Big Valves

[crf450 0 1 Cars]

Dave, your quite right the pipe Eddie's chose for the primary's was 16swg 17/8"o/d tube.

To help him decide the overall design of the system I had to make him 3 different sized stubs which he bolted onto a finished exhaust port then fitted one of his many different bends to which he then flow tested.

Making the stubs was a right nightmare as I had little experience in flaring tubes or making tooling to do it, I also ended up turning the tube for the stubs out of solid.

After Eddie flow test all the stubs he made me a drawing of the whole system which I took to Tony Law exhausts along with my car.

The drawing details included,

Diameters and lengths of primary's and secondry's, diameter with three options for length for the main pipe and which cylinders were to be connected.

Cheers Martin

[fiji bob 0]

martin do you mind putting up a pic of the pic? doesnt have to show any detail im just interested in seeing it

[PumaRacing 2]

Dave, your quite right the pipe Eddie's chose for the primary's was 16swg 17/8"o/d tube.

Also most interesting then. I wouldn't say exhaust systems is really my speciality or something I get involved in much but I did write a computer programme many years ago based on flow requirements of gases at high temperature and it says 1 7/8" o/d pipe for outputs around his target of 70 bhp per cylinder. I would say from past experience that most people go far too large on exhaust systems so clearly his views and mine agree in this area.

 

All that remains to be seen then is if we end up closer to 280 bhp or 245/250. Whatever the outcome it will be very informative for all concerned and I will be quite happy to be proved wrong and learn something new from this.

[phatgti 0]

excellent thread gents.

 

dave i have vizards tuning the A series from my metro days, its been lent out so i shall have to go door knocking.

 

i understand what your saying about the theory and actual practical side of it, i dont have access to a flowbench but if i can understand the "theories" behind flow seperation and the way gas acts at different temperatures and valve lift then i'd be happy.

 

martin, do you know of any websites or books on the subject of manifolds or systems as i understand some of what you wrote but the lingo lost me a little - stubs etc...

 

thanks

Wayne

[Batfink 201]

something tells me I should be measuring my Maniflow manifold ; then getting depressed on its primary lengths and diameter

[crf450 0 1 Cars]

martin do you mind putting up a pic of the pic? doesnt have to show any detail im just interested in seeing it

No probs,any offers for hosting pic?

[blackscooby 0]

No probs,any offers for hosting pic?

CRF450...

 

You have PM re hosting.

[blackscooby 0]

Apologies for the delay !

 

http://www.peugeotsport205.co.uk/temp/Picture.jpg

[fiji bob 0]

cheers gents

[cybernck 402 1 Cars]

excellent sketch .

 

i would have expected that primaries would be tuned length across all 4 cylinders though .

[crf450 0 1 Cars]

excellent sketch .

 

i would have expected that primaries would be tuned length across all 4 cylinders though .

They are the same length at 28.5,the drawing isn't to scale.

Cheers Martin

[Alan_M 66 1 Cars]

Anybody measured the Maniflow system?

[cybernck 402 1 Cars]

ahhh, you mean they're curved but it doesn't show in this planar view?

[petert 588]

All a good read guys, but back to the original question, there are two reasons for changing valves in an Mi16:

 

1. A bigger head, what ever the size, allows a much better inlet seat to be cut, giving a better flow out of the bowl. The std. seat has just one 45 deg. cut, which then drops straight into the bowl. A well cut 3 angle seat needs a bit more metal to be done correctly, than what's available with the std. inlet valve/seat. It's the resultant 3 angle seat that makes the thing flow well, not necessarily the size of the head diameter.

 

2. Changing from multi-groove to single groove collets increases reliability.

[MartinR 0]

point 2 is up for debate i think.

 

my thinking is that it doesnt make a difference. What i will say though from personal experience is that Ford changed the valve in their 2 litre Zetec FROM a single collet groove TO a triple collet groove

 

the mind boggles

[Ahl 4]

the mind boggles

Does it really?

[Robsbc 0 1 Cars]

I see Longmans big valves are 35.5mm and Puma's are 36.5mm

[Ahl 4]

I see Longmans big valves are 35.5mm and Puma's are 36.5mm

The mind boggles!

[MartinR 0]

Does it really?

[B1ack_Mi16 67]

Bigger the better

[Guest puggti]

Bigger the better

The mind boggles

[petert 588]

You guys have lost it. I'm going to post a big valve vrs. standard valve flow chart next week just to end the agony of this thread.

[sorrentoaddict 1]

I would say that the very QUESTION behind its thread IS INDEED impossible, rendering such discussions (relatively) fruitless - here is why:

 

1) it is not plausible to ask in the first place whether BVH is better than a std. size valve head (or only sliiiightly bigger, like the BTCC MI16), because:

 

some tuners have spent AGES in developing the flow potential of a STD. VALVE

MI-16 head, which is ENTIRELY different path and results, compared to SOME OTHER tuners, who have spent also many development months into porting & seat & throat shape solutions that would make possible the theoretic advantage of the bigger valve seats - therefore WOULD YOU EVER expect that either one of these tuners would say that the other's concept is better ??? --> NO, simply because there is no way to prove it - when, one sunny day we will see a dyno shoot-out of 2 engines (it will not happen, never, but just imagine it PLEASE), in EXACTLY same spec. as refers to block, intake, Engine Management, and exhaust - only differing in the heads, supplied one by a BV-favoring tuner, and the other by a std-valve-size afficianado.

Now, WHATEVER the winner engine is (if AT ALL possible to say WHAT will be a win, whether a broader & sexier torque characteristic, or some lousy, unusable 1.73 BHP at 8,300 rpm.....), the reason for the better performance will NOT be due to SIMPLY the STD.VALVE SIZE OR BIG VALVE SIZE, but due to the level of success (and suitedness to his own valve size concept) in the design of the ports/seats/throats/port-to-chamber-entrance-geometry, that the very tuner in question managed to develop.

 

So whichever solution proves to be better, the reason will not be IN THE VERY BV OR SV solution, but of course in the ingeniosity & engineering brilliance of "the author"...

 

This should be very clear to ANYBODY who conceives engine tuning as something more than just adding-on components & "bolting-on" solutions (it reminds me of that sillly bloke some time ago on this forum, that asked whether he can order online and fit himself the 3-angle seats & big valves )...

 

And one more point:

 

If engine tuning (especially the gas flow part of it) could be based ONLY on logical thinking, I would easily say that on a 83mm bore MI engine, big valve seats would never easily give power, due to the obvious shrouding effects - but only a very shortsighted person would fail to understand that the majority of head design is based on some hard-to-predict parameters, which are not always FULLY justifiable by physics and sound logic.

 

The argument of Mr. Baker anyway seems absolutely sound and makes sense - that on mildly modified MI engines BVH is the better way to go - but then again it should be only done by someone who has done it more than 3 times - as I am fully convinced that by just fitting BV, without very delicate modifications to suit, it would only drop the flow/power potential of the head (especially at part-throttle and generally low- and mid-rpm-range)..

 

I believe that now it is clearer why posting questions like "BV MI - to be or not to be ? " are simply a waste of time trying to find the answer - but nevertheless the searching for the answer sometimes makes for the most interesting reading.

 

 

cheers

 

 

alex

[sorrentoaddict 1]

forgot to add - the "notch" beneath the inlet seat (actually above it when fitted)

is considered to be beneficiary on the MI head (according to some reputable french tuners) only when it is in conjunction with rather long duration cams (more than deg. for example) - why this is so, should be very clear, having in mind the amount of time that the valve head passes away from the seat edge and the consequent decrease of gas entrance speed (if w/o a notch) -

- but I stress that this explanation is what the logic says, while not always it is the true path in head design - more than once it has happened to me that those heads that I believed I had made a mistake while porting - made surprising results.

 

Anyway, with milder cams it is believed that the throat transition into the seat should be smooth (for eg. rally engines, where part-throttle drivability rules)

 

For fulll circuit engines, with very long duration cams, the notch most probably gives better cylinder filling - of course only at very high rpm.

 

who knows...

[phatgti 0]

its a good thing i blended the seat into the port then whilst using piper 270's, the car is very driveable on and off cam.

 

good post there sorrento, an impartial opinion, of course Mr Baker is going to talk up big valves, its what he deals in.