Ideal Tract Length Xu7

[28CRAIG 2]

I have got a standard XU7 bottom end with a standard XU10RS head with 1.2mm of lift on the inlet cam and 1mm of lift on exhaust cam, it is going to have 43mm throttle bodies when I get the other pair back with a inlet tract of 310mm but they will catch the bonnet so are going to need modifying.

 

I should be able to get away with maximum track length of around 430mm which will probably be far too much but just looking for a rough figure of the ideal minimum and maximum for the engine spec.

 

Also I will be able to run 8 injectors with four at the head and the other four around 110mm to 150mm from the head does that sound about right?

 

Thanks Craig

[EdCherry 34 1 Cars]

1.2mm lift on the inlet! damn thats som lary cams.

[28CRAIG 2]

1.2mm lift on the inlet! damn thats som lary cams.

 

 

Standard gti6 cams the 1.2mm of lift at TDC is done by adjusting the cam timming with the early pulleys.

[Cameron 16]

1.2mm lift on the inlet! damn thats som lary cams.

 

That's worrying as mine have roughly 2mm.

[EdCherry 34 1 Cars]

Didn't know the measurements where at TDC... just thought it was overall LOL was a bit of a sarcastic comment.

[Cameron 16]

 

Seriously!?

[28CRAIG 2]

 

I might try for a bit more lift when it's up and running, i think 2mm inlet and 1.5mm exhaust will be the limmit as the head has had a slight skim but not sure how much.

[welshpug 1,675]

check sandy's info posts, but you have to be very careful with the 6 head and cams, there's bugger all room in the standard pistons compared to Mi16's

[28CRAIG 2]

check sandy's info posts, but you have to be very careful with the 6 head and cams, there's bugger all room in the standard pistons compared to Mi16's

 

I know there is very little valve to piston clearance on the 6 engine just not sure how much room there is in the XU7 (just had a look 1.5mm inlet and exhaust may have to machine some pistons ).

 

Any way lets keep it on topic so does any one have any useful info about inlet tract lengths and not just say Jenvey recommend 360mm so stick with that other wise Peugeot would not of made there throttle bodies 310mm and Sandy would not go through the effort to make them longer.

Edited June 18, 2009 by 28CRAIG

[wracing 19]

well it totally depends on what you are looking for. the inlet tract length can be optimized for torque at different points in the rev range.

 

i believe its long for good bottom end torque and drive ability and short for a high revving engine

 

but then its not as simple as that as you have cams and whatnot to throw into the equation.

 

if you correctly match a lot of variables then it is possible to achieve a volumetric efficiency above 100% at certain rpms

 

currently i don't know of a way to calculate or simulate inlet tract performance dynamically therefore unless you want to be on the bleeding edge i would suggest that you copy what others have just to good effect.

 

sorry cant be of much help

 

james

[Sandy 191]

Tiral and error is the only way really, but I'd expect 370-400mm to work well on this set up.

[28CRAIG 2]

Tiral and error is the only way really, but I'd expect 370-400mm to work well on this set up.

 

Thanks Sandy that is the answer i was looking for, after reading about Dixons on the rollers loosing 20bhp atw mid range with 45mm shorter trumpets i wanted to make a set that can be adjusted easy.

 

THROTTLE BODIES

[28CRAIG 2]

Just to check is that including the 80mm from the base of the valve?

[drmo 5]

Just to check is that including the 80mm from the base of the valve?

Yes

[28CRAIG 2]

I have designed some new trumpets with spacers.

 

These will replace the longer plastic trumpets.

 

Then using a cut down gti6 inlet manifold that the direct to head bodies will be mounted on so i can run 8 injectors and use of spacers to achieve different lengths.

[James_R 3]

Hmmm naughty looking.

[DrSarty 99 1 Cars]

Where did the DTH ITBs come from Craig?

[28CRAIG 2]

I think it was a group A 309 gti16 that used them, they have peugeot sport part numbers on the bottom and are made by Solex

[Batfink 201]

Its an interesting subject. Now reading books on engines leads me to believe that the higher the revs the closer to the valves you want to get the throttlebodies. (cant remember why now lol).

I'm thinking of running short inlet manifold and longer trumpets though this leads to the problem of the bonnet. My thoughts are what would the effect of curved trumpets be compared to a curved inlet manifold. What upsets the airflow more - before or after the throttleplate.

 

Kev

[Baz 421]

From reading books etc always leads to belief that better response is always achieved from running the throttle butterflies as close as possible to the combustion chamber, but it's obviously not always a viable option. The length of the complete inlet tract just changes the characteristics and/or the power delivery really.

 

Off the shelf manifolds are only really on offer because they do the job the easiest, without too much mofdification, they do the job pretty well yes, but by no means are they an optimum.

[Oberon 0]

Don't quote me on this but some Kawasaki bikes I beleive had inlet tract lengths of unequal lengths to get a more even power spread across the rev range, if its of any use.

[DrSarty 99 1 Cars]

This is a slog to read, but it's worth the investment. Click the smiley!

 

[unariciflocos 49 1 Cars]

Its an interesting subject. Now reading books on engines leads me to believe that the higher the revs the closer to the valves you want to get the throttlebodies. (cant remember why now lol).

I'm thinking of running short inlet manifold and longer trumpets though this leads to the problem of the bonnet. My thoughts are what would the effect of curved trumpets be compared to a curved inlet manifold. What upsets the airflow more - before or after the throttleplate.

 

Kev

 

I've had countless arguments with a friend of mine with an engineering degree in internal combustion engines and he said that the carbs/tbs need to be as close to the combustion chamber as possible because the mixture freezes the further it's made. Of course this does not apply if you have the injectors near the head as with the std manifold. Conclusion was get the carbs/tbs as close as possible and the adjust inlet length using trumpets.

 

This is just theoretical, we've done no testing to prove this, so might as well ignore me if you think I'm talking bs.

 

I'll be solving my bonnet issue by tilting the engine to the front with custom engine mounts.

[DrSarty 99 1 Cars]

?

 

I think you'd be hard pushed to freeze petrol!

 

And whilst there's an element of truth in what's being said there - and I acknowledge the language barrier - that doesn't agree with some high performance engine set-ups actually having injectors outside (before) the throttle bodies, visibly squirting the fuel into the trumpets.

 

You get better mixing and atomisation with the injectors further out, and the charge temperature is lower too. But if you run only one set further out, you can suffer fuel drop out at low RPM and have to map accordingly, making it rich at low revs to compensate.

 

With close-in injectors you get better throttle response and low RPM and cold engine running.

 

It's always a compromise....unless you run staged injector sets.

Edited October 16, 2009 by DrSarty

[Galifrey 1]

?

 

I think you'd be hard pushed to freeze petrol!

 

The petrol doesnt freeze, but its vaporisation acts as a coolant, the intake temp then drops sufficiently for water vapor in the air to freeze on the manifold and the injector stopping all fuel flow. Pre fuel injection it was known as carb icing, I am sure you have heard of this Sarty

 

It is the reason most cars have some way of warming the air entering the engine or use coolant to warm the manifold.