Big intake valve in small bore.

[fekbmax]

So what's the biggest intake valve you guys would recommend in a 4.140 bore. I know the big valve in the edly  head will physically fit and clear the cylinder, I'm wondering what you guys think, ? I have had a few say run the biggest valve you can to take advantage of the head porting and others Say its best to un shroud the intake valve and have some clearance around it.

[plovett]

My opinion is to use the Reher Morrison formula for the optimum intake valve size, which if I remember right is 52-53% of bore size for inline valve heads like the FE.

That puts you in the 2.15-2.19" range.   I think you also want a certain ratio between intake valve size and intake port throat size.  Maybe the throat should be around 90-92% of the valve size.  Not sure about that.  I'm sure the engine builders and more specifically the head porters can flesh that out a bit.

I hate the idea of putting a bigger valve in there just because it physically fits.  After spending thousands of dollars on cylinder heads it seems like a crazy thing to not put the right size valve in there.  Bigger valves can be cut down a few hundredths.

JMO,

paulie

[plovett]

I'd also ask your head guy about notching the cylinder bores, especially if you are going to the large side of the size range.

paulie

[blykins]

A 2.190 or 2.200 will fit just fine. 

[plovett]

A 2.190 or 2.200 will fit just fine.

That's what drives me nuts, Brent.  Engine builders tell you what "fits".  Cylinder head porters tell you what's "best".  No disrespect intended here.  It may be that a 2.190 or 2.200" valve fits and is also the best size.  I don't know.  My point is I am going to talk to my cylinder head guy about the best intake valve size for my next motor.   He's a head porter who also happens to build engines.

JMO,

paulie

[jayb]

The biggest restriction in the intake runner is the valve.  Making the valve as large as practical is a generally good policy, I think.  Mark Dahlquist, who is an Engine Masters competitor who posts here from time to time, put a 2.400" intake in his EM Pontiac and finished 9th and 10th in the contest in 2013 and 2014, respectively.  His whole induction system was based around using that big valve.

The issue you run across with the FE are valve shrouding by the bore, notching requirements, and limiting the size of the exhaust valve.  I went to a 2.300" valve in my high riser because it showed a 20 cfm gain over the 2.25" valve at 0.800 lift, with the 4.375" bore size that I was using.  I'm also going with a 2.425" valve in my new set of SOHC heads, assuming that the initial tests yield a flow improvement over the 2.300" valve that I'm currently using in that engine.

You can buy custom valves from Manley one at a time.  What I've done in the past is buy one each of different sizes or styles, and have them tested with the heads and the bore that the engine will be using.  If you go up in valve diameter and don't see a significant change in flow, then the smaller valve will do just fine.  But if you do see the change, its probably worth going with the larger valve.

I'm sure there are lots of opinions on this; these are just mine.  It has worked for me - Jay

[plovett]

I'm not convinced that the biggest valve that will fit is always the best, Jay.  But, I'm not a cylinder head porter, and I do believe flow numbers are meaningful, especially if tested on a bore tube that matches the cylinder bore.  And like you said there are other considerations like shrouding, notching, and leaving room for an effective exhaust valve. 

In general, it seems like the trend is towards using the available space for a larger intake valve and a smaller exhaust valve.  At least compared to 20 years ago.

paulie

[plovett]

All right, I know I'm talking too much, which is unusual for me.  So please forgive me.  This is a subject I am very interested in though, so I hope my ramblings bring more educated/experienced voices into the discussion.

I think big valves tend to help low-mid lift flow the most.  The curtain area is an exponential function of the diameter and that is key at lower lifts?  I know they can help high lift flow as well, but what I am getting at is that I think once the intake valve is open "far enough"  and "out of the way" of the port, then the port itself becomes more of a limiting factor?

I also think there is a misconception that low lift flow has to help low rpm power and vice-versa.  Low lift flow can help high rpm power because it helps flow during the overlap period when both valves are open.  High lift flow helps high rpm power, too.  It's just that it's not as simple as low lift = low rpm power and high lift = high rpm power.  I'm just scratching the surface, of course.  I'm really throwing myself out there as a sacrificial lamb to get the cylinder head guys to come pummel me and give us more info.   

paulie

[fekbmax]

I'm feeling a bit better now lol. Shouldn't over think things so much but sometimes things roll around in the head and gets separated from the gravel up there at least for a moment. I was told the Big Valve would fit and be my best bet to complement the work done to the cylinder head so I said have at it. I checked it anyway ya know, no head gasket even and indeed the big valves fit as I was told they would.  Shame on me for questioning the guys in the know.. LoL  Thanks guys.. 

[Joe-JDC]

I have a little experience with this on the flow bench with years of testing that very concept.  A couple of years ago, I had a friend who had a set of CJ heads that ran well, but wanted more.  He brought me the heads, and they had 2.190 valves installed with 1.710 exhaust valves.  I flowed the heads before touching them, and was dumbfounded with how the intake did NOT flow.  A well know engine builder had installed the larger valves with 30* seat, but did not do an appropriate valve job, and the flow was down to 230ish cfm.  I cleaned up the heads, installed a 2.100" intake valve, and the heads flow 280 cfm now.  I have seen all brands of heads do the same thing, only to lose airflow.  There is also another down side, and that is the weight of the valve increases, requiring different springs to keep them from bouncing or valve float.  My question is:  Why install a larger valve if it moves the edge closer to the chamber wall, and cylinder wall and decreases flow?  Bigger does not always mean it will flow more.  I got the same flow out of the BBM heads with a 2.090 valve as with the 2.200 without any porting.  Same with the Survival head.  I got 352cfm with porting and 2.150" intake valve.  The Edelbrock heads work well with 2.150 intake and 45* seat.  I also have always tried to keep the throat diameter at 89-90% for intakes, and 88-90% for exhaust valves.  Ultimately the heads work well with anything over 70% bias for the exhaust flow.  Divide the exhaust flow by the intake flow.  Another thing I have used in the past is to flow the intake tract without the valve, (valve stem installed upside down) and then see how much flow is lost around the valve.  If you can get a valve job and port shape to keep the flow to within 5% loss with the valve installed, you have just about optimized the port and valve job and unshrouding.  There are many more things to consider in a good valve job than a larger valve.  JMO, but it has been my experience.  Joe-JDC

[plovett]

indeed the big valves fit as I was told they would.  Shame on me for questioning the guys in the know.. LoL  Thanks guys..

Long as it fits, KB Max.  I'm not sure that's a good engine building philosophy.  EVERYTHING is more complicated than it seems at first.

JMO,

paulie

[cjshaker]

I'm really throwing myself out there as a sacrificial lamb to get the cylinder head guys to come pummel me and give us more info.   

paulie

Don't think it's not appreciated, Paulie
I always wondered if there was a point where the valve came so close to the bore that it effectively sealed off the flow at that point. Ford obviously knew this when they notched the cylinders in the 427. With super high lift cams, I wouldn't think you could get a notch deep enough to help that much. Jay is working with a maximum sized bore though, and if he's testing with a bore tube I'd think the data should be pretty accurate. Edit to add, for his combination.

[plovett]

I have a little experience with this on the flow bench with years of testing that very concept.  A couple of years ago, I had a friend who had a set of CJ heads that ran well, but wanted more.  He brought me the heads, and they had 2.190 valves installed with 1.710 exhaust valves.  I flowed the heads before touching them, and was dumbfounded with how the intake did NOT flow.  A well know engine builder had installed the larger valves with 30* seat, but did not do an appropriate valve job, and the flow was down to 230ish cfm.  I cleaned up the heads, installed a 2.100" intake valve, and the heads flow 280 cfm now.  I have seen all brands of heads do the same thing, only to lose airflow.  There is also another down side, and that is the weight of the valve increases, requiring different springs to keep them from bouncing or valve float.  My question is:  Why install a larger valve if it moves the edge closer to the chamber wall, and cylinder wall and decreases flow?  Bigger does not always mean it will flow more.  I got the same flow out of the BBM heads with a 2.090 valve as with the 2.200 without any porting.  Same with the Survival head.  I got 352cfm with porting and 2.150" intake valve.  The Edelbrock heads work well with 2.150 intake and 45* seat.  I also have always tried to keep the throat diameter at 89-90% for intakes, and 88-90% for exhaust valves.  Ultimately the heads work well with anything over 70% bias for the exhaust flow.  Divide the exhaust flow by the intake flow.  Another thing I have used in the past is to flow the intake tract without the valve, (valve stem installed upside down) and then see how much flow is lost around the valve.  If you can get a valve job and port shape to keep the flow to within 5% loss with the valve installed, you have just about optimized the port and valve job and unshrouding.  There are many more things to consider in a good valve job than a larger valve.  JMO, but it has been my experience.  Joe-JDC

Thanks for sharing that info, Joe.  I truly appreciate it. 

paulie

[plovett]

I'm really throwing myself out there as a sacrificial lamb to get the cylinder head guys to come pummel me and give us more info.   

paulie

Don't think it's not appreciated, Paulie
I always wondered if there was a point where the valve came so close to the bore that it effectively sealed off the flow at that point. Ford obviously knew this when they notched the cylinders in the 427. With super high lift cams, I wouldn't think you could get a notch deep enough to help that much. Jay is working with a maximum sized bore though, and if he's testing with a bore tube I'd think the data should be pretty accurate.

No problem, Doug!  I'm acutely aware of the limitations in my knowledge.  If I can get JDC and other knowledgeable cylinder head guys to tell me how I'm wrong (or accidentally right),  I think that's great because I'll learn from it and my next engine will be that much better. 

I'd let someone kick me in the junk all day long if I could gain 50 hp, and I'd  be thankful for it.   

JMO,

paulie

[blykins]

Paulie...

I suppose I used the wrong choice of words, or interpreted the OP's question incorrectly.

Let me rephrase.

I have never seen where a 2.190" valve has been a detriment to flow on this particular bore size and engine scenario.  Ratios and percentages are nice to look at, but if you're going to look at any, look at the valve vs throat ratio and the intake flow vs exhaust flow ratio. 

As for low and mid lift flow numbers, the valve job has just as much to do with this than anything else.   The primary angle is key here.  You are correct that the low lift numbers help everywhere.  As soon as you crack the valve open, you want stuff to start moving.