Thoughts on Valve size?

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Valvebounce

Valvebounce

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What real world experiences have you guys had with upgraded valve sizes on a SBM with a 3.940 bore and small port heads?
"Conventional wisdom" says that 2.02's suffer from shrouding. Yet plenty of guys have slapped J heads onto 318's. (Biggest hurdle there is getting over the miserable compression ratio that combo typically yeilds)
I've got some 1.88's/1.6 which I had planned to fit to some 318 heads. But I'm wondering if it's worthwhile to take the next step. (2.02) Cam will be an XE 274.
Since I'll likely be getting the guides done too, I might even go to 5/16 stems if I go bigger than the 1.88's I've already got.

What thoughts have you?
 
I think that the Magnum style 1.92"/1.625" valves would be a good compromise while providing thinner valve stems for better flow. Just gotta sleeve down the guides in LA heads. I believe there are a variety of heights available to help get the geometry correct.
 
Not sure what your HP goal is but a L76 (340hp 327ci) used 1.94 Intake / 1.50 exhaust.
 
What is the use for the car/engine? Your comment on the 318 CR with the large chambers seems to imply that you want to preserve lower RPM torque, but I would not want to make any assumption.
 
Valvebounce said:
What real world experiences have you guys had with upgraded valve sizes on a SBM with a 3.940 bore and small port heads?
"Conventional wisdom" says that 2.02's suffer from shrouding. Yet plenty of guys have slapped J heads onto 318's. (Biggest hurdle there is getting over the miserable compression ratio that combo typically yeilds)
I've got some 1.88's/1.6 which I had planned to fit to some 318 heads. But I'm wondering if it's worthwhile to take the next step. (2.02) Cam will be an XE 274.
Since I'll likely be getting the guides done too, I might even go to 5/16 stems if I go bigger than the 1.88's I've already got.

What thoughts have you?
Click to expand...
I have found, cut 1.88 down to 1.84, 1.60 to 1.56. same sizes used in poly head 318. use sst nail headed valves. this size does not shroud in chambers, will provide more flow and port velocity. I did this on 273 heads used on 273.
 
I tend to go up in valve size in order to put the seats where I want them. It's not just a flow thing - it's cheaper than replacing seats, and there is a performance gain in getting the valve job up to performance quality. Now for 318 heads, the upgrade is 1.88 intakes, and 1.60 exhaust. For 340/360 that's 2.02/1.65 or 2.05/1.65. With the cam, the 1.88 will do just fine.
 
Jim Laroy doesn't think a whole lot about valve shrouding, so I wouldn't either.
 
What are your performance goals. Smaller motors like more port velocity. I would be more concerned with compression ratio than valve size. long time ago I put together a mostly stock 340 save for an Erson Tq40 cam. I wound up putting the small valve closed chamber heads and intake from my 273 on the 340. eddy LD4B intake and hooker headers. Took it out to the drag strip and it ran 13.80 with a peg leg rear axle 3.23 Gears and stock converter. It had a diesel problem and was hard to shut off hot but it ran good.
 
There is a lot of potential in the stock valves.
I'd mainly go bigger for moper's reasons plus it can help low lift numbers. Just make sure you open up behind valve and bowl to take advantage of it.
 
What moper said. Also, to see much gains, a 70 degree bowl cut should be done. If you are using OEM style valves a 30 degree back cut is worthwhile. And as for shrouding, if your machinist uses a Serdi machine, a de-shrouding cut out to the bore line is pretty a straightforward operation.
 
Thanks for the input guys.
I intend to use the engine for a bit of low buck 1/4 mile use. Wail on it some, and see what breaks first. If I scatter it it's only a 318. 360's here are just too expensive.
Heads I have now already have 1.88's. And the zhorst valves are pretty sunk in.
I'll have to measure where the CR is down the track. I have cheap slugs with a 1.745 comp height. And .028 head gaskets. No-one likes a motor that's doughy down low. Horsepower sells cars, torque wins races.
I already have a set of brand new valves in the stock 360 size.

A bloke at an auto parts shop was telling me a while ago that he'd fitted 2.02's in his 318. I dont think he had it running yet though. Obviously I'll give it a home port job too.
 
The 2.02's fit in and th valve shrouding issue is a valid one but one not worth getting into or worry about. It worked very well in my old 318.

For a purely driven street car with little to no real performance as on parts, the stock valve is fine and so is a 1.88/1.60. Though a performance build would be happier with larger valves, a mild 318 will perform very well with its stock valves or 2.02's.
 
Valvebounce said:
What real world experiences have you guys had with upgraded valve sizes on a SBM with a 3.940 bore and small port heads?
"Conventional wisdom" says that 2.02's suffer from shrouding. Yet plenty of guys have slapped J heads onto 318's. (Biggest hurdle there is getting over the miserable compression ratio that combo typically yeilds)
I've got some 1.88's/1.6 which I had planned to fit to some 318 heads. But I'm wondering if it's worthwhile to take the next step. (2.02) Cam will be an XE 274.
Since I'll likely be getting the guides done too, I might even go to 5/16 stems if I go bigger than the 1.88's I've already got.

What thoughts have you?
Click to expand...
A lot has been said and covered already and some excellent points made, I'd like to add a little more, say..'dive further' into some of that.
The '1.88 intake valves in a 318 head' changes the shape from the seat to the top of the short turn so much, that you better know how to port heads-properly shape it, blend the roof/bowl/runner or it'll be weak and less than a stock 1.88 360 head...especially in the lower lift. If you don't do that work, you end up with possibly matching peak flow...the the entire way to peak could be 20cfm behind. As for the exhaust, there is a decent little port, it holds it's own with factory spec'd 1.50 in ported form to the 1.60 j or x in mildly ported form, so it will actually support a 1.78/1.88 int valve, and boy does that port move fast...
The 360 head at 1.88/1.60 with a good compression aka GOOD CYLINDER PRESSURE is an easy one, a lot easier than working a 318 head when it comes to making 350-400hp, because it just flows more air and will flow even more if you port them and at lower lifts...which is where this goes next.
It is easier and you just get more flow throughout the lift range with a 2.02 over a 1.88 in a 360 head, testing back to back factory 2.02 J vs 1.88 J , 2.02 wins, I have found it hard to get 205cfm@.300 lift from a 1.88 intake valve, but it was the casting I used. There are so many greater cylinder head guys out there, well...maybe not many...but whats said in this post is not the 'end all'
Someone mentioned the 1.94, the skinny stem idea, the valve shouding thing...
The 1.94 intake valve is a great idea, but in 11/32 stem "less weight" 1.60 exhaust valve and installed in the 360 heads you have, with a bit of bowl/guide porting they give 250/190 cfm.

Last for those who don't know. The factory 318 chamber valve de shrouding cut is about as big as the bore of a 340.
IMAG2480.jpg
 
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I think a .060 relief would cover any shrouding issues.
Also, on a simple bang for the buck, installing the larger valves, shrouded or not, bowl ported or not, is still a win win.

Of course as the official said, the more extensive work done the better the returns. No one can argue that. However let it match your build and not over run your wallet.

A far reaching example would be fully ported W2's on a mildly cammed (XE262) 318. But you get the idea.
 
rumblefish360 said:
I think a .060 relief would cover any shrouding issues.
Also, on a simple bang for the buck, installing the larger valves, shrouded or not, bowl ported or not, is still a win win.

Of course as the official said, the more extensive work done the better the returns. No one can argue that. However let it match your build and not over run your wallet.

A far reaching example would be fully ported W2's on a mildly cammed (XE262) 318. But you get the idea.
Click to expand...
The seats are cut for 1.88/1.50 in that pic.
Guys just do not need to worry about shrouding on a 3.94+ bore and 1.88 or 2.02.
 
Valvebounce said:
I'll have to measure where the CR is down the track. I have cheap slugs with a 1.745 comp height. And .028 head gaskets. No-one likes a motor that's doughy down low.
Click to expand...
High 7's SCR with typical chamber volumes and 4 valve relief pistons tops.
 
I know it's not "best practice", but since I'll get is square decked anyway, I'll probably get some extra taken off. And I have a family member with the gear to shave the heads down too.
I lot more faffing about than just buying better slugs. But it's more about making use of what I've got. I have way too many cars, and projects in the works to be throwing lots of money at it.
 
rumblefish360 said:
Oh I know that feeling!
Click to expand...
X$ $$$ ..two,Rob... For me here: a GOOD valve job,1.88/1.60 combo,will get the job done... That cam's right at the .490" lft zone.. Good gears ,tuning ,good compression ... Maybe
.I would step a size down,&personally: car weight,willing to deal with tuning,and the rest of your combination,would kinda help....
 
Valvebounce said:
What real world experiences have you guys had with upgraded valve sizes on a SBM with a 3.940 bore and small port heads?
"Conventional wisdom" says that 2.02's suffer from shrouding. Yet plenty of guys have slapped J heads onto 318's. (Biggest hurdle there is getting over the miserable compression ratio that combo typically yeilds)
I've got some 1.88's/1.6 which I had planned to fit to some 318 heads. But I'm wondering if it's worthwhile to take the next step. (2.02) Cam will be an XE 274.
Since I'll likely be getting the guides done too, I might even go to 5/16 stems if I go bigger than the 1.88's I've already got.

What thoughts have you?
Click to expand...

I have real world experience with 2.02" / 1.6" ferrea 5000 series valves in a pair of "915" J heads fitted to a 318 with a 3.940" bore.

I cc'd the chambers of the stock 318 heads with 1.78" / 1.5" valves, they came to 66.5cc and had never been removed since they left the factory until that point.

My J heads with the ferrea valves also came to 66.5cc. deck machining history unknown, but looked minimal and the valve job looked factory spec.

At an estimate, I'd say the ferrea valves reduce the chamber by about 4cc compared to stock 1.88" / 1.6" valves.

With dome top pistons bringing it to 10.3:1 and a comp thumpr cam (227/241 on 107) she made 352hp corrected at the fly on a water-brake engine dyno with an exceptionally flat torque curve. I've since ported the heads and put in solid flat tappet cam, but it was a lot of fun in that configuration.

Personally, if you're looking to make more than about 300hp I'd start with something with more port cross-sectional area than an old school 318 head.
 
I'm not actually sure what the car would weigh.
Thanks for your input Frosty.
The "next" engine will get a pair of J heads with 2.02's etc. (I actually have the heads already) This build is to use up the other parts I have first. I really want to run forgies in the next build. but keep the CR low so as to run Barametric compensators/amplifiers on it.
I have so much on with a young family, and too many projects that build might be a while off.
 
"Barametriccompensators/amplifiers on it."

LMAO! I have never heard that description before!

EXCELLENT WORDING!
 
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