i got to beating the valves out of an old slant head i got saturday and i got to thinking so i went and got my caliper and checked the valve size compared to the high performance 1.77 and 1.44 oversized valves and there ain't much difference between them. on the intake its an extra .15 and .08 on the exhaust

i asked one local machinist and he said a good port & polish job would be better so i want a second opinion from yall, then i'm getting the third opinion from the best machinist in north carolina

so is it really worth it?

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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

It depends

I am interested in the answer too.

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Chris'
Autobody
Restoration
Service

Anything you can do to make a SL6 head flow more air is "worth it".
One of the best "bang for the buck" improvements for a SL6... porting work AND oversize valves.
DD

It can be "worth" in upwards of 2 second of the ET ON the drag strip assuming everything else remains unchanged.

Yes do it.


Greg

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http://www.youtube.com/hyperpack

Every little thing helps.. a lot of little things turn out to be a big thing.

If you need to buy new valves.. why not bigger ones?

Same with the camshaft.. etc...

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2 seconds.... please explain Greg. Share your secrets.

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Chris'
Autobody
Restoration
Service

I can add that bigger valves and a ported head along with a 4bbl and 2 1/4" exhaust made my otherwise stock '67 Valiant over 2 seconds quicker in the 1/4 mile. Same stock '67 short block, cam, etc. 3.21 gears and a column shifted 3-speed. Previous best was 19.23, current best is 16.86. The car is much more fun to drive and still gets good mileage.

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Joshua

Good then. Because I spent the money and did the work already. I can't wait to see my results.

Thanks for the reply.

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Chris'
Autobody
Restoration
Service

I didn't expect the results I got. I was expecting to go from mid 19s to mid 18s. When I got a 17.2 time slip I was thrilled. Who knew 8.5:1 and a such a small stock cam would respond so well? I should add that I recurved an electronic distributor and paired it with an HEI module and coil. Muffler is a Dynomax Super Turbo which sounds pretty good, but is not loud at all. It just happens to sound like it has an engine now.

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Joshua

2 seconds that sounds to good to be true i might have to go for that

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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

HI Slanting,

Yes, it is worth it. The .15 and .08 are not, strictly speaking the the numbers to look at. Calculate the area in that .015 band you are adding to a conventional valve. Much as the surface area of a sphere increase as the cube of the radius, the addition of the "sidwalk" on your valve increases the area exponentially, not linearly. You will be amazed at what proportion of the original valve surface area you are adding.

And yes, you can use larger valves. Look at the unshroud pics I shared a few weeks ago...you run into a practical limit in the between cylinder strips and the cut you can make in the original valve seat. the 1.77 is a great all round compromise, and since everything in engines is a compromise with something else, at least that valve compromise is one that will only help.

Mill of .100 from the head while you are in there, and use one of the new cams from the group buy. But be extremely wary of buying cams because you head a cool lope onetime. If you engine won't settle out til 5000 rpm and you live in the world below 4,000, you will curse the day you got the racing cam. Lou (Dart 270) showed me the value of a 270 cam for instance for daily running. I can also tell you of a machine shop in Henderson that is "supposed" to be good, but from which I have never seen a "built' engine last. They commonly don't mike cam bearing fit and I have seen several of these gems where the bearing welded to the cam and rotated in the block. Just a little HP loss.

rock
'64d100

you lost me

but more compression would be nice what would i be running with .100 off the head

and i ordered the erson 270 cam from the machinest on monday

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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

Well The whole Story is here:

http://www.slantsix.org/forum/viewtopic.php?t=13007

But the Short Answer is I went from a Stock Head (except for Milling) To a 1.70 / 1.44 Valve head with Professional Port and Polish work and .100" off of it and went from 17.2 to 15.2 Without any other changes in Exhaust,cam, gearing, Intake, timing etc. I recommend Going bigger with the valves however. more like 1.82 / 1.5 As long as you dont have to start notchin' the bore to get em to fit. Also I have a 5 angle on the Intakes and 3 angle on exhaust. 5 angle makes a bit more flow supposedly. If you are thinking about sending your head out, send it to Mike Jeffires - Long time slant racer and Head flow guru.. Many people have a jeffry Worked head with good results.

Greg

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http://www.youtube.com/hyperpack

What he's saying is the surface area of the valve increases significantly with a small change in diameter:

A=∏ R² Therefore, for a stock valve with a diameter of 1.62" (by your measurements), surface area is calculated as follows;

0.81x0.81x3.1415=2.061 in²

An oversize valve @ 1.77";

0.885x0.885x3.1415=2.460 in²

That's a gain of .399 in² for an increase in diameter of .15"

That's about a 20% increase.

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1970 four-door Dart, 225/A-904/2.45 gears. 0-60 in twenty three minutes!

Newslanter,

Thanks! That is exactly what I meant! I didn't put the numbers in o as to let him do the calculation and have it hit him, but your replyt is probably as effective with less fog from me. The 20 % gain is huge in my opinion because when combined with porting and polishing and a decent induction system...I think THAT head work is easily the most bang for the buck once you get past the initial getting to run good stuff of ignition an so on. On the other hand the even larger valves take machining work that begins to cost so much more for a tiny flow gain that personally I havn't found the gain worth the pain. You probably looked at my pics of unshrouding the 1.77 valves...now imagine the cut for the even large ones and the gasket problem with them. Oncve you move to no gasket between cylinders....ummm kinda chancy. I haven'ty searched here but I know some guys posted flow bench data and I recall the flow increasing more than 20 % for the 20% increase in surface area....a truly worthwhile expenditure (in my opinion)

rock
'64d100