327 build - fine tuning

Propane, Butane, LPG, GPL, C3H8, C4H10
C3H8
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Re: 327 build - fine tuning

Post by C3H8 »

Referring your comment on the recurve. In most cases the recurve will be substantially different then gasoline, however no two modified engines would have the exact same numbers usually. The generalized numbers quoted in these forums is aimed at factory produced, low compression engines produced in the 70's 80's, etc., with the same camshafts. The engines were generally very close to each other (less then 5%) in power, torque and operating ranges.

An engine modified by one individual is unlikely to be the same as an engine modified by another enthusiast. Each modified engine will likely have a variation in the curve.

Steptoe and storm brought up the plugs and ignition system. I forgot about the plugs in my original post and it is quite possible to have detonation with plugs that are in the wrong heat range for the use. Again this is something that was less likely to be of a serious consequence on mass produced low compression engines with the old 3 speed automatics or 4 speed standards but modified engines along with the use of newer overdrive transmissions may require additional testing.

Did you damage the engine? Not likely as long as you backed off when the detonation occurred. The unfortunate part of LPG is when it does detonate you don't hear it until it gets fairly severe. That is why reading the plugs is important during the initial changes. with your transmission you have you may have to alter the curve to compensate for the higher load factors in overdrive. One solution might be one of the boxes that allows programming the curve with a laptop to match all the criteria. When overdrive tranny's were introduced at the factory level most had computer controlled advance systems that retarded the timing in overdrive gears compensating for the load factors. Getting the perfect curve manually will take time and patience.

Marc
Posts: 26
Joined: Mon Apr 23, 2012 8:54 am

Re: 327 build - fine tuning

Post by Marc »

Hello
I checked the saprk plugs are all right, same gap on all of them.
Ignition is no problem neither.

I first had to find an oil leak on engine then when it is doen I 'll re-tune ignition advance the right way.

Thanks

schwoch1
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Location: Burlington, WI!!!

Re: 327 build - fine tuning

Post by schwoch1 »

In my experiences with Vortec heads, they very rarely need more than 32 degrees of timing TOTAL to get the job done. If you are setting your initial timing at 10-12, you should not need more than 18-20 degrees of centrifigual advance to get a total of 28-32 total. Also, just my opinion, ditch the vacuum advance, at light load with your cam you may get some bucking/surging because the timing is over advanced. You have to be careful with vacuum advance, because it is very easy to end up with over 50 degrees of timing under light load, which is not needed on a non egr/modern cylinder headed engine! Also, double check that your timing marks are spot on, there are many different balancer/timing cover/timing pointer combinations that a small block Chevrolet can have, and you could end up with the wrong combination of parts that will lead you to think you have 30 degrees of timing, when in actuality you could have 50+! If your timing numbers are what you say they are, you should not have any pinging happening. I would also recomend as others have, get a wideband sensor so you can see what your actual air fuel ratio is, without it you are basically guessing what it is, and guessing usually leads to bad results!!!

Hope you follow this, and I hope this helps!

Mike
1967 GMC 2500, 351 V6, soon to have 430 Buick with propane

Marc
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Re: 327 build - fine tuning

Post by Marc »

Reading through your posts and considering better my engine (cam, CR, vortec heads) I consider now a different theoretical curve. The good thing is my Accel 52 serie is completely tunable.
I plan to add a stop bushing to limit mechanical advance, and add more springs so it will release lead at low rpm. Curve should be (from Accel spread sheet for distributor):
Initial 10, mechanical 16. total should be 26 reached @ 2400.. I would retune idle mixture screw before test drive.
- If it appears right after test drive I could try to connect vacuum advance (max 7°) and listen to pinging at low load.
- If not right without VA I would have to add even more spring load to get total @ 2700

I think this is good plan.
From topics on vortec heads on gasoline engines, these are running with 30 or 31° total with good performance thank to head's high efficiency chamber. So I guess I only need a little less total ° as I run 10:1 CR and on propane...

Thanks

Frank
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Re: 327 build - fine tuning

Post by Frank »

It probably wouldn't hurt to experiment with running less total advance. I would think that Vortec heads have better combustion than slant six heads and 65CrewCabPW found that his Dodge pickup runs well with "16 - 18 degrees or so at WOT and high rpm (3600)".

viewtopic.php?p=11320#p11320

I don't think it's a good idea to base your timing advance on whether you can hear pinging. If you don't have a chassis dynamometer, I think it would better to base your total mechanical advance on the setting that gives you the quickest 0-60 mph or 1/4 mile acceleration. Once this has been determined, your ideal vacuum advance is what gives you the best fuel economy.

Marc
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Re: 327 build - fine tuning

Post by Marc »

Frank,

It is interesing conclusion indeed from 65CrewCabPW.
So CR 10 - 10.5 and efficient heads can make great efficiency at less advance, and that make sense. Flame propagation on LPG is faster than gasoline for stoechiometric and lean mixtures which is what we want for our cars.

I also read on a towing truck from gasoline to propane they base tuning was increase initial +3 and retard total -5°.
It goes in the same direction then 65CrewCabPW for his owing truck, and my car with long overdrive is the same as towing... heavy load at low rpm.

The thing is of course I can play with the dizzy curves and test drive but it is a lot easier to start good from the curve basis and only have to adjust distributor rotation lock and see which gives me the more power, than maybe re-adjust initial.

So when I dismentle my accel 52 distributor I may try the intermediate stop bushing and heavier springs to get :
10-12 initial (seems clear everybody say this is good)
12 mechanical @ 2600 RPM (curve start @1400RPM, only 6 mechanical @ 2000 RPM)

In the actual configuration the engine pings with 21° @ 2000 RPM under load. So here it should be better @ 16 to 18° @2000.

Thanks,

Marc
Posts: 26
Joined: Mon Apr 23, 2012 8:54 am

Re: 327 build - fine tuning

Post by Marc »

What is the influence of the camshaft profile on advance? if the cam is low to mild it helps build up pressure at low rpm and so less advance would be needed.
My cam is mild agressive 1500 to 5500 rpm so I may need more advance at low rpm then 65CrewCabPW ?

If I'd copy 65CrewCabPW I could try even with the bigger bushing and heavier springs :
12 initial
8 mechanical @ 2600 RPM (curve start @ 1600 Rpm, which gives 3° @ 2000 rpm)

This is far from steptoe on his engine, and far from what we said here at the begin of this post writing,... but why not, I don't know...

I personnely think I should first try :
10-12 initial
12 mechanical @ 2600 RPM (curve start @1400RPM, with only 6 mechanical @ 2000 RPM)


Possible theorical curves are :
http://www.jegs.com/InstallationInstruc ... -52200.pdf

Steptoe
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Re: 327 build - fine tuning

Post by Steptoe »

What is the influence of the camshaft profile on advance? if the cam is low to mild it helps build up pressure at low rpm and so less advance would be needed.
My cam is mild agressive 1500 to 5500 rpm so I may need more advance at low rpm then 65CrewCabPW ?
Higher the cylinder pressure the faster the the flame, less timing..
I have around 11:1 with a bottom end high torque cam...so much so its hard on starter motors with high initial advances.
Im still running around 32 degs in around the 2700 mark....
Where the total is all in also depends on the final axle ratios....
So say u have a 350 trans and 2.7 gears one is working around town in the 1000 to 2000 rpm range.. with VA in at cruise speeds
Have a say 4:11 and the rpm range is around 2x.
Therefore one has very different timing curves to suit.

I messed around for years .. like u , hit in miss , timing runs on hills and got close to correctly dialed in... on a budget
Excellent learning curve..
But basically the guys here told me .. boiled down to this... "you will not get it fully correctly dialed in until you stop messing around and get some serious equipment to do so..."
Then I got a Innovate data logger and accessories with O2 rpm, tps imap and knock... damn near a grands worth in this country.
Now not only did I get dialed in and recover the cost in less than 1 yr in fuel bills but was able to experiment with mixtures timing see how far could push lean mixtures with more timing and a heap of other stuff.
For the 1st 2 decades this sort of equipment was horrendously expensive and not even available in most workshops....the the 21st century came along and this equipment became affordable and available to the home workshop.

Bottom line, u will like me, and many other will continue to be going around in circles get close to dialed in specs...close enough for acceptable performance/ efficiency....the odds of hitting those specs and KNOWING when u have are very unlikely.

This is not just LPG... I was always good at setting specs on an engine.. but looking back .. having a data logger back then .. put it this way...Im sure we would have had our engines stripped down but the race officials every meet to make sure everything was kosher.
My Spelling is Not Incorrect...It's 'Creative'

storm
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Re: 327 build - fine tuning

Post by storm »

Steptoe wrote:Then I got a Innovate data logger and accessories with O2 rpm, tps imap and knock... damn near a grands worth in this country.
Do you remember the part numbers? I can't, for the life of me, find a knock sensor accessory on their site.

I was thinking the LM2, and the LMA-3 (AuxBox) but none of the accessories that I can see on their site target knock sensing.
,
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

Steptoe
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Re: 327 build - fine tuning

Post by Steptoe »

I used a knock sensor off an isuzu think it was.. they are pretty well generic..
The tpi off a jappa and made my own bracket to suit..generic Bosh heated wide band O2
The only reason one really needs a knock sensor is when dialing in the VA for cruise economy.. it is the only time other than light part throttle load that the VA should operate.
I do suspect that one of your issues is u have the VA operating in a vaccuum band width outside the above... that it should not be in
Dont even think about dialing i a VA until ALL other parameters are established... Only then will u know what the vacuum characteristics of your vehicle are
My Spelling is Not Incorrect...It's 'Creative'

storm
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Re: 327 build - fine tuning

Post by storm »

Steptoe wrote:I used a knock sensor off an isuzu think it was.. they are pretty well generic..
This may need to be moved to another thread but how did you connect the knock sensor up to the innovate data logger?
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

Steptoe
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Re: 327 build - fine tuning

Post by Steptoe »

Thru the modular addon that allows the rpms and 4 other components to be added
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storm
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Re: 327 build - fine tuning

Post by storm »

Thanks Steptoe, I'll contact you if I have any more questions regarding setting up.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

Marc
Posts: 26
Joined: Mon Apr 23, 2012 8:54 am

Re: 327 build - fine tuning

Post by Marc »

Hello

I had no chance to drive the car and play with distributor settings recently... I had to fight an engine leak..
I bought a AFR kit with wide band lambda sensor, I bought AEM kit 30 4100.

Now please tell me when I am going to use it the AFR at lambda 1 should be 15,5 for propane, but what if the system is set for gasoline, it is going to show 14,65 instead ?? In the manual of AEM I did not see indication how to use if to change fuel, I asked their technical customer service but so far no return.


Thanks

C3H8
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Re: 327 build - fine tuning

Post by C3H8 »

http://www.schnitzracing.com/manuals/AEMWBK.pdf
This site gives a PDF instruction sheet showing voltage readings for all fuels including gasoline, methanol, propane, ethanol and CNG for the 30-4100. Is that what you wanted. Lambda 1 means the same on gas or propane. Lambda 1 is 14.5 on gas and 15.5 on propane. The chart shows the voltage output is the same also. 2.34 volts on the 02 sensor is 14.68 on gasoline and 15.74 on propane. Have a look at the page and see if it answers your question.

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