Bigger valves in 302 heads?

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Lelo Dart

Lelo Dart

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Is there any advantage to running the 1.88 - 1.6 valves on the 302 heads? Once again I'm getting a lot of conflicting information. Bigger valves slowing velocity? Only the exhaust? Bigger = better? Valve shrouding? Would really like to hear from somebody with some personal experience. 318, 30 over, kb167 pistons, xe268h cam, Holley 570, 302 heads and a few other goodies. Have a second set of heads that I was thinking about the valves and maybe port matching my performer intake. Never done any porting so I'm not even sure about that.
 
A set of 1.88/1.60's would be great for those heads. You won't see any real valve shrouding with those, and you'll definitely see some extra flow and hp out of them. The 302's still have the smaller 318 ports, so I really don't think that going to 1.88/1.60's is going to kill your flow velocity, and the larger valves will help the flow big time on the top end.

I wouldn't go up to 2.02's though, the rest of your build is pretty mild and doesn't need the larger 2.02's. Some argue that you get valve shrouding with the 2.02's. Even with those I personally don't think its a huge issue, although it might limit the benefits of going to the 2.02's. The magnum head valve sizes, 1.92/1.62, are about as big as I'd go on a 318 unless it was a very stout build. I also think the fact that the factory 5.2 liter Magnums come with 1.92/1.62's tells you that shrouding isn't an issue with 1.88/1.60 valves.

A set of 1.88/1.60's and some gasket matching should make that a pretty nice 318.
 
I don't see any benefit to openning a set of valves in a small port. If the cylinder heads have had port work and flow higher than stock, it would only help if the size of the valve is restricting flow. This can only be proven with a side by side bench test, so it's moot on a situation that has no test work, like in your case.

Valve size vs port size should be relative. The most flow and velocity that you can get throughout the entire port, with the smallest valve at the end is always best, to eliminate shrouding and increase volume.

I have a set of 302 heads and I only did mild cleanup on the castings, in the runners to clean up the runners joined areas and burrs. The ports in the 302 head are shaped specifically to increase velocity. They can be used differently with higher flow applications, but those who port and remove the swirl pattern at the valve window, just before the seat are utilizing the head for higher RPM HP to make up for lack of low RPM velocity.

Basically, unless you are doing some pocket work, guide work, overall porting, etc, it's not worth the effort. Think of it like having a gigantic door in a small hallway. You have to walk sideways to get to the door handle and it doesn't make passing through it any more effective. It actually goes the other way and works against you.

I have a set of accidental heads that have 1.88 1.60 valves that are open chamber 318 port size that I got back from a machine shop after sending them 360 J castings and about the only thing I can do with them is port them and deshroud the tight ends near the intake seats for a forced induction engine that will have the cylinders deshrouded.

That cam will like a little port work on those heads, but bigger valves with no port or deshroud work won't increase anything, but turbulence coming into a .030 over 318 cylinder. In fact, an .030" over helps the current intake valve flow transfer better on the tight side of the intake valve to cylinder wall.

If you port exhaust to 1.60, remember that you should be at 70% intake to exhaust flow, so you'll need to make up the difference in your exhaust system, like going with a symetrical int/exh lobe lift or full exhaust. I think you'd be better off with a 2 1/8- 2 1/4 outlet exhaust per side into a 2.5 full exhaust, your current split ratio cam and a 1.5" exhaust valve.
 
There are a couple reasons I like the larger valve (1.88s). As Dave says - there's not much shrouding, it allows me to place the intake seat at the point furthest out into the chamber because it uses fresh metal, and in terms of low lift flow it adds some there. With the cam you have i don't agree that there will be any issues with "too big" killing torque even with the as-cast pushrod pinch. Another very easy way to get another 10-15cfm throughout the lift range is a 30° back cut on the intake valve if you are runningn a stock type valve. This is already done if you're running a performance stainless valve.
That being said - whether or not you can feel any difference is totally up in the air. I always go with larger valves - so I have no back-to-back comparisons. I just have results of the larger ones to go by.
 
We used to put the Chevy 1.94/1.50 valves in them with great results. We dont deal with the 302 heads any more, waste of money now that there are the new EQ, Indy X and the like out there.
 
#4323302 Cylinder Heads..

With the stock Intake Port Volume at {120 CC}, installing larger 1.88" Intake Valves
will have 'from Zero to Minimal Gain'.

Unless you perform some port work (Bowl Area) and (General Porting), stay with the
Stock 1.78" Intake Valve.

Just by going to larger valves without some port work, will have 'minimal gain', and that
gain will only be at Higher RPM's, not for Low-End Torque and Response.

Same thing wth the Exhaust. With the stock Exhaust Port Volume at {55 CC}, again installing
a larger 1.60" Valve will have 'Zero to Minimal Gain'.
------------------------------------------------------------------------------------------

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As a reference the 'J' Cylinder Heads with a 1.88" Intake Valve and Exhaust Valve 1.60" has
24% Larger Sized Ports.

* Intake Port Size = 149 CC
* Exhaust Port Size = 69 CC
 
There is no reason to spend time and money on 302's when you are looking for more performance....302's are NOT a performance head....they have freakishly small ports....save your money and get different heads if you are looking for more performance. JMO
 
I think it's counterproductive on a high RPM head, unless you are into it for your own bowl, pocket, guide grinding, etc. They can make HP, but it depends on how much work you want to do. If you are paying someone else to do this, as stated above, it's not worth it on high RPM to run a 302 runner casting, untouched ports and big valves.
 
If you port them in the process, short turn blending, then they will help...if not, they might could actually hurt flow due the big overhang of the short turn..but that could be remedied somewhat if a multi angle cutter that does a nice throat cut is used... but typical without porting/blending the short turn just becomes steaper...and the flow sometimesdrops off at an earlier/lower lift.
We have a machinist that uses something like a custom 7 angle cutter , it does a really nice chamber bowl cut/'well' looking blend from the chamber to the seat and the valve job alone picks up 10-15 cfm on average.
 
If you yourself do the work to save the money, they can be worth the effort. I would do the larger valves and port the head. The performance level of the heads is more than the raw numbers suggest. Ma MoPar sold these heads when they found out they made 55HP more than the 360 head did.

As mentioned above, the newer set of heads available today make them a better deal than reworking the 302. If your paying someone to do the work o the head, it is a loss of money a d performance.

The 302 can be ported to a 340 size window and flow pretty nice.
 
Lelo,,,,,,,

Looking at your '318' Engine Modifications.

* KB 167 +.030" Pistons Flat-Top Pistons with Notches = (9.0 - 1 Compression)
(9.5 - 1 Compression with a Decked Block)

* Comp-Cams EX268-H
.454" Lift / 268* Duration / 110* LSA / 106* CL (218* @ .050" Lift)

* Comp-Cams Valve Springs #901 (#242 Load-Rate @ 1.250")

* Holley 570 CFM (Avenger)

* Edelbrock Performer Intake

Everything states a Maximinum RPM of 5500 for 'peak horsepower'.

Stay with the 1.78" and 1.50" Valves, and perform your own minor 'Head Porting'.
A) Gasket Port Matching for both Intake and Exhaust
B) Round off the Valve Guide Boss in the 'Valve Bowl Areas'.
C) Remove any 'high spots' or 'cast flashings' inside the Cylinder Head Ports.

I'm sure you are having the Machine Shop perform a Competition Multi-Seat Valve Job,
with a minimum of 5-Angles (70* - 60* - 45* - 30* - 15*) in the Valve Seat.

And a 30* Back-Cut (.025" Wide) on the Intake Valve, as this will improve CFM greatly
through the Intake Port.

The #4323302 "High Swirl' Cylinder Heads can be a 'Funtional Mid-Performance Head', and with
some 'smart tricks' are a decent component on a 'Mild-to-Moderate' Street/Strip Performance 318.

The 'key' to this Cylinder Head, is getting a proper Competition Valve Job, and blending the 'small'
Intake Port to 'match-up' with the Performer Intake Manifold.

The 'Best Trick',,,,,,,,, matching the Cylinder Head Intake Ports to the Performer Intake Manifold.

$T2eC16ZHJIkE9qU3k6p3BRSOvLRiF!~~60_14.JPG
 
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