ace_nz

40 degrees at 4000 revs and light load is normal, lean cruise mixtures burn slowly so you need lots of advance, it helps fuel economy heaps, like vacumme advance on a carb.

definately standard, you can see the oil cooled crown hole.

squish or quench is very important at all engine speeds, look at formula 1 heads and pistons, or any high reving bike engine, its mechanical octane. Removing the squish band from rb heads just increases the surface area of what is already a large deep chamber, id be adding in squish and biasing it to the exhaust side to increase the burn speed and reduce trapped end gases which cause detanation. (rb30 head gasket is 55 thou. will crush to 50)

what was the timing with the standard computer? 14 degrees is way to retarded, your exhaut gas temps must have been high, your tuner is way to conservative, get the timing up to 20 degrees at least.

its not goin into the radiator via a hole in the cooler? never heard of auto consuming oil

you dont need to touch the buckets, to get back the lifter preload you loose buy reducing the base circle size on re-ground cams you need to increase the stem height of the valve, buy either welding the valve tip, using a lash cap, or if your doin a valve grind at the same time cut the seats deeper, wouldnt go deeper than about 20 thou. though

theres slight variations between deck heights on all engines but not enough to vary comp ratios alot. Idealy you want 40 thou piston to head clearance to optimise squish, which is mechanical octane despite what some people might tell you.

26 has sodium exhaust, 20 and 25 doesnt

how can 25 heads with comp ratios of 9 to 1, smaller crown on the piston and a shorter stroke have the same cc chamber as 26 heads that have 8.5 to 1 comp ratio, if the stroke of the 26 is longer and the crown on the piston is bigger then with the same chamber volume the 26 comp ratio will be higer than 9 to 1.

70 according to the wiseco information sheet, all the ones ive ever done have been at least 66, theres an obvious difference between 25s and 26s the 26 chambers are alot deeper, all these 63cc rb26s must have been milled heaps to get them that low, if you do a comp ratio calculation using 63cc chambers youll end up with higher than the factory 8.5 to 1.

120 is hard, anything less than 70 is getting very dodgy, the bolts will pull into the head after a while and clamping load is lost. Id be checking for bend through the cam tunnels, they may need line boring.

use a bunch of feeler strips to take up the preload in the lifter then rotate the enginel, or make up a solid lifter, just machine up a solid center to go in the bucket.

Are those rods small block chev modified to suit?

cam timing is out, to much overlap

32mm

most of your gains seem to to be around 400" thou, are you goin to use a cam with this sort of lift? Also do you have velocity readings?

tapering like that is a cheap way to try and stop piston noise, it prevents the top land from slaping the bore when the piston rocks. Wisecos are a far superior product.

yeah you know, got your beast fired up yet?

knife edging the divider can actually increase turbulance, look at the edge of aircraft wings they are not sharpe, port matching is not nessasary as long as the port is smaller than the exhaust primary, infact the lip left acts as a dam to reversion gases.

this is an rb20 i did ages ago

you wont make huge gains from porting on modern cylinder heads, but tidying up the short side radius and blending the seat to port transitions will help low to mid lift flow, on the exhaust the flow likes to go high so around the valve guides and the long side needs attention, also a nice radius on the short side is always good without opening the port cross sectional area to much, velocity is extremely important. Back cutting valves helps as well.

how does starting the burn sooner affect what happens on the next stroke, there is no flame front on the overlap stroke. Also if your only running 25 degrees of advance at 3000 rpm your missing out on alot off off boost response.

on rb25s with the vvt the oil gallery at the front is very close to a water jacket, make sure your gasket is correct in this area. All the RBs have non torque to yeald head bolts so theres no need to replace them. Also check oil cooler, uncommon for them to fail, seen it happen on a few subarus though.

also slow cranking speed

Cam timing, specifically inlet closing point