Dan the man
Well-Known Member
Are bigger intake valve's better for low lift flow? 3 angel, or 5 angel valve job? Just asking, trying to learn
Improving low valve lift flow
- Thread starter Dan the man
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replicaracer43
Grumpy Old Man
- Joined
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First define your idea of "low lift"
mygasser
Well-Known Member
here we go again 
A bigger intake valve will increase low lift flows, with minimal porting peak flow will occur at a lower lift.
Five angle valve job and back cutting the valve will smooth out low lift flow.
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junkyardhero
Well-Known Member
do we? i assumed everybody, just like, knew....Perhaps we should define 3/4 race cam first
.100,.200 and .300
Rat Bastid
Dunamis Metron
The valve is the restriction up to .25 L/D ratio. After that, it’s the throat size that takes over.
Ironracer
Gearhead
Shoot, actually y'all are pretty educational ! I was wondering if Dan, the OP, was thinking about using a low lift, non-radical cam, to improve performance ( if he ever found " The Car"
Sorry buddy, what is the L/D abbreviation?
Lift vs Diameter?
This could be a very good way to increase power and still get improve mileage going with your thoughts.
Ironracer
Gearhead
Dig it Rumble! I mean I figured there was a reason why he was asking.. just knowing him, from on here, I think that's what he'd be looking for..
The way I always read it, up to .400 most of the time. Other writers have listed .450. My best guess is it is dependent on what Rat B was saying. I’d go with that myself since changing parameters of valve size and what’s behind it modified or not and when it takes over (the bowl area) are or become a point of perspective or actuality.
Rat Bastid
Dunamis Metron
Yes, lift to diameter ratio.
and....
Good question Dan! I e read up from several sources and this is what I have learned. The answer can be a simple yes BUT it is not always that simple. Let’s start with the valve itself.
A 1.88 vs a 2.02. The larger valve will flow better everywhere.
Why?
The diameter of the valve has more area in which the air and fuel can pass on by into the cylinder. But……
That’s just the valve itself. Let’s just assume the valve job is done at the best advantageous angles and the valve is set in its seat at the perfect placement height. If the bowl area under the valve is t sized and/or ported to it’s best size, the valve will not flow it’s best.
When you take out a 1.88 valve and install a 2.02 without any work under the valve, the gain is very small, just a slight improvement at best. The gained curtain area isn’t maximized. It’s kind of a waste of a mod at this point. Also it’s why a factory 2.02 head is a more or a prize head over a 1.88 head or the same casting.
And then this is where Rat AB’s comment comes in.
Oh… crap… the valve job isn’t a in stone set of numbers. It can change from a number of things and first on the line is what exact valve is used and is it modified from stock or OOTB?
Sometimes, all things dependent on what they are, the after market valve could be made just exactly what the head guy wants….. and sometimes not.
Depending on how the valve shape is, will help determine how the valve job will go. Then again, the valve and the seat can be modified since the head guy knows something better. Which of course is dependent on the purpose of the head. Yep! Everything has changed yet again!
I’m not really well versed in the in’s and outs of what is good for this that and the other thing. There’s also rules to play by, what you can and can’t get away with & im sure even more stuff I’m leaving out.
I’ll just say, I have been blessed by some really knowledgeable people that have handled my cylinder heads to assist in the goals I have spoke to them about.
I wish I could comment more on this topic but I can’t and if I did, I’ll probably just be corrected. So I’ll sit back and read along and learn something. NO sense of running the gums when there’s nothing to add. And if I’m wrong above, I’ll be corrected and learn something.
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Ironracer
Gearhead
Hey I know you weren't talking to me man but that's definitely informative! I must have got blessed when I bought a 360 out of a Cuda 25 years ago, J heads, Big Valves, you cannot put your thumbnail between the intake and exhaust valves, work done to them with a bunch of additional porting and gasket matched to the big gasket, ( I actually had to send back two, or three, sets of gaskets till I got one that really fit) and a ported Strip Dom, also Gasket matched.
The c/d is lower than it is with a smaller valve
Hey Ironman! Glad you picked up something. I’ve read this from 3 or 4 sources. If your J heads are at least bowl ported with the 2.02 valves, all that remains is at what percentage and what kind of valve job they did. I can’t really help here. I’ve seen head porters argue (kind of, at least constructively.) over the percentage to be ported. So I’ll opt out of that one. On the valve job, the best I got is more angles the better, but this may not be the case on every head/valve combo.
Stand by for a head porter!
@PHR - Mr. Porter should be able to help a lot here. @Rat Bastid who is chock full of info can probably shed some light on the in’s and outs of various cylinder heads as well. @pittsburghracer He can tell you what he does for what he works on.
Hey Fishmen! What is the C/D abbreviation?
Coefficient discharge
Ahhhhhh, thank you! Yes, a term I should have mentioned.
Ironracer
Gearhead
Hey Brother Rumble, appreciate it Sir! I ended up losing the block, but for 500 bucks, I got those worked heads, the Holley SD, And a B@m HoleShot 3000 stall. After all of them years, I'm thinking about shoving that stall up in that thing, (even though it's a looser unit) right now you caint get none of the 3500 Tight I've been reading about on here.... the heads and intake have been on my 340 for over a decade, they run good in that Duster with the 4:10 gears, just with the 2200 Mopar performance stall( which they discontinued years ago) after I went from 225/.60/15s which the car, was from a dead launch, with no foot breaking, would just blow the tires off, go sideways, and immediately sometimes turning into like fully sideways 90°. So I put 295 50 15s on there, and now I think taking advantage of that traction, I need more launch out of the hole! Car actually moves out pretty good though it's got a low gear set transmission out of a later model van.. I it would have been nice to convert it to a 4 spd, that's always where my heart's been at with everything I've drove! Hope I derail the thread but I don't think Daniel mind he's a pretty decent cat
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