cost to have head ported

I was wondering about what it would cost to have a 250 6cylinder head ported so I could put 1.84 1.50 valves in it

 

Do you mean ported as in having the runners ported or are you simply wanting the valve seats enlarged to accept the larger valves? There is a difference.

 

since he wants larger valves im guessing he means inlarged seats.

 

The head would have to be ported to match those larger valves so I would think you would want to get prices for each part or all of it.
The prices that are charged vary a lot from one shop to another. It all depends on what they do and how they do it. Check the Yellow pages for shops in your area that do high performance work. Ask for references - and then check the references before you give them your head. See what valve they will install - stainless?, tuliped?, or just stock valves that are cut to fit. Ask what kind of seats they install and if they install new guides too.
If you are going to get your head done, get it done right.

 

...you can't get...air out..if you...can't get...air in..

......

 

The bigger valve sizes won't be of much help in the power department.
The intake tract is not able to take advantage of the valve sizes.
These are the sizes, a v8 uses.
The single carb, log manifold, and port config isn't up to the larger valve flow ability.
But, maybe you have some other mods that might make use of them.
A cam with improved timing would get far more gains using the same airflow you now have.
A motor's power comes from total airflow thru the motor.
Improving one point with restrictions in other places, still restricts the total flow.

 

a cam alone is still just improving one point






if you do take the head in for work you could also mill it down to bump up the compression. if you plan on using an aftermarket head gasket you should have it milled anyway since there a little thicker then stock ones

 

I agree with Bluegrass, the key word is "TOTAL". capabilities of a particular engine. Anytime you remove a head, be it iron or aluminum, it should be straight edged and resurfaced for a good seal and a minimal amount of compression ratio increase. The only way to make a real seat of the pants increase in compression is with smaller chambers or special pistons. You can also mill the block to zero deck heigth, with flat top pistons too.

A good example is when mavman was racing go-karts at age 8yrs old, you can take a new B&S 5HP engine and remove the head. Take some drywall sanding cloth and put it on a piece of thick window glass. Work the head back and forth a few times then turn it over and see how much the surface is out of square. After lot's of elbow work, it will be perfectly flat and square, with some good sealing and a tad bit of help in total combustion. Course that was a million years ago and new techniques and billet heads are now the deal. Sorry for the long post, but it may help a few guys in understanding more about performance mod's. Time for a nap now.

 

Cam: your missing the fact that the cam has a profile that can be improved to allow more airflow under the curve, up to the limits of the intake tract..
The total flow limits the power than can be developed.
The total airflow limits max rpm that the total intake and exhaust will allow.
The cam also limits airflow, that's why a gain can be realized over a factory cam..
Most of these motors are no more than 70% efficient in airflow vs the cylinder displacement filling at peak torque. The design was never a hi performance intent.
Improving even 10% thru the whole tract will gain power.
Just bigger valves won't do it, in this motor.
First place to improve is the log manfiold/carburation, then the cam, then porting with a rise in compression, then improved exhaust.
Cam selection is related to rpm. No use to select a cam that peaks at 5500 rpm if the total airflow won't support any increase in power much beyond 4500, as one example.

Dave, you take me back to those B.S. days when we ran super stock and limited modified.
I ran the limiteds as high as 9800 rpm down the long road course straights.
The cams were in the 290 to 305 dregree durations on alky fuel. (For those who think a cam change is still a big restriction) in a little motor.
Most people not familuar with these little motors would never believe how far we go with them.
My son and I now run big karts!. Open wheel sprinters, Ford powered at well over 500 hp still on alky.
Nice to hear from you again.