NITROUS OXIDE ( nos / n2o ) advice forum

It has been suggested by some people who are inadequately informed, that the Spider fuel delivery is adversely affect by acceleration and as a consequence causes the front cylinders to run leaner than the rest.

It didn't seem that my 35 years of experience was enough, to convince some people that would not be the case and a consequence I decided to get an INDEPENDENT ASSESSMENT from the MOST KNOWLEDGEABLE person (especially in the field of fuel delivery), that I've ever had the privilege to know.

That person is Bruce Robertson (from Australia where else) and he's responsible for the design and manufacture of the BEST carbs in the world; http://www.smartcarby.com/index.htm
Johnny Barb discovered the guy and was so impressed by his knowledge that he put us in touch and since then we've exchanged numerous technical emails and he's been good enough to post a couple of VERY TECHNICAL posts on my forum.

After providing Bruce with a bunch of technical data about the Spider and asking him what he would predict the effect of accelerative G-force would have on the fuel flow through the Spider, he sent me the following reply;

HI Trev, the answer I have is for every inch of length of spider tube facing fully forward at 1 g acceleration the change in fuel lbs per hour exiting the spider tube will be changed from 125.28 lbs per hour to 124.67 lbs per hour.
For the spider tubes facing rearward the fuel rate increases the same difference. So the total fuel is still the same but the distribution is different. For the spider tubes facing sideways there is no change as they are not subjected to G force.
The result is the same whether a single jet is used or the individual ones are used.

So the general rule is for 1 g and 1 inch you change the flow by 0.5%. For a 2" long spider tube the flow will change double that to 1% change and for 2g's the change will be double etc.
A powerful sedan drag car is about 1.75 G as an average for acceleration beyond 30 feet of track with around 2 to 2.5 g at the hit on the line. Most cars trail off to about .6 or .7g at the finish line.

I'm calling the brass tubes you have that form the spider legs, the spider tubes. Because some of them are facing forward they will flow less amount of fuel under G-force.
Fuel density affects the numbers a little bit as does viscosity but I've used average figures for unleaded.

Bruce

For anyone who doesn't see how insignificant the effect of G will be on the fuel delivery from the above email, here's the reply I sent him;

Hi Bruce,

MANY thanks for the assessment.

Based on those figures, even if the front tubes pointed directly forward (which they don't as they aim diagonally towards the front 2 cylinders), I guess you'd agree that such a small change in flow is unlikely to result ANY serious component failure, if any at all?

Best regards

Trev

His response was

Absolutely correct, its negligible. Have a good day. See ya.

I hope this puts an end to ALL speculation about the Spiders ability to deliver adequately EVEN fuel to all cylinders.

I've had to make the following statement numerous times over the years but here goes one more time;

JUST BECAUSE an engine suffers a failure when using a nitrous system IT DOES NOT 'AUTOMATICALLY' FOLLOW that the nitrous system ACTUALLY CAUSED the failure. There are NUMEROUS other factors that are all to easily overlooked, that are more likely candidates for such failures and by FALSELY BLAMING the nitrous or nitrous components all you are doing is MISSING THE OPPORTUNITY to find and deal with the ACTUAL CAUSE, which puts you at risk of a repeat of the failure.

That is a very interesting read Trev. I've had a look at Bruces site and those carby's he makes are so very very nice. The guy obviousdly knows what he is talking about when it comes down to fuel delivery with his carbs.

You may have misunderstood my concerns with the fuel delivery from the front legs of the spider.

It is not about G force affecting the the VOLUME of fuel from the front spider legs. It is more about G force affecting the direction of delivery.

I have tested my spider in free air with fuel and nitrous flowing. The fuel dribbles from all the legs and drops onto the front of the nitrous legs so the fuel can be drawn into the nitrous flow. I did not see any appreciable suction effect of the nitrous plume that caused the fuel stream to be drawn forwards away from the end of the fuel legs into the nitrous stream. Maybe you have a WON video to show this effect?

My own basic testing showed that with the plate inclined backwards just a few degree's saw the fuel from the front legs was a slave to surface tension and tended to stick to the bottom of the fuel leg which caused some of the fuel to miss the opportunity to be drawn into the nitrous stream. Therefore the fuel that cannot be drawn into the nitrous stream from the front legs would tend to run off the manifold onto the floor of the plenum. I guess this would mean that under acceleration that this excess fuel would tend to seep backwards on the floor of the manifold ??

It is NOT the actual fuel volume from the front pipes of the spider that I am questioning. It is the diection of the fuel flow and where it ultimately ends up.

As I have said to you via private email before. I have had satisfactory results on the dyno with the spider once I had jetted it to suit my inlet manifold design. But on track it behaves in a different manner?

THIS WAS MY MAIN CONCERN !!

Now lets talk about the effects of airflow in the inlet manifold affecting the fuel flow from the front legs of the spider when the car is running a 1/4 mile pass.
I cant comment on this and we both know that we cannot see this effect in real life. So we have to rely on our plug readings. And my plug readings showed very lean on the front two cylinders (if not melted) of my V8. And lean on cylinders 3 and 4, and then progressively rich to the back cylinders.

I have already concluded that the best way to run a spider (in my opinion and from my own testing would be):
High presure fuel delivery of 3 bar.
Jet the spider fuel legs and not the pulsoid outlets.
Jet the spider nitrous legs with less gas for the shorter runners of the inlet manifold.
Make the spider fuel legs longer than the nitrous legs.

If the fuel leaving the legs of the spider has a good head of presure behind it and the jets is in the leg it will have more velocity at its outlet in order to make it, no! Force it to flow where it is needed. If the fuel leg of the spider is long enough it could be made to drop the fuel in front of the nitrous stream so it has no choice but to go where it is needed. And if reversion is an issue when the inlet valve is closed at least the fuel will be in with, or in front of the nitrous stream.

And heres my own personal thoughts on how the spider could be a world beater on nitrous delivery!!!

Fit fuel injectors in the inlet runners of the manifold and use the spider for nitrous only.

I'm sure you will have your own comments in reply but as this is an open forum I'm happy to voice my opinions based on my own experiences. And I'm happy to take all comments and feedback to enlighten me.

Regards
Perry

Hi Perry

Interesting post but i have to disagree with some of it...

Take my engine as an example, which is not a lot different to yours in a general sense.. 4.7 ltr with FI (not carbs)

Now when I ran lower Nitrous (150/200 hp) I also had a problem with 2 cylinders.. BUT..it was the back two.. not the front...now when i was running that sort of hp I basically had a single crossfire that fed into the plenum across a hole in the middle of the plenum , much like feeding down the spider in the centre of your manifold (or Rons)

Now as previously stated my problem was with the REAR 2 cylinders running lean and somewhere on here is a very nice piccy of a rear plug that I totally melted....a bit like Rons...

Now its a KNOWN fact amongst 928 owners that those cylinders run lean under any sort of forced induction BECAUSE OF THE PLENUM INLET MANIFOLD DESIGN, and therfore I never even thought of blaming the crossfire.

In fact when I changed to my Fuel discharge tubes for my DP/Revo system and sent my plenum to WON to have them fitted it became obvious why all 928s have the rear cylinders problem...there is a huge internal casting at the rear which I suspect was originally designed for a fitting bolt to be drilled through the plenum and although it was never used, the internal part was left (no idea why, ask Porsche lol)

So Trev and the guys did some VERY clever diagnosing/drilling/removal and my rear cylinder problem was gone...

The point I am making is that I had absolutely no problem with the front two cylinders either from gravity or G-Forces affecting direction of travel..and IF there had been it might have actually improved my rear cylinder problem..but it didnt of course as it didnt exist....only my badly designed plenum did.

Just one final thought about G-Forces and direction of fuel travel....

When a Top Fuel car loses a cylinder or 3 its NOT usually the front cylinders...normally its middle or rear...and a Fueller has a LOT more G-Forces than any of us run....

Just a few thoughts...

All the best Brett

Daniel Bernoulli is rolling over in his grave.

All info and feed back I get is always taken on board Trev. I still have my opinions just as you have yours. I'm not sure how my test results on dyno and track can be called anything other than actual data? I understand that my data is totally specific to my engine only. Thats why I have asked to be put in touch with anyone who runs a spider with good results so I can get first hand information. The only information on the spider is what it should do. I want to talk to someone who has got one tuned and running because they will have information about how they set it up. Or in fact if they needed to do anything to it at all to run well on the track.

My testing and analysis of whats going on with my spider setup may be flawed in your opinion. But at least I am doing some real world testing and trying to come up with some information about how this thing works with my engine. I havent found anyone else coming back with any useful test data from the track. And maybe my results are one thing and my understanding of those results is another which is wrong. Without trial and error there would be no data. Once all the wrong answers have been identified and sifted from the equation all that can be left is the truth eh? So someone needs to do testing of some sort with a spider on the 1/4 mile.

The spider is on the back burner for this year as I am working on the blower + won system as you know.

I'm not sure how my test results on dyno and track can be called anything other than actual data?
I'm ASTONISHED AT THE STUPIDITY of that question!!!!!!
Sure you can call it "data" but as I've CLEARLY pointed out in my previous posts;
1) YOUR "data" IS WORTHLESS & INCORRECT because it is NOT carried out in a the way the Spider IS USED.
2) Even if it had been correct and useful "data", YOU have used it to JUMPED TO SENSELESS CONCLUSIONS.

Your test is just as WORTHLESS & INCORRECT, as if I carried out a test to determine if a rat could live on the moon, by seeing how they managed to perform HERE. Just as my test would be TOTALLY UNREPRESENTATIVE of the conditions the rat would experience on the moon, so to is your testing of a Spider in open air TOTALLY UNREPRESENTATIVE of how it performs in the manifold of a running engine.
IF you can't understand that SIMPLE LOGIC then you need to wise up and you need to realise, that you've NO business testing and 'ANALYSING' a product that you're TOTALLY INEPT to do.


[color=#00FF00]Your talking about the fuel flow tests I did ages ago. The testing on the track and dyno is with the spider fitted to a running engine being run in anger either on the rollers or on the 1/4 mile. How can the results I see from a pass on the strip not be data that has been obtained from using the spider as it is meant to be used?

We will never agree on this matter. But I will pick up the spider next year and tinker again when I'm ready. Maybe by that time I'll have another viewpoint on how to use it. I will be using a complete spare engine for this testing only and I will have a selection of manifolds that I can cut about and play with.
Regarding the test of seeing just how the fuel gets drawn into the nitrous stream due to the capture area set up around the discharge tube end as the nitrous exits at a high speed.
would you expect to see maximum capture of fuel on a rig in free and still air, or from a rig inside a manifold on a running engine? This is where our thoughts go in opposite directions isnt it ?

I'm off to finish the pulsoid brackets on my DP system now

Not a lot I can say to that really is there.

I have to accept the overwhelming evidence that you have provided. My testing has been shown to be flawed and therefore any conclusions I have made have been of no use to anyone.

The part about me making untrue claims makes it sound like I'm trying to discredit the spider. This is not the case. All I want is a working item. Or should I say, an item that works on my own engine. Hence my thoughts on the modificatins I intend to make to my own spider next year.

I will keep my test results to myself from now on. I want to stay on the froum because its a good place to be

Hopefully this will draw a line under this debate and our differing thoughts.

Is that acceptable ??

Perry

Hi Perry

Its a shame this situation has arisen.

I am a little unsure why you decided to "pick and choose" which pieces of Trevs advice you were prepared to take but it wasnt your brightest moment.

When you are listening to a World expert, you dont normally argue and then say "I can do it better"

While we are clearing the air, I never understood why once you had started improving your times so well, that you then decided to change to a blower, that seemed a huge backward step to me, partially because you cannot control a blower with a Maxx lol... so you cannot have progressive control, and that leads to pistons and crank vanishing out of the side of the block....

The idea of then adding back the nitrous with either a spider or DP or Revos seems pointless and could be engine critical

The main point is that you need to decide in which direction you need to go with your engine...either Nitrous or otherwise and stick to whatever decision you make.

If you decide on Nitrous then listen to Trev...totally and you WILL get the times you wish...

Or not, as you wish...

I hope you take this in the manner its offered, as good advice (hopefully)

All the best Brett

Thats cool Brett!

The blower thing is another avenue I've wanted to explore for a long time.

While I'm having the new engines made I might as well find out just what I can do on the blower. In an ideal world for me I'll end up with a blown engine, a spider engine and a dp engine in 3 different cars.

But all the builds will be based on the same engine and tranny. So each engine can be swapped from car to car ?

I'm also tinkering with a turbo fiat at the mo. That will be interesting with front wheel drive.


Regards
Pel

Is that acceptable ??
Not entirely for the reasons given above but just by enough for me to put a hold on my intentions for awhile. I have NO desire to be even slightly disagreeable with ANYONE but being a Yorkshireman I don't hold back when the line is crossed and unfortunately you went way over that line.
All I can say at this point is that I'll give the matter some further consideration.


Ha Ha!
I already know that Trev... Thats sommat we Southerners lack. The old plain speaking thing. I'm sorry if my comments came across as anti spider. We discussed this before via pm about my comments starting an anti spider campaign. I never thought about how many folk look in but dont contribute to the WON forum. The comments I was making about my own issues could easily be misconstrued as being a fault with the item itself as opposed to how to use it with my own engine. I can see how you would think would be me trying to trash the spider. If I wasnt serious about using the spider I wouldnt already have a built a 3500 Rover lump which is already fitted into my Sons Escort with a spider + holley 600dp carb and a hoffy manifold to try again.
The car still needs brakes and suspension sorting out but we hope it will be out for shakedowns next year at the Ford show at the Pod.

I'll say again:
After reading Bruces comments I can see that volume of fuel flow from the spider legs isnt an issue now. And your coments about me doing Bruce a great dis service are unfounded because i only commented on the carb issue. In fact after visitng Bruces website I got online and tried to order one of Bruces smartcarbs for my spare 4.6 engine for the V8 Spider powered MG Midget. Unfortunately Bruce could not sell me one of his carby's because he is based in Australia and he prefers to attend and set up his carbs on the customers engine so he knows that it is optimised and working from the word go. Thats a bit of a bummer really.. I like the look of those carbs he builds.

Hi all. There are some things to consider when assessing engine performance variation from a dyno to the track.
As you all are aware I was asked to calculate the fuel flow change for the spider under G-force. What I worked out is correct but its only the flow rate. The direction of flow and how it differs has been discussed in this thread also. The affect of G's on the fuel droplets after they have left the tubes is that the point of where the fuel is shooting to is moved. The air in the plenum cannot accelerate the droplets. The situation is this, the car is changing velocity and its not until a fuel droplet is hit by a solid object like the manifold walls etc that the fuel droplet has its velocity changed to be in sync with the car. For instance all the drag cars with tunnel ram manifolds especially the sheet metal ones, run rich on the rear cylinders at launch. Its the rear wall of the manifold slamming into the droplets that results in a lot of fuel running down the rear wall of the manifold and into the rear cylinders.
What happens next is the hard to part to understand.
A little background is in order here, engines input energy to the fuel prior to combustion. The principle concern with combustion is the completeness of vaporization prior to ignition. It has been proven that perfect vaporization is not optimal in some situations. It is also evident that the level of vaporization achieved in the common mans engines is far from adequate. Its important to understand that there is a difference between inputting energy and achieving vaporization. Vaporization can be achieved by reducing pressure and also by increasing pressure. Within the intake system of the engine there are areas of high vacuum even at WOT. The valve curtain area is always a low pressure (high vacuum) location.
Vaporization will always occur in the valve curtain area.

Compression is an energy adding part of the cycle of engine operation. The air heats up when its compressed and that boils the fuel. Simple.
However one must also consider the ability of the chamber to mix the gaseous fuel for maximum homogenization with the air. Valve curtain vaporization results in good homogenization, compression vaporization relies principally on the squish action for homogenization. Squish is well after ignition.
Depending upon the effectiveness and balance of just these 2 examples and how much vaporization is achieved at each stage is the final environment of the chamber at ignition time.

The g-force will always enrich-en the rear cylinders if there is an opportunity for some of the fuel to redirect from front to back under acceleration. How the cylinders react to that enrichment will not the same for each engine. There is only a fixed amount of energy in a given engine for vaporization. Unless you change something you cant alter the vaporization energy methods used by the engine.
Consider an example engine with a large cubic capacity,low compression and small valve curtain area. That combination may have a lot of vaporization within the valve curtain. However when vaporization is achieved by pressure reduction the energy supply for that is taken from the air temperature (discounting the valve heat as that's only applicable to the fuel contacting the valve). Air temperature is a severely limited source so this example engine will reach a limit of vaporization achieved as you continually en-rich the mixture. There is only so much energy to go around and if you shove too much fuel into the valve area you eventually reach a point of reducing the amount of fuel gas issuing from the valve.
Now consider an engine with sufficient valve lift and duration to considerably increase the valve curtain air pressure. This engine must now vaporize by compression rather than pressure reduction. So its a going to be a totally different environment at ignition time.
There is obviously vaporization happening from these 2 example sources in all engines, but its the percentage of influence of each style that alters the final result as to the sensitivity of a cylinder to being rich or lean.

What I have said above is one of the principle reasons for why peoples personal experience with engines differ. Some say they blow up rich some say they blow up lean. The reason why it blow's up is there is excess hot aggressive oxygen during part of the combustion phase. This oxygen may from the atmosphere. Any time you don't achieve homogenization of fuel in a gas form with the air and or nitrous you run the risk of melting something.
The common reason for melting is " it became too lean". Unfortunately most people only think of the cylinder as having an AFR that we can measure in the exhaust. Thats not the case, you have to think about what it is for the entire time of combustion. The burning AFR may vary greatly from 17:1 to 10:1 during a stroke even though the average AFR may be 12.8

A cylinder with less efficient vaporization will go through great extremes of AFR during a burn. Heat from the burn is used to vaporize liquid fuel, its a very dangerous tuning style to use for high performance. You can get away with it easily in low HP per cube designs but not when you start to push it.

Thanks for all that Bruce I just wish I understood it all as well as you do. Having said that, it seems that knowing about it doesn't help a great deal to overcome the problems unless you're designing/building the engine from scratch, as there are so many variables to cope with already, when you have an existing engine design/spec to work with.

The point I made is this. Any time you dont achieve a sufficient vaporization and homogenization there will be areas that are leaner than others. Any time you overload a cylinder with fuel you limit the amount of vaporization that can be achieved. It doesnt matter how much fuel you shove into a cylinder once you reach the point of not enough energy to gas sufficient enough chemicals with enough octane to support your engine your going to detonate. What people dont realize is that street unleaded petrols have low octane chemicals in the low distillation temperature ranges(there cheap). Race fuel are much high octane chemicals in the low temp range (there expensive). What the distillation temperature range tests mean is the first chemicals to turn to gas are the low temperature ones. What needs to be achieved is to turn enough molecules into a gas but also to have the gas mixture consisting of chemicals far enough up the distillation chart to be enough octane for your engine. This is a critical thing to get right at ignition time. Getting it wrong results in damaged spark plugs. Simply shoving heaps of fuel into a cylinder and then not having enough temperature generated in the cylinder will result in lots of low temperature chemicals in gas form at ignition time.
The main reason why a rich cylinder on Nos will melt, is lack of sufficient heat to vaporize the fuel. Nos is a double ended sword you have to add more fuel and it also freezes everything.

So would it be beneficial to atomise the fuel as best as possible just before you spray it at the back of the valve? This would reduce the amount of energy needed from the engine to vapourise the fuel yes?

Most certainly, which is why we developed the Atomising Fuel Discharge Tubes.

Are the tubes available as a service / upgrade part??
Jasons Escort will be ready for shakedowns next July so I might as well plan ahead.

They are available to special order only and may not suit all applications due to the design.

We're currently working on a replacement/upgrade to the current Venom fuel injector, which will have the same features/capability as the tube but in a more conventional injector/nozzle package.
Hopefully we'll have those in production by say March next year.

BTW you wouldn't believe how many new and yet further advanced products we are currently working on, that we hope to either be launching to the general public or making available to select customers early next year.

This stage of the WON REVOLUTION is going to blow EVERYONE'S socks off.