At what performance level (HP) are oversize valves a must on a 225, because otherwise you are leaving a lot on the table? Thanks

FYI, I put a ported head upgraded with stainless 1.70" and 1.44" valves on my '67 Valiant's 225 along with a 390 CFM Holley with an Offy intake and 2 1/4" exhaust off the stock manifold. I dropped over 2 seconds off my 1/4 mile ET. The engine still has the stock cam and short block. The head was milled to achieve 8.5:1 compression ratio. My best ET with the car is 16.86 at 79 MPH. The car has late disc brakes, 3.21 geared 8 1/4 rear axle and 3-speed manual trans.

For comparison my '66 Dart with an unported head, 264° Comp Cam, 390 Holley on a Clifford intake and Clifford shorty headers with 2 1/4" exhaust turned a best of 17.049 seconds in the 1/4 mile. That engine needed more compression, a better advance curve in the distributor and more head work with larger valves. Also, that car had 4.10 gears so it should have been quicker than the Valiant still. The lesson is that good head work and a decent compression ratio are vitally important to performance.

This past weekend I drove the Valiant over 600 miles and made about 10 1/4 mile passes at the strip and averaged 20.5 MPG. If I drove slower and could throw out the drag strip passes the mileage would be even better.

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Joshua

Ditto after this a nice set of headers maybe? See you like the 390 Holley aswell - love the carb once it is dialed in it stays that way.

I saw that Edelbrock made/makes jet plates that take weber jets etc - for fine tuning 4150 Holeys, but I can't find any part numbers..

Getting back to topic - yes a lot of performance is left on the table.

A 1.7/1.44 valve set, and with these valves porting will need to be done, plus a mild bump to say 9.3 is worth ~ 43bhp at the same rpm, but will make peak power ~500 rpm higher up in the rev band torque the same effect at original peak ~29lbft more, peak 500rpm higher

This keeps stock bbd, stock ex manifold

These results are from my sim software, but so far it has been quite accurate


Remember the stock 225 head is still the same design as far as inlet tract, and valve sizes are concerned as the 170

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Fanie Gerber
It's never junk, it's just a part you're not currently using

http://www.valiant50.co.za
Just say I own a few Mopars

Interesting question. If I can rig it, I'll scoot up to Woodburn in the next couple of weeks and make a pass with my stock valve head.

I have oversize valves in my present build, but need to pull the head regardless for work. My current head's porting is a tad more extensive than the street port on the uncut earlier head, but that should be overcome by the shrouding if the oversize/bore argument is to hold.

I have recent numbers from Woodburn and Medford that are pretty solid, so it may tell a tale.

With the bore size of the Slants, shrouding of the valves by the cylinder walls is a big concern. With this in mind, my build is only .30 over.

I feel an experiment coming on!

CJ

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As noted, the head on any SL6 was designed for 170 cubic inches so any work you can do to improve air flow nets good gains when combined with a 225.

The best thing about over-size valves is they allow you to raise the seat / valve head so it is not "sunk" & shrouded by the chamber's roof. Tell your machinist - grinder to keep the valves as high as possible in the chamber. Doing this also helps reduce chamber volume, which gets you more compression.
DD

A simple, elegant idea!!!

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After futher thought, wouldn't this make the valve stem "shorter" as the rocker arms see them?
Are we talking about tenths or thousandths? If less than a tenth could this be figured into a head mill to make up the difference? That would eliminate the need to re-grind a new cam base circle. Or new pushrods.

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You can get .030 to .060 of rise, so it is well with-in the adjustment screw's range and helps off-set some of the length change from head milling.
Most important, low air lift flow is a lot better with "cracked-open" valves (think "overlap event") when the valve seat is near flush with the chamber's roof, then when the valve seats are sunk into the port's pocket.
DD

i got a question about oversized valves

WHERE do i get them

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1973 plymouth duster 225 slant six .30 over, erson 270 cam, 9.5 to 1 compression, big valves, headers, and a holley 4 bbl
http://cardomain.com/ride/3135091

hey that thing got a hemi? naw its just a slant six

http://cgi.ebay.com/ebaymotors/225-Slan ... enameZWDVW

Ya, Ya SSD. Some day I will learn to resize and name links as good as you

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"where do I get them?"

In my case I had literally dozens of good Chev v8 1.72 intake 1.60 exhaust valves and springs available ......some brand new.

I asked the machine shop (Chevvy guys) to make my slant head a Chev.

With a big lift cam and lots of decking I had to get some Smith Bros pushrods to get things right.

Yep SBC valves springs retainers all fit with a little machining.

It helps balance out the Ford trans and rear end........

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Yeah....Im the one who destroyed this rare, vintage automobile.....

And then you have the 300 Ford valve crowd. There's a lot more machine work though.

CJ

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Part of Tyrde-Browne Racing

I have SI 170-144 valves with SBC springs thanks to my machinest and the car has yet to reject them

TF

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Even in moderation i am excessive!

http://tinyurl.com is your friend
copy http://cgi.ebay.com/ebaymotors/225-Slan ... enameZWDVW + paste = tinyurl! http://tinyurl.com/5huwn3

http://tinyurl.com/Oversized-valves

Like that?

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