Big Valves

[petert 588]

Well done Andy. Your data verifies the data I have. I'm currently getting some flow work done to assess the differences between 10, 15 and 20 deg. 36.4mm valves. I'm also testing 30.5mm exhaust valves. I'll post the data here when it's done.

 

The reasons for me moving to bigger (and longer) valves is to:

- repair some damaged seats

- use single groove collets (and other Kawasaki components)

- use top hat solid lifters

 

I think it's more important on street heads that the valve seat area is 100% correct. The place that cuts my seats uses an automated machine (Sunnen) with a tungsten carbide cutter that cuts the seat, upper and lower cuts, and the vertical drop in one pass. None of it is done by hand. Once the valves are faced, the head can be assembled. This gives reliable, repeatable and accurate seats (assuming valve guides are good!) As the process is also quicker than doing by hand, the cost saving is passed onto the buyer. If your head place is still cutting seats by hand, find another one.

Edited August 14, 2005 by petert

[Mattsav 1]

Well I'm still sweating away on the flow bench. I've lost count of the amount of time I've spent on these heads now.

 

I've got the 36.5mm inlet valves from Puma Racing to flow off the seat which is what I've been struggling with.

 

Total area under the graph has increased by 10%

Flow at 0.500" is up by 6.7%

 

The port shape is a real bitch, even copying the port is a nightmare. Both ports look identical but the flow bench tells a different story.

 

The curves in the graph were tested back to back to avoid any calibration errors (std port tested, head moved to modified port and tested)

 

As usual, ignore the actual numbers off my flow bench as they dont mean a lot.

 

Peter, Sunnen's are OK but the tripple air float Serdi machines are simply the best

Cutting seats by hand, urghhhh the thought of it, next you'll be telling me people still lap valves

[Robsbc 0 1 Cars]

Well done Matt....You just need to practice on a few more heads now....I can now see the people queuing up...

 

Rob

[Mandic 0]

Well done Matt!

 

 

That's really impressive!

[Mattsav 1]

I haven't stopped yet but its a step in the right direction.......

[Shevy 4]

I haven't stopped yet but its a step in the right direction.......

<{POST_SNAPBACK}>

 

Thats excellent news Matt, I knew you would get there in the end.

I'll give you a bell soon to see how far away you are with my B/V head.

[petert 588]

I finally have the results of some big valve flow tests I've had done. I had four different valve angles tested, 5 deg. to 20 deg., to see what might be an optimal angle for the port. The valves were tested in an otherwise standard head, with just 3 angle seats, blended into the standard throat. I'd have to say I was surpised how poorly they performed at low to mid range lifts. But this verifies how important it is to do the "full job". When you compare any of the four sets of results with the standard head, it is clearly a waste of money just changing the valves. You need to spend the money on porting to get the best results. As a reference, I've also included the figures from a factory Citroen race head (circa '91-92), fitted with big valves. All tests were done on the same flow bench at 28 inches.

Edited December 16, 2005 by petert

[petert 588]

Here's the four different valves as tested:

[engine killer 6]

dear all,

 

i will have my Mi16 rebuild very soon. big valve head is on the list and enquiry e-mails have been sent to Mr. David Baker but unfortunately still no reply. probably his order booking is too full already or my request was a bit cheeky. i had my head from richard longman long long time ago so both inlet and exhaust ports were ported and i am on tight budget this time. would very much like just getting the big inlet valves and bore out the inlet throats to match the enlarged valve size and blended into the port etc and it will be a bit cheaper i guess. does anyone know any alternative to get in touch with him apart from pumaracing@aol.com? thanks a million.

 

secondly, i will also have my jenvey 40mm tb exchanged for a bigger set. is 45mm tb the best suit for the over bored (85mm) Mi16? or shall i go for 48mm? thanks again.

 

e. leung

[smckeown 1]

yes thats the correct email. here's the extract from his homepage:

 

Order and Enquiry Status

 

Jan 2006. Booked solid until probably March so no orders or enquiries for now please. I'll start looking at enquiries again in mid Feb.

 

That's why he's not replying i'd expect

 

One of his current jobs is my BV head and bottom rebuild, so we should have some conclusive results from his work (complete build) in feb i'd hope

Edited January 7, 2006 by smckeown

[engine killer 6]

what a relieve

 

anyway, i will still get him do mine somehow sooner or later (if he accepts my order )

 

any though of whether i should get 45mm tbs or 48mm tbs? i am also using a pair of fastroad cams too.

 

gosh! mail the head to UK is expensive too about 100 quid!

[smckeown 1]

when I spoke to longman's recently about the 3 heads they offer (group 'a' standard valve sizes, 1mm larger inlets, 2mm larger inlets and exhaust) they confirmed that option 3 is for race purposes only as the power shifts up the rev range significantly. This was for the 8v, but shifts in powerband are worth considering during a build, as you may need to increase the rpm limit of the bottom end to make use of the BV head.

Edited May 7, 2006 by smckeown

[niklas 1]

when I spoke to longman's recently about the 3 heads they offer (group 'a' standard valve sizes, 1mm larger inlets, 2mm larger inlets and exhaust) they confirmed that option 3 is for race purposes only as the power shifts up the rev range significantly. This was for the 8v, but shifts in powerband are worth considering during a build, as you may need to increase the rpm limit of the bottom end to make use of the BV head.

 

Nice to have the results of your Puma BV head to compare to this...

[sutol 0]

Good grief , Lots of opinions then and not a lot of info, here is my two penny worth--

I have found that big valves and big carbs do tend to give more power but only if the motor is willing to rev and make use of it. Beneficial to racers but not a lot of good any where alse when 95% of the time the motor is not at or near peak revs. Better I find to fine tune everything else, concentrate on derestricting inlet and exhaust, get the fuel and sparks right, get the cam timing right and if you can afford to then lighten and balance the flywheel as a start. The engine will suck in what it needs and be torquey lower down which is where you need it especially pulling out of corners. It's not a lot of good wheelspinning out of a bend at 8500rpm when you could be covering more ground at 4000 two gears up and not loosing time having to change gear.

Not the opinion of everybody I'm sure but it works for me and it's cheap if your budget is limited.

[S13Nick 0]

im no expert but surely bigger valves meaning more airflow into cylinder meaning more fuel= more power, and a bigger exhuast valve gets rid of the gas's quicker! yes????

[Sandy 191]

That's the theory and some engine builders slavishly stick to that.

 

The reality is (IMO), that you need to use three aspects of the flow and gas pseed relationship to get the maximum charge into the cylinder (getting it out is much easier). First is to get sufficient, controlled gas acceleration during the initial-medium valve opening before and around TDC, which is more about clever cam timing than "maximising flow", second is the major valve opening period while the piston is truly pulling charge in, to slightly beyond BDC and finally the ram charging period, where again, the cam timing (combined with port/tract design) plays the leading role.

The problem with "Big valves", especially on the XU 16v, is that the first aspect is limited severely by the cam profiles you can use and how they're timed, partly because of the inlet/exhaust valves are so close at TDC with bigger valves. The success of this phase influences the success of exhaust scavenging and the initial inlet charge acceleration. During the middle phase, where flow is more or less dictated by curtain area, you can get a "smaller" valve open faster (less restriction on cam profile at TDC and less inertia) and some people (in terms of port shape) can achieve similar flow rates at high lifts with the smaller valves as with bigger valves (I can't detail how this is achieved without breaking professional confidences). During the final ram charging period, you can dwell and close a "smaller" valve more precisely due to lower inertia and the way the gas speed changes at lower lifts (Again, I can't detail this fully without breaking professional confidences).

 

Many experts will tell you that big valves = more flow and therefore less cam duration is needed to achieve the same cylinder filling, so the engine will work well over a wider rpm range; in theory that's true. My experience however, is that bigger valve engines are more sensitive to cam profile and timing and the undesirable side effects of a less than perfect cam profile with bigger valves are more pronounced than with smaller valves (mostly a boggy and unresponsive engine, that seem to make the numbers at the top, but feels horrible low down and thin in the mid range and at part throttle). Since most of the engines we're talking about on this forum are one offs, using off the shelf cams, without the facility or budget to experiment with a wide range of cam profiles and complementary inlet/head/exhaust designs; it makes more sense to me, to get to an ideal set up quicker and easier with standard valves.

 

I've achieved 97lbft/litre and 133bhp/litre from XU 16v engines I've built and set up so far, on standard valve sizes; with (if I say so myself ) immensely flexible power delivery and very sharp throttle response. To me, the way the power is delivered is more important than the numbers (but harder to convey!)

Edited June 13, 2008 by Sandy

[Guest levis]

May I drop my question here.

 

As I've read most of information here concerns N/A engines.

 

What about Mi16 Turbo.

 

My questions:

 

I have 2 heads from XU9J4 DFW and D6C - is there any differance between them ?

 

I have an option to buy a head from XU10J4RTE (T16) - is there any differance (I know about sodium exhaust valves)

 

Changing valves for bigger ones and porting head - are they worth in Turbo engine - There is no flow, but air pressure, made by turbocharger - that is why I am asking..

 

Thanks

[DrSarty 90 1 Cars]

I don't know for sure, but I would speculate what Sandy has last said probably still applies.

 

I say this because the risk of valves overlapping and touching each other (clashing) still applies whether the engine is N/A or F/I; it's a physical restriction.

 

Furthermore I would guess that other restrictions/limitations also stay the same, such as valve train inertia and how much the valves/ports (head in general) can physically flow. Naturally, sodium-filled valves in the T16 head will be lighter, and maybe there are some differences in the head in comparison to the Mi16. But my point is that that still is nothing to do with whether the engine is N/A or turbo'd; they are just physical component differences.

 

So in short, I don't think big valves are really necessary or even worth it period, as there are other simpler and perhaps cheaper areas where modifications can yield better all-round results, such as driveability.

 

I'd be very interested to hear what a genuine expert says.

 

 

P.S. The 2 Mi16 heads are the same IIRC. The lower power from the DFW is a result of a different cam profile and pistons, and maybe the cat in the exhaust. I stand to be corrected but I believe that to be accurate.

Edited August 7, 2010 by DrSarty

[Guest levis]

ok, so for Turbo it is not worth to put a bigger inlet valves.

So the only differance between T16 and Mi16 heads, are sodium valves ?

You said that timing shafts are different on DFW and D6C - which camshaft would be better to use to achieve around 300-340 hp. Maybe there is a need of changing them to some custom ones ?

[wracing 19]

For that sort of output standard cams would do fine on a turbo engine

[Henry Yorke 269 3 Cars]

ok, so for Turbo it is not worth to put a bigger inlet valves.

So the only differance between T16 and Mi16 heads, are sodium valves ?

You said that timing shafts are different on DFW and D6C - which camshaft would be better to use to achieve around 300-340 hp. Maybe there is a need of changing them to some custom ones ?

from what I have read historically, quite a few T16 owners run Mi16 cams. I think they are just a more aggressive profile, but it would be worth doing a search or asking on a T16 forum.

[Sandy 191]

I have little experience of turbo engines, but there may well be a better case for larger valves with forced induction. Valve to valve proximity is less of an issue since boosted engines run much less lift at TDC, also the greater pressure differential means that you're not trying as hard to resist low lift loss of gas inertia. You can also use a wider seat for a given throat size, which aids valve cooling and resists seat burning better. Flipside, off boost the engine could well be less responsive.

[Josh_Quant 27]

anyone know whats the best size valves to use for big valve 2.0 mi16/s16 head that i want to build and what car they from??

[stefan 4]

Which ones are the best to use for your head (car/application), I can't say, but the biggest, and off the shelf, that I know off, are from a 1.4 tu engine (106 etc.) with 36.4mm. They need machining to match.

There is a lot of work involved with a BV head/engine to get it right, and might not be everyone’s cup of tea.

[engine killer 6]

http://www.pumaracing.co.uk/

 

Dumping a set of BV seems not too difficult but opening the throat needs a lot of skill.

 

The one I trusted most in HK said he is not competent to do it properly but the one I do not trust (plenty negative comments) said it would be easy. So I strongly recommend you to find a proper mechanic to do the job.