BigBlockMopar]

Hi BBMopar,
We talked over at MS forum, so I thought I give you my thoughts.

I used to run the GM type HEI with MSD blaster coil. The spark was really, really weak and lots of misfires. When I went to ms sequential and LS coils, it was a night and day difference.

Hi, saw your name around here, thought it might be you.
I've maxed out the dwell settings for the Blaster SS coil with the dwell-table in MegaSquirt at 2.8ms at higher rpms and full load. Anymore dwell and it starts to auto-fire itself, causing way too early ignition.
Have been looking at the Blaster coil's spark sometime back and it didn't appear to be that powerful. But since I don't 'feel' misfires, I let it be.

I only have a MSD TFI coil to try out at the moment, or some stock e-core coils. Benchtesting the TFI coil it made some good and strong appearing sparks.
With the (low max) rpms my engine is turning I don't think I need COPs already.
I'm not sure I'll be doing sequential ignition on this engine yet, but like to try it on the 360cu I'm building.