Race Engine Forum UK

That's very useful, SirYun, and an excellent website. Thanks very much.

I have a friend who is handy with CF so I'll have a chat to him (although strictly speaking our race class has a blanket ban on the use of CF - maybe I can paint it and say it's Fglass!).

The clearance will definitely be tight, since I'll have to leave room for the motor to rock around on its mounts without the airbox banging against the wall. Unless I attach the box to the wall and use a flexible skirt to attach to the trumpet base plate... Hmmm.... Oh well, nothing's ever easy!

If space eventually is a problem what about a curved intake trumpet? Jenvey(.com) do them.


http://i103.photobucket.com/albums/m127 ... /AH42c.jpg

i have no hard data but i would prefer a very short and wide stubstack with an eliptical flare (but a large radius should work too). that can be about 1.5cm deep and still work well airflow wise.

putting 90 degree turn into rampipes just does not seem too sensible.


the flexible skirt idea sounds excellent!

This is a good topic, widely read with good contributions from members, well done.

I don't want to bring the thread to a grinding halt. But I do want to take the guesswork oout of things like this so - for the general interest/education of all - I want to say that regarding what works and what does not with rampipes and bends etc - in terms of flow loss - it can only be determined by dyno comparative test or - easier on a flowbench. I have one, we can use it.
If the bench says flow loss - it's generally going to be a loss on the engine, (bit of a sweeping statement but I do know the right test methods) I can, from time to time, do this free - so if you have something you want checked out just get it to me by arrangement via e mail ccroftengines@aol.com

We'll publish the results and everyone can learn from it, me included.

GC

SirYun wrote:i have no hard data but i would prefer a very short and wide stubstack with an eliptical flare (but a large radius should work too). that can be about 1.5cm deep and still work well airflow wise.

putting 90 degree turn into rampipes just does not seem too sensible.


the flexible skirt idea sounds excellent!

Ive read and seen some good results with trumpets. Seems, long ones are much better then short ones due to velocity flow. The entry shape is mega important, and eliptical and bell shapes worked best. The bending of them reduces the flow slightly, but not by much unless you go like 90 degrees as air does not like going round corners. Again as Guy says, flow testing is the answer. Conclusion is to fit longest and straightest you can get away with and flow test for results. I for one would like to see the results as i might need a similar type of Ram Box made.

Andy.

"Seems, long ones are much better then short ones due to velocity flow. "

There is a lot more to it than that; The general rule of thumb is that a long inlet tract works well at low Rpms and gives good low down torque, but robs back at high Rpms, short ones give the opposite, although there are instances where this is also wrong and any theory must be born out on the dyno test. You can tune the power band on an engine to where you want it by playing with the total length, space permitting of course!
The 'inlet tract' length is measured from the valve head to the edge of the intake trumpet.

This is also true on short and long inlet manifolds. Long for torque, short for power.

Andy.

The reality vis-avis length is more involved than ever thought previously and is now only being understood by means of very advanced software.

The behaviour of the engine's torque curve is now indisputably accepted to be a function of the total intake chord length and X sectional area from valve to exit of rampipe (relative position of throttle plate is irrelevant), plus exhaust tract dimensions valve to manifold junction (s) & cam FL timing - among other things of course, bore size, CR, cam lift, duration, LATDC, combustion chamber layout & shrouding, valves etc etc etc. The full list is long but those are the main ones. You can play with cam timing and tract lengths/ex layouts to get the power band you want. Which is very handy - I mean swapping rampipes is easy to do in situ.

What is interesting is how flat the upper rpm power curve can be if you run a LOT of overlap - narrow lobe centrelines - eg twin cam 95-102 deg IN FL and 100-103 EX FL, compared with the more conservative 108/112 timing that we all ran for years. For a long time a lot of overlap was considered very bad practice for low-down torque. Not so if you get your whole engine package right (integrated). I suppose it depends to an extent where you want your power curve, no n/a competition engine has useable torque everywhere. Mind you, you have to watch your valve-piston clearances with kind of timing.

To avoid a situation of 'what you see is what you get' (which most people quite naturally have to run with because they cannot afford costly testing)you either have to do back-to-back dyno or software analysis. The latter will tell you the best rampipe length for given engine parameters stated, to get optimum area under the speed/torque curve.

Huw Davies Fire 1108cc unit (see GC V/W, results and feedback) is a good example of what I'm talking about - very precisely tuned intake length, where analysis and dyno agree to within 3%. Check out his top-end power curve - see how flat it is, that is what the software can do, quite extraordinary.

G

[quote="Guy Croft"]This is a good topic, widely read with good contributions from members, well done.

I don't want to bring the thread to a grinding halt. But I do want to take the guesswork oout of things like this so - for the general interest/education of all - I want to say that regarding what works and what does not with rampipes and bends etc - in terms of flow loss - it can only be determined by dyno comparative test or - easier on a flowbench. I have one, we can use it.
If the bench says flow loss - it's generally going to be a loss on the engine, (bit of a sweeping statement but I do know the right test methods) I can, from time to time, do this free - so if you have something you want checked out just get it to me by arrangement via e mail ccroftengines@aol.com

We'll publish the results and everyone can learn from it, me included.

GC[/quote]


Guy,

I'm currently getting together the parts for a throttle body set up for my 16v turbo, as far as I am aware no-one in the UK has done this yet, although there are examples in Europe I have seen. I have already got the inlet manifold sorted out and ready, I have chosen which Jenvey TBs to use (singles - model: SS) and am currently researching the plenum, I have many pictures, ideas and theory on this subject I can share.
If you and the other people on this forum want to help (checking the flow of the manifold would be a start), I can start a new thread and make it into a bit of an on-line project between us. Let me know what you think.

Martin.

Yes, by all means,

GC

Ok, I'll put something together this evening.

Martin.

Here is the airbox which my good friend Uros Piperski and I have built from fiberglass.
It's acctually "Pulorator" unit from some BMW but we customizied it to fit space.
It's not finished yet...




I'll soon post some pictures of build process :!:

Won't the filter at the back have no direct cold feed? Would it not be better to trunk it round to the front of the engine bay to get direct Ram Air? Seems you have plenty of room for it. The build looks excellent by the way.

Andy.

Filter is putted in there just for mapping of ECU,an right above i,on the hood there is a scoop.
In final form of the car it will be placed next to the opositte wing in the cold air box with it's own hood-scoop.
Actually there's no space in the front.There are radiator and the oil-cooler so it would suck hot air if filter would be placed there.

Dynodave wrote:Those ram pipes look too close to the inner wing on cylinders 2&3 to run any filtering system except filter socks.
Are the length of those ram pipes critical ?.Do you loose much power with shorter rams ?
In my experience filter socks loose around 6 bhp on a 200bhp engine.(new ones )

Hi Dave,

The socks we have tried don't just give a horsepower loss - they totally strangle it at higher revs so the motor just can't breath.

We're currently rebuilding the front of the car (after a race incident) and we're experimenting with fully enclosing the air space between the cold air intake, the wing, firewall and ram pipe plate, so we can put a filter in the air intake and keep clear of the ram pipes themselves. This will require some flexibility in the build somewhere to account for engine movement. I will post some pictures along the way.

Being a race car, every horsepower is critical (and six even more so!), the ram pipes have been tuned to length and even the angle of the carbs has been fine-tuned by milling the intake manifold, so I'm loathe to change any parameters that affect flow if I can avoid doing so!