Big valves or not

[Glen440]

I have a Volare Roadrunner with a 440.
The motor is .030 over with 10.5 Trw slugs, stock crank and rods with Arp bolts.Right now it has the .528 Purple shaft cam in it. ported 452 heads with stock valves,torker intake, 750 holley, 1'7/8 hooker hedders, 727 with factory high stall and 4.30 gears. I am wondering if putting a set of 906's with 2.14, 1.81 valves on it will make a big improvement.I have a set of professionally ported 906's that the valves are sunk. The car has not been to the track since I replaced the 400 with the 440.So I have no baseline, but the motor is coming out soon so this is the time to do it.
The 8-1 compression 400 ran 13.15's all day long with the top end from the 440 and 3.91 gears. I am thinking that the 440 should be good for high 11's. The car weighed 3750 with out driver. Peoples advice is appreciated.

[Chris A]

You have a decent combo and should definantly be running the bigger valves. I would just get the 452's pro ported and put the valves in them if the 906's are sunk. They have the same basic port configurtion except for one or two spots. Check out the other topics on 452's VS 906's. Good luck.

[DartGT66]

The bigger valves and bowl porting is definitely a good help in a big block. Do the 906's have stock size valves that are sunken, and you could bring them back to surface with the bigger valves? If that's not the case, don't bother, valves that are sunk are not a good thing for performance. Instead, put the big valves to your 452 heads.

[MopART]

Ditto...... I can affirm what has already been said. LET THAT MONSTER BREATHE.

[Krep]

I agree with the others, bigger valves make the 906 and the 452 come alive (with proper porting). Also when the valves are sunk there is a loss in performance. Keep the valve up as fare as possible. If you are on a buget, increasing the exhaust valve size has greater benifits than the intake. So if you have to choose...

[Glen440]

The 906's have stock valves still so going to the bigger valves should fix them. Should I get hardened exhaust seats? The car will be driven daily as long as It doesn't cost too much to drive it. I've priced head work
and looks like for machining, guides, and stainless valves around $800cnd.

[340king]

I have to disagree about the need for bigger valves. My engine builder has ported many a RB head. They have optimized the port for the stock valves. Then tried another port optimized for the bigger valves. Both ports flowed the same. Now, I have posted this info before and was basically called a liar. It is the truth as I see it and have a lot of faith, nearly $13,000.00 worth, in my engine builder.

I did post way back the flow numbers they were getting from the stock valves and that was the source of the disbelief. Since you already have the bigger valves, you are not out anything to go there. Just remember they in themselves are not a magic bullet.

[DartGT66]

Well, you can't optimise a head with sunken valves, can you? But you can fix them with bigger valves. I odn't call you a liar, maybe your machine shop just knows something that all others do not. However, I have homeported several sets of BB heads. I do not have a flow bench, so the only way to verify how the heads work is to drive them at the track and verify the performance. And according to my experience and with my skills, porting the heads with stock valve size leads to a performance gain, and installing bigger valves and porting the heads makes the cars run even better. And in the case of BB even with pretty small cams. But ofd course it costs some too. I can't take the same performance out of a 2.08/1.74 head that I can from 2.14/1.81 head.

[Speedy#1]

I'd have to agree with 340king i would say larger port's and good modern valve desighn would give you more bottom and high range .

[Tim_K]

Everyone says sunken valves cost power, so it must be true, but I've never heard a good explanation of WHY this is. Extra cc's in the chamber, reducing compression? The valves are now blocking part of the port? Something else? What?

[ChristianCuda]

Since everybody elses 2 cents are here I might as well cloud the masses with my added 2 cents.

On big blocks all heads will warm up to template porting. But the bigger valves will depend on each application and also the 452 will perform better to porting that the 906 due to a constriction on the 906 casting that is not on the 452 or 346 castings. I have stated all this in other posts. The bigger valves are not always needed but one thing that is shown is that the 1.74 valve is way to small for a big block to breath. Imagine if you could open you mouth wide for intaking air and then had to exhale only through your nose. It takes longer to get all that air out well same goes for the heads. I always increase to 1.81 exhaust valve but keep the 2.08 intake. going any larger then needs more deshrouding on the head and cylinder to make any better power. And with a properly ported intake port the 2.08 flows very good for a motor under 600 horses which is most of our motors. Especially a street motor that is naturally aspirated. Now if you have a blower or turbo than you would benifit more with a larger valve. But then you may also have more than 600 horses too.

Anyway I thinks thats more than 2 cents worth.

Christian

------------------
68 'Cuda 383
Working on adding EFI

[340king]

Tim the reason for the drop in performance with sunken valves is the shrouding that takes place at low lifts. Valves are opened quite slowly on the bottom of the lift and spend quite a few degrees just getting to .050" lift. Imagine shrouding the valve for even .010". This would effectively decrease the duration of the cam quite significantly, as flow would not start until the effects of the shrouding are overcome.

You bring up a good point Christian. Why put larger intake valves in a head design that flows so poorly on the exhaust. The flow balance on the cast factory heads is well below the 75% range. The exhausts need more work to get to optimum performance without increasing the intake flow. I just don't like seeing a guy spend money on bigger valves that could better spent elsewhere thats all.

[DartGT66]

The low lift thing is only one point; it can be cured by reworking the chamber and that's what I always do in the heads I work with. Another thing that the short turn in both the intake and exhaust is too low in both intake and exhaust ports in mopar heads. When the valves are sunk, the port floor comes even lower, not a good thing. With bigger valves you gain more height in both intake and exhaust and can make a better working radius there.

[Speedy#1]

iS that the only way you can raise the valve hieght is buy using larger valves?I can understand larger valves on the exh but why spend the extra cash on the intake?I was wondering because i may bee doing this myself in the year or so.

[chrisfly]

I have to agree with the majority here. You are running a pretty good cam and porting the heads with bigger intake and exhaust valves will wake this machine up. Just be careful when porting, bigger isn't always better. If this is a dual purpose machine, I would do a mild to medium port job to keep the velicity of the mixture up. You ideally want 350 400 cfm for optimum power. If you port too big, you will lose your velocity and the thing will be a dog on the street. A good website to take a look at is www.hughesengines.com. They have complete stage1,2,3 heads with big valves at a reasonable price. I bought their stage 1 heads and am running a 540/550 lift camshaft. Hope this helps

[Glen440]

Thanks Guys!
I'm going to go with 340King and just port the 452's and keep the stock valves. I ported them a couple years ago as close to the mopar templates as posible. I'm going to clean them up and use them another season.
I'll get the 906's done in the summer and I'll get to see the performance gain! I'm sending the short block out instead. Its time for rings and bearings. I bought it off a guy who had it built 16 years ago. It was driven hard enough to break hemi springs!
Thanks for advice
Glen440 ~Mopar forever~

[ChristianCuda]

Glenn Since you mentioned springs i remembered. Make sure you put New or Known Good Valve springs on that 452 head cause without it all the work is for naught.

Christian

------------------
68 'Cuda 383
Working on adding EFI

[Christopher]

I'll throw my 2 cents worth on this,and I'm agreeing with what most of you guys have said.On my 440, I have 452's with the big valves and no porting or bowl blending,they are as factory produced except the chamber cc's are at 80.I also have a set of 906's that have the stock valve size in them and they too are at 80cc's.I wanted to see if the bigger valves really were worth the extra money as I have several sets of NOS small Mopar valves on the shelf.I swapped the 452's for the 906's and the car slowed down 3 tenths in the 1/4 mile.I swapped the 452's back on and the following weekend,the car went back to running 11.30's.

[ROADRUNNR]

has anybody read mopar muscle jan,feb &mar 99 issues about bb heads? they claim bigger valves in 346&452 castings with minimal porting is the way to go. they claim what really makes these heads breath is a 30 degree seat.

[ehostler]

What is the minimum over-bore to get the 2.14/1.81 valves to work in a 383, without interfacing the cylinder wall?

------------------
'96 Dodge Ram 1500 SLT CC 360 4X4
'68 Charger 383-4