Xflow tuning thread

[eattsie9 350]

Hi everybody

 

I thought it would be a good idea to get a bit of a tuning thread going for people like me who have no clue what to do.

 

Would be great if you wise gents could explain a bit about adjusting timing with stuff like stock dizzys up to msd programmable units and what you have found to work well for anything from a stock rock up to off chops & boosted engines. oh and carb tuning/jetting.

 

hopefully it will help some people like me who have no clue yet but are keen as to learn and give it a crack

 

Cheers

[mcfly94 169]

For a stock 250 (larger valves, extractors, 2.5" straight through) I ran 28* locked timing through street fire cdi, superconductor msd leads, msd blaster 3 coil and TFI dizzy with module.

Ran AFR about 14.3:1 through the standard webber.

Ran very well started as soon as I turned the key (AU Starter, 0GA Earth for Engine and Battery, 575cca Battery) and felt more responsive and felt it had more torque through the rev range, also returned 500km to 57 litre tank for town driving with 3.27 rear gears and c4.

[eattsie9 350]

awesome, thats pretty bloody good fuel economy for a xflow

 

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[Clevo120Y 815]

The first thing I do when tuning an engine for the first time is check that the balancer TDC mark is accurate, I do this by using a physical stop on the piston with a stopper in the sparkplug hole in number 1. rotate the engine till it stops and mark the balancer in line with TDC mark on the timing cover, rotate the engine the other way until it stops and mark the balancer again, the timing notch on the balancer should be exactly in between these 2 marks. Then when this is confirmed correct I move the balancer till the notch points to the 10 degree mark on the timing pointer, using liquid paper mark the balancer in line with TDC mark on the pointer, move the balance again until that new mark points to the 10 degree pointer and make another mark on the balancer at the TDC pointer again. What this has done is given you timing marks not just at TDC but at 10 and 20 degrees also, this makes setting and reading the "all in" timing easy. When the second mark is flashing at the TDC mark using the timing light the ignition is 20 degrees advanced, then it is just a case of advancing the dizzy along the scale on the timing cover to get your total timing at all in revs which would be as an example on the 10 degree pointer plus the 20 on the balancer gives you a total of 30 degrees advanced.

The XE dizzy has a problem with snapping the cast pin that holds the centre bit with the triangle pointers on it to the centre shaft, when this breaks the centre bit moves and the timing all goes to shit, to avoid this from happening I pull that centre out and file that locating pin off and replace it with a steel pin and it will never break, I will do a thread on how I do it at a later date with pics.

That is all from me for now I will add some more when I get more time

[Clevo120Y 815]

Also for best WOT power the fuel ratio should be between 12.7 and 13 for unleaded fuel.

[eattsie9 350]

wow i have alot to learn, thanks heaps

 

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[ando76 4,354]

One of the first things I do when tuning a car is make sure it is actually getting full throttle!!  You would be surprised at the amount of times that this isn't occurring because of one reason or another,

 

incorrect - cable adjustment

                 throttle pedal action

                 return spring tension

                 pin position at the throttle linkage etc. etc.

 

Once you have established that you have full throttle and there is a throttle stop working to not stress the cable, I move onto checking the position of the throttle blades at idle.  Too many times I have seen the idle circuit (particularly oh Holleys) totally destroyed by someone opening up the idle too far just to get the car to run. 

 

You should be able to get the car to idle with the butterflies JUST cracked open (even on a cranky engine) with careful adjustment of timing and mixtures. Base timing MUST be set with the butterflies as close to closed as possible.  This ensures that the carby actually retains an idle circuit and ensures a smooth transition onto the mains. 

 

Float level should also be checked at this time to ensure that we are not flooding the carb.  On Holleys I actually take the bowl off and adjust the float level off the carb.  I turn the bowl upside down and make sure that the float finishes up half way between the screws in the bowl (that hold the float assembly).  Simple when you have re-usable gaskets.

 

Once all that is good I move onto checking manifold vacuum at idle and setting idle mixture.  If you don't have an O2 sensor fitted in the car you have to go old school and adjust the mixture to get the best vacuum at idle.  small adjustments at a time.  There is some good you tube videos from Holley on this very subject. 

 

Once you have the best manifold vacuum record that figure and then remove the bowl and metering block (on holleys in talking here cause if you have a stock webber you should ditch it and get a performance carby LOL.)  and check power valve sizing.  we want half of the manifold vacuum here.

 

Ok once that is all sorted we can look at timing adjustments as so eloquently detailed by Clevo120 above.

 

If you don't have access to a dyno and don't have an O2 sensor in the car the rest is just guess work and feeling how the car is performing on the street and addressing any issues from there.  Jetting without these two tools is left to plug reading which is a black art and requires patience and a good stretch of quiet road and a box of plugs. 

 

With the dyno or O2 sensor on the road, we can look at the AFR readings and change the jetting and air bleeds (if you have a good carby) to get the best performance from the car. 

 

This is all assuming that the dizzy - leads and coil are all doing there job and the engine actually has compression on all cylinders, something that also should be checked before tuning.  If we have a programmable ignition we can also play with timing at given rpm and load points and make some serious power and get the engine very happy right across the rev range. 

 

Yeah there is just a little bit in it to getting correct tune - and then once you have all that you have to watch the weather and altitude to get the last little bit out of the car - well in a race application anyway - lol.  That's my two cents worth.

[gerg 10,871]

Just on the subject of idle adjustments: not many people are aware of this but ALL 4-barrel Holleys have secondary idle circuits, even the non-adjustable and emissions models. As the secondaries don't get used anywhere near as often, the fuel in that bowl can go stale very quickly, particularly in a hot engine bay. To keep the fuel fresh and flowing at a light trickle, very small idle ports are drilled below the transfer slots. When doing up a carby, these have to be cleaned out as they can easily carbon up being so small.<br /><br />The primary throttle blades need to be adjusted with the carby off so that the transfer slot shows as a little square from underneath the carby. This is to ensure that there is vac signal in that circuit ready to pull fuel in as soon as you touch the throttle. Otherwise if there's no slot showing, you'll get a stumble off idle.<br /><br />If your cam is too lumpy at that idle setting for the engine to run and you need more idle air, don't simply open up the throttle more, as ando76 said, you will lose your idle mixture adjustment because your fuel will be drawn more from the transfer slot, which is a non-adjustable circuit. Instead, try adjusting the secondary blades to get more air in, and if desparate, drill 3mm holes in the throttle blades. An old hot-rodder's trick is to drill through the bottom of the air cleaner stud hole, which opens out into a cavity under the carby that sees manifold vacuum. BG carbies actually came with an idle air screw already in there for this reason.