4k Headwork For 5k Block

[keslider55]

hey guys was going to build my 4k up as some of you know but i now have a 5k bottom end lined up. my question is. what work will i need to do to my 4k head performance wise to match it to my bottom end. i will be rebuilding the 5k bottom end using all new bearings and using mahle pistons with the 8cc dish, getting everthing balanced and flywheel lightened. I'm planning on running the tighecams 474 profile cam. i was hoping for something around the 11 - 11.5:1 comp ratio to suit this cam.

 

so info i need is headwork needed? shaving, porting, valve work, springs etc?? also would twin 32/36 webers be an overkill? if so what would be suitable.

 

thanks in advance.

 

The engine is not a daily driven car. I'm hoping for a high revving top end motor. cheers

[Taz_Rx]

4k head on a 5k block will lower the CR to around 8:1. For 11'ish:1 CR you'll need to use the 5k head and plane it considerably.

[philbey]

You'll need to get a 5K head to go with the bottom end, I ended up with about 12:1 using the mahles and a 5K head, shaved but only for flatness.

 

A 4K head has a larger combustion chamber so you will end up with much lower compression.

 

I reckon you'll be fine with the stock valve springs, mine ran .48 lift with stockies and it was 12 months before one failed.

 

Port match to your manifold. Tell your engine builder what you're aiming for and let him work out what needs to be done head wise.

[philbey]

Taz, you wont need to plane it considerably, the 8cc Dish pistons will push it quite high. (21cc vs 8cc).

 

Again, let the engine builder do the work.

[Felix]

With the shallower dished pistons use a normal flattop 3k or 4k head and skim to desired CR.

 

Keep in mind a stock 5k with 9.5:1 CR has a total combustion chamber volume of 43.71cc (including head, piston dish, and gasket volume).

 

A 5k head (~16cc std) with the 8cc dished pistons gives around 13.5:1 CR. :happy: Good for overheating and popping head gaskets.

 

 

A normal flat top head has around 30-36cc in the head. Head gasket volume is around 5cc from memory.

Edited May 26, 2010 by Felix

[tioklou]

of course if you have a 4k-u twin squish head you could put it on your 5k without any mods...the cr will be ok...

[Felix]

of course if you have a 4k-u twin squish head you could put it on your 5k without any mods...the cr will be ok...

 

With the stock 21cc pistons, yes.

 

Not with aftermarket 8cc pistons.

Edited May 26, 2010 by Felix

[philbey]

Yeh that's a good point felix.

 

Like I said I only discovered 12:1 was the CR I was going to get after I got the rebuilt engine back. Fortunately, I've got a big cam so my DCR is low enough to be useable.

 

also fortunately I don't mind a monster cam because I'd have problems going to something more pedestrian.

Edited May 26, 2010 by philbey

[keslider55]

wait so 4kc head is ok to skim untill 11:1 with 5k block with 8cc pistons or not???

 

is there an easy way to tell the builder how much to shave or what cc to get the chambers to???

Edited May 26, 2010 by keslider55

[philbey]

The easiest way is to tell him what CR you're after and let him do the numbers.

 

There's a lot more than just combustion chamber and piston chamber, there's crow to deck height, ring land to crown, crown diameter vs bore diameter etc etc.

 

Let him CC your head and pistons and do the numbers.

[keslider55]

alright cheers mate will do. so you reckon springs, 3 way valve grind and port match to manifold and I'm all set for heads? what size webers or su's etc should i run with this setup engine. i wanna run twin so i can have the 4 sock filters! haha just bit of wank and sound!!!

[altezzaclub]

Twin inch & 1/2 SUs on the Lynx manifold, or twin Webers- you could use 40DCOE or 45's.

 

Webers better, but more expensive to buy and to run.

 

Anyone got some real-life experience on engine life using foam socks V. paper filter & airbox??

[philbey]

I'm running a 2 stage oiled foam filter on mine, not socks but foam.

 

The key is cleaning and reoiling the filter, I need to reoil mine.

 

Mine is a road car I wouldn't be so sure about foamies on a dirt car.

[keslider55]

so twin 40mm webers wont be over/underkill for tjis setup?.

 

thanks for the help guys.

[Raven]

I'm running a 2 stage oiled foam filter on mine, not socks but foam.

 

The key is cleaning and reoiling the filter, I need to reoil mine.

 

Mine is a road car I wouldn't be so sure about foamies on a dirt car.

 

I run a foam filter on my dirt bike and if its safe for a a dirt bike, its safe for a car :D