Pro Stock John

iTrader: (34)

Can a savvy person explain how the velocity will slow down with too big a valve?

And also, how do you determine the best size valve for various combos?

I for example have a 4.060 BORE and 4.075 stroke. Would you run a 2.05/1.60 combo or a 2.08/1.60 combo?

JPR

I will take a stab at this, I will give a brief outline first.

Lets take stock cubes to begin with, 346 ci divided by 8 = 43.25 ci per cylinder, within those cubes and cam eventing you only have so much air per RPM that can be meaningfully injested into the cylinder upon intake stroke. So, to elaborate just a little more, 85% of your gross cam lift is whats called your "usefull flow area", so for example, if your running a .550 lift cam, .476 lift would be your target flow number that will be mostly used at high RPM, it has to be over shot to .550 to realize this .476 value twice. Basicly, air weighs 90 lbs per square inch accelerated under vacuum, and your trying to expose the back side of the valve to as much air tonage as possible in the rpm band for a quick and efficiently filled cylnder at particular RPM's. Now, getting to the velocity part of the question, Bigger valves don't necessarily disturb the air speed which is also called velocity, granted, there is more surface area that the air is exposed to but unless you have compromised the minimum clearance allowed for that sized valve "shrouding" = not good. Basicly, it's the design/volume of the runner and valve seat throat design that determines velocity and how much pressure is getting displaced per intake stroke. Small runners with high flow is known as a high velocity runner. Large runners with the same flow or lower are called lazy runners. I can post some volume vs air flow numbers coupled with dyno quotes if that would help also. IMO, a 2.05 valve for a 4.00 bore is fine, as long as the combustion chamber has been re-sized which they usually are.
Joe.

<small>[ June 01, 2002, 11:02 PM: Message edited by: JPR ]</small>

Scalpel

iTrader: (4)

Basically, doesn't this boil down to Bernoulli's equation (as volume of air flow or any gas/liquid increases velocity decreases)?

<small>[ June 01, 2002, 10:25 PM: Message edited by: NastyC5 ]</small>

JPR

Nasty,
"Basically, doesn't this boil down to Bernoulli's equation (as volume of air flow or any gas/liquid increases velocity decreases)?"

This is true.

Volume and velocity are two different things, there related, but rated different ways. To further that conversation, we would have to establish a base pressure vs crossectional area, there both equally important but you have to find the ballance that works the best and it's all cubic inch sensitive. As a side note, velocity becomes less important with larger cubic inches because of the stronger vac signal thats being generated. The addage for velocity I like to refer to is, if you had to blow a quarter off a table, would you use an 8" garden hose or an 8" straw? I know it sounds a little strange, but thats an example of volume vs velocity using the same pressure but 2 different crossectional areas.

<small>[ June 01, 2002, 11:30 PM: Message edited by: JPR ]</small>

MDL-01C5

GOD!!!! I LOVE this forum!!!!!
Where else on the millions of sites comprising the internet can you find this type of powerful, experienced knowledge
<img border="0" alt="[judgement]" title="" src="graemlins/gr_judge.gif" /> <img border="0" alt="[judgement]" title="" src="graemlins/gr_judge.gif" /> <img border="0" alt="[judgement]" title="" src="graemlins/gr_judge.gif" /> <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" /> <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
(Sorry, I was momentarily overtaken with glee at the sheer mass of info available on this forum...other forums have their purpose and niche, but for hard-core tech-- this is unmatched anywhere <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> ) <img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" />

<small>[ June 01, 2002, 11:08 PM: Message edited by: MDL-01C5 ]</small>

Cam99SS9

What would be good valve sizes for a H/C setup that I may add a ProCharger at a later time?

<small>[ June 01, 2002, 11:25 PM: Message edited by: Cam99SS9 ]</small>

JPR

Cam99,
Funny you should mention, we just set the "National record" for the fastest stock cubic inch blower car in the nation using only 6 psi. It ran 10.77 with the best MPH of 126-127 and there is more in it! It's going back together with a 8 psi pully and ARP head bolts that were unfortunatly unavailable upon the time of installation. I used Ferrea 2.02's on the intake and 1.60's on the exhaust with a small 216 cam. The exhaust is flowing big numbers to say the least.

<small>[ June 01, 2002, 11:31 PM: Message edited by: JPR ]</small>

Cam99SS9

Congrats JPR!!!

That's some times! I was thinking of going 2.055/1.60 exhaust with a fresh new set of LS1 heads from the factory with no milling to keep the compression down. I just installed the LS6 intake tonight, and before I got it was pondering getting the Holley/Lingenfelter aluminum intake. If I do the ProCharger I was going to do the DSC-1 tuner kit, and get about 48lb injectors and a monster fuel pump.

I will probably to the H/C combo with the 224/224 w/112 initially, but if and when I do the ATI, I will change the cam over to something with a little less lift intake and exhaust, a bit more duration on the exhaust side and a lobe seperation of about 110 or so. At that point I will put the Aluminum intake on after getting it port matched and a little taken out of the inside. Would like to try to get about 10 psi with that setup.

<small>[ June 01, 2002, 11:33 PM: Message edited by: Cam99SS9 ]</small>

Carlitos

Cam99:

Ummm...someone correct me if I'm wrong but wouldn't it be better to go with a WIDER LSA when going FI? With the extra overlap of the 110 LSA, you will lose some of your intake charge out of the exhaust. You would probably be better off getting a cam with a 114 or wider LSA.

Also, do you have a built bottom end? I'm not sure the stock bottom end will handle 10psi for very long. From what I've noticed, anything more than about 7 or 8psi really should have a built bottom end. Anyone?

'Los

TimZ28

LSA alone doesn't tell you anything about overlap when comparing one grind to another. A cam at 112 could have more overlap area than a 110. It all depends on the where the exhaust closes and the intake opens as well as the profiles of the lobes. Everyone gets hung up on LSA around here and for the most part it is meaningless unless you are comparing two otherwise identical grinds.

Tim

Carlitos

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by TimZ28:
<strong>LSA alone doesn't tell you anything about overlap when comparing one grind to another. A cam at 112 could have more overlap area than a 110. It all depends on the where the exhaust closes and the intake opens as well as the profiles of the lobes. Everyone gets hung up on LSA around here and for the most part it is meaningless unless you are comparing two otherwise identical grinds.

Tim</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"><img border="0" title="" alt="[Razz]" src="gr_tounge.gif" /> I understand that. I was, for simplicity's sake, assuming "two otherwise identical grinds" <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> Besides, he posted that he was ADDING exhaust duration (all else being the same this alone would increase overlap) AND he is going to tighten the LSA. He did not mention using more aggressive lobe profiles (such as going from an XE lobe to an XE-R lobe).

Now how about some info on whether or not a 114+ LSA would be better than a 110 LSA for a FI application based on what he has posted so far. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

'Los

Crazyquik

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by JPR:
<strong>
As a side note, velocity becomes less important with larger cubic inches because of the stronger vac signal thats being generated. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Wouldn't this be the case with a stroker/long stroke motor as well? An engine with a longer stroke is going to have a stronger and longer vac signal. It could also use a longer duration cam because you're pulling air in longer.

J.

JPR

Using the 346 ci motor in the above example, I was explaining that air weighs 90 lbs per square inch acellerated, I used that as a constant. So any addition to the cubes over that example would be a higher amount/stronger signal to the intake valve/runner and will increase the amount of air injestion be it all bore or stroke or both. So, yes, your statement is correct. Thats why you can run a 234 int duration cam with a large cubed motor and hardly sound radical, but use the same cam in a smaller cubed motor and it sounds like a pro stocker.

<small>[ June 02, 2002, 07:38 AM: Message edited by: JPR ]</small>

Bob2of3

iTrader: (11)

All this info, My head hurts <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />

LAter <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

WS6 TransAm Girl

Great reading here <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
<<The addage for velocity I like to refer to is, if you had to blow a quarter off a table, would you use an 8" garden hose or an 8" straw? I know it sounds a little strange, but thats an example of volume vs velocity using the same pressure but 2 different crossectional areas>>

I like that comparison, makes perfect sense!