Resizing Welded Coolant-Passage Openings

[Pierre]

I just had the coolant-passage openings TIG-welded shut on two BCP heads, a non-turbo '160' and a turbo '398'.

The plan, if advisable, is to reopen some of the passages to the same size as the passages on a SCP head and reopen the others smaller.

The goal is to leave as much aluminum as possible to firm-up the cylinder-heads a bit and for the headgaskets to rest-on.

The used B23FT headgasket presently laying on my lap only has two openings as large as the coolant-passage openings in the cylinder-head and block.

The rest of the openings go like this:

- six 3/8'' (approx.) ones located on the exhaust-side and the back;

- two 3/8'' ones at the back;

- four 3/16'' (almost) ones on the intake-side.

So, can some welded coolant-passages in the head be reopened even smaller than standard SCP ones to somewhat match the 3/16'' and 3/8'' openings in the headgasket?

Thanks in advance for your input.

[Alex Buchka]

So.. Why did you do this? If you use ARP studs an SCP head won't flex enough to blow a head gasket.

That is, unless you are running methanol, 14:1 compression and 40psi of boost. But that's pretty unlikely

[Pierre]

Sorry, the welded heads were BCP, not SCP... My mistake.

Originally Posted by Alex Buchka

So.. Why did you do this? If you use ARP studs an SCP head won't flex enough to blow a head gasket.

That is, unless you are running methanol, 14:1 compression and 40psi of boost. But that's pretty unlikely

[Captain Bondo]

Yeah, match the headgasket openings.

You probably should have had a 405 done if you were going to the work of fixing BCP's...

[Pierre]

Originally Posted by Captain Bondo

Yeah, match the headgasket openings.

You probably should have had a 405 done if you were going to the work of fixing BCP's...

Wouldn't using a 405, without larger exhaust-valves, accentuate the potential imbalance between intake/exhaust flow on a turbo-engine?

I only know the theory of such imbalance from reading on here, though.

That is why I chose the '398'.

I had the '160' done as well because it received blended-bowls, polished combustion-chambers, a .060'' shave, etc..., a few years ago.

That was for a non-turbo project that ended-up never happening.

I am now thinking of trying the '160', strenghtened a bit by the welding, on a B21FT that I have and on which it would provide 9:1 CR.

Regarding a '405' head, I was planning on having one done this coming Thursday anyway, just in case.

[Karl Buchka]

Afaik, the issue isn't really the openings, it's the size of the jackets in general. A cut-away of a BCP and an SCP head reveals that.

[Pierre]

I think it should add, at least, a little more support for the headgasket between coolant-passage and cylinder.

That just might allow using the BCP '398' head from a B21FT on my bigger-bore B23FT.

My power goals are an eventual 250HP, at most.

[Wagner]

Are you going to replicate the Volvo Group A cooling system? If so, here's a link to a site where you have some pictures of the parts and a good picture of the cylinder head with modified coolant passages.

http://www.volvogrupp-a.se/bilen.asp.htm

[Pierre]

Originally Posted by Wagner

Are you going to replicate the Volvo Group A cooling system? If so, here's a link to a site where you have some pictures of the parts and a good picture of the cylinder head with modified coolant passages.

http://www.volvogrupp-a.se/bilen.asp.htm

I wasn't aware of that possibility but I will have a look at that for sure.

Thanks!

[Pierre]

Originally Posted by Wagner

Are you going to replicate the Volvo Group A cooling system? If so, here's a link to a site where you have some pictures of the parts and a good picture of the cylinder head with modified coolant passages.

http://www.volvogrupp-a.se/bilen.asp.htm

I wish I could read Swedish better.

Looking at the pictured upside-down cylinder-head, the latter shows the nine standard SCP passages plus a few extra smaller ones.

Maybe my modest power goals (an eventual 250HP, maximum) wouldn't benefit from such a modification.

[EricF]

Originally Posted by Karl Buchka

Afaik, the issue isn't really the openings, it's the size of the jackets in general. A cut-away of a BCP and an SCP head reveals that.

I think there's at least one very thin section between the chamber and the water jacket on BCP heads, and I was also under the impression that the imprint of the head at the deck wasn't so important as the thickness between the chamber and the coolant passage?

[JohnMc]

Wasn't there more to the 'Group-A cooling system' than just those 5(?) extra holes in the head? Wasn't there also some extra piping outside the head, perhaps using the heater passages?

It seems like the headgasket is in charge of making sure not a lot of water goes from the block into the head along its entire length, but instead gets routed back around the back end of the head.

The B20 head has a full length perforated brass tube that distributes the flow from the thermostat along the entire length of the head. Since the OHC head doesn't have that, I guess they are trying to make the cylinder head temps more even by making water flow through it horizontally rather than vertically.