Exhaust and intake valve size.

[MNGSX]

I started with exhaust in the title for a reason.

I am playing with engine simulators. IE "desktop dynos".

I will probably take the time to write up some thing serious about the effect of valve size on a turbo 4g63.

Forget about what cams and turbo.. etc.. I have just a generic cam and turbo entered in. I have'nt taken the time to entire exact specs for what anyone uses for that stuff. I just needed a baseline virtual engine to test one valve size against another.

On 2.0's the power curve rises with rpm and flattens a bit at high rpm with stock valves.

Add 2mm to the intake and the curve moves up a bit 10-20hp in mid to upper rpm but stays mostly the same shape.

Add 2mm to the exhaust with stock intake valves and you get a bit more power than what the intake increase did. It also changes the curve. It just keeps climbing.

On 2.4's its even more dramatic.

The stock valve size curve climbs then dips at high RPM.

Go 2mm over on the exhaust and you go from an engine that lost 60hp or so from peak to redline to one that only lost 20hp.

I guess my non scientific explaination of a scientific simulation is that on a turbo 4g63 increasing exhaust valve size is probably more important than intake size. It is dramatic on stroker motors. Aparrently a modified head yet with stock size valves does'nt have anywhere near as much trouble filling the cylinder as emptying it.

If on a 2.4 some crazy macinist installed exhaust valves the size of the factory intake valves the SHAPE of the power curve is'nt that far off from a 2.0 with stock valves. The power is definately increased over the 2.0 yet it increases almost as linearly and not leveling off until as late.


I was just looking to see what was limiting things more. Intake or exhuast flow. It's not surprising that on a turbocharged engine it is more limited by the exhaust side than the intake. Don't read this and blow off intake size increases at all just that maybe if you only have money to put in oversize valve for one bank of valves do the exhaust valves. Maybe punch out the intakes 1mm and the exhaust 2mm etc.. It sure seems to take a shine to exhaust valves and it has a viagra like effect on a stroker or 2.4's powerband.

 

[silverbulletAWD]

Very interesting! Here's a few thoughts with which I hope to progressivly work towards a point:

To my understanding, the bigger the valve the better for all out top-end HP. Being that it's the last restriction in the intake tract. I assume their could be a calculated loss at lower RPM's though.

At what point does shrouding come into to the equation? As in, at what point will you loose too much flow.

If it's not that much of a loss why dont we do just like the V8 guy's have been doing for years and notch out our cylinder walls to clear bigger valves?

I'm thinking the seats would probably be the limiting factor, but were there's a will there's a way.

If larger valves are an option, thats good. I just hooked on a new lead for custom stainless valves for cheap. And apparently he can go very custom. This is only in the very early stages yet though.

BTW, can we talk about seat angles on this one or should we start a new thread?

Andy

 

[MNGSX]

Originally posted by silverbulletAWD
To my understanding, the bigger the valve the better for all out top-end HP. Being that it's the last restriction in the intake tract. I assume their could be a calculated loss at lower RPM's though.

Valve increases really don't change the low end much at all just the mid to upper RPM. As for the "last restriction in the intake path" a intake valve is'nt the only one. Any combustion byproduct that did'nt exit the head on the exhaust stroke is a restrictor. You could have the most potent cold side on your head but if the engine can't get it out it does'nt matter. All the data indicates that everybody is doing it wrong by putting more time into what to do to the intake when the biggest weaklink in the entire head flow process (besides cams) is the exhaust valve size.

 

[wishihadatalon]

think velocity on a 4 valve per cylinder car not flow or so i have been told. but i have also been told that on a n/a 4 valve car that if you have a bigger intake valve and a smaller exhaust valve that when the exhaust valve opens and you have both valves open for a fraction of whatever that it pulls more air in to make a bigger mixture. which is why n/a cars run more overlap for the extra suction of air. but on our cars with a turbo pushing air you want less over lap b/c you would just be pushing air through. so if you go with a bigger intake valve to free flow and a normal exhaust valve you would have maximum velocity to shoot the exhaust air at the turbo.
again this is what i heard from a friend building a all motor northstar feiro. please correct me if i am wrong b/c i am trying to learn this stuff.

 

[MNGSX]

so if you go with a bigger intake valve to free flow and a normal exhaust valve you would have maximum velocity to shoot the exhaust air at the turbo.

Wrong. Think about a rotory and how their exhaust ports and lack of valves can spool a larger turbo per liter of static displacement. The turbo is'nt mounted right behind the valve but at the collector. A larger valve will flow more air into the manifold and since the manifold has'nt changed there will be more velocity in the turbine housing.

About the NA cam overlap.. What they are shooting for is when the exhaust pulse is dwindling and there is a slight vaccum behind the exhaust flow as it exits the chamber. That can help pull in air.

Exhaust valves are usually smaller than intakes because an intake charge is cool and dense needing more of an opening. Exhaust gases are thinner and hotter they kinda want out like steam in a pot.

Since only a handfull of engines were ever designed to use a turbo from the starting board the exhaust valves are the same size as what was effective for a NA application.

With a turbo car you have air being shoved in so the difference between a std and even a 2mm oversize intake valve is'nt extreme.

What goes in must come out. We have pleny of help on the way in if you ditched the t25 bi***. A turbo is a restriction in the exhaust flow. Granted the only good kind of restriction I know of yet still a restriction. In a perfect world the only impedment to exhaust flow would be the turbine wheel.

I can input flowbench test #'s into the program. It does some estimating based on how it flowed with the valves it was benched with as compared to the size it was changed to. It is pretty accurate... From that I mean it can not only hit the broadside of a barn but only a few boards away from where you were aiming at.

You can also change everything about the cams including advancing or retarding them. Each can be manipulated independantly of the other.

There is also IVC (intake closing) and EVO (exhaust valve opening) plus lift to input. But I will share this about what I am looking at for bumpstick numbers.

IVO: Intake valve opening.

On the intake opening the valve any substantial number of degrees before the piston reaches BTDC (TDC before the intake dowstroke) gains very little up top and sucks down the low and mid RPM power far enough to make the up top gains not worth it. I'm getting good results with 2 degrees before TDC.

EVC: Exhaust valve closing.

Some degree of overlap is good.
It is more important that I say that when the overlap occurs in relation to the piston stroke.


Exhaust valve closing timing is measured based off the TDC of the exhaust stroke... ATDC after top dead center of the exhaust stroke. On a turbo engine the intake flow helps to push out the tail end of the exhaust stream. So losing a vary small percentage of the intake flow out the exhaust just before the exhaust valve closes can more than pay for itself by eliminating the "bad" air oxygen depleted from contaminating that new cylinder charge. Their is a point at which too much exhaust valve timing past ATDC will hurt things just as their is a point where too little is throwing power away as well.

Gaining overlap by opening the intake earlier really sucks as compaired to holding the exhaust open longer. There is a sweet spot where the exhaust valve open timing increases don't hurt midrange much at all yet make big gains up top. While it may be a certain number of degrees wide of a sweet spot but it has a relatively sharp drop off. At some points you gain 5-10hp up top by adding 1-2 degrees of exhaust valve timing past TDC yet only lose 1-2hp from the midrange. At the top edge the slope goes the other way with 5-10hp lost from the midrange and only 1-2 gained up top. It is a plateau shaped response. Steep good changes leveling off then steep bad changes.

I also played with advancing and retarding both cams the same number of degrees also different numbers of degrees and in different directions. One cam advanced and the other retarded. Suffice to say from what I have found adjustable cam gears are definately a power producing component in the right hands and not just blingage.


I put in HKS 272 specs dialed straight up and played with retarding and advancing them. On 2.0's they did great but they look a little small when you up the CC's of the engine. On a 2.3 they are about as or less aggressive as the 264's. I'm not saying that 272's make less power on a 2.3 than a 2.0 just that putting them on it is like putting 264's on a 2.0. I had to edit to clarify a bit. The 272's are just fine on bigger engines as an intake cam... It's just that bigger engines with bigger boost seem to like a more aggressive exhaust cam than the 272.

On 305 chevys like one of my friends cars who went wild with roller cams and rockers before anything else... It loped and idle like crap with nothing down low and a boring midrange. It finally woke up at high rpm.. The same cams in a different engine... A 406 small block idled only slightly different than a factory camed 350.. It had a streetable midrange and screamed mid to almost redline. I guess the point is that since the popularity of strokers these cam MFG's need to update their 4g63 cam selection.
.

 

[silverbulletAWD]

I would be very interested to hear what your software determines to be the optimal valve timing on a 264/272 and a 272/272 combo. For those of us who will still be running a 2.0 motor this year. With a peak HP level at 7k-7.5k. The reason why I ask for both is because I'm trying to decide if it's worth upgrading to a 272 intake yet this year or not and wait untill next year. And to find the best spot to degree my cams to. I would also like to see how close your calculations come to HKS's specs.


BTW MNGSX, I would still like to hear your thoughts on shrouding and largest feasible valve sizes and their added values like I talked about in my last post.

Andy

 

[MNGSX]

Originally posted by silverbulletAWD
I would be very interested to hear what your software determines to be the optimal valve timing on a 264/272 and a 272/272 combo. For those of us who will still be running a 2.0 motor this year. With a peak HP level at 7k-7.5k. The reason why I ask for both is because I'm trying to decide if it's worth upgrading to a 272 intake yet this year or not and wait untill next year. And to find the best spot to degree my cams to. I would also like to see how close your calculations come to HKS's specs.


BTW MNGSX, I would still like to hear your thoughts on shrouding and largest feasible valve sizes and their added values like I talked about in my last post.

Andy

http://www.engintecs.com/albums1/album07/hks272camspecs.sized.gif

I need to find the 264 specs

What I get from experimenting with intake cam changes is that intake cams don't cause anywhere near as much gains as exhaust cams.

This is true no matter what size engine. A forced induction engine just does'nt need as much intake cam..

To get really accurate for your machine I'd need to know alot.

Bore (exact like 86mm or 86.5mm)
stroke well I know that 88mm
Cylinder head.. Actual 10pt flowbench sheet prefered... if not tell me mods and I'll find someone elses sheet close to it. Important
compression ratio Important
compressor map Important
fuel
N20 if so how much? 25, 50, 100 etc


Lets put it this way on an alky engine that is making 500hp at 6000 rpm and 800hp at 9000 rpm with out N20 at all... Holy scatershield batman.

Bad example I don't want to say everything about what I'm doing it will be a monster.. But I needed to use more duration than a 272 on both cams.. Not that much on the intake side but more on the exhaust side by a long shot.. It seems on these engines the exhaust side is where it is at. Hmm bye bye factory exhaust seats on my second head.

I'll plot 272/272 vs 262/272 this weekend and try to do something in excel..

I'll do a stock valve size head with mild porting... like bowl work.... 2.0 engine.. etc.. kinda a McD's DSM engine..

If you can only afford 1 cam get the exhaust cam.. Match that with your turbo size as big cams and smaller turbos is kinda :thumbdown but hit that one first...

As for 272's street probably run it straight up so the intake opens 6 degrees before TDC... For the track or if you don't mind a small.. neglible to most lower end drop... ADVANCE it about 4 degrees... You lose some 4k down but gain everywhere else..... Like I said any intake VO before TDC on a turbo car does'nt do to much.. So you move 4 degrees of open to where it makes more power. This also cuts the overlap in half 4 degrees from 8 degrees... This was a high boost setup I ran... Just a sec I'll lower it and see... Nope same effect at 15psi...

As for the exhaust cam... Run it straight up..

The only improvement would be more total duration so you can keep the exhaust valve closing where it is and still open it sooner... That means a different cam....

 

[MNGSX]

The valves in our head are at different angles than say a 2 valve per v8.

It is a different animal... Where the valve is closest to the cylinder wall most of the flow is going more towards the pison than the wall... The valve as it lifts is also moving farther away from the wall as well..

It's probably not a non issue but definately not an area to miss out on sleep over... It just is'nt an app with bad shrouding problems.

I don't know what to call feasable valve size.. I have run 2mm over on both valves and just on either side in both directions...

Quite frankly the exhaust side of the chamber is as big as the intake side... You could go as big as the intake..

It would'nt help low or mid power but on the top half I would'nt be surprised that with the same cams it had atleast 50 more HP to peak hp at 15psi boost .. There is an over 100hp difference if you run 2 bar...

There is'nt much room to increase intake valve size.. Maybe 2mm over... The even if you modfied the head alot to get more there is'nt room due to bore size... umm for most people... that is.. The stock intake valve is damn close to the bore in that one corner.. Find someone's head pic with a fire ring gasket mark still on the head.. You will see then.

Now the exhaust side has enough space to grow alot if you don't mind new larger seats and the necessary bowl and inner port enlagement to make use of them.

IMHO if it is no holds barred on a 2.0 bore go 1-2mm over on the intake... It helps but does'nt touch the exhuast gains... Then go to the same size exhaust valve as the intake valve if you boost heavy.. One half of the chamber will be a mirror image of the other. You will probably see a spool time decrease to..

I cant calculate that but IMHO it will be a good one.. Any energy that was spent trying to push around the small valves has a pretty good chance to go to pushing the turbine wheel..

 

[Defiant]

You guys see how much nuance enters into this equation, don't you.

Another issue with large exhaust valves is valve face cooling, most of which is done through contact with the seat. The larger the valve, the more metal you have to cool, and the more there is between the stem and the seat.

Then cam timing, overlap.... it gets really wacky. What about staggered lobes, so the overlap cris-crosses in the chamber?

I still say it's well past time to develop camless hydraulic valve actuation. You'd have the same flexibility as you do with fuel injection.

Ah, someday.

 

[silverbulletAWD]

I say it's time for one of us to start grinding our own cams! I found a grinder yesterday for $19,500. I'll have to wait a few paychecks to pick that one up though... HA! Well, anyways a guy can always dream. Maybe someday... As for valve face cooling, maybe it would be worth looking into a different material for the exh. valves? I wonder at what point we would run into a problem, if there would be one, and how to deal w/ it.

I dont know if the material is different or not from the int. and exh. seats, but what about swaping in some intake seats on the exh. side?

I wans't considering the valve angle either when I was thinking about shrouding. Good point.

As for my personal setup it goes:
-85mm bore
-88mm stroke
-My flow bench wont be done til' next spring so for now my head is mild to heavily ported w/ stock int. and 1mm over exh. valves.
-8.5:1 compression
-50 trim in T04E, dont have the map right here.
-110 Torco
-no NOS

I think I'm going to leave it all the same this year. Except I might go from the 264/272 to a 272/272 setup.

I think this is turning into a very valuable thread. Iwishihadatalon, if your Northstar Fiero buddy is Will, tell him to come on over and join in. That guy knows his stuff!

Andy

 

[MNGSX]

Originally posted by Defiant
You guys see how much nuance enters into this equation, don't you.

Another issue with large exhaust valves is valve face cooling, most of which is done through contact with the seat. The larger the valve, the more metal you have to cool, and the more there is between the stem and the seat.

Then cam timing, overlap.... it gets really wacky. What about staggered lobes, so the overlap cris-crosses in the chamber?

I still say it's well past time to develop camless hydraulic valve actuation. You'd have the same flexibility as you do with fuel injection.

Ah, someday.

The hydraulic valve actuation is a good system...
If you mean by cris crossing overlap holding one intake and one exhaust open a little longer to add a little more spin it might be worth a look.

When you increase valve size seat contact increases... The circumference increases. One big cooling option is sodium filled valves they would be atleast 100 degrees cooler than OE sized valves.

What works in a simulator is'nt easy to replicate in some cases. This does'nt mean that what you find out is wrong... like choked exhaust flow. You may not be able to do the perfect thing to fix it but only what you can.

Originally posted by silverbulletAWD

I say it's time for one of us to start grinding our own cams! I found a grinder yesterday for $19,500. I'll have to wait a few paychecks to pick that one up though... HA! Well, anyways a guy can always dream. Maybe someday... As for valve face cooling, maybe it would be worth looking into a different material for the exh. valves? I wonder at what point we would run into a problem, if there would be one, and how to deal w/ it.

One posibility is intake and exhaust valves that intefere with eachother since they are pointed towards eachother. But lift at overlap is'nt high, turbo cams don't have too much overlap therefore it may only happen if a TB goes...

Many cam companies will enter your specs into their CNC and grind em up... I wonder how titanium is for valve heat disipation? I know its pretty expensive but can it disipate heat better than stainless.

 

[silverbulletAWD]

Titanium is exactly what I was thinking of. I'm going to see about getting some info. from that new valve guy I found and talk to him about making some really big titanium exh. valves. I'm thinking of identical valves to 2+ intake valves. In case we want titanium on the intake side as well. If for nothing else, to remove some weight from the valvetrain.

Now for the seats, could we swap over some stock intake seats? Can those even be boughten from mitsu? Could we CNC them ourselves? Oh yeah, duh. What metal would they have used for stockers?

 

[MNGSX]

A chromemolly alloy is probably what the exhaust and intake seats are made of.

 

[Defiant]

Originally posted by MNGSX
The hydraulic valve actuation is a good system...

I've heard of it being researched, but I don't know by whom. My idea is to have a total-loss system using engine oil and a separate pressure pump for it. All you'd have to do is blow them open, and let the springs close them. You could provide varying lift and duration by the amount of pressure and the number of pulses on the stem. You'd do away with a conventional throttle, and power and powerband should increase by an order of magnitude.

If you mean by cris crossing overlap holding one intake and one exhaust open a little longer to add a little more spin it might be worth a look.

I've not heard of this being tried, either. Seems like with a bit of fiddling, you could get some interesting turbulence and scavenging effects in the cylinder.

But I don't for a moment think I'm going to be the one to come up with anything new. There's just too many brains working on these things, and a lot of them are much higher-output than mine.

 

[wishihadatalon]

my friends name is chris we are in grand rapids. should be done in a few months. he is going to be ordering his tranny this week so he can start making mounts. he is shooting for 100hp per liter. this has been a very good topic.

 

[silverbulletAWD]

Oh, well I guess there is more than one Northstar Fiero! Cool I'm in Holland. You have to meet up w/ us sometime this summer at Stanton or Martin.

I've also heard about the hydralic valve project as well and I hope some one gets it figured out. That would be the best setup. I dont know if it would take a seperate pump or not though. I would think if they were going to go as far as to figure this all out they could figure out how to use the engines oil pressure to open the valves. It would automaticly match itself to the engines RPM and if an extra amount of lift was needed up top some kind of accelerator could kick in by means of a regulator type setup or an auxilary pump. The more I think about this the more I want to try it...

I've heard of the cris-cross idea before too. I know it's been done and I can't remember were I saw it. I'll try to find it back. I think this is another really good idea.

Defiant- dont be so hard on yourself! Just think, if everbody thought like that were would we be? Not this far... Besides, the brainiac's are over rated. They often miss the obvious in an attept for a great achievement. Or over-engineer while trying to impress their dork buddies.

Andy

 

[Big Woo]

Here are a few items to concider.
1: a bigger valve = a bigger hole, bigger holes usually flow more(but nt always).
2: A valve is concidered to no longer be a flow restriction once it has been lifted 25% of its diameter
3: Try not to just look at valve size, cam specs on intake and exhaust opening and closing times, and their phasing in relationship to piston speed and rod angle can be just as rewarding. The idea is to make everything work together, not just optomise one aspect. We can carry this on much much furter to include compression ratio, intake and exhaust runner lengths, flow coefficients, compressor wheels, and housings, exhaust wheels and housings, exhaust manifold pressure, and so on and so on.

4: in general opening up the exhaust side will produce more top end power on a turbo car, but turbo spool up in also an issue, it has a similar effect as switching to a larger A/R turbine housing.

 

[Defiant]

Originally posted by silverbulletAWD
I've also heard about the hydralic valve project as well and I hope some one gets it figured out. That would be the best setup. I dont know if it would take a seperate pump or not though. I would think if they were going to go as far as to figure this all out they could figure out how to use the engines oil pressure to open the valves. It would automaticly match itself to the engines RPM and if an extra amount of lift was needed up top some kind of accelerator could kick in by means of a regulator type setup or an auxilary pump. The more I think about this the more I want to try it...

I'd think a separate, high-pressure pump just for the valve actuation. With something like huge-capacity fuel injectors firing on the ends of the valve stems (or maybe something completely deviant, like Butterworth valves), the stems riding in some kind of ventilated guide that'd let the actuating oil drain off. If you no longer depended on acceleration/deceleration ramps to keep a lifter in touch with a cam lobe, you could have a _much_ lighter valve assembly, which in turn could be more easily worked with hydraulics. A spring would be needed only for closing, as cylinder pressure keeps a valve seated. A desmodromic scheme could also be worked out, and a complete elimination of actuating springs could be attained. Multiple shots from the injector could be used for timing and lift variations. At this point in the progression of electronics, valve control should be gravy. Tuning possibilities would be vast, with whatever goals -emissions, raw power, economy- not only controllable, but even summonable.
It works great in my head, there's just the real-world and its dollars between me and realization.

 

[silverbulletAWD]

I like... Your right, it would take a seperate pump to get the needed pressure to control 16 of these valves. I wonder if you could control two valves at the same time w/ one actuator using some kind of a plate or bar to connect the two rocker arms... I also like the idea of eliminating the spring all together, but I'm wondering if there is a unit available that would could even meet our packaging, speed, adjustability and durability needs. As well as probably a few other needs. Well, you guys know a bit more about electronically programmed hydrualics than I do So I leave it be.

Back to valves, I think we are all of us in this thread fully realize the importance of properly matching ALL of the engines components for optimal performance. Big Woo, your 100% right about that. And if you really ment to say "nt" instead of "not" in #1 than I agree w/ everything your saying. Fi not I must be missing something. And BTW, I'd love to take this discussion further. This has been a really good one. However, I think the author originally intended this thread to be about valve sizing (primarily exhaust) and its affects on an otherwise identical setup. We've just been exploring the realms of possibility.

Andy

 

[MNGSX]

Originally posted by Big Woo
Here are a few items to concider.
1: a bigger valve = a bigger hole, bigger holes usually flow more(but nt always).
2: A valve is concidered to no longer be a flow restriction once it has been lifted 25% of its diameter
3: Try not to just look at valve size, cam specs on intake and exhaust opening and closing times, and their phasing in relationship to piston speed and rod angle can be just as rewarding. The idea is to make everything work together, not just optomise one aspect. We can carry this on much much furter to include compression ratio, intake and exhaust runner lengths, flow coefficients, compressor wheels, and housings, exhaust wheels and housings, exhaust manifold pressure, and so on and so on.

4: in general opening up the exhaust side will produce more top end power on a turbo car, but turbo spool up in also an issue, it has a similar effect as switching to a larger A/R turbine housing.

1. It depends on other things done to the head. Like the size of the exhaust port on the head. Bowl enlargement goes with valve enlargement. Done properly it will flow alot more.

2. I know that is not right. Even the stem is a flow restriction.

3. I have been looking at cam specs. I optimized the cams for a given bor, stroke, compression ratio, and boost level then looked into valve changes. I agree as to making everything work in unison. Compression ratio as well as boost pressure matter alot too. Combined it is the dynamic compression or effective ratio. Compression ratio alone is just a static compression ratio. As for intake runner length one need only have flowbench data that used a head with that intake attatched to it. Exhaust side flowbench data is a bit tougher. I know all about exhaust manifold pressure being a problem too.

4. A larger A/R turbine housing is less restrictive (I know Duh! right) but it is less restriction further from the head. Now how does flowing more exhaust into the same A/R turbine housing by making the valves less restrictive hurt spool? If the manifold and turbine A/R stay the same and the only changes are the exhaust valve size I believe that spool will be improved. You have more flow thru the same size passages. Like I said before.. think rotory engine exhaust flow. Even giant valves wont flow as good as a rotory's exhaust flow but being able to get more out of the cylinder and into the manifold will be a good thing.

 

[Big Woo]

1: well of course other things come into play

2:Well the general rule of thumb is that once a valve is lifted 25% of its diameter it is no longer concidered a flow restriction, but you don't have to believe me go look it up for your self, it is published information, not my own ramblings.

3:Ok

4:Yes, but velocity may no longer be a constant.

5: interesting I am from Ravenna Michigan, about halfway between Grand Rapids, and Muskegon, Stanton, Martain, Thunderbird OK

As far as pneumatic valve control goes some of us may already know that Renault pionered this back in the 90's, and in their original control pressure system they used 2100 psi of pressure for valve control to run to about 16 or 17,000 rpm. Later they went to a constant pressure system that maintained a certain pressure during the entire valve cycle. Today companies like Honda, Renault, BMW, Mercedes, and Ferrari are looking to electro-hydraulic, and electro-pneumatic valve control systems for their respective F1 teams. Just some more food for thought.

 

[silverbulletAWD]

2. Is this following the theory that at 25%, the open area is = or < the valve openings sectional area?

5. Cool, I'll let you know when we'll be at the tracks.

 

[MNGSX]

Originally posted by Big Woo
2:Well the general rule of thumb is that once a valve is lifted 25% of its diameter it is no longer concidered a flow restriction, but you don't have to believe me go look it up for your self, it is published information, not my own ramblings.

The valve itself is not really restricting the much at all above 25% of it's diameter in lift. I guess I track with that. However a larger valve, seat and bowl will still flow more.

Originally posted by Big Woo

4:Yes, but velocity may no longer be a constant.

I think that is more dependant on the cam duration. Less duration will yeild more peak velocity and less total flow. Conversly an engine with more duration could have less peak velocity yet a higher average velocity. In fact the right cam with larger valves could help velocity. The same duration with a nice steep ramp rate on the cam. Then again the only thing I'm concerned about is getting the most waste gases out of the cylinder. So big cam and big valves for me.

With larger turbos and esp those that like higher pressure ratios the much improved exhaust side flow will make a big difference on the top end. IMHO not improving exhaust valve size because of exhaust velocity worries is like inproving induction velocity on a nascar via a restrictor plate. Someone runing higher pressure or higher displacement will see the most gains where as some engines very little. Their are alot of nuances. FYI I am mostly thinking of a displacement enhanced 4g63 runing atleast 25 psi for my calculations.

The most radical valvetrain changes coming will not be hydraulic or coats. It will be electromagneticly actuated valves.

http://legend.me.uiuc.edu/astubbs/acc_2001.pdf

 

[Rogue_Ant]

Originally posted by MNGSX
The most radical valvetrain changes coming will not be hydraulic or coats. It will be electromagneticly actuated valves.

http://legend.me.uiuc.edu/astubbs/acc_2001.pdf

Last time I heard, they were having 'real-world' trouble keeping up with the rpms of diesels, none-the-less high-revving 4-bangers...



Rogue

 

[MNGSX]

Originally posted by Rogue_Ant
Last time I heard, they were having 'real-world' trouble keeping up with the rpms of diesels, none-the-less high-revving 4-bangers...



Rogue

At one time the only thing with direct port injection was diesels too but that changed. VVT was unheard of as was VVL and not even having a trottle body like BMW. One design of electromagnetic valvetrain having problems in testing does'nt mean there are'nt others doing better or that the problems encountered will not be eliminated.

I guess we all long for the day of no timing belt, throttle body, or cams. Just the optimum valve actuation for each RPM, throttle position and boost level... It would allow alot of options for ALS too.