Race/rally Engine Rebuild

[screamin']

We've just pulled down my motor to re-ring it and while we are there I want to lift the compression as much as we can.

Plan A is to shave some more off the head and block, fit a thinner head gasket and re-ring.

Plan B if there are any bump top pistons out there we can use instead? Has anyone come across these?

The engine is an N/A RB20DE fitted with ITB's. Has cams and head work etc. Has to stay 2ltr.

The motor has been going well for the last five years racing, but after 20+ years the rings are finally too worn to put up with. We want to get the best out of it while it is out because it's so damn reliable it'll be a while until next time.

Also, does anyone know about new/better cam followers for them too?

Cheers

[Branelly]

What sort of power were you making before? And what do you plan on making now?

[Gerg_R31]

is it dedicated track? if so remove 0.350" off the counter weights in a lathe, and knife edge the front of the counter weights with an angle grinder. Then have it re balanced. The positive effects of this will reduce unsprung weight, the negative effects is it will effect the "throw" of the crank and will give you a really laggy take off from stationary which is not benifitial for a road car

do you know the current piston dome/ dish/ valve releif volumes? or alternatively you could speak with nitto and they could organise a set of JE customer designed pistons (or custom for short)

comp ratio, look in n/a mods explained, ive posted up the formular on how to work out your static compression ratio

http://www.skylinesaustralia.com/forums/topic/362638-na-modifications-explained/

how much lift does the current cams have? too much lift with high compression will increase the risk of pistons hitting the valves due to bigger domes, or large amounts ground of block and head

also the pistons can get fly cut or have valve relieves machined into them to help increase piston to valve clearance but they add more volume which will lower your comp ratio then you'd have to shave more off, fly cut again, etc becomes a limit to a point when you'd end up chasing your tail

[XRATED]

I'd be verry tempted to just run another bottomend from a wrecker... Just buy a couple of bottomends.

Take as much off the head as you can, thin head gasket etc. Then just use the head on cheap wrecker motors ... pop and slot.

Or have a look at late model motorcycle pistons?? short skirt, good ring spacing, designed for high rpm and cheap etc?

Actually, have a look at stock rb turbo pistons... depending on the pin height you might be able to cut the edge of the piston crown down to be 0 deck, while the center 'bump' will come up higher into the combustion chamber= more static CR.. etc

I'd try and keep as much weight in the crank as you can though... rb20's suffers from lack of torque as it is.. I'm guessing on dirt you need some grunt to get you out of a hole.

Good luck

Justin

[screamin']

The car is used in rallys and rallysprints, predominatly gravel, but also runs tarmac.

As far as aiming for a power output? I can't, because no one has built an RB20 with ITB's and no turbo. Think I'm the first somehow. Has been running this setup for the last four years and it's been going well. Was last dyno'd making 135rwkw on a stock bottom end with 230,000km on it.

The car got stolen and thrashed cold, so we've pulled it down and found some damage, hence the rebuild.

Won't be knife edging the crank or doing anything to loose torque, it's really important that the car launches hard off the start line as being rwd you can loose seconds easily.

Cams have about 1mm more lift than standard, but still has a stack of clearance when checked with no head gasket. Pistons are standard RB20DE with the valve relief. On measuring yesterday, we should gain a heap of compression the block decked and the piston sitting a tad proud. Plus a little taken off the head.

Don't think I'm going to have time to get into modifying pistons, has to be running again in a couple of weeks.

Cheers for the thoughts guys.

[SKiT_R31]

I'd definitely run a thinner HG and deck the block if possible instead of shaving the head as it yields both better quench and reduced combustion temps due to less heat soak on compression stroke (as I was once told by an old mechanical engineer when building my N/A).

Do you have adjustable intake and exhaust cam gears? An issue I has with shaving/thin HG was throwing the cam timing out a few degrees, which shifted power more than you would expect, 2 gears adjusted on the dyno afterwards would be quite useful for getting delivery and the best peak power/torque figures where you want them.

wer/torque figures where you want them.

[screamin']

At this stage we are doing all three, a little off the head, deck the block and a thin head gasket. Should get the compression over 11:1, but doesn't look like we can get much more going this way. Yes it is running adjustable cam gears.

Found some bump top pistons in the US, just wont have time to get them here, bore the block and run in and tune before the next event, so will stick to the shaving for now.

[Dale FZ1]

Guessing an R32 is not a BDA basher, but how does it perform on gravel? Nose heavy bias give any complaints regarding balance?

[screamin']

More competitive than you might think! BDA's are $100,000 cars out here, so can't compare.

Weight split is pretty good with at least 40% rearward and the lead weight of an engine helps generate good corner speed. Usually I am competing for 1st 2WD at most events against a Fiesta Cup car, that on gravel can be upto a second a km faster than me. Rotaries, turbo KE70 Corollas, A886's, and the odd WRX have been put to shame.

Just so you know I'm not lying...

http://www.mbop.org.nz/images/stories/results/2011/2011%20rallysprint%20series%20rnd%201.pdf

http://www.mbop.org.nz/images/stories/results/2011/rcc%20rallysprint%20series%20rnd%202.pdf

http://www.mbop.org.nz/images/stories/results/2011/2011%20old%20coach%20rd%20results.pdf

End of the day it comes down to knowing your car and how it will respond in any given condition.

It's not a world beater by any means, just a hell of a lot of fun!

[Dale FZ1]

Got any in-car? If you're competitive and enjoying it, win-win

I'd say NZ gravel roads would be much kinder to you than the goat tracks commonly encountered in Queensland.

[screamin']

Yep, got a stack on You tube, a couple here:

[Beer Baron]

great vids. it's kind of hard to see but is there a cage in the front of it? bit scary if not!!

either way, it puts on some good pace for a lil NA 2L 6. and some nice driving too.

[screamin']

Yep fully caged, just painted black and fitted tight to the pillars because I don't want to see it when driving.

We found a heap of internal engine damage when we pulled it down, so much so would wouldn't expect it to start, let along run as good as it did in those videos. Had a slight fuel issue in a Targa where we couldn't get enough 10% ethanol fuel, causing some bad detonation. Then the car got stolen and thrashed cold a month ago, just to put the icing on the cake. So there better be a good performance jump once we are done...