[Puter]

Stupid question and maybe a wasted post.

I have an 86 shortblock. I have E7 heads on there now that are worn out. I bought a set of GT40s from an Explorer. I am planning on cutting valve reliefs with either a Lisky or Indy In Head Piston Cutter and going down ~.15". I would rather not tear the GT40 heads apart if I do not have to since I have not done that before.

So my question is this - can I use the E7 head as the guide for the cutter? In other words, does the intake valve touch the piston in the same place between the two heads?

 

[RacinNdrummin]

It should, Im pretty sure all the geometry is the same.

 

[Kato Engineering]

depth relationship as measured from the SEAT is different.

you will have to put it on,
cut one,
take the head off,
put other head on,
check the depthand RADIAL clearance.


you stated .15

that is way too much!!!!

 

[Puter]

you stated .15

that is way too much!!!!

Why?

As I understand, there is .3" of material. What is the minimum? .18"?

 

[Kato Engineering]

you ONLY need to remove the MINIMAL amount of material to gain or achieve the needed minimal .080 to .100" EXTRA AIR clearance when the valve is open at / near TDC.....A


when your primary test reveals that you have NO clearance, you must remember that the valve is allready OPEN a little bit ( unless you have a full flat top such as a 1986 HO piston).......you only need to cut out as much as needed to ADD to that amount that is allready there.

 

[Kato Engineering]

OFTENTIMES THE exact LOCATION OF CUTTER WHEN IN YOUR sample HEAD OR YOUR piloting HEAD WILL ACTUALLY INTERFERE WITH THE SEAT because the backside of cutter will hit the seat before the piston is at the correct place near 10 degrees before tdc...
so, on my own piloting head, I have cut the seats a BUNCH deeper than what would be needed to seal an otherwise good valve...naturally this makes the head JUNK...

when piston is LOWER IN THE BORE than wher the valve actually is when it hits, the cutter will make an incorrect cut.
it could even be in the wrong spot, and eyebrow ends up being too deep....less compression...

 

[Kato Engineering]

as piston raises in bore relativeto the head / deck,...
the valve is actually CENTERED further UP towards the intake port side of piston......


think about it...



the best illustration is with a cut away head that shows the open side of chamber and all valve gear working....

 

[Puter]

( unless you have a full flat top such as a 1986 HO piston)

*points up to my original post*

So, I place the piston at 10-degrees BTDC to cut.
I have to cut the seats of my worthless E7 head to use whatever cutter I use.

Sounds good.
I figure I will clay and measure how much I need to cut.

http://sbftech.com/index.php/topic,12817.0.html

 

[Kato Engineering]

actually the refrence to ..."10 degrees BTDCto cut"... is only a REFRENCE... because it depends on the CAM shape and where the cam is installed and timed...

the point of intersect of a just closing exhaust valve is about 8 to 10 degrees before tdc... and the intakles closest proxmity is somewhere between 8 to 10 degrees AFTER tdc...

you have to LOOK....


the reason to have to sometimes cut out material out of a sample head is because the THICKNESS of the tool cutter is more than the valve .....

once again...all of these factors vary GREATLY as the cam is changed from actual timing events as specified on cam card..as compared to WHERE EVER innaccuracy ther is from just "lining up the dots"....!!!!!!!

as caM is retarded or advanced..it changes WHEN and WHERE the valve hits the piston.

 

[Kato Engineering]

if you wanna really understand, then you need to have someone cut the head open so only one side of the chamber can be seen from the end...
then you can see both valves and their relationship to the piston as both open and close as pston goes up and down.

 

[Zeet's5.0]

Thanks for the tips Kato.
How many heads do you have cut up?
Any of the aftermarket heads using different valve spacing?

 

[Puter]

I don't have the means to cut up a head.
I just want to bolt on a set of GT40 heads onto an 86 stock shortblock that now has E7s.

I don't have a cam card, nor has anything been changed from stock on the shortblock.

Sounds like it will be a lot easier to just put other pistons in.
Thanks.