i am rebuilidng a a12 engine for my 120y and was planning to turbo it not just yet but later on so my question is should i run stock compression of 8.5.1 or increase to 9.5

will i be able to turbo the engine with 9:5 compression with 98 octane fuel??

thanks!

what ya doing with car? what you trying to achieve?

less compression = able to run more boost

result of less compression... worse off boost, better on boost

more compression gives better off boost performance, but means you have to run less boost so not as much power on boost

a road car is nice at stock compression with up to 10psi boost, decent performance off boost but a decent kick on boost too

i wouldn't increase compression in a boosted application... you are just limiting boost and therefore prob shouldn't bother putting the turbo on at all (that said even 3psi gives a good power increase, but not many people can resist dialing the boost up higher once they have the turbo there)

typically people lower the compression for a turbo setup, this allows you to run more boost but creates the situation where you have poor performance off boost and a big power kick when boost comes on. (suitable more so to drag cars or maybe circuit cars, not a road car really) but there is no point doing this if your not running over 10psi, and if you are running over 10psi you need better pistons and head gaskets and all that gear

hi the purpose was just to give a bit more power for street race any i dont want to transplant another engine in.

say i didnt turbo it and just put in higher compression pistons what the higest i can run safely on 98 octane fuel with out too much problems with timing and tuning

how much power gain will i get with higher compression pistons??

thanks!

woops i meant street use not race!!!LOL

10.5 compression is i think considered the normal maximum for reliable performance on 98 octane

just bumping the compression does nothing compared to boost in terms of performance. it does help a bit but if your really looking for a drastic gain in power boost it

leave it as it is. You'll have a hard enough time keeping the head gasket from blowing as it is.

So my stock A12 running 25 degrees timing and 18 psi is a ticking time bomb? I dont think so. It has the stock head gasket but I am running water injection (not that really helps the head gasket issue).

Properlly installed head gaskets should hold up quite well.

PS - 18 psi at the inlet runners; not straght off the turbo.

diymark - any chance of you providing some useful info on your experience

its extremely difficult to even get stock head gaskets these days, are you using ones from nissan or a brand name one?

how long you been running turbo and is it daily driver?

how is it all setup?

there was a European dude running 25psi daily on a stock a series for years successfully so your not alone, though we never got a lot of detail on his setup, and not many people have achieved this. a lot of home turbo converters have struggled over 10psi on budget builds.

Its still a work in progress as Ive had it 20psi with more timing but backed it off to 18 psi and 25 degrees.

I've sorted the jetting but I still need to install my bigger radiator (its a alli 300zx radiator squeezed inbetween the chassis rails and pokes up 50mm above the radiator support pannel). So its pretty much the biggest you will fit in a B310.

Also I will do a write up once I'm finished but I still have to like mentioned; install the radiator and Ive got a gilmer drive to go into it aswell. Then I will look into a stud kit for the head and a cooler thermostat!? Maybe.

By stock gaskets I mean just like the normal paper type ones with the steel rings around the cylinder bores however I got an ACL one and I just call that a "stock" one - sorry for any misleading info.

Really you wont just blow a head gasket untill the head lifts (ie too much boost or warping from over heating) so a good quality paper type headhgasket should be fine - but I'm looking at getting a stud kit for the head so that it wont lift.

Speaking of which; is there that much gain of a stud kit on a A series motor because seeing as the head bolts arnt torque to yeild I'm thinking that torquing them another few Nm wouldnt hurt? Would it?

cool, the biggest problem i had in my turbo a-series days was the rings, though i think mine and probably many others struggled with tuning. even when i had efi on mine it was never really well tuned.

if you get the tune spot on it should be a hell of a lot more reliable and therefore be able to run more boost/timing/compression etc