ck_79ta_build

Can anyone tell me the correct complete gasket set I will need for my olds 403? It has KB pistons with an 0.024 over bore
thanks

joe_padavano

FelPro 2601104. The only thing different from other SBO gasket sets are the head gaskets due to the larger bore. 403 top, 350 bottom.

ck_79ta_build

Does is matter that the middle bolt hole is not on there for the 403(top one)? I noticed the one I took off has three holes.

joe_padavano

Those aren't bolt holes. Those are for the dowel pins that locate the heads. The 403 block doesn't have a dowel pin at that middle location.

ck_79ta_build

my bad, trying to learn too much at once lol. thanks for the info

CANADIANOLDS

Don’t use the Felpro head gaskets. Use Cometics with .018” or about that thickness.

ck_79ta_build

Does cometics have a complete gasket set? and whats wrong with the felpro?

CANADIANOLDS

they have all the gaskets you need. The reason for using the thinner Cometic head gaskets is to keep piston to head quench tight. The thick felpros kill that.

if that engine hasn’t had the deck cut, you’ll be about.040” with the cometics and over .060” with Felpros

olds 307 and 403

Measure how far the pistons are below deck and decide from there. The Felpro are .042" compressed, Mr Gasket MLS .040" and Cometic are available as thin as .027". Cometic and Mr.Gasket offers full Olds Gasket sets as well as Mahle, just not with the unique 403 head gaskets.

BillK

It looks like the KB pistons are about .010 taller than most of the other aftermarket replacements. If I did the math right they should only be down in the cylinder about .005" so the Fel Pro gaskets should be fine. Just want to mention that the Fel Pro 260-1104 gasket set does not include a valley pan or any type of intake gaskets.

brownbomber77

Factory are .018", Cometic's are expensive and still .027". There was a guy who used to have .011" thick that I bought but no longer offers (Smitty?). Another option is just cutting the cylinder head .024" to make up the difference in gasket thickness from factory to the inexpensive Fel Pro.

BillK

That really does not affect the "squish" or "quench" (piston to cylinder head) dimension which is why guys want to use the thin gaskets.

To be honest with you there have probably been thousands of Olds engines rebuilt using the Fel Pro or other composition gaskets and I would bet that in 80% of applications it really does not make any difference. If you are building a high compression engine and looking for every bit of horsepower you can get then by all means worry about it. Otherwise the Fel Pro gaskets will work just fine and to be honest with you unless the head and block surfaces are freshly machined I think you are taking a chance on the metal shims.

joe_padavano

^^^This. Not everyone needs a 12:1 drag motor.

CANADIANOLDS

Here’s the truth . The lower the compression, the more critical it is to have minimal quench. The bigger the bore, the more critical is it to have minimal quench. So both of those are present with the typical 403.

the higher the compression, the less the need for quench..infact, a tight quench on a high compression engine can have negative consequences.

on a high compression engine the molecules in the chamber are very active , that’s why there isn’t the need for a tight quench. On a low compression engine, there is very little of that, so you need the tight quench to help create activity or get the molecules moving.

the real benefit is the activity from the tight quench, not really the additional compression..but it doesn’t hurt.

CANADIANOLDS

Factory .016 steel shims can be used on a 403. I’ve done it many times. Its easy.

this should have the experts here pulling their hair out..even used ones.

now tell me how it’s all wrong?

ck_79ta_build

Thanks for all the info. Definitely not looking for a drag car, the only major thing I'm doing performance wise would be the KB pistons.

CANADIANOLDS

Just because you’ve seen the 403’s at .027” from cometic, doesn’t mean that’s the thinnest they can do. Believe me, they can be less then .027”

and..the felpros are not .042” compressed. I’ve told you that before and why they’re not.

olds 307 and 403

The 403 or all Felpro Blue head gaskets? What do they measure compressed? I was just going by what my caliper said on a used set of 350 gaskets.

cutlassefi

Sorry but you didn’t. Half the stroke is 1.6925, plus rod @ 6.00, plus cd of piston, 1.615, and you get 9.3075, or at least .020-.025 below a normal SBO deck height.
And to measure the compressed thickness of a Fel pro, gasket, their techs will tell you to take a dial caliper and measure them new just behind the fire ring. Then deduct .005 or so from that.

olds 307 and 403

Mark, what do the Felpro measure? I have a brand new set of Felpro 307 head gaskets I can measure.

BillK

I did the math right but I was going by my AERA software for the deck hgt which they say is 9.312

cutlassefi

Gotcha but that measurement isn’t even close to reality.