New engine !

[SKiddell]

Bike carbs (shorter overall length) are a golden opportunity to alter the overall length of the inlet tract, some torque will be lost low down but there are benefits for cars that want to rev out. (this is one reason why bikes and F1 cars get big rpms, inlet tract design)

However if you want torque at low revs, a longer inlet tract is desirable, the car will pull tree stumps out but wont rev much past 7000.

There are some specific maths around it, and its not "bigger is better" there is a sweet spot that can be hit by tuning the overall length (and using pulse plates) which is all relative to a specific engine, I have it on a tee shirt somewhere.

Not going to say anymore as info costs, but your on the right track

 

[H3nrY]

Hey all, I finally got the car to a testing bench here in Belgium
This is the graph:

You can see a dip (small flat spot) at around 3500 rpm. will have to address this drop. its have not really felt it when driving, but the torque curve is doing badly because of that drop. At around 3700rpm, the cam starts kicking in. Starting from then, the graph seems very good.

These are the actual numbers in detail:

So its 194 at the wheels and I´m very happy with that the car feels good. The torque is around 270Nm at around 5000 rpm. According to the bench, the engine hp is producing 218.3 ps, so the loss from the engine to the wheels is reasonable.

 

[SKiddell]

PS is slightly different to HP

194 rear wheel versus 218 at the fly doesnt stack up it seems a little low

Typical Z losses are around 18%

What sort of dyno was it, a rolling road, or a hub based dyno

 

[H3nrY]

PS is slightly different to HP

194 rear wheel versus 218 at the fly doesnt stack up it seems a little low

Typical Z losses are around 18%

What sort of dyno was it, a rolling road, or a hub based dyno

Skiddel, it was a rolling road. I thought HP = PS ?, didn´t think there was a difference in those two. Yes, I find it strange also that the loss of the engine compared to the wheel PS is very light. The place I went to is pretty famous in Belgium. They normally put R8´s and stuff like that on

 

[rallymanDP]

Hendryk

I think that you could still get a better ( i.e. flatter ) Torque curve if you carried on development with the intermediate settings of those Bike Carbs - I have never seen a curve like that on any Engine, & the sudden drop around 3,000rpm is quite dramatic !

Yes, I know that on the Road, you could drive through it, but it could still be an improvement to dial that out, and it would be nicer to see a more 'diagonal' progression on the Graph.

Anyway, I would dare to suggest that it looks more like a realistic maximum Gross Power of around 230bhp at 6,000rpm, which still offers a fair amount of Fun from your 'Z'......no ?

 

[H3nrY]

Duncan

Yes, you´re correct. It´s not that you feel it when driving- But it would be better to see that spot gone. And for the fun part, I still get excited when revving it up to around 6900 rpm. I have been thinking about installing a short ratio gearbox. I dont really need to drive that fast.

 

[Nigel Brook]

I'm wondering if your exhaust could be the problem. L6 engines in standard form can produce a flat spot at around 4000rpm and whilst I can see you have a Janspeed header (which I am not familiar with on an L6) I wonder whether the system is up to the job. What diameter system are you using ? Does the header have a Y pipe collector on the end of it which ideally should be as far away from the end of the header as physically possible ? Just a thought.

 

[rallymanDP]

Yes, I think that the Flat spot on the 'L' Series Engines around 4,000rpm is well recognised nowadays, Nigel, and the Home-made Exhaust originally fitted onto this particular 240Z certainly produced that problem - it was one of the 6-into1 variety of tubular manifold and a 'Heath Robinson' load of welded-up Pipework after that.

That is why we replaced it with a good condition Janspeed Manifold and system. I have fitted quite a few of these over the years & have found them to be an ideal Road-spec system, having the correct length Primaries & Secondaries to eliminate the Flat-spot. Wish they were still available at a sensible price.
That made it slightly better, but still the mid-range mixture was well out of synch. After some research we found that it was impossible to buy the correct Emulsion tubes for those particular Bike Carbs to rectify the mid-range fuelling. If it was the Exhaust system at fault, then the flat spot would be around 4,000rpm, whereas the Graph shows it to be around 3,000rpm - telling me that it's not the exhaust, but the mixture.
Obviously it would be best to see the CO2 & Hydrocarbon readings all along the Graph to verify that, but all we can do is suggest a remedy & then try changing things to suit.

 

[Rob Gaskin]

Yes, I think that the Flat spot on the 'L' Series Engines around 4,000rpm is well recognised nowadays

I disagree, my car picks up really well at 4000.

Perhaps try changing the 6 bike carbs for 2 2" SUs

 

[SKiddell]

Good Rob...see you at Santa Pod then, you can show us how it picks up

 

[rallymanDP]

Well, you've obviously got a proper Exhaust Manifold & system on your 'Z', Rob !

Perhaps I should have said a potential Flat spot around 4,000rpm......

 

[SeanDezart]

Now, now girls - start another thread re holes, 4k revs and exhausts and stop spamming Hendriks'.

Top spammers this week - Skidden, Mr Gaskin and Duncan.

 

[SKiddell]

Sean

Get back to sorting out your overheating problems

If you want a decent engine you can borrow mine, you'll have to get used to winning races though

 

[rallymanDP]

Sean - this stuff directly relates to Hendrik's Engine, so naff off !

 

[SeanDezart]

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[H3nrY]

I'm sorry - drag-racing is not relevant to this subject and your engine's hardly FIA homologated.

Duncan - references to 'lucky' Gaskins' flat-spot don't rate as directly relevant either to Hendriks' case !

Stop spammers now !

Hendrik - mine has no flat spot - modest power-rating too.

Thats a very nice curve there Sean!
To all, I don´t mind the replies, that´s what a forum is all about. Will see on what to do to get rid of the flat spot. Will have to sort it out with some tech guys over here. Sean, you´re from France I think?

ps. one thing I did forget to mention, which I did found odd. The test was done in 5th gear. The guy started to rev up in third, and then switched to 5th and revved up all the way. He stated that it was better to do in fifth, as there would be no wheelspin and the loss of power would be minimal on the bench. Anyone familiar with these statements?

 

[SeanDezart]

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[zbloke]

Mine was done in third - you can see the gear-changes.

Why is there a dip in power at approx. 5250rpm?

Can you feel this when driving?

 

[SeanDezart]

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[Nidge74]

No, I'm from London which is why these hill-billies keep having a go !

Now now Sean, you know that's not true.
there are plenty of people from London on the forum that they don't have a go at.

Great thread by the way, interesting figures too.

Experimentation is the key to eliminating the flat spots unless you know some technical genius anywhere.