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I have several different valve for my 8V some stock size other are +1mm.
My thought is the intake stock are more nailhead design on the intake vs the SI +1 and the new vendor +1 as shown below
https://drive.google.com/file/d/196W...ew?usp=sharing
The exhaust valves are also quite different
https://drive.google.com/file/d/1lEN...ew?usp=sharing
So my question is which valves should I use?
well, if all things are equal so to say as far as working valve locks and retainers go then , I'd go with the first valve on the left in the first pic and the second one from the right in the second
the valves with the necked down stems
from what I understand a flat face valve is wiser in a turbo motor but if the valve faces on those two are dished .. I still go with 'em
(mine are dished but flat would be better .. so "people say")
I'd consider polishing the edge of the dish to remove the sharpness where the flat and dished areas begin though
I've found finding locks that fit my valves was challenging.. with the comp LS spring locks as the round little locking ridge in the comp locks doesn't come close to fitting my LRE valves
comp ridge is U shaped and way to small (these were the part # pope recommended with the LS beehives and retainers I have no idea what valves he had with those U locking groves though)
my valves need something like
__
...I
../
^that
the eye has a "thing" for seeing "flow"
old layman's law.. if it floats , flies or flows
if it looks good
it probably is...
more important than the valves though .. is the valve job applied to them
if you're invested in the valves make sure to back it up with the valvejob
Yup, basically what Johnny Dodge says, but the devil is in the details. after porting and flow bench testing these 8 valve heads for 20+ years what I've found makes the most power is a shallow nail head intake, and a tulip exhaust.
The valve angles and seat angles are IMPORTANT! The intake seat 45degree should be .100-.125 wide with a 30 degree back-cut, and a .075 wide and straight (almost sharp) margin. (the straight/sharp margin helps prevent back flow during overlap)
The exhaust should be a large radius tulip, with a .125 45 degree seat and a .085 wide 30 degree back-cut. Also, the margin on the exhaust should be a .060 radius.(NOT STRAIGHT)
For any 8 valve head with gross valve lift less than .550 the plus 1mm. valve is the best option. there is no gain with the big IMSA valves unless you have a "Huge" cam.
the intake seat (in the head) should be a top 30deg. 45 sealing seat, 70, then 75 below the 45. exhaust seat in head 30-45-70. Hope this makes sense and helps; Don't know what others do, but this works well for me.
PS. These metrics are for a G head, but I think I would do the same on a swirl.
This photo should give you an idea what I'M talking about.
exhaust valve makes sense.. like a nice snug cattle run .. no turns sideways..nowhere to go but through and out
..no corners for a cow to stand in with it's rump blocking the flow of the herd...which brings to mind the word "stall"
Thank you Gentlemen for your thoughts. ;)
K, had a question on my mind for a few days.
if the isma valves are semi useless without a really "big" cam , what would happen if one used the +1mm intake valves but still used the isma sized exhaust valves ??
- maybe like using a duel pattern cam ?..or maybe WITH a duel pattern cam?
if more goes in with the boost cranked up shouldn't we allow for more to come out when the only thing pushing is the piston like in a N-A motor ?
as an asthmatic .. I fully understand not being able to inhale .. because I can't exhale first..
So i know this post is a few months old but I wanted to touch base on it .Quote:
Originally Posted by Dr. Johny Dodge
Think of it like this. You have 30psi on the back of the intake valve when it opens you only have a certain amount of time for that air to make its way into the cylinder.
Now once the combustion cycle is done and the exhaust has to get out you could have a few hundred psi of cylinder pressure.
Which do you think is going to have a harder time getting air through it?
I would focus more on the intake side of the head than the exhaust side especially if you have a stock style exhaust manifold.
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I'm thinking the larger exhaust valve (not a +1) would allow more exhaust gas, to exit more quickly,
.. thus possibly improving the force applied to the turbine ..sooner and more forcefully ..thus getting that 30 pounds to the intake valve more quickly..(???)
So what happens when you go with a bigger valve and you kill velocity of the exhaust?Quote:
Originally Posted by Dr. Johny Dodge
Say you have a rotating door and 10 people walk towards that door yet only 3 people get in the door before it rotates.
Now take those same people and have then run towards the door. Now you may get 6 people in the door.
You could use the ole garden hose reference here as well. Turn your hose on and let the water run out on a fin from a paddle wheel. Now stick your thumb over half of the end and spray it over the same paddle wheel. Which one is gonna spin that wheel faster?
The one with more velocity right?
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ok, I can work with the garden hose referance..
if you have a house with a 1/2 inch water line running from the city water pipe at the street you have the average house's water pressure at the kitchen tap
if you change that 1/2 inch pipe to a 3/4 inch pipe .. the water pressure at the kitchen tap goes way way up..
you still have the same sized openings in the casting of the kitchen tap but more flows through , more quickly..
That would be more in reference to the exhaust port.Quote:
Originally Posted by Dr. Johny Dodge
Also you have to take into account pressure behind the 1/2" or 3/4" line. If the pressure at the main line remains the same then flow of the water may increase, but the velocity of the water could diminish. We are talking about whats happening at the valve. Cylinder pressure will remain the same with a big or small valve but how fast it travels through the valve will be determined by the size. Go too big lose velocity or speed. Go to small lose flow.
Obviously you need quantity of air to spin the turbine, but a faster moving air will get it moving faster. Thats where valve size vs bore size comes into play. As compression increases (boost) biasing towards the intake valve over the exhaust valve size starts to have a measureable influence on power production.
David Vizard goes over this in depth in alot of videos and in his book about porting heads. Figuring the valve sizes based off this figure, that would put exhaust size around 35mm which is stock size. Increase the boost and the size will bias more towards the intake which would decrease the exhaust valve size even further.
https://uploads.tapatalk-cdn.com/202...e936058c37.jpg
https://uploads.tapatalk-cdn.com/202...4a8b3ac39e.jpg
https://uploads.tapatalk-cdn.com/202...447216f50e.jpg
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ok, if we have the boost cranked up to 30 pounds we have effectively increased density and mass entering the cylinder..
this same increased density and mass still has to exit the cylinder when the exhaust valve opens..
with the piston pushing up at the same speed and with the same force , that increased density wants to be more easily released.
like the kitchen tap hooked up to a larger line , the effort to rinse the spaghetti sauce from your plate is lessened..
so , considering the insides of the tap fixture remain the same .. like your exhaust port and turbine housing remaining the same .. more force must therefore be applied to the turbine..by more easily available force
so , velocity is more the product of the passages than the exhaust valve ..relative to the force of pressure trying to flow through them
thus I surmise the larger valve would allow the greater density of the exhaust to exit more easily thus filling the passages and reaching maximum velocity more easily
and , to pose a question .. if as you state a same size or relatively smaller size exhaust valve is "better" .. then how is it that on a same size engine ..TWO exhaust valves ...are better ?
if so there would be no 3 valve ford mod motors , no 4 valve motors and definitely no 5 valve motors .. because as we know the auto manufactures wouldn't spend the resources putting more open valve area in the heads..(?)
and going back to my other example of being asthmatic ..
atmospheric pressure fills your lungs when your diafram relaxes.. like a normally aspirated motor when the piston moves down during the intake stroke..
asthma is the tightening or restricting of the bronchial passages entering the lungs
when you exhale .. your diafram pushes up against your lungs to push the bad air out..
like your piston during the exhaust stroke
and this pushing force cannot be increased..
with the restriction.. you have no flow and therefore no velocity..you only create "cylinder pressure" during your exhale or exhaust
problem for asthmatics.. is they can't get fresh air in because they are still full of bad air..
thus I'd say reducing the valve size would only compound resistance to flow and increase back pressure against the rising piston face
increasing the water pipe size .. or increasing the intake plenum size .. in fact improves access to supply .. to either fill the cylinder or sink .. so increasing access to supply at the exhaust has to work similarly
now, if that supply is the ability "to do work" and we're expecting the water coming from the tap or the exhaust coming from the motor , to "do work" by rinsing the plate or spinning the turbine.. then increasing the available energy to do work .. should perform more work , more easily and as a result , more quickly
Im going to do some computer simulations and only change the exhaust valve size and see what it shows. Really we are just guessing. Ive read and read and read on this subject everyday for the last month because i wanted to know what i should go with. Every big name in the the head industry is all in the same boat as far as increasing intake size over exhaust valve size with an N/A or turbocharged engine. Supercharged or Nitrous are different and they all agree to increase exhaust valve size over intake. That is due to N/A's scavenging effect as well as the turbos ability to (once spinning) help draw air out of the cylinder.
With SC youre forcing air in with nothing helping draw it out so you would increase exhaust valve size to help the exhaust get out.
My head I am building i went with 44 intakes and 35 exhaust so we will see what Kind of power I can make.
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Neat please keep us in the loopQuote:
Originally Posted by Loudexploder
So I ran some simulations on Engine Analyzer Pro.
The 35 mm valve made a couple more hp and torque average and about 1 hp more peak than the bigger 37mm exhaust valve.
Obviously I dont have flow numbers for either so when running these simulations I used the same discharge coefficient for each valve while only changing the valve size
Basically the valve has a theoretic max flow based off of its size. The amount the valve actually flows compared to that theoretic max flow gives us our discharge coefficient. So assuming each valve would flow the same percentage of its max value was how i tested the two differences.
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I seen no changes in spool but the exhaust pressure was 1-2psi higher with the small valve but still remained less than intake pressures. My thinking would be that the smaller valve would have to be moving more air into the exhaust manifold for pressure to become higher.
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interestingQuote:
Originally Posted by Loudexploder
ok, but I have to ask
did your computer simulation include the larger pass through hole of the larger valve seat required for the 37mm valve and by extension the somewhat increased valve bowl volume that would result in machining the head for the larger seat .. and the extra material removed to smooth out that new machining job??
if not I can understand the lesser flow number
without the larger pass through all the 37mm valve head is , is a larger obstruction to the existing flow of the smaller valve as there's more valve face to have to go around to exit...through the still same sized hole
(???)
it would be like putting a three foot wide door over a two foot wide door frame..
same size hole .. but you have to stand further back to open it and go around..
bigger valves mean nothing .. it's the bigger seat and the work to install it that makes the real difference
Thats why I said I used the same discharge coefficient.Quote:
Originally Posted by Dr. Johny Dodge
A 35mm valve can flow a max of 436 cfm @.5 lift. If the DC is .39 then it would flow 170cfm
A 37mm valve can flow a max of 481 cfm @.5 lift. If the DC remains the same .39 then it would flow 187 cfm
Of course its not going to take into account the seat size or bowl size but if either of those werent sized correctly then it would show up in the flow numbers.
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So here is some more info I've ran across. If you read through this thread there is alot of good info as to why you want to keep exhaust velocity up and dont want to go too big on lift or valve size.
https://www.speed-talk.com/forum/vie...php?f=1&t=2183
Quote from the thread
Exhaust velocity is only useful at one point in the cycle, the end. If you lift the valve high for better flow when the piston isn't even half way up, you will lose velocity at the end of the stroke to help fully evacuate the cylinder.
Getting the ex valve opened at the right time to blow down enough pressure before the piston starts rising in the cylinder and just open enough to to keep pumping losses down as the piston rises, leaving enough velocity at the end of the stroke to be useful in savenging.
There was a guy on there that actually changed valve size and came to the same conclusion. I think going too big on the exhaust valve is going to cause excess pumping loss, basically blowing too much exhaust out before the piston gets moving and it loses velocity then doesnt scavenge the cylinder completely before the valve closes.
- - - Updated - - -
So here is some more info I've ran across. If you read through this thread there is alot of good info as to why you want to keep exhaust velocity up and dont want to go too big on lift or valve size.
https://www.speed-talk.com/forum/viewtopic.php?f=1&t=2183
Quote from the thread
Exhaust velocity is only useful at one point in the cycle, the end. If you lift the valve high for better flow when the piston isn't even half way up, you will lose velocity at the end of the stroke to help fully evacuate the cylinder.
Getting the ex valve opened at the right time to blow down enough pressure before the piston starts rising in the cylinder and just open enough to to keep pumping losses down as the piston rises, leaving enough velocity at the end of the stroke to be useful in savenging.
There was a guy on there that actually changed valve size and came to the same conclusion. I think going too big on the exhaust valve is going to cause excess pumping loss, basically blowing too much exhaust out before the piston gets moving and it loses velocity then doesnt scavenge the cylinder completely before the valve closes.