Headwork (head Needs To Be Recond)

[Brezza]

Hey Guys,

my engine blew and i spun a bearing and the piston has hit the head and done a little damage.

so basically i am up for rebuilding/reconditioning the head.

i was just wondering is there anything that the mechanic can do to the head to increase low down torque? obviously there is the option of going for cams.

but i am not really interested in spending $1000 ontop of everything else for cams.

so really is there any machining that can be done which will increase low down torque?

Brezza

[R31Nismoid]

increase the compression a bit

[STATUS]

Hey Guys,

my engine blew and i spun a bearing and the piston has hit the head and done a little damage.

so basically i am up for rebuilding/reconditioning the head.

i was just wondering is there anything that the mechanic can do to the head to increase low down torque? obviously there is the option of going for cams.

but i am not really interested in spending $1000 ontop of everything else for cams.

so really is there any machining that can be done which will increase low down torque?

Brezza

Its tricky as any potential head work works the opposite, enlarged ports, valves etc all slow intake charge down at low rpm (big benefits up high) so other than upping the static comp a bit there is not much you can do with only $1000.

[N1GTR]

Cams wont cost you $1000 by the time you've done it.

You'll be doing springs, buckets - there's another $1000 with ease if you go tomei, jun etc.

[Swiper the Fox]

Its tricky as any potential head work works the opposite, enlarged ports, valves etc all slow intake charge down at low rpm (big benefits up high) so other than upping the static comp a bit there is not much you can do with only $1000.

this is not entirely correct...we have back to back tested heads and actually found the opposite depending on the set-up.

[STATUS]

this is not entirely correct...we have back to back tested heads and actually found the opposite depending on the set-up.

i KNOW this but he has Only 1k to spend..... hardly enough. Machine cost to relieve cam valley, reco head, repair damage and cams blow his budget way out.. port work... way out of budget.

If you have more to spend the possiblities are endless but with 1k... your limited.

Edited April 30, 2009 by URAS

[Swiper the Fox]

i KNOW this but he has Only 1k to spend..... hardly enough. Machine cost to relieve cam valley, reco head, repair damage and cams blow his budget way out.. port work... way out of budget.

If you have more to spend the possiblities are endless but with 1k... your limited.

I realise this...thats why i said...not 'entirely' correct.

but you said "any potential headwork works the opposite"

that statement was what i was refering to. People regard what you write as gospel given your reputation...i just didn't want your words taken out of context.

Edited April 30, 2009 by DiRTgarage

[joe blo]

i read it as being he doesnt want to spend $1000 for cams ontop of whatever fixing and rebuilding it costs. not that he is only going to spend $1000 total.

i am currently getting a rb25 head reconditioned at the shop. its costing me $495 plus $211 for the topend gaskets and valve stem seals. dunno exactly what there doing to it but. so yours will be around that plus whatever the replacement parts cost plus a little bit more if it needs to be machined if its broken.

on a side note... if im putting a rb25det head on a rb30 na block it brings the compression to 8.2:1 i think. should i get it shaved to up the compression abit? could i shave it enough to get it back to the 9.0:1 compression of a rb25det motor without anything hitting from shaving it too much?

[aDrew_C]

I'm looking at getting this done soon. Basically for response without buying cams you've got; bigger exhaust valves + valve springs, light clean up of the head, exhaust adj cam wheel and increase the compression.

[rob82]

this is not entirely correct...we have back to back tested heads and actually found the opposite depending on the set-up.

What - from everything I have seen I would tend to agree with URAS. Are you talking your flow bench figures again or actual dyno testing and when we talk low rpm I would condsider that to be below 3000rpm on a RB26.

[Swiper the Fox]

What - from everything I have seen I would tend to agree with URAS. Are you talking your flow bench figures again or actual dyno testing and when we talk low rpm I would condsider that to be below 3000rpm on a RB26.

actual dyno and real world on road and track results.

you must get out more as what you have seen is conventional thinking...i must admit though we were a little surprised with the results from what we tried.

most of the power runs were from 2500-3000rpm

we build and design our engines to perform for a given rev range... below 3000rpm is for shopping centre carparks.

Edited April 30, 2009 by DiRTgarage

[rob82]

actual dyno and real world on road and track results.

you must get out more as what you have seen is conventional thinking...i must admit though we were a little surprised with the results from what we tried.

most of the power runs were from 2500-3000rpm

we build and design our engines to perform for a given rev range... below 3000rpm is for shopping centre carparks.

I can smell the clutch burning from here in getting your cars off the dyno with no torque under 3000rpm!!! Are you sure there was no other changes that may have cuase the extra power - like compression???

I've been around cars for long enough to know that not everything makes perfect sense but in these cases I always try to determine why a specific change caused an undesireable result. Usually there is always a reason.

[Roy]

I tend to agree, you slow velocity, you hurt low to mid torque as you affect cylinder filling. No doubt there are exceptions, but they are that, exceptions and more likely only the case when you habe 900hp of turbo hanging off a built motor with plenty of other suff going on in the head and inlet

[Swiper the Fox]

I tend to agree, you slow velocity, you hurt low to mid torque as you affect cylinder filling. No doubt there are exceptions, but they are that, exceptions and more likely only the case when you habe 900hp of turbo hanging off a built motor with plenty of other suff going on in the head and inlet

you obviously do not get it Roy...im not talking massive port size. Just changes to port and combustion chamber shape. This aids the intake charge to properly fill the cylinder more uniformly and aids in cylinder distribution. On the hot side the small amount of extra size that may result and tiny loss of gas velocity can be made up by changing the thermal properties of the gas path by retaining heat. This is one of the reasons Ben likes the stock manifolds and why i thermal coat everything.

Chat to Ben about it as im just a dumb engine builder and drag racer who has no idea.

Edited April 30, 2009 by DiRTgarage

[discopotato03]

I think there is a lot to be said for keeping the heat in exhaust gas , basically its the thermally driven expansion that you want to evacuate the cylinders and drive the turbine/s .

You have to pay for the fuel to make the heat/expansion/cylinder pressure to drive the pistons so letting the heat escape is throwing velocity energy and money away IMO .

Also some people consider that the valve size ratio is wrong in big bore RB twin cams , the exhaust is said to be a little small and if 0.5mm oversize valves are available they don't go astray . I think they can be used with std modified seats as well .

Increasing valve size does to a degree what changing to mild cams does but the valve train dynamics get to stay the same (aside from a little more valve innertia) .

My theory is that if you make an engine more volumetrically efficient it should make more torque rather than less .

If it were me I leave the cams till later because I see them as a bolt on , maybe relieve the lifter bores if big cams were on the to do list but that can be done in situ if careful .

Lastly again IMO GTRs are such a PITA to get turbos etc off I'd concentrate on porting/valves/springs while its pulled down because its not cost effective to go there again to finish the job properly .

I strongly believe that there are things you can only achieve with properly modified heads and bolts ons by themselves won't give the best results .

Do it once , do it properly , all cake then .

A .

[Guilt-Toy]

Chat to Ben about it as im just a dumb engine builder and drag racer who has no idea.

Yeah. your 14 second rb20 street car tells the whole story.

[Tangles]

cost of headwork varies between how much you get done overall.

I went for an adjustable exhaust cam gear wheel, Tomei 256/256 cams, Tomei 8.8mm valve springs, 87mm x 1.2 Cometic headgasket + all other gaskets, valve guides/seals/etc, $2500 in new parts

plus another $2000 for porting and machine work, installation, rundown testing, tune etc

full potential has been held back, but ready to unleash the beast within

awaiting my GT30r bb-iw turbo right atm, hopefully pickup and start installation this arvo. with that on, serviced with new fluids, redoing/cleaning/heat-wrapping intake/exhaust pipes, will get a tune in a few weeks, expecting a very meaty two-fiddy

[Roy]

you obviously do not get it Roy...im not talking massive port size. Just changes to port and combustion chamber shape. This aids the intake charge to properly fill the cylinder more uniformly and aids in cylinder distribution. On the hot side the small amount of extra size that may result and tiny loss of gas velocity can be made up by changing the thermal properties of the gas path by retaining heat. This is one of the reasons Ben likes the stock manifolds and why i thermal coat everything.

Chat to Ben about it as im just a dumb engine builder and drag racer who has no idea.

LOL, you are right i dont get it Read what i posted and i think we are saying the same thing, i said dont port to hurt gas velocity, you said dont go for huge porting, instead work on comb. chamber and tweaking inlets etc...improving cylinder filling...is what we said worlds apart???? No doubt you have a better understanding of the dos and donts but i am just going off my understanding of fluids.

Yeah. your 14 second rb20 street car tells the whole story.

Thats not fair, my car may only run 12s but i can fall from great heights pissed at a good rate of knots

[Gerg_R31]

as a fellow engine recondtioner there is alot to be added

porting: porting is not noitced down in the lower rev range, forced induction porting is usually bigger ports but usually the same idea in they way it is ported out as the n/a ports, too much taken out can slow down the flow, too much polishing can prevent the air fuel mixing. there are also many different methods and ways ports are done and can have different effects in different engines

stiffer springs: with standard cams pointless, only needed if the maximum coil bind of the springs will be greater then the maximum lift of the cam

seat pressure: standard is usually around 60 ft pounds 80 to 100 ft pounds is the maximum

cams: most if not all cam grinders will tell you at what rpm the cams will kick in, n/a cams having more overlaping can lower the raised compression ratio due to being open longer and less time to compress, forced induction has less overlapping bringing up the compression ratio, sometimes if the cams are too big it can drain the power

combustion chambers: surface grind the head CC the chambers after the valve seats have been cut and make every chamber exactly the same

valve seats: usually there is a standard 3 angle crown seat and throat but there is many diferent cuts to add better flow, there is the raidius which is the 3 angles rounded into each other right up to cnc seat which have 29 angles on the throat and crown

compression ratios: very debatable, changed via piston cc's reboring/honing block, i prefer to make the pistons flush with the deck, run a cosmetic head gasket and then take the remainder off the head, 10.5:1 is the most on pump fuel and its shitty quality. 12:1 if u can garantee good fuel with octane boosters