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Hi all , the Spider turbo engine is now stripped down and looks in very good condition internally . The only thing not almost perfect is the cracks between the valves in both heads . Not really an issue since I have a good pair of heads anyway .

The thing I need to know is how the turbo and N/A pistons compare ring land wise . I'm sure I did see a pic from USMB showing both types side by side and they looked the same (except for the bath tub in the crown) . Now provided the higher CR N/A pistons (9:1 I think) have strong enough lands then thats probably way to go .

We have a pair of stuffed (cooked) heads to cut up so in time we'll know how much can be ported from these heads . Will also look into chamber mods so may end up having a CR in the 8.5 - 9.0 CR when finished .

Another area to check is what cam profiles this engine has , if anyone has access to Australian Vortex worhshop manuals this one is from a late 87 build AWD car . The cams have an 8 insted of an A on them , no middle band and one end one .
I at last got a look at an early (86) workshop manual today and its interesting to see the things covered in the 87 but not the 86 one ie the FT transmissions . Its also interesting how the cam profiles changed in the early and late variants (3 plug/4 plug) of the EA82 engines - basically the later ones are a bit longer turbo and N/A no doubt because of the more acurate controls on the 4 plug engines .

Anyhow if anyones run N/A pistons/cams in a turbo engine I'd like to hear all about it . We intend to do something about that pathetic exhaust header and I think this and EGT's may have a bit to do with the head cracking issue . Also we want the longer turbo flange to open up the choices with factory style turbos . Possibly a Forrester BB one will be the go .

Cheers and thanks , Adrian .

From what i know the NA pistons have a thiner crown than the Turbo ones. Dont know about the ring lands though but know what you are on about and do remember reading the same post on USMB.

You will wanna stick with the turbo cams. Using NA ones is gonna waste power.

Well to tell you the truth even the N/A cams are not what you'd call long duration for a two valve motor . I believe even the N/A spider EA82 with 9.5 CR pistons is 20 60 - 60 20 which gives 260 deg inlet and exhaust duration is reasonable .

The 87 manual shows different profile cams for cat and non cat equipt EA82 Turbos and surprisingly the non cat ones are 12 58 - 60 20 which is basicaly like the above exhaust wise and like late L MPFI-T inlet wise just advanced 2 degrees (87+ RX-T inlet timimg is 14 56) .

I think the important aspect is that the N/A cams are longer duration which would better suit their high static compression ratio pistons . I also think its significant that the non cat turbo cams run literally performance (Vortex) N/A valve timing which is longer duration than the turbo inlet duration . The fact that there's no cat restriction south of the turbo means less in the way of reversion issues . The advanced turbo inlet timing I reckon is about having a tad less overlap in the scavange phase .

My plan is to run a larger bore (and more modern) Cat (very likely an R33 GTST Skyline 2.5L turbo cat) which should remove most of the std 21 yr old cats restriction . A better header should also help things significantly .

I had a feeling that the N/A piston crowns would be thinner but thats ok if they are thermal barrier (ceramic) coated because they won't run as hot and be possibly lighter as well . I also want to look into barrier coating the chambers and exhaust ports as well because cool heads are reliable heads . Valve faces are a chance too .

Thoughts ? Cheers A .