Perferable intake valve size?

[casual]

What would be the perferable intake valve size for a N/A 4.0 or 4.2L mini stroker? Cleaned up head/ported lightly, unshrouded & polished chambers, using a 229 Mopar cam!
Exhaust valves are 1.55" and intakes are a set of 2.00" Ls6 intake valves and obviously they are too big for what I need! I do however want to use them because the tuliped underside! So I am getting them turned down and was curious of what size would suit me best!

Idk my limits yet, but should I get them turn down to 1.92-1.93" which is slightly bigger than stock? Yes SBC valves are 1.94" but there were give aways and are tuliped and I'd love to use these!

[Cheromaniac]

The 2.00" intake valves will be just about OK and shouldn't cause any shrouding issues.

[casual]

The 2.00" intake valves will be just about OK and shouldn't cause any shrouding issues.

Shourding is pretty bad..I am using a 7120 cast from a 93. I've done what I can to unshroud both intake & exhaust valves..did a little extra work on the intakes cause the valves are 2.00. Honestly they are just to big, shrouding is worse than stock & honestly the will kill my low lift flow..at least my heads telling me this. Using such a small cam & not going all out, I feel they will hurt more than they will help right? I did not go all out on porting, I just did what I could without getting to serious! I polished the chambers & exhaust runners as best as possible as well, opened them up very very slightly & tear dropped the guides! I remember seeing the "big valve" head on the Zj and saw its torque curve..and I really do want to avoid that problem..from the graphs he posted, he didn't have much low end..and thats where I'm looking to gain..low & mid range!

I can get these turned down to stock size if wanted or needed! Which is what I want to do perferably, but wasn't sure if I'd gain from something slightly bigger (1.92-1.94)? I know in a N/A application, you want "the most air through the smallest hole"...I know theres ways to calculate the perferable sized valve for ahead by run shape, size, volume & such but I haven't found anything on it yet.
Also was thinking maybe it is best to go slightly bigger & get the seats ground to start with a fresh seat? Head checked out just fine when it was magged. But its had 291k on it as well.

[Cheromaniac]

Shrouding is pretty bad..I am using a 7120 cast from a 93.

It's not an issue with the intake valve but anything bigger than a stock exhaust valve will be shrouded pretty badly unless you grind the chamber wall area closest to the valve.

[casual]

Shrouding is pretty bad..I am using a 7120 cast from a 93.

It's not an issue with the intake valve but anything bigger than a stock exhaust valve will be shrouded pretty badly unless you grind the chamber wall area closest to the valve.

Ya I cut a bit from the exhaust. Hmm I may just run the 2.00" then. I'm having a local shop called Pettis performance build my motor and I'm extremely happy with them.

[casual]

My guy at Pettis is suggesting I get them cut down to a 1.94". I'm gonna do some more reading before I decide though..
They also suggested that I get my chambers & valves coated..faces & backsides. Said because how high our intake temps are that the coated backside & face of the intake valve would allow the intake charge to stay cooler, vs being heated by the intake valve!
I've seen this often in high performance motors, but always thought the coating was not very durable! I remember reading a thread on the srt4 forums of a guy who had his piston tops coated & 102k later he pulled the head and the coating was almost non-existant! Is this worth my money?

I already polished my chambers..but thought maybe I should coat my valves to help lower combustion temps & possibly detenation! Also though of maybe just polishing the valves vs coating them...what say the crowd?

[Cheromaniac]

Just stick a Thermotec heat barrier to the underside of the intake manifold. That alone will reduce intake temps. substantially. Sonce you've already polished the chambers, just polish the piston dishes and be done with it.

[CobraMarty]

I read a recent article about this, Valve Lift/Diameter Ratio.
It said that for HP Street looks for about .25 and hard Core Perf. .28-.30 and pure race engines .35.

So what I can find on our Jeeps 4.0 with 1.6 rockers-
the Intake lift is .408" which is .255" cam lift on 1.91" valve
the Exhaust lift is .414" which is .259" cam lift on 1.5"valve

So stock Intake L/D ratio is .408/1.91= .2136 - I guess pretty poor
And the Exhaust L/D ratio is .414/1.5= .276 -seems pretty good

With 1.7 ratio rockers-
Intake L/D ratio is .434/1.91 = .227 better than stock
Exhaust L/D ratio is .440/1.5= .293 even better, but stock was good before

What does this all mean? ? Just something else to consider when comparing and building an engine.

For the 4.0 it looks like the stock intake valve size is fine, it just needs more lift. And the exhaust could need a bit bigger valve size. Many seem to want to run big valve heads with emphasis on bigger intake valves. Just something to think about. I'm going to back test this on some known engines and engine builders.

The article did not mention or talk about head flow characteristics. I agree it is important for the whole head/engine package. I'm just saying what the article was talking about. I had not seen this looked at in this way before. I will follow it and test/compare it in my future readings. It is just something else in the world of head/engine theory.

[casual]

Just stick a Thermotec heat barrier to the underside of the intake manifold. That alone will reduce intake temps. substantially. Sonce you've already polished the chambers, just polish the piston dishes and be done with it.

Done already Dino..I copied every mod you did on the 4.0performance website:) And my intake & header are ceramic coated as well this go around!

I read a recent article about this, Valve Lift/Diameter Ratio.
It said that for HP Street looks for about .25 and hard Core Perf. .28-.30 and pure race engines .35.

So what I can find on our Jeeps 4.0 with 1.6 rockers-
the Intake lift is .408" which is .255" cam lift on 1.91" valve
the Exhaust lift is .414" which is .259" cam lift on 1.5"valve

So stock Intake L/D ratio is .408/1.91= .2136 - I guess pretty poor
And the Exhaust L/D ratio is .414/1.5= .276 -seems pretty good

With 1.7 ratio rockers-
Intake L/D ratio is .434/1.91 = .227 better than stock
Exhaust L/D ratio is .440/1.5= .293 even better, but stock was good before

What does this all mean? ? Just something else to consider when comparing and building an engine.

For the 4.0 it looks like the stock intake valve size is fine, it just needs more lift. And the exhaust could need a bit bigger valve size. Many seem to want to run big valve heads with emphasis on bigger intake valves. Just something to think about. I'm going to back test this on some known engines and engine builders.

The article did not mention or talk about head flow characteristics. I agree it is important for the whole head/engine package. I'm just saying what the article was talking about. I had not seen this looked at in this way before. I will follow it and test/compare it in my future readings. It is just something else in the world of head/engine theory.

THIS!
This is exactly why I was unsure of a valve size on the intake. Although I won't have more lift, just a stock 87-95 cam set at -4* vs -8*..possibly even 0*. Anyway, I know a little here & there from my older days porting heads for fun & as a hobbie/side jobs...I know the 2" valve is far to big for me! I don't have a flow bench now but I did once upon a time and I learned alot from it! The exhaust's will be a 1.55" which will help me, so long as they are unshrouded which they are.
I think my intake is getting cut down to a 1.94", unless anything thinks I should just have them turned down to a 1.91"? Which is back to stock!

[92tank]

I read a recent article about this, Valve Lift/Diameter Ratio.
It said that for HP Street looks for about .25 and hard Core Perf. .28-.30 and pure race engines .35.

So what I can find on our Jeeps 4.0 with 1.6 rockers-
the Intake lift is .408" which is .255" cam lift on 1.91" valve
the Exhaust lift is .414" which is .259" cam lift on 1.5"valve

So stock Intake L/D ratio is .408/1.91= .2136 - I guess pretty poor
And the Exhaust L/D ratio is .414/1.5= .276 -seems pretty good

With 1.7 ratio rockers-
Intake L/D ratio is .434/1.91 = .227 better than stock
Exhaust L/D ratio is .440/1.5= .293 even better, but stock was good before

so want you are saying is the stock valves are actually to big to start with?

[CobraMarty]

I'm not saying a thing. Just giving the info.
I think it is not the valves are too big, I think that the lift is a little too little. If you increase the lift with the 'stock' size valves then L/D ratio would be a bit better. It doesn't take much. Intake valve lift of .458" gives Intake L/D ratio of .24 and .477" gives Intake L/D ratio of .25

[casual]

so want you are saying is the stock valves are actually to big to start with?

Yes actually...for a stock cam jeep. From everything I've found the optimal size would be 1.78"...I'm sure this is not 100$ accurate, as I only calculated for the intake runner length of the head. The smaller valves would get air moving quicker at lower lifts & not sacrifice much anywhere else..thus better flow, thus more power lower in the rpm range..it may get choked a bit up top..but 1.78" with a stock 4.0 head and 5300rpm is perferable according to the math I've done!

To make power in a naturally aspirated engine..don't go bigger valves..the key is the most air through the smallest hole. This will give great efficiency, better flow at lower lifts (bigger valves kill this) & even more flow as higher lifts..also you can unshroud them ect ect..alot can be done with stock sized valves. You can get aftermarket valves which are swirl polished and lighter weight ect ect..Which is basically what I've done..My valves were turned down to a 1.92" to fit into the newly ground valve seats!

The valves are also being backcut..I believe 19* & 25*..this will help low lift flows & shouldn't have any adverse effects!

[CobraMarty]

so want you are saying is the stock valves are actually to big to start with?

Yes actually...for a stock cam jeep.
...perferable according to the math I've done!
...better flow at lower lift(bigger valves kill this)

This hits it on the head. There is math involved as well as practice.