Best heads for 253 and building to a restricted class

[stickym]

hey guys just thought i would ask here as alot of members are very knowledgeable ... i need to build a 253 for the 4.2l class in boat racing ... now pretty much it is a budget class so engine mods are restricted to keep it close racing .....

regulations are
block: maximum of 60tho'

manifold : standard gmh 4bbl no porting etc

heads : must be standard gm heads(not vn)no port or polish allowed .. not sure i think valves can go to 2" and 1 7/8. but must have 30%,45<and 70% seat cut or something rather.. will get baack to u on that Roller rockers permited

cam: open, must be hydraulic. any brand ........catch it has to run standard valve springs L34's i think

pistons: standard or standard replacement only ... no forgies , flat tops allowed
no special rings standard or standard replacement only

carby : 4bbl rochester or holley spreadbore 4150# i think

fuel pump open , premium only NO METHANOL

crank: standard, balancing permitted no polishing lightening etc
rods : AS aBove

ignition open can be regraphed

so i need to no wat recommendations you have on building a motor with a hydrualic cam with l34 springs .. and otherwise a standard motor really... and what are the best heads for a 253 cheers


Have fun looking for soem good ideas so its competiive without spending a bomb like most motorsport

 

[Immortality]

something with small ports and runners to maintain airspeed, not sure what the specs are on L34 springs but i'd imagine that if you wanted to get any decent life out of them that you would need to maintain a decent rev limit

best bet is to talk to some of the other competitors to see what works for them.

have a look at this for head flow numbers of some early heads

http://www.yellaterra.com.au/_resource/image/pic-cylinderhead-alloy-diagram.gif

 

[stickym]

the motor will be revving at 6-7ish on the straights maybe even a tad more

 

[Immortality]

there is a guy on the other commodore forum, TK383 who builds some of these motors, maybe speak to him, better yet, try him on the Aussie V8 forum, same user name

 

[ari666]

you allowed to taper the bores?

 

[stickym]

umm not sure mate .it doesnt say anything about it , guess its all in the interpretation of the rules haha... what exactly does this achieve?

 

[ari666]

loosens up the bottom of your stroke which means your engine revs much easier. has the distinct disadvantage of wearing rings really quickly and losing some of your CR, but my engineer used to do it on his commodore race car cos' he said the benefits outweighed the losses.

you really need to figure out where your average revs are gonna be, cos it may work out that a simple early HT head would suit you best. they have the smallest valves and the highest compression, so i am guessing they will be ok, but ive read that the VK black group A heads supposedly breathe best out of all holden heads (pre-vn) good luck finding them though, and i think the valves may be a little larger than what you want/need. there is a whole section of head info in the holden bible, if i can find it (and if i cbf) will post up some part numbers so you can go hunting round.

edit* actually, this is quite interesting. what sort of revs and what sort of torque is the engine going to use? i.e. 7k prm is your max, but how often will it drop down to 3 and where will it spend most of its time?

 

[Pub247]

They would be B cast heads your talking about ari?
identified by the B cast onto the head these are rare.

I think your biggest advantage is you can use flat tops to bring up the compression with whatever fuel you can use. Add this with where you need the powerband and being hampered by your springs and get a cam custom ground by wade or something they've probably done them before.

Pity you dont get to lighten the bottom end but if does say you can balance it. With a new piston which might be lighter than stock (dont go 60thou over you'll leave the bores to thin if your going to race it) youmight be able to loose a little weight with a balancing