EA82 Turbo and N/A piston details .

[discopotato03]

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 .

[Suby Wan Kenobi]

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.

[Gannon]

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

[discopotato03]

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 .