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The mkiv Supra Owners Club

Time to find out the damage...


Chris Wilson

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I managed to stick a rod through the block on my RB25 engine in my Skyline, at the then new Anglesey circuit, a few months back. The car came back on the end of a rope and was pushed, in disgrace, into a corner, and left to fester. I am now taking a bit of time out to pull the engine and have a look what happened. Lots of revs and ignoring how many hours on track the thing had done are the generic cause, it should have had a refresh ages before the "bang". I suspect rod bolt failure to be the actual cause, we'll see. I'll post pictures. I hope to replace it with a new RB26 engine which has been in build for about 2 years and still isn't finished.. The incentive to get on with it has now arrived!

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RB25 is 2.5 litre, weaker rods, but shorter stroke, single throttle body, rather than 6 throttles, more basic plenum, hydraulic cams, single turbo, blah blah. A good engine, but not as sophisticated as the RB26, which is in 4 wd Skylines. Mine is just a 2wd one, as it's lighter, more fun, and easier to work on (and cheaper..).

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What spec will the RB26 be Chris?

 

Quite decent.

 

All steel (crank and rods) very trick FORGED pistons, but with hollow crowns for oil cooling, 280 degree cams with 11mm lift, oversized throttle bodies, fully worked head, Motec M800, light flywheel and clutch, blah blah. Can't decide on turbo set up, probably twin, but maybe a single. looking for a track reliable 600 HP max, with great torque and quick spool. I think there are still photos of the early part of the build and the bits in it at

 

ftp://ftp.chriswilson.tv/skyline_stuff

 

Something like race engine build folder, or similar.

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Chris,

 

If you were to fit 6 throttle bodies on the RB25, would you expect any marked improvement? Has anyone done it?

(my gut feeling is 'no', but lots of people think otherwise)

 

With fairly long duration cams (much longer than the stock hydraulic ones) you would get a marked improvement in throttle response, but top end power would remain similar. It would take a fairly sophisticated ecu to make the best of it (dual mapping or better capability). People tend to jump to the RB26 rather than spend a lot on the RB25. Mine makes about 460 flywheel BHP with very basic mods.

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They are going on the RB26, I have pics of them next to stock ones at:

 

ftp://ftp.chriswilson.tv/Skyline_Stuff/RB26_Race_engine_Pics/next

 

I had them flow tested on the new head, after the porting was done, and the manifold and plenum matched to them, and they made quite difference, comapred to the stock bodies.

 

Yes I can imagine as they were opened up by quite a bit. They must flow quite a bit more air. My eyes nearly popped out of my head when Mark told me how much to take out of them. I got a bit worried when all the tapped holes and take-offs started to break through, but he'd already warned me of what I was about to witness ;)

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Engines out today, will get some photos, but apart from the big `ole in the block I found the causes of the low boost, a warped turbo flange and blown turbo gasket, and a split in the underside of the flexi hose from the turbo compressor outlet to the I/C hard pipe. It was mainly hidden by the Jubilee clip. The car has wanted for attention for months, but just got thrashed instead, so it's no surprise the thing has issues. I have decided to build the new engine on ported, but otherwise stock cast iron manifolds, i have had nothing buy aggravation with this Apexi single turbo manifold, and the IHI turbo, which has warped its flange three times now. Quite why they decided M8 studs were adequate to hold the thing on, I don't know. It's things like blowing gaskets and warped flanges that REALLY do my head in with these aftermarket turbo kits, I'll happily accept the added complication of twin water cooled GT2860-5's if the things work reliably! A mouse has been lodging in the coil valley, too, and eaten the coil pack loom, so to top it all I have had squatters...

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Engine is now partly stripped and it's a proper job, as I suspected. Rod bolt failure, the rod then lathed through the crank main bearing girdle, poked a hole in the block, and the main oil gallery. The pistons eaten a bit of the head and bent two valves, probably breaking the guides, too. Sump is knackered, so is the crank. Glad it was only a fairly stock thing!

 

http://www.gatesgarth.com/bang/bang.html

 

 

How do you load up pictures WITHIN the forum post, like Wayney did with his exploits abroad?

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