327 build - fine tuning

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

Post by Marc » Mon Apr 23, 2012 11:40 am

Hi,

Here are my engine specification :
327ci, 10:1 compression, comp cam HE268 - 218/218 @ 0.50 total 268 duration, vortec heads L31 for propane applicatin with hardened seats and stainless steel valves 1.94 / 1.50 , standard 1.5 rockers, RPM edelbrock intake, tri y thorley 1 5/8" headers in magna flow 2.5" exhaust.
On top of it, I am installing a new impco 425 and model E regulator, and the distributor is also new, accel 52100 with advance curve springs and I also have a accel 300+ ignition box.

I know I could improve with more compression and dual pattern cam (higher duration on exhaust) but so it is right now in the car, Chevrolet Camaro 1968, with T56 transmission coming soon and 4.11 rear end.

I know engine tuning is different on any engine, but folowing my specifications can you tell me what advance curve you would set?
Initial
total cent
va
@ rpm ?
Or dual curve?

And how should I set the max gas flow valve on the impco 425??


Best regards

franz
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Re: 327 build - fine tuning

Post by franz » Mon Apr 23, 2012 11:57 am

This sounds like a good solid engine, and the compression is just about right where it should be for a streetable engine.

You should have a #19 gas valve in the 425 to start with, and I would not change the max gas flow adjustment until you have the ability to test the exhaust fuel mixture under load. A standard O2 sensor with a digital volt meter is all you need, under a long full throttle pull (up a long incline for example).

With that combination of compression and cam, I think I would start with about 8 degrees base, with about 14 degrees of centrifigual, and about 6 degrees of vacuum. Be prepared to change these if you detect any detonation or pre-ignition, there are many other factors that can change what you need. There is no need to advance the timing any further if there is no increase in torque, before detonation.

You dont need a dual curve ignition if you are running straight LPG.

Franz

Marc
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Re: 327 build - fine tuning

Post by Marc » Tue Apr 24, 2012 9:24 am

Thank you Franz.

- please can you tell me @ what RPM I should first set the total cent advance?
- then, through reading the posts here, I notice it is a good think to/from route the water hoses to model E regulator with Y (not through) on heater hoses and to install Gann M-456 in line thermostat on the return hose from regulator.
I searched to buy this Gann thermostat but it seems here in Europe it is impossible to find.. any advice?
- O2 sensor on exhaust seems a good thing to do in a second step to fine tune max gas flow on mixer.
It is then still open loop to the mixer, is there a real advantage in going to a close loop system in terms of efficiency and fuel economy on a carb small block V8? (I read the problem of the vacuum can reactivity to control mixture.. )

Car is a w-e, nice weather condition driver used for crusing and sometimes hard driving on winding roads..


Cheers




Best regards,


Marc

Imperial73
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Re: 327 build - fine tuning

Post by Imperial73 » Wed Apr 25, 2012 9:23 am

Marc, Sjak here. I read your email.

For the Gann, contact Frank, the board host here, he can possibly deliver it to you.

With your car + intended driving, I wouldnt go closed loop.

Regarding the advance curve, you could try to begin with e.g. 28 degrees initial + mechanical @ 2000/2500rpm.

But as Franz already mentioned, a lot of things can influence this, so be prepared to do some trial & error.

Marc
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Re: 327 build - fine tuning

Post by Marc » Tue May 22, 2012 2:46 pm

Hi people, Hi Sjak

1. ADVANCE CURVE
I followed your recommendations, I got new distributor all installed, engine running and I tuned to the desired advance curve. I got the results as :
6° initial @ 700,800 rpm
20° initial + mechanical @ 2000 rpm
28° initial + mechanical @ 2500 rpm
7° vacuum.

I have tuned this with one very light and one midium spring and no stop bushing on a Accel 52100 serie distributor and I plugged it to a multispark box Accel 300+.
First ime good time, I didn't have to remove and try again with other springs/ bushings.

2. IMPCO 425 idle mixture
Then when this was done I wanted to tune the new impco 425. Bud at idle, turning the screw doesn't change a thing niether in rpm niether in vacuum.
I have 23 full turns from one end to the other on the idle screw.
It is now +/- @ 10 turns out from max lean (max lean is turn in completely if I read the topics on this forum correctly)
What should I do?
I think I will go to tune it with a O2 sender at a mechanic shop. (I don't have O2 senseors at home)


Thanks for your inputs

Marc

franz
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Re: 327 build - fine tuning

Post by franz » Tue May 22, 2012 3:37 pm

First off, never try and adjust the fuel mixture with a vacuum gauge, all that accomplishes is checking vacuum. The O2 sensor or exhaust analyzer is the real process for accurately setting the idle fuel mixture.

The 425 idle mixture adjustment screw on the side of the mixer body should have a significant effect on the idle mixture. If you have a bad vacuum leak, it will be less effective. If this cam has a relatively lumpy idle followed by low manifold vacuum, it may be difficult to set idle mixtures as well.

The max gas flow valve is the last thing to set, and from many, MANY, fuel system installations, it is rarely necessary to adjust. You didnt indicate which gas valve the mixer has. For your application, it should be a #19.

Franz

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Steptoe
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Re: 327 build - fine tuning

Post by Steptoe » Tue May 22, 2012 5:32 pm

Im running a similar cam, bit more lift, small chamber cast fuelie heads and compression a little more 10:5 to 11:1
GM HEI on manifold vaccuum... in a 69 camaro 350 T350 27 gears
So long as the intial is low, in the 8 to 12 range so as to take excess load off the starter and prevent dry solder joints in the armiture..ie I have 210 to 230 lbs of cyclinder pressure turning over on the starter
Idle (intial +VA) around the 14 to 18 ball park....LPG allows a lower idle rpm than petrol, I have about 550/600 in N and 450 rpms in drive, and very sensitive on the idle mixture...
Not having sensitive adjustment (as mentiuoned above) usually means a vac leak, be it in the idle diapham...(and also check the adjustment screw is under the tab on the idle diapham during assembly and the port behind is not blocked or restricted) Also it is very important the main metal 'back' of the mixture adjustment diapham be perfectly straight.
Another 'vac leak' can be the seconday butterflies not adjusted correctly..a secondary symtom of this is not being able to drop idle rpms right down with the idle speed adjustment screw...so as to choke and stall the engine.
I also believe a missadjusted .

The cent curve I have found on most dizzys that once one gets total (intial+ Cent) all in below around 2500, one runs into issue where the cent is working at idle rpms...eg to get my HEI total all in at 2800 it comes off around 700/800 rpms.
Higher the compression, more accruately higher the dynamic compression at a given rpm the faster the flame across the chamber less advance required....ball park for a stock petrol engine on lpg can be as much as 32/34 degs total, higher compression down to 28 total... I run around the 29/30 total.

Without a data logger and knock sensors be very conserviative on the all up (intial+cent+ VA) and stay under 42.....I run about 37 at the moment... can run more but there seems no advantage at cruise with my final gear ratio.
Basically your intial is not very important other than easy start/turn over of the engine....then add enough VA to to meet what the engines needs for idle ...establishe with no VA attached, and adjusting intial in it place.
So u are looking at the VA at the idle and at the top end cruise.....generally whatever one works out between intial and idle is what one settles for at the all in (intial+cent +VA) and that is under safley the 42.
6° initial @ 700,800 rpm
20° initial + mechanical @ 2000 rpm
28° initial + mechanical @ 2500 rpm
7° vacuum.
So fires up on 6 degs easy start good
VA kicks in and idles with 13 degs
Total 28 degress all in at 2500 , that suits lpg very well espec with your final gear ratio.
Cruise above 2500 and all in 35 degs... Good
I think u could add a bit more to the idle with that cam...either 2 or 3 degrees intial (which changes total...and watch for detonation be it WoT or light load and could be in a very narrow rpm range.) or more VA 3 degs....again watch for light load detoation in narrow rpm range.
Beyond that u need correct 'tools' to dial in the engine tuning specs.

O2 sensor..havnt got one?
you have spent a lot on money getting the car this far, scrimping now would be a shame on that time effort...
A sensor in NZ is about $120....about 80 US....u can use amulti meter as suggested above or a gauge, for best results a data logger...what ever u do use, it will end up cheaper to by a O2 sensor etc than paying the local workshop to tune and use theirs... not just for idle but cruise, up hills , light load heavy load etc etc.
Where we have talked others into going this way be it hear or camaros.net those who have achieved heaps and no regretts... those who havnt are still blindly messing around.

The power valve..factory setting out of the box is generally pretty right, if in doubt open out another 1/2 turn till get a O2 sensor...Factory height from base in a a couple old threads.
Make sure the lever in the converter is exactly the correct height.

Ther is no majic timing/ fuel adjustment for your engine cam etc, transmission, final gear ratio car weight combo.
All here is is a ball park starting piont, from there it is "fine tuning" the idle circuits, cruise circuits, power ciruits bit by bit along with establishing ideal idle timimg, cruise timing at given rpms, and power timing.
There is no need to advance the timing any further if there is no increase in torque, before detonation.
Take particular note of that...over advancing is slow death to an engine and always blamed of faulty parts or workmanship if someone else built the engine..
More advance makes a engine sound nicer...it is a very strong equivlient of a optical illussion.

OH and when running VA on manifold vaccuum....It has to be all in no more than 1" above the intial idle vacccuum....

Why gone LPG... running economics???
I would take a stab you will get around the 9 to 12 mpg (4.54L /gal) with that final diff ratio....
At the end of the day, a engine turns over X number of rpms per mile...that is x times engine volume per mile...And every rpm require a given mixture ratio withing that volume. Therefore running a small engine at a given rpms will use less fuel OR a large engine running at a lower rpms with use less volume.
Just a thought.
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Marc
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Re: 327 build - fine tuning

Post by Marc » Thu May 24, 2012 7:36 am

Hi

Thank you Steptoe.

When I looked at vacuum gauge at idle I have 12 psi vacuum, at 1200 rpm and above I get more like 17-20 psi.
At idle with that vacuum the total advance is not much, as vacuum advance is not full.

Impco installation is new, so there should be no vaccum diaphragm ptoblem in the impco 425.
After reading you I have to look for setting the secondary butterflies correctly. I remeber at installation the secondary betturflies were a little bit open at close position, and the primary were well completely closed at this position.
However there is no problem with the idle speed screw to drop the rpm at idle very low.

How should I correct the settings for the secondary butterflies?


Regards

Marc
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Re: 327 build - fine tuning

Post by Marc » Thu May 24, 2012 7:48 am

And yes the engine like more advance at idle... I hear it clearly, it helps him. Now with the low vacuum, I have like 11-12° total at idle. initial is more like 8 then 6° also..
But to give more total at idle I would have more strain on starter.
So maybe to get more advance at idle I could give a little bit more VA with 8-10° full but it will bring me closer to the 37° total at cruise...
All a question of compromise..

Anyway now I need to get the mixer to answer to adjusting of idle mixture screw..


Regards

Marc
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327ci - fine tuning - detonation to fight

Post by Marc » Mon Feb 17, 2014 9:33 am

Hello

I come back on advance curves.
My new T56, speed transmission is now installed and I could drive the car this w-e.

I notice very clearly pinging now in 5° and even more harsh in 6° gear while accelerating at low rpm (~ 2000 rpm)
If I accelerate hard on the whole range 2000 to 5000 in 3° or 4° gear there is no detonation and the engine runs very well!

In 6° gear @ 2000 rpm I am @ 75 mph and vacuum is only 8 psi so there is no part throttle.
Why is this detonation only appearing at wot in high gear? And why should I now tune the ignition curve so that mechanical advance comes in later? and how should I start with the curve for test-setting then the total (initial + mechanical) that the engine can take?

For remind here is engine spec :

327 ci chevrolet with 10:1 CR, comp cam 268HE (218/218 @ 0.050) vortec heads.
IMPCO 425 straight on 4 barrel holley plate
8° initial @ 700,800 rpm
22° initial + mechanical @ 2000 rpm
30° initial + mechanical @ 2500 rpm
7° vacuum.
I have tuned this with one very light and one midium spring and no stop bushing on a Accel 52100 serie distributor and I plugged it to a multispark box Accel 300+.


Car start and idles great, it also runs great (appart from this pinging)

Thanks for your input

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Steptoe
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Re: 327 build - fine tuning

Post by Steptoe » Mon Feb 17, 2014 2:58 pm

I notice very clearly pinging now in 5° and even more harsh in 6° gear while accelerating at low rpm (~ 2000 rpm)
Try riding up a hill or start off in top gear on a 12 speed bicycle.. At those low rpms and not helped by the cam the engine doesnt quite produce enough torque in that gear....which is why we have a transmission with gears.
In 6° gear @ 2000 rpm I am @ 75 mph and vacuum is only 8 psi so there is no part throttle.
Is this at cruise?

What vacuum range does the VA work in? sounds like u have no VA at light load which is when the VA should be in.
And quite possible may need another few degrees in it at cruise... If have no VA @8" vacuum @2000 rpms and only 22deg advance....more advance more vacuum
But do not go over 40/42 deg intial+cent+ VA

And have the mixtures been sorted/ dialed in with AFR/ O2 sensors?

Also note.. carbed engines because of the nature of carburetors have narrower efficiency ranges than injection.....injection and 5/6 speed transmissions, higher OD gearing have become the norm in recent years, hand in hand.
In saying that .. I have a very bottom end toque cam in my camaro.. with bit over 60mph @2000 rpms.. small slopes ok , bigger slopes have to change to lower gear... yours at 2000/ 75 mph and a cam a little less bottom end will certainly require more use of the gears at low loads......or change the rear end / final gear ratio which will help at best.
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C3H8
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Re: 327 build - fine tuning

Post by C3H8 » Mon Feb 17, 2014 8:56 pm

Pinging is simply caused by the flame front reaching its maximum pressure prior to the piston reaching top dead center. Most of us know that. This can be caused by a few different reasons and corrected by various methods. Pinging or pre-ignition is caused by incorrect timing (set to far advanced), advancing too fast, lean mixtures in some cylinders (usually the farthest from the carb), carbon build up in the combustion chamber leading to hot spots, high compression. On the data you listed I can see a few choices since you have a special cam, higher compression, etc. Without a dyno, knock sensor or combustion pressure tester it is largely trial and error on the road. Some suggestions not in any specific order as to the best solution.

1. Retard your timing 1 or 2 degrees at a time until it goes away. 30 total may be to high on a 10:1 compression or the advance needs to be slowed down.
2. Slow down your advance so it does not advance as rapidly. Try slightly more tension on the springs.
3. Try richening your cruise mixtures a little. One of the main problems here is the corner cylinders can run leaner then the middle cylinders. Your pinging might be only on random cylinders and richening the mixtures might correct this.
4. Check your vacuum source on the vacuum advance. Also make sure there are no delaying check valves to slow the vacuum drop in the advance line. Also depending where you get the vacuum you can actually end up with vacuum higher then expected if you use throttle body vacuum. The air flow rushing down the throat can artificially raise the vacuum to the vacuum advance. Do a vacuum check directly on your vacuum advance line at cruise speeds and see what the readings are.

Marc
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Re: 327 build - fine tuning

Post by Marc » Tue Feb 18, 2014 5:18 am

Thanks for input!
For information my rear end is 4.11:1. The T56 trans has final 6° gear 0.5:1.

I will follow step by step as C3H8 recommends, starting with richening mixture and retarding advance.
If it doesn't go away than I may try adding a stiffer spring to lower the curve.
However I guess the curve should be preserved for bottom end torque on propane as it is stated on this forum engine on propane runs better with more advance on low rpm.
It is not the purpose to re-set the curve as for a gasoline engine isn't it?

Also steptoe ok of course as the engine doesn't pull enough torque at low rpm in high gears it has more difficulty on accelaration. But on highway cruising and slight acceleration at that point should not create detonation.

Then last question, as I didn't know it was detonation (as the engine does not ping in other circumstances) I drove still some 15 miles on highway with that pinging, most of it slightly and once it knock harder.... I am worried I may have caused damage!
I didn't notice any engine problem though once I left highway, I tried it hard in lower gears and there was no pinging, and engine is still strong, start quick and has smooth idle with no smoke....
What do you think?


Regards,

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Steptoe
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Re: 327 build - fine tuning

Post by Steptoe » Tue Feb 18, 2014 2:31 pm

Have a look at your spark plugs for excessive amounts of little melted balls of metal.
Detonation on a street engine tends to be a slow death.. unlike a track car and everything can let go with a melted hole in a piston 2/3 of the way down the track.
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storm
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Re: 327 build - fine tuning

Post by storm » Tue Feb 18, 2014 3:39 pm

I'd replace the spark plugs and also check the ignition system (plug leads, dist cap, etc.) just to make sure everything is in proper working order. Then I'd be going through the things C3H8 mentioned. It's no use setting timing up on an engine where the ignition system has seen better days.
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