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Math Check Please

352Ford

Plastic
Joined
Nov 29, 2006
Location
Shoreline, WA
It’s been too long since I have done this stuff and I want to make sure I am not being retarded. I am putting an intake manifold on a ford 302. The intake I am putting on is sitting too high (intake ports aren't matching up). It is too high about 0.135", so I should machine 0.065 off each face of the intake manifold or is it 0.0325"?

The block has been decked and the heads milled, but nothing has been angle milled so everything should still be 90 deg.

Thanks
 
I used to work in an engine machine shop and I believe there is a formula or chart to tell them how much to take off the port sides and bottom of the manifold to make it fit. You will have to check with a speed shop or engine machine shop to get the specs if you are going to do it yourself. I never did that job myself so I can't tell you much more.

edit: the 289/302 is my favorite engine because it is as close to an OHV flathead Ford as you can get with out having an Ardun setup on a flathead.
 
The port faces are square (thanks), what formula are you using? I don’t think I stated the misalignment properly.

Using the intake mounting face as the reference plane, the port of the intake is 0.135” higher than the runner port on the cyl head ( like this http://www.mustangcentral.net/tech/intakeindex/scribe01.jpg ). So the intake manifold doesn’t need to drop 0.135” in the vertical direction of the carb mounting plane, it needs to drop down about 0.095”.

Am I thoroughly confusing everyone yet, or just myself?
 
Sine or Cosine (.70711) of 45 degrees times vertical drop, divided by 2.

.095 X .70711 = .0672 divided by 2 = .034" off each face (head or manifold)

See - you had nearly the right answer all the time if you used your .0325" :D

John
 
All right I had to end up taking about 0.059 off each side to correct this. Which is way different than calculated. I would really like to know the proper formula for this and why mine doesn’t work. From this examble the last division by 2 seems wrong, but that makes zero sense.

Gasket misaliment/4

Or

((Sin45 X gasket misaliment) X Sin45)/2


Anyone?
 
According to the illustration the correct formula would be tan45 * (.135/2) = 0.0675 off each face.
Still doesn't match what you had to take off though.. strange stuff..
 
Panza-
You are using the same formula I am using except I divid by 2 at the end. I am starting to think that is wrong, I did it because I am taking material off two faces. I proibly could have taken a bit more off (maybe .0085") and been fine. That would indicate that your formula is correct.

can we get confirmation on that?
 
See? you guys listen to old farts like me, and no one bothers to challenge the statements made :D

In my head, I assumed that since you were trying to get something to fit down in a "vee" block (if you will), you would take off half as much calculated (since your were doing both sides) to get it to drop the desired amount.

This is an error. The only way one side would line up, then, is if you shoved it sideways - not correct.

My dumb a$$ statement. :cool:

Proven wrong by practice.

John
 
Seems a bit strange to me...

When you say the manifold is "too high about 0.135"" how are you measuring that? Is that distance down the intake side of the head? Or is that distance between the bottom of the intake manifold and the block?

According to the Rebuild Ford V8 book (you can read inside) the amount shaved from the intake port mating face of the manifold is the same as the total amount shaved from the heads and deck. That is... if you shave, say 0.020" from each head and 0.010" from each deck (top of cylinders) then that will move the ports "down" by 0.030". In this case, according to the book, you would have to mill 0.030" off of each side of the intake manifold OR 0.060" off one side of the intake manifold.

So... in your case IF you are measuring "down" the face as per the link you gave then you should be milling 0.135" off EACH face of the intake manifold OR 0.270" off of one face.

If you draw the picture you can immediately see that the book is correct... for any distance "d" down the face of the manifold that the ports are mismatched you will have to mill "d" off of the face of the manifold.

Incidentally... according to the book and my own experience 0.135" seems like an awful lot for mismatched ports.

-DU-...etc...
 
Void-
That only works if the parts fit together before the machining; these are 3 sets of parts (block, heads, intake) from 3 different sources that have never been put together. I measured missaliment in the plane of the intake mounting face, like shown in the internet link above.
 
Hmmm...

OK well try this:

Rotate your engine either on the stand, in your mind, or on a piece of paper 45*.

The angle between the two planes of the intake manifold are 90* (yes?) One of those planes is now vertical and the other is horizontal.

In order to lower the vertical port by 0.135" you will have to shave how much off of the horizontal plane? Note this will not change the position of the ports in the horizontal plane.

Do you see what I mean now?

IF the two planes of the intake manifold are MORE or LESS than 90* then your 0.059" might be correct.

It shouldn't make any difference where the parts came from IF the angles are 90* (as you said in your first post).

-DU-...etc...
 
If you were measuring the .135" "height" difference on the intake gasket, which is at 45* to the horizontal plane, then yes, the above calculations would not work. The previous calculations were dependant on a direct vertical drop. The position the (angled) intake holes will move relative to the vertical plane is a completely different story....
 
MitsTech,

I am responding to 352Fords original post(s). He (she?) says he measured the distance as per the picture; "down" the face of the intake manifold. He asked how much to shave off EACH face. He did not say there was interference at the bottom... there might be, but he didn't mention it. If there was he might have to shave even more off of that dimension (about 0.19").

I am making two basic assumptions here:

1. That he accurately measured the mismatch of the manifold to head ports as per these instructions.

2. The angle between the two intake manifold to cylinder head interfaces is 90* as he said it is.

Where I disagree with the book I mentioned earlier... is that IF both manifold-to-cylinder head ports are off by the same amount, then both faces on the manifold have to be shaved and not just twice as much off one face.

Would it help if I drew a picture?

-DU-...etc...
 
johnoder: I made the same mistake as you the first time but then I looked at his illustration and it occured to me that "too high" wasn't measured vertically
 








 
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