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Discussion Starter #1
Hi all,

Going to get my pistons off of chrisK. Decided on CP cos of the low silicon content. Now eventually I'm going to be running a gt3076 or gt 3040 and wanting to run pretty high boost. I'm thinking for race situations I'll want to run about 25/26psi.

My question is if I go with upping standard compression ratio to 9:1 with the pistons will this sort of boost level still be safe ?

I was going to do 8.5:1 but am using a 1.6mm HKS HG so this woudl end up even lower. Besides chrisk says that with a higher compression the car will be much more driveable.

I am thinking of a compromise and lump for custom 8.8:1s to try and keep it close to stock.

Anyways high boost on raised compression built engine, good or not ? and why ?

Cheers
Adam
 

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A higher compression car will be more responsive and spool a turbo quicker, but generally you cant boost quite as high as its higher compression to start with. Theres a couple of guys in the UK running around 1.6 bar currently on built engines and they're looking towards the 2 bar area on optimax / super unleaded in the near future.
 

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Discussion Starter #3
Hi Steve,

Yeah I only ever run it on optimax/super anyway, being in the UK myself, so thats not a worry. I know the standard compression is 8.8:1 (I've got JDM rev1 obviously not USDM). Thats a good start because 1.6 is like 23ish psi but I am wondering if all things being correct, EMS etc could I safely run >25 on a 9:1 ratio.

Cheers
Adam
 

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I'd of thought so, providing the engine is built to take it. My personal view would be to try and limit yourself to 1.6-1.7 bar, I've seen many built 2 litre engines run around this sort of boost on the streets. When you start talking 1.8-2 bar I think it starts to get a little dangerous.

At the end of the day, you could make the same power with an ever so slightly larger turbo at slightly less boost.
 

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Discussion Starter #5
Thats fair enough Steve but everyone always seems to think that like 20psi is high boost on an MR2 for some reason, I'm wanting to run 25-30 because thats the sort of level where the gt30 series is going to be hitting the peak of it's efficiency. Otherwise im not using all the potential of the turbo. I am doing this to hit high hp with as little lag as possible so a larger turbo isn'y an option. These turbos are both capable of 500-550hp. If we look at the evo they run like 19psi out of the box i think (correct me if i'm wrong) but i don't know what the compression ratio is.

How much will the HKS 1.6mm HG lower compression i'm thinking that from 9:1 it might drop to like 8.8:1 which would be nice.

Cheers
adam
 

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Dont know the HG / CR question I'm afraid.

You're right, the MR2 community seems inherrently scared of boost when it comes to pump fuel in certain 1/4's.

However if you want to look at some of the cars in the UK there are a number of them running high boost. Theres a chap called Dan up in Manchester who is running an HKS 3037 at 2 bar since importing - although I've pleaded with him to get the car remapped for UK fuel lol! Andy up that neck of the woods is currently running a GT30R at 1.6 but ran out of fuel so is going to be fitting larger injectors again and retuning for the 2 bar area. There's another running a GT28 of sorts up around 2 bar, or atleast thats the plan last time I heard. Lol theres even a quick spooling ct26 hybrid pushing up around 1.7 bar.

They are there, but none of these cars have stood the test of time yet. I personally take the view 22-25psi is a decent amount of boost for any car! The 25-30psi area is when it starts getting less reliable.
 

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Discussion Starter #7
That's cool. I'm going to ask on imoc and see if anyone pipes up! ;)

I think the point is I would only run this high boost level at the dyno or on the 1/4 to basically get the times and the HP figures. I will probably pootle around on about 20-22 i'd think (hoping these figures will net me somewhere around 450hp)

Anyway cheers for the info...if anyone else wants to chime in 'd be greatful on experiances of higher than stock compression with high boost.

Cheers
 

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Yup try imoc, Andy, Dan, Neil, Dino and co on there are the high boost peeps lol. Andy was making 410 at the hubs at 23psi, so thats pretty much right on the money for what you'd want on a daily basis.
 
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