The V8 Owners Forum -

I've spent the last day or two looking at wideband sensor kits. The AEM kit looks pretty good but there is a simplified version from Innovation to be had which involves less wiring. Ideal. I've sent some questions to the sellers

Andrewrv8 wrote:I've spent the last day or two looking at wideband sensor kits. The AEM kit looks pretty good but there is a simplified version from Innovation to be had which involves less wiring. Ideal. I've sent some questions to the sellers

If you really are keen on sorting out your carb yourself then PM me an email address. I'll send you a spreadsheet which allows you to compare any jet and rod combo with any other, it will give you the difference for both cruise and on the powerstep as a percentage.

I don't really like giving out settings for carbs because some people in the past have assumed that they will be spot on and then they feel disappointed when things don't turn out to be right on their carb, they put no effort into learning how the carb works which annoys me!

Having said that a setting which may well work on your carb would be:-

83 primary jets, 65-47 rods, silver rod springs, 80 to 83 secondaries.

The primary circuits with the above setup are 16% leaner than the stock setup on cruise and 0.2% leaner than the stock setup on the acceleration circuit. (In other words the same as stock). I actually use a different setup with modified rods but it works out the same as the above setup!

You are looking for AFR figures of around 14.5-15:1 on cruise (any leaner and I have found that the engine won't run well). 12-12.5:1 during acceleration (without the secondaries being open). 12.5-12.8:1 at WOT

I been using an AEM for about 2 years and well worth the money.
I've just fitted a second AEM gauge to the other side of the engine and both gauge read the same at idle and wot and for most conditions but at very light throttle the left side reads 14.7 and the right side reads 13.5.

So now I need to figure out why.
Is it due to bad fuel distribution at light throttle?
Is it wear on one side of the throttle spindles?

The fuelling is a holley TBI and the manifold is a 360 offy.

The throttle spindles are worn more on the left side than the right so that's my first guess at what's causing the different readings.

The lambda that controls the fuelling (closed circuit) is on the left side.

All part of the fun but any comments would be appreciated.

Regards Denis

It could be many many things.

Camshaft wear, rocker wear, lifters, manifold designs, injectors not balanced, possible air leaks in either intake or exhaust, valve sealing differences, slightly different port shapes etc etc

stevieturbo wrote:It could be many many things.

Camshaft wear, rocker wear, lifters, manifold designs, injectors not balanced, possible air leaks in either intake or exhaust, valve sealing differences, slightly different port shapes etc etc

Yes indeed. As I said , all part of the fun.

Initially I will focus on the fact that the butterflies on the left may be opening slightly earlier due to the worn throttle spindles.

Regards Denis

Try swapping injectors side-side.

On a TBI that should be fairly easy ?

Wouldnt imagine spindles could be worn that badly ?

And is the difference at idle, mid, high ? all rpm ranges ?

stevieturbo wrote:Try swapping injectors side-side.

On a TBI that should be fairly easy ?

Wouldnt imagine spindles could be worn that badly ?

And is the difference at idle, mid, high ? all rpm ranges ?

The difference is only at light throttle (initial movement of the pedal) when driving. Idle is perfect. Medium throttle is perfect and WOT is perfect. I had ruled out the injectors as the idle balance is ok but I will try swopping them side to side.

The spindles are worn on the left due to return spring bias and cable force.
I can feel about 0.5mm movement when I lift the spindles.
Regards Denis

No seals on the throttle spindles?

DaveEFI wrote:No seals on the throttle spindles?

Afraid not. It's a Holley Projection TBI unit (4 butterflies and 4 injectors on the atmosphere side. It's really a 4 barrel carb with injectors instead of venturi and jets.

Regards Denis

I'd also check you don't have a (slight) exhaust leak on one bank.

DaveEFI wrote:I'd also check you don't have a (slight) exhaust leak on one bank.

Will do. Thanks

Regards Denis

Update.

I have spent many hours trying to discover why the mixture on one side of the engine was richer than the other. (I have a fuel ratio gauge on both sides of the engine)

After eliminating as many of the obvious reasons and some not so obvious I decided it was a manifold distribution problem. The manifold in question was an Offenhauser 360 single plane item and I have now changed this for an Edelbrock performer dual plane item and the problem has disappeared and mixture balance is spot on throughout the rev range.

My reasoning is that the offy manifold distribution was affected by the RV8 firings sequence such as pots 5 & 7 firing adjacent to each other. This effect happened mostly in the rev range 1000 - 2000.

The new Edelbrock distributes the fuel across the engine and eliminates adjacent cylinder interference.

I suspect I will loose a bit of top end performance but the initial torque improvement will put me further down the tarmac before the loss of top end will matter.

Thanks to all who gave comment previously.

Any new comments welcome.e

Regards Denis



Having

Interesting stuff, I run an Eddy manifold on my 4.6 lump, I must admit that I think I'm losing some top end BHP due to this manifold but overal it is a decent design. I have port matched my manifold to my gas flowed heads. Some people on the forum reckon that is is not required, I did it anyway!

sidecar wrote:Interesting stuff, I run an Eddy manifold on my 4.6 lump, I must admit that I think I'm losing some top end BHP due to this manifold but overal it is a decent design. I have port matched my manifold to my gas flowed heads. Some people on the forum reckon that is is not required, I did it anyway!

When I changed the single plane manifold for the dual plane Eddy I was in experimental mode and didn't do any port matching. Now that the mixture balance is sorted I will remove the manifold and spend some time matching it to the heads. The heads are TVR big valve 500's and the ports are stretched to the limit so I will have some work to do on the manifold. The heads are also skimmed so I may have to have the manifold faces skimmed to get the ideal match.

I will try and find a safe road to do some seat of the pants tests today.
All hell seems to break loose when the turbos kick in hard so ideal conditions are necessary to carry out full blown tests. I really need some sticky tyres as the current tyres limit the amount of power I can safely put down on a public road.

Regards Denis