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Big Valves


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103 replies to this topic

#1
Batfink

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Now I know this has been argued in the past but im still really confused as to when they are required!

Pumaracing Dave is pro big valves but crf450 and his engine builder say they are not needed. Ive been to Shenpar and they didnt think they were needed.

So - in what situations will BV heads be beneficial - race or road or what ? low, mid or top end power??

Any dissadvantages???

I really need to cut through all the bull thats all over the web and understand the real world truths so I can decide whether I need them

#2
Batfink

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I should add that Im building a 2.1 mi16 hillclimb engine (if this will help on my situation specifically)

#3
PumaRacing

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How will more 'opinions' make any difference to your decision or understanding of the issue? If you spoke to 1000 people and 500 said one thing and 500 another would that leave you any the wiser?

It isn't a matter of opinion, it's a matter of flow and physics all of which is explained on my website. I see no easy way of adding anything further which would help the matter.

#4
Batfink

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ive looked at your website and it doesnt really answer my question.
You say you will see a gain of X bhp with big valves

That doesnt tell me anything.

If the extra power is at 1000rpm then its a waste of time
if its only at mid range then its probably no benefit. Your website gives a very generalised performance increase using big valves.
Are you really saying that a BV head will give 20% across the whole rev range!

If its so cut and dry why do some tuners disagree?
Im not trying to critisise your work but my race head and cam is coming to around 2k in price without BV's (its got Solid lifters BTW) so obviously any added bhp claims need to be well thought out before I shell out the money.

#5
PumaRacing

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ive looked at your website and it doesnt really answer my question.
You say you will see a gain of X bhp with big valves

That doesnt tell me anything.

I find that quite astonishing but a complete rewrite of the site to answer questions I'd never previously considered might have to wait a while.

Unless you're building a 100 litre ship's diesel engine I suspect the gains in peak power aren't going to come at 1000 rpm though.

#6
Jonmurgie

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That's not a very helpful answer now is it? :)

All Batfink is saying is your not giving any indication of WHERE the extra power will come with your Big Valve heads! Do you not know? No need to re-write your entire (rather interesting) website, but perhaps just add a few more details where it's lacking?

Not meaning to have a go at all... have read all the stuff on your site relating to the Mi16 tuning and head work etc. and found it very helpful indeed.. what's your turnaround time for headwork at present?

#7
Batfink

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I never said the site should be rewritten. I just said its not helpful to me :) Its a general guide that doesnt go into quite the detail I require. But then its not meant to be anything more than that is it?

Lets not get pedantic over my 1000rpm comment and just educate me on more specific BVH facts. Where are the benefits in power? Where in the rev range etc.
believe me I'm ready to listen

#8
PumaRacing

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All Batfink is saying is your not giving any indication of WHERE the extra power will come with your Big Valve heads!

Which after the hundreds of hours and thousands of words I've devoted to explaining how extra airflow affects power on both my website and places like the pinned 2088cc thread above strikes me as astonishing. There's an old saying. Give a man a fish and you can feed him for a day. Teach a man to fish and you can feed him for a lifetime.

I try to teach people how engines work. That way they can answer their own questions based on a good understanding of first principles. Answering each individual specific question limited to one particular engine or one particular element of that engine is a waste of time. It does nothing to further the person's understanding and you know damn well the same, or a very similar, question will pop up again in the near future because they learned nothing from the answer to the first one.

The answers to this sort of question don't just lie in the tuning article for a specific engine. They lie in the power and torque articles, the general tuning article, the 2088cc thread above and other threads where I've discussed the BV Mi16 head. Having said that, the Mi16 article even has power and rpm targets for different stages of tune. What more does anyone need - blood ?

#9
Adnic69

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Thats all very well to get on your high horse knowing in detail about lots of production engines and how to get the best out of them. However when people ask you questions (the only reason we ask is because we dont know) you should try to explain better not just treat us as being thick.
Stop throwing your f***ing toys out the pram and start being a bit more sympathetic for the less understanding members, we cant be all as smart and arrogant as you.

#10
Batfink

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how about a simple pointer or click through to the specific area I should be reading rather than this pointless bickering.
Like you - my time is better spent than reading every single thread in the hope its gone offtopic to talk about BVH's hense this post

#11
Sam

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What do the big BHP engines run ? If Martin hurried up we'd know what was needed :) I know on the TU engines they aren't much use.

Probably worth listening to the people who built the big power engines, can't say much fairer than actual evidence rather than a textbook explaination.

Edited by Rallye, 27 September 2004 - 04:24 PM.


#12
Batfink

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well Kev Light didnt make good power and I dont know anyone else with built engines :)

And then whenever BV's are mentioned everyone has a hissy fit

#13
fiji bob

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crf450`s engine should be interesting once its finished isnt it using original valves? but hotter cams?

#14
PumaRacing

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crf450`s engine should be interesting once its finished isnt it using original valves? but hotter cams?

I'm dying to see the results for that one too - especially after seeing the pics of the valve throats. However, whatever it does it still won't prove whether it would have gone better or not with a BV head so we end up no further forward. Even if it had back to back tests with a BV head that wouldn't prove whether the BV head had been ported properly.

The simple answer is there are no simple answers. Most of the VW Golf tuning fraternity swear that BV Golf 16v heads don't work but then most of them don't have flowbenches. The first thing that happens when you fit BVs is the flow drops - until you get the port shapes exactly right. Then it goes ballistic. So of course most of them never got BVs to work and their opinions are not surprising.

The perfect BV Mi16 head for a road car is not the same as the perfect one for a race car. Some very curious things have to done to allow longer duration cams to work properly. And no, I'm not saying what those are.

#15
phatgti

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and i dont blame you mate.

havnt seen eye to eye with you on a couple of occasions but theres no point giving away information that makes you money.

every tuner is different, my father says the big valves aint always necessary - a well flowed head is a better investment and that the 2 together work very well in some circumstances (to contradict that statement he's recently developed a 1275 mini miglia head with smaller than standard valves and a huge amount of headwork, it see's over 150bhp from a single 45mm weber with a carbon ramair box, apparently the customer can just drive past rivals out of corners due to the huge torque but loses maybe 2 horses to the most powerful engine in the series)

it depends on what you want.


oh and kevin, 2k for a head? for pity's sake please contact dave @ brunswick.

#16
crf450

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I'm hoping to have my new engine in and set up this year although I keep giving myself deadlines which keep passing,but I am now making real progress with my car even if it's a lot slower than I would like.
I can't see as waiting to see if my engine produces the power or not will tell you any more than we already know when you consider it fact the touring cars used standard size exhaust valves and only 3/4 of a mm bigger inlets.
I am told they didn't use bigger inlets because this would have meant compromising the cam profiles to stop the valves colliding and this was also one of the reasons we didn't use them on my engine,this coupled with the fact that my head flows enough air for well over 300bhp if you lifted the valves enough.
I have no idea if bigger valves would have make a big difference when using milder cam profiles. If I had to guess I'd say if Puma say they are worth while they will be. It's also worth remebering all our flow bench tests were done using a 86mm spigiot not 83mm they may make a big differance when used with the a smaller bore of the Mi.
Dave, it sound's like Eddie's not modified the valve throats on my head as you would, I'd be interested to here your thoughts on this.
Cheers Martin

#17
base-1

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id be interested to get a similar spec puma head commpared to yours Martin (as in what you want the engine for and cam profile etc) and see how different they are, would be very intriguing

#18
PumaRacing

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I'm hoping to have my new engine in and set up this year although I keep giving myself deadlines which keep passing,but I am now making real progress with my car even if it's a lot slower than I would like.
I can't see as waiting to see if my engine produces the power or not will tell you any more than we already know when you consider it fact the touring cars used standard size exhaust valves and  only 3/4 of a mm bigger inlets.
I am told they didn't use bigger inlets because this would have meant compromising the cam profiles to stop the valves colliding and this was also one of the reasons we didn't use them on my engine,this coupled with the fact that my head flows enough air for well over 300bhp if you lifted the valves enough.


The Superflow power target based just on peak flow at full valve lift is an awfully crude means of estimating power. Remember, a valve only hits full lift once each cycle. It spends most of its time either opening or closing. The whole flow curve affects power and in fact much of the benefit of 4v heads compared to 2v heads is better flow at low valve lift. My own computer systems map the whole flow curve against the whole cam lift curve to produce what I call the "camflow" curve which is a plot of head flow v crank position. What this does is model the entire time/area integral of the cam/valve system and that produces something you can meaningfully base power predictions on.


I have no idea if bigger valves would have make a big difference when using milder cam profiles. If I had to guess I'd say if Puma say they are worth while they will be.


Bigger valves are if anything more important on mildly tuned engines than full race ones. By getting power from flow rather than cam duration you preserve low rpm power and a wide power band. It's very hard to make up for lack of head flow by using hotter cams. Roughly an extra 12 degrees of cam duration to compensate for a 10% loss in head flow. That's like moving from a fast road cam to a rally one with the consequent loss in driveability.


It's also worth remembering all our flow bench tests were done using a 86mm spigot not 83mm they may make a big difference when used with the a smaller bore of the Mi.


Bigger valves would work even better in a bigger bore.

Dave, it sound's like Eddie's not modified the valve throats on my head as you would, I'd be interested to 'hear' your thoughts on this.


We discussed it on the phone a year ago. He apparently thinks a step under the valve seat is a good thing and I don't. It's kind of academic though because whatever you get you'll never know if it would have gone better or worse done differently.

Obviously I don't know anything about the cam profile you are going to use so it's hard to estimate anything about your engine's potential. If you have gone for ultimate race tune with no thought to tractability you might get close to your power targets. If you've stayed moderate on cam duration I'll be impressed if you exceed 245/250 bhp at 7600 rpm.

Without doubt though, if I'd been building an engine with 88mm bores it would have had big valves in it but also perhaps some very unusual mods to enable long duration cams to be fitted too.

#19
phatgti

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i blended the step under the seat into the port, there does seem to be a conflict of opinions though, to me its a restriction, no matter how you look at it.

dave, you know of any good books to read about this kind of thing?

ive read john waltons "practical gas flow" which i found interesting.

#20
PumaRacing

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dave, you know of any good books to read about this kind of thing?

Gas Flow in the Internal Combustion Engine by Annand & Roe

Any of Dave Vizard's tuning books. The Mini one goes into a lot of detail about head work.

The Superflow flowbench manual has some good info but needs careful interpretation i.e. you need to know a lot already to appreciate and evaluate what it says.

However, regardless of what you read and think you've learned nothing gets close to having a flow bench and seeing the actual port and seat shapes in front of you. You simply can't learn porting from a book even if it has drawings and dimensions to follow.

The flowbench only goes so far too. Eventually you move past simple flow numbers into gas speed and other matters. I can alter the shape of an engine's power curve and affect the peak power by several percent by doing things to the ports and seats and valve shapes that the flowbench doesn't register as a material flow change.

In a way that's why such questions as "big valves or small" is far less important than how well the work was done. No two people will ever port a head the same and the gains on what looks similar to the uneducated eye might be 20% extra power or zero % extra power.

Some time ago I sold a set of ultra big 45mm CVH valves (42mm is std) to someone who wanted to do the porting themself and have the seats cut by the local engine reconditioner. The port shapes to get those big valves to work is immensely critical. Somone else in the same circle of friends had a std valve head done by me and both cars went to the rollers on the same day with the same cam, carbs and other engine bits. The engine with the std valve head gave more power. If I do a full spec 45mm head it'll put out 15 bhp more than one of my ported std valve ones on that spec engine.

Just because they couldn't find that 15 bhp doesn't mean that big valves don't work on CVHs - or any other engine.