coscast vs gm heads

[deek]

whats the real difference between them?other then the purase head problem,if you have a gm head that has been repaired what is better about a coscast?

[andy_gte]

it really depends on the age of the head, the very early coscast heads had stronger valves and guides, but the later ones are amost identicle

[Rs1]

There 2 types of gm(ks) head, one of which the material is a bit soft....therefore ****,lol.
Apparently through ****loads of heat cycles the headbolts/studs lose torque??
The other ks if well repaired should be fine. If your going to the point of heaving in ported and big valves etc. there really no need to search high n low for a coscast. The early coscast do have bigger guides but you should have any probelms with the smaller, be it iron or bronze. The bronze are just more forgiving, should you bend a valve your less likly to have bits of guide floating round your engine.

[rudd86]

thats what bronze guides are for aha...
I have a coscast off a let with round tooth type pulleys, does that mean its the stronger type?

[Lee H]

The earlier Coscast won't have GM stamped on the dizzy end. If its on a LET its not going to be a really early one unless its been changed at some point.

[montytronix]

I guess...but could be wrong....

the spec on the GTE's were good early on - then the recession hit hard sales slumped and cheaper materials / workmanship was sought....yuppy traders hanged themselves etc after loosing loads ££££££££...yuppies werent buying many fast cars anymore
the insurance companies hit the hot hatch market.....killed it

Cranks were lighter and stronger / flywheels the same / costcasts had good flow and build material....then the Accountants moved in and GM cut corners to suit

[Giles]

This has been covered lots on here. loads of info if you search.

You guys have missed out that as STANDARD the early CosCast heads had approx 1mm bigger inlet tracts (hence they flow more as standard).

They will also except bigger inlets in the OE seats.

As for bronze and iron guides - IIRC it is more todo with bronze offering less friction than iron (important at high revs and heat build up), as well as bronze being a better conductor of heat to take the exhaust steam heat away from the valve. NOTE: no head came with bronze guides as standard.
Colsobro guides will only cost you about £100 the set plus another £80 for a propoer fitting job. Then of course you need to work them a bit, check clearences and ream them if needed.