4V pocket porting

[billfisher]

i am building a forged turbo mark viii. i like the b heads

i am going to clean up the secondary, no egr.
i purchased 8 frpp stainless valves.(back cut, undercut stems.) i am going to spend my time doing a basic port of the primary. contour and enlarge it a tiny bit and use the new valves in the primaries and leave the stockers in the secondaries.

 

[billfisher]

i am only out to get some flow on the backside of the primary ports that is factory limited.



1. back cut the exhaust seats to match ports.
2. removed flash in the exhaust ports
3. raised the exhaust port roof a tiny bit.
4. altered the inner short side.
5. removed a lot of the divider and knife edged it
6. more or less gave each exhaust valve its own gas path.

7. removed the shroud over the primary port in the chamber and laid it back to match the other port.

8. altered the primary bowl to change the gas angle more perpindicular. mainly after the guide.

the primary runner is really badly designed for power.

9. removed the short side bowl 'dam' and reshaped it resembling a short side.

10. where the primary port goes from square to round i lenthened that trasition from a 'step' to a ramp on the floor.

11. on the roof i eliminated the transition and raised the roof to the bowl.

12. removed the guide protuding into the secondary port.

13. blended ther runner to bowl

14. sanded it.

15. blended bowl to seat.

16. left the rest of it the hell alone.

all of that without removing a lot of meterial. gentle little alterations.

 

[billfisher]

PICTURES.

 

[Stan Weiss]

Without before and after flow testing there is no way to tell if the changes helped or hurt.

 

[billfisher]

yes there is. have you looked at the ports. pocket work will hardly hurt a disastrous factory design.

the factory design does everything possible to eliminate half of the valve. shrouded nearly against the valve.
a short side the has a SHELF. not a radius, but a straight edged shelf.
a bowl shaped more like a spoon than a radius.
a transition from square to round that is a full blown STEP.


even YOU can hardly argue it cant be mildly altered for better performance.

crap if i just short sided it and deshrouded it its a massive improvement. add racing valves and it is improved.

but the dyno will tell N/A, eh? it isnt like it has to be much better to be an improvement over 276ish rwtq bolt-on tuned B heads are known for.



just buy yourself a set of b heads and remove the valves. after that make a statement like 'you just dont know if its better or worse" please. these arent any where near my first set.

 

[billfisher]

cragg clacks flow bench is sold so no numbers. i might try nashville and see what i can find.

B head stock numbers are typically 233intake at 28" .500 and 160 exhaust at .500".

 

[Stan Weiss]

cragg clacks flow bench is sold so no numbers. i might try nashville and see what i can find.

B head stock numbers are typically 233intake at 28" .500 and 160 exhaust at .500".

Without before and after numbers you do not know what has happened at different lifts. Did it improve at high lift and hurt low lift? Improve low lift and hurt high lift? Is most of the improvement at a valve lift past what your cams will lift the valve. What happened to the velocity in the bowl and port after the porting?

 

[billfisher]

well you are in luck. i funally found a flow bench in nashville that can flow 4 valve heads. ill get them done in the next week or so. and provide you with the basic info.

 

[billfisher]

before number can be found anywhere for stock B heads. at all lifts. so really i will know what has changed. of course the valves bias low lift because of their design, but stock cams only lift .425 anyway so thats my only parameter.

 

[Gearbanger 101]

well you are in luck. i funally found a flow bench in nashville that can flow 4 valve heads. ill get them done in the next week or so. and provide you with the basic info.

So how are you going to add all that material back in there to get the before porting flow numbers out of it?

 

[billfisher]

come on now dude. im going to assume these heads are the same as 100,000 other "B" heads out there.

 

[billfisher]

i guess i am trusting that this bench is close to others. i should have thought of that. well we'll see.


Anyone got flow numbers for B and C cylinder heads at 28"? - Corral Forums


that is a link to the flow numbers i am trusting to be accurate. they look like the AFR, AFM, and other porters numbers.


the company only charges 67.oo per hour for testing. i cant recall the name. but its on lebanon road in nashville. i have called them.

 

[Stan Weiss]

To compare your numbers to other peoples number they have to have been flowed at the same depression, normally 28 inches of water. What bore size were they flowed with, for modular normally 3.57 inches. Then were the exhaust flowed with or without a pipe. Either method is fine but the with a pipe numbers normally are higher than without a pipe for the same head.

 

[hotmustang331]

cool....good luck on the #s Bill.

Flow #s stock will only change a small amount....even if his #s are on the high side of stock #s, it will be safe to say that his work didnt hurt. Im expecting a 15-20CFM increase....B heads have alot of potential.

 

[billfisher]

i expect to pick up 40 on the intake and who knows on the exhaust.

you would have to see how badly the exhaust seats mismatch the bowls to believe it. i would bet .030. the inner short side on the exhaust is a classic factory shape. the exhaust port piches noticably there. i was told removing the exhaust guides is worth 7cfm usually, but i didnt do it. i expect to get 100k miles and i dont want to shorten it for a few cfm.


the frpp valves are rated to flow an extra 11 cfm over stock all by themselves. each.

 

[billfisher]

this is head flow data from Erich on corrall. he did similar mods to his b heads. i did a little more, and a little differently and he used stock valves with no backcuts or trimmed stems.

The eb heads in the table are my mark VIII heads before and after bowl blending and straightening the short side radius. $150 worth of mild porting.

the only diferences are : he straightened the short turn, i gave it some radius(there isnt much there), i blended the transition from square to round, but we did the same bowl work, and i have racing valves, and finally he didnt desroud the intake valves, and i did.

i raised the roof on the exhaust and i gave individual gas paths.

here is a cnc from MMR of a perfect stage III exhaust port.

this is an expert porters hand work. he has access to a flow bench.

after consulting i agreed that leaving the floor alone is wise without a flowbench to actively work with. velocities on the floors are already low.

 

[billfisher]

note: on his exhaust port that he cut material from the sides of the port near the exit and i didnt. again, without a flow bench to work, with less is better.