2.02 intake valves... Overkill??

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bighammer

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I found an interesting read on the internet in regards to head work. I always thought the larger valves was something I needed (or at least really wanted) but according to this machine shop (they specialize in mopars) the larger valves may tend to hinder performance on a street car. Here is a link to the page: http://www.bjrracing.com/small_block_heads.htm

I will copy and past the info here as well:

"The 340 and 360 will be covered together just as the 273/318 engines were. Once again the same will apply for the 340 engine just as the 318 mods applied for the 273 engine. A good 340/360 engine shouldn't need more than 160/168 cc's of intake port volume and 250 cfm's of air flow. More airflow is a plus but not at the cost of a larger port runner.

Even though the strokes are different in the 340 and the 360, the rod length is the same. The piston speeds are different but the port can remain the same and this is why. On the 340 engine you should use the 1.88 intake valve to keep the port velocity up in the larger runner. The same modifications that were done to the 318 heads will apply here also. A good 340 head with the 1.88 valve should flow in the 235/240 range @ .500 lift and 160+ @ .200 lift if the port is properly done. The same air flow will apply to the 360 engine. The specs stated above would be a very good street/strip head and would satisfy most 340/360 engines.

There is no need for a 2.02 valve until you're racing at high RPM's above 6500. The valve size is just too large for any low RPM engine, and bottom end TQ and throttle response will be suffer.

With the air flow stated above, the 340/360 should be capable of making over 550 HP. The need for more than this will result in you spending big $$$$ and won't be very streetable. Anything more than this would be considered race only.


Just for reference for stroker engines, a 318/349 engine would use the 160 cc 1.88/1.60 valve 340/360 head. And the 360/408 engine would need a 180/185 cc head and air flow in the 280/290 range or more with a 2.02 intake valve and a 1.625 exhaust valve.

In any case, the intake to exhaust port flow ratio should be kept to 70% for best results. Superflow states that anything above 60% won't really be noticed in a street or drag engine. Ratios above 80 and 90% have been seen and only help high RPM engines like NASCAR where high efficient exhaust flows are needed to make HP at 9,000+ RPM's. Obviously heads like this aren't cheap or useable for street use."

I found this info to be very interesting. I realize that there are quite a few owners of 'full on' drag cars, but I think the majority of members drive their street mopars, and maybe an occasional trip to the track.

What do you guys think about the above info? Has this been the general consensus here? The author seems to be very knowledgeable.
 
Sign me on. This debate has been around for years. When I bought my street(262 voodoo cam) engined 360 dart, the paperwork had a machine shop doing 2.02 valves.
 
There are different schools of thought on valve size. Mostly based on cingular experiences. In terms of BJR - he's got history here and a lot of what you read from him needs to be taken with several grains of salt.
In terms of my own opinion - I'd say you will never feel a "drop in torque" or feel a poorer response from larger valve and it will enable me to make more power all around. I will always run 2.02 or 2.05s when I use iron heads. I don't believe in large volume ports - my heads rarely involve even removing much of the guide boss or major reshaping in the bowl. One of my most efficient engines has 2.05/1.60s, makes 450hp, and gets over 17mpg (422" small block). Those are 596s that were what I call stage II - meaning bowl blending, gasket matching, and some work on the roof, pinch, and short turn. It makes that figure on pump gas with a hydraulic cam lifting the valve .500". The power was figured off weight and 1/4 mile mph.
In terms of cost vs reward - I always replace the valves anyway, and the larger valve lets the new seat be placed out further with maintaining the stem height so the geometry is good. So it all makes sense to me to do things that way.
 
Ask Jim Laroy what bigger valves do through the entire RPM range on the dyno. He'll tell you.
 
I'd say a full tank of gas or a dirty air filter has more negative affect than larger valves.
 
I think I would trust the Chrysler engineers before I would take any advice from that shop. Wasn't there some ??? Questions about bjr ???
 
oh brother

next they will say the 4bbl is overkill on a 340 too

the probably recommend a hogged out 2bbl would give you more velocity and according to the theoretical long island bench racing clubs desktop dyno calculations would win street races even in new jersey lol
 
Clearly larger valves are a help even on low RPM mild street engines. The early 340s are probably the best example.
 
Thats what I was thinkin, Rob. Chrysler engineers put em in factory 340 cars that beat up on a lot of bigger engines in the 60s.
 
Sure Chev Dodge and all them manufacturers put in 2.02 on the HP motors so they would go slower . Does not make sense , maybe on a stock 318 they don't help , but on a 340 seems to work well
 
a street light to street light build (street driven) is very different than a build for quarter mile performance.
it's always the combination....a size 10 shoe on a size 5 foot will never work very well.
 
Sure Chev Dodge and all them manufacturers put in 2.02 on the HP motors so they would go slower . Does not make sense , maybe on a stock 318 they don't help , but on a 340 seems to work well


wrjjol.jpg


Engineers and manufacturers, and ESPECIALLY Chrysler, LOL, were not known for needlessly throwing money at something with no real benefit.
 
My thoughts.

If the head needs valves replaced, step up to a 1.94 or 2.02. If it doesn't run what you got when on a budget.
 
With todays intake and cam technology and a well thought
out extracting exhaust system you can create quite a bit of
streetable power and torque without the larger valves.
Its more about filling the cylinders with charge speed and cam
timing than giant valves.
When you add bigger valves you must unshroud them so they can work at a higher engine speed or the charge speed will be lazy.

Moper got it right was with his assessment
on new valve seats and maintaining stem height.
 
I stopped reading when I saw BJR "racing"....:violent1: :banghead:
 
It's a good question though which is why it comes up so much. I'm fairly certain that the reason mopar went smaller had more to do with the upcoming emissions packages and parts sourcing than anything else. The combination of the 340 and 360 being available at the same time (one part # vs two) made it make sense. It wasn't like an "AhHa!" moment in regard to needing more power.
BJR is right to some extent. A smaller port and valve will be more responsive, but response time and power are not the same values and the affects on them are not that dramatic to cause such a vast difference between them. If you are interested in economy and are not concerned with overall power, smaller will provide a certain advantage. (There's a reason Magnum heads use 1.92s.) The question is how much of advantage, and at what cost. Having owned and street driven a 318 with both the factory 318 heads and then X heads, I prefered having X heads on it. Even with 3.23s, with a stick, in an E body there was no discernable "loss" in low end or softer midrange with everything else the same. The car scooted with both. So while I agree with the premise and the physics - my experience has been it's not a big gain in response and a small loss in overall power. In my car there was no discernable loss in response and it felt a bit faster.
Using the shoe size analogy - it's more like a size 11 1/2 vs a size 11 and I can wear either of those.
 
They are only overkill if'n they hit the cylinder wall when you open them!
 
I used to think bigger truly is better but looking into things like discharge co-efficient --well the picture is not quite as clear. In short a 2.02" valve-don't hesitate. J.Rob
 
For all rpm ranges airflow is the key (it's why two intake valves work so well ). So if you can go to 2.02" I think it's a great idea .
The intake port volume can have a negative effect at low engine speeds but it should not be confused with valve size.
The 2.02" was proposed for the 5.9L Magnum engine but it was superceded by the Hemi even though engine performance was the same.
 
And 3-1/2 years later, Jadaharbi disagrees with what? My sense of humor?
Ha ha ha ha ha ha....

I think.... he is trying to hint at.... maybe, install 2.15 or 2.30 valves and notch the cylinder wall????

ROTFLMAO...!!!!!
 
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