Offset Valve Guide ?????????

[Anonymous]

Hi Everyone,

I was thinking about running larger than a 1.94 intake valve. I think I've seen offset guides that were .055 offset. That would allow me to run a 2.05 intake with out crouding the short side radius any more than the 1.94 valve does.
: Question. Where do you buy offset guides? I did a search and can't find them.
: Are they oversize in diameter so I can cut out the valve guide boss inside the port? I'll keep part of it for streamlining anyway.

This is for a Carbed engine.

John

 

[80broncoman]

I myself don't belive there would be a advantage to running an intake valve larger than a 1.94 in the stock head. I don't think the factory intake port is large enough to see much more improvment. If you start grinding away at the port I think you will strike water long before you will need the 2.02 or larger valve.
You are talking about a stock 300 head, right?
Jim

 

[Anonymous]

I'm talking about a PORTED 300 head.
There is a lot more meat to these heads than you might think.

John

 

[80broncoman]

When I said stock I meant a stock casting. Ported or not I can't see the advantage to going that big. If the port can be made to have a square area as large as the vavle then it would work. Maybe I haven't looked at it close enough.
I am sure someone has flowed one of these heads, right?.... anybody?
Jim

 

[StrangeRanger]

Bigger valves give a benefit only if the flow bowls are opened up to the maximum diameter the valves permit, usually that's about .140 (2 x .070 wide valve seat) less than the valve diameter and if the ports are also opened up to have the same cross-sectional area. This increase in area reduces flow velcities at any given RPM. If you take Ricardo's rule of thumb that volo. efficiency is optimized at a flow velocity of 140 FPS and usable in the range of 40-240 then:

To gain full flow from the stock 1.78" intake valves, with the flow bowl diameter opened up to the maximum possible, you need a port area of 2.02 sq. in. This will produce optimum flow velocities at about 2900 RPM and be useful from 800 to about 5000.

Increase the valve diameter to 1.94" and the port area must increase to 2.45 sq.in. Flow velocity is optimized at about 3500 RPM and the range becomes 1000-6000 RPM.

Increase it to 2.02" and the port area has to go to 2.68 sq. in. and the optimum RPM increases to about 3850 and the range becomes about 1100-6600.

Unless you're building a race-only motor is there any real need for a 2.02" valve?

Also given the restriction in the exhaust port from the %$#@ water jacket, even if you get the stuff in there, how are you going to get it out?

 

[Anonymous]

Well, I was interested in seeing just how much flow could be obtained from a 300 head with no welding.
But, as you pointed out, there is little to be gained.
It's just that the 4.0 and 258 AMC's are running a 2.02 valve with very good effect with the High Port head.

They must not have read the book!

John

 

[broncr]

Bigger valves give a benefit only if the flow bowls are opened up to the maximum diameter the valves permit...
...To gain full flow from the stock 1.78" intake valves, with the flow bowl diameter opened up to the maximum possible, you need a port area of 2.02 sq. in.

So.. 1.78 - (.14 x 1.78 )
= 1.78 - .2492
= 1.53 is the optimum stock flow bowl diameter..?

a 2.02 port area woud be 1.42 per (square) side..?

PLEASE, correct me if I'm wrong?

As this was my first port job on a 300 head - I took it pretty easy. Knowing the optimum flow bowl diameter and port area will be a great benefit to opening it up properly, whether it's stock OR 1.94's .

Thanks for the info. For some reason, the "end parenthesis" comes out " 8) " oh - now I see why

Broncr

 

[Thad]

There is another point to consider, as the valve becomes bigger so does valve shrouding increase.
Some time back it was posted that the combustion chamber need to be setback with 1.92 or bigger valves, because as the valve gets bigger it gets closer to the chamber wall.
After porting a 300 head, opening was mostly on the top of the ports because of exhaust ports on eachside IMHO it would be almost impossible to open up enough to support a 2.02 valve, especially when opening up the exhaust port to balance.
Taking SR's Ricardo numbers: 2.02" valve needing 2.68 sq/in port area that some thing in the order of a 1.34" x 2.0" port.

On a SUPERFLOW bench my head flowed average 245 CFM w/ 1.92", wish I had the money for ExtrudeHone. One Desk Top Dyno says that's good enough for 398 HP.

 

[xctasy]

Gee dudes, look at Chrysler Australias 265. It had 1.96 intakes, and 2.7 square inch at the intake port. This is a port area 89% of the valve area, enough for a 300 hp engine reving to 6500 rpm from just 4.3 liters. This had a low volume runner, and could cope with the size becasue of its angled valves which had very little shrouding.

Cleveland 351 4V's had 3.3 sq in for a 2.19" valve, way too much, or a port area 88% of the valve area. This was with a high volume runner

So a 1.77 for a 2.2" port is about right. I agree with you, hog out that head about 100 thou on the sides and roof, and you'll get your 2.7" easily!

 

[Thad]

Hey John,
Up is the way to go, more materail and it lessens the angle of port center line to valve.
Pics of my head was posted on the old forum, can't send now offshore Brazil. Some one may have or remind me first of next month and I'll copy you.
What are you going to use for your intake manifold?

 

[StrangeRanger]

So.. 1.78 - (.14 x 1.78)
= 1.78 - .2492
= 1.53 is the optimum stock flow bowl diameter..?

a 2.02 port area woud be 1.42 per (square) side..?

PLEASE, correct me if I'm wrong?


Broncr

1.78 - (2 * 0.70) = 1.64 bowl dia.

This is an approx. number based on required valve seat width and may vary from head to head due to casting and machining variances. Measure twice, cut once.

The ports are rectangular, not square but you can work the numbers to get where you need to.

 

[broncr]

[quote="StrangeRanger PLEASE, correct me if I'm wrong?"

1.78 - (2 * 0.70) = 1.64 bowl dia." Ahah - Now I see...thanks

"The ports are rectangular, not square ..." I have my stock intake/exhaust on the spare engine - so I was just "guestimating"(square) - but I follow... adjust for rectagular. Thanks again.


Bob

 

[Anonymous]

Hey Thad,

I saved the pics of your head a long time ago. It's a monster compared to the stocker.
Now for the intake. I thought that a little Sodium Silicate, some fine Ovine Sand, 40 pounds of 356 aluminum, some propane, a little nitrogen degassing, combine using an old recipe and see what pops out.

It'll be a while, I'm recovering from having the crap sued out of me by the X, but it'll happen.

John

 

[Thad]

Sorry

Been there, done that------twice---------- and they got the T- shirts
enough to give a man a permanent case of dysentery.

Could you post the pics, give some of the newbies an idea of what is possible.

 

[Anonymous]

Sure, I'd love to.
But like I said, it'll be a while.

John

 

[addo]

These pictures, Tadeo?





Links repaired, November 2005

 

[broncr]

Sorry
Could you post the pics, give some of the newbies an idea of what is possible.

ADDO,

Thanks, from the only "newbie" on this thread :roll: .

Broncr

 

[Thad]

Thanks John

Hey Broncr we are all newbies here, just different degrees

 

[broncr]

OK. I'm just new to 300's.'got a couple billion revs behind me though. (really).

I saw one of John Forces' unassembled heads from his 300mph+ rig, up at Bandemier. It looked like you could almost slip a tennis ball through the ports.

Broncr

 

[StrangeRanger]

Yeah, but Big John isn't exactly concerned with low-RPM torque, drivability or how well it survives bumper-to-bumper traffic. More airflow = more HP but it also requires more revs. which ultimately will sacrifice the bottom end of the rev band