How much to cut on intake manifold

LevonH said:

A little history on this issue.

454 LS-5 0 decked to .013 with flat top piston 290 heads which cc at 100.9 CC

Block was decked and I'm sure the heads were as well. I cannot be sure of the amounts but I am getting oil in the chambers on deceleration. I have an UNCUT Edelbrock Performer RPM on the engine. I suspect I need to cut the intake and need an educated guess as to how much. From what I can figure out the block appears to be cut between .025/.030 to get the deck height and have no idea on the heads.

Any one care to offer some advice????

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Assuming the intake is as it should be (big assumption) it would be the same amount as was cut from the head gasket surface in total.

But,,,, you never want to take this for granted as stuff varies a lot more then manufacturers like to admit too.

Easiest way to tell is to bolt the intake to one head with one gasket & see what gap you have on the other side.
Or in extreme cases bolt it on with no gasket

The gaskets are .060 so,,
For an easy one, if you bolt it on with one gasket & it comes close to no gap on the other side you would take .030 off each side
If it were say .030" you would take .015" off.

Be sure to correct the angles while you are whacking on the thing too as they may be off.
You can tell if the bottom is a different width than the top by more than about .010" max.

Don't forget to check the china wall (ends of block) to be sure the intake is not going to sit on the block before sitting on the heads.
This will not work real good

If the heads are cut more than about .020" the intake side of the head should always be cut the same amount on a Rat & 1.2 times as much on a small block.
I use 1 to 1 without issue but 1.2 is the correct number.
Just for info, the number for the bottom of the intake (top of block is 1.7 for SB & 1.9 for a rat)
This means if you take .020 off the sides you want almost .040 off the bottom.

All that said, I never want to cut the intake to fit the engine unless you have no choice like the engine is assembled & you don't wish to take it apart
The reason is if you correct at the intake you are now married to those parts.
You cannot change intakes,,, and,,,,
if you sell the intake to someone they are not going to be real happy with you either

LevonH said:

Hi Mike. Thanks for the input. I know there is a way to determine if the head decks were cut (measure the triangle shaped are on the block side of the head) but is there any way to determine if the intake faces were ever cut and if so how much?

Perplexing problem when machine shops only cut the block surface.

Also on your point about the intake being correct--- How would you know if it is right or not?

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Couple of ways,
First is the way I described above by bolting the intake to one head & checking the other side.
If it is wider at the top of the gap than the bottom you split the difference when you machine it.
If it were say .030 at the bottom & .040 at the top,,,,
When machined you would take .005 more off the top edge on each side.
Actually it is not a bad idea to leave the bottom edge so it crushes the gasket better buy a couple of thou so in the above case you could cut .003 more off the top instead of .005 more but this is not necessary & I just match the angles

Second is to either buy or make a gauge
To make one all you need is a couple of pieces of sheet metal about 10" long x 1" wide x .062" or so.
Bolt them together on one end so you can spread them like a divider
Make the bolt tight enough that they will stay where you adjust them.
Lay them on each intake surface of the heads like a big Vee with the bolt towards the valley.
Now set them on the intake itself & see if the angles are the same.
If not take your new tool with the intake to your friendly machine shop & he should be able to match the angles

Now,,, all that said,,,
If the angles are within about .005 of each other you are fine.
The gasket will take care of this.
Most factory heads are no where near correct especially on small blocks.
Some aftermarket heads (and intakes) are even worse

I hate to resurrect an older thread but I am really having a hard time with oil consumption.
I bought a std bore 454 and then went through it completely. After the bore/hone you could see one sleeve in a bore. Otherwise it was really hard to notice..undetectable along the top. I dont want to assume anything as I am beyond my expertise here. But after reading this thread I took a few measurements with ONE gasket ( .060 ) installed. The top of the intake is .037 gap. The bottom is .016. Was the block and heads milled a little? I have 350 miles on my rebuild and have not been able to enjoy it as I pull in perhaps 2 qts every 50-100 miles. Not sure what my next move is with the angles I have. Any suggestions?

Went out and took the gasket OFF and then took another measurement. The back of the intake is .008 from the head and the front is just under .040. I am way lost now.

Jeff,make a new post in this Engine forum and title it

(MIKE WOLFPLACE/BILLK/TOM MOBLEY/HELP EXCESSIVE OIL USE

They are our resident engine experts that will definately chime in to help you out.

But we could use more info,was a block trq plate used when block was honed,what type rings were used(low tension/moly/plasma moly),were leakdown & compression tests performed & what were results,what was done to heads & what are the casting ids,were there new guides/valves along with type valve seals,was mixture too rich on startup causing possible fuel wash of cyls on startup which the HASTINGS RING MFG states as a real viable issue leading to poor ring seal that some engine builders dont aggree with . I tend to believe it because i had seen a few startups of fresh motors over the yrs with over rich mixtures due to stuck chokes and or carb issues ets and the rings never seated well in thoses motors and they required re-ring to get then squared away.

Also,what testing have you done with respect to the intake its self?

From the pics you posted it looks like 3 of 4 intake ports were leaking on the bottom side due to the black erars seen in the lower parts of gaskets,but its a little hard to tell for sure. but if thats the case it could be your issue.

Man you state you go through 1-2 qts in 100 miles,yikes,it must be a bug fogger.

The Hastings ring site also stated they found a 350 olds with a mech fuel pump that was suking oil out of the crankcase and mixing it with the fuel so keep that in mind too,They did 2 re-rings but it still burned a lot of oil then they replaced the f/pump and no more oil burning.

scott