Jump to content
SAU Community

Rb25 Rebuild

HKS-R33

By HKS-R33,
in Engines & Forced Induction

 Share

Recommended Posts

HKS-R33 Experienced

HKS-R33

Posted
Posted

Hey, im currently building an rb25 and i was wondering what compression ratio i would have if I'm running CP pistons that give 8.5:1 compression ratio and use a tomei 1.2mm head gasket.

The tomei website says that by using the 1.2mm headgasket, it drops an rb25's comp ratio to 8.6:1.

I have been searching and i couldn't find a proper answer.

Any help would be appreciated.

Mike.

Link to comment
https://www.sau.com.au/forums/topic/247677-rb25-rebuild/
Share on other sites
discopotato03 Grand Master

discopotato03

Posted
Posted

I think the way to go is at least 9.0 to 1 CR if not a little higher ie 9.3 .

You have a golden opportunity to fit slightly larger exhaust valves which you can buy in direct fit form - as in dimensionally the same as std hydraulic R33 RB25 except for the 0.5mm over size head .

The std exhaust valve seats in the head are just opened up a little internally .

Big bore twin cam RB heads are a bit short on exhaust valve and port size probably because of the late 80's thinking that went into their design .

I'd aim for the slightly higher CR and exhaust valves to make the engine breathe better and make good power without having to resort to high boost to make the torque .

Cheers A .

Link to comment
https://www.sau.com.au/forums/topic/247677-rb25-rebuild/#findComment-4300893
Share on other sites
R31Nismoid Grand Master

R31Nismoid

Posted
Posted

Yeah up the comp.

This isnt 1995 anymore, fuel is a lot better and can handle more over what it was designed for back then with the 98's of today.

With all the ethanol fuels coming in and so on its only getting better.

Link to comment
https://www.sau.com.au/forums/topic/247677-rb25-rebuild/#findComment-4300948
Share on other sites
HKS-R33 Experienced

HKS-R33

Posted
  • Author
Posted

Thanks for all of your input guys. Im running a GT35R with a .82 Ex Housing. I am using a Tial 44mm Wastegate. I am definately going to be putting bigger exhaust valves in it. How big should i go and where can i get them?

Also, how much power would i be able to get out of the standard camshafts before id need to upgrade.

I was expecting to have to lower the comp because of the big boost that i will be running. If i wanted to keep the comp at 9:1, what combo of pistons and head gasket would i have to run.

Im also contemplating whether to go metal head gasket or o-ring the block and use the oem nissan one.

Link to comment
https://www.sau.com.au/forums/topic/247677-rb25-rebuild/#findComment-4302185
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • MBS206
      Duncan's V37.......race car?

      By MBS206 · Posted

      Even more fun, leave all the ADAS stuff plugged in, but in different locations, hopefully avoid any codes!   And honestly, all these new cars with their weird electronics. Pull all the electronics out Duncan, and just shove an aftermarket ECU and if needed a trans controller in, along with a PDM. Make it run basic but race car styled!
    • Duncan
      Duncan's V37.......race car?

      By Duncan · Posted

      To follow up a question from earlier too since I had the front bar off again (fking!) This is what is between the bumper and the drivers side wheel And this is the navigator side, only one thing but its a biggy! So basically....no putting coolers in the wheel arches without a lot of moving other stuff. Assuming I move to properly race prepping this car I'll take that job on and see how the computers respond to removing a whole bunch of ADAS modules
    • Duncan
      Duncan's V37.......race car?

      By Duncan · Posted

      So I prepped the car for another track day on Wednesday (will be interesting to see coolant temps post flushing out and the larger reservoir, with a forecast of 3-14 being 20o cooler than last time I took it out). Couple of things to mention; since I am just driving the car and not taking a support vehicle, I took the rear seats out and just loaded the back up Team Trackday style. Look at all that space! To cover off removing the rear seat....it is weird (note the hybrid is probably different because it wouldn't have folding rear seats) Basically, you remove the lower seat base, very similar to a r series but it is a clip that pulls forward to release the base rather than it being bolted down. Easy Then, you need to remove the side section of the rear seat on each side. There is a 14mm head nut at the bottom of the side piece, the it slides upwards off a hook at the top to release; you also need to unhook the seatbelt from the loop at the top. Then the centre piece is weird. You need to release/fold the seats forward with the tab in the boot on each side From there, there are 2,x12mm headed bolts holding the rear of each seat to the folding bracket, under the trim between the rear seat and the boot (4x christmas tree clips there, they suck). The seat is out but you can see where the bolts attach to the bracket
    • RP1421
      S15 Spec R

      By RP1421 · Posted

      As discussed in the previous post, the bushes in the 110 needed replacing. I took this opportunity to replace the castor bushes, the front lower control arm, lower the car and get the alignment dialled in with new tyres. I took it down to Alignment Motorsports on the GC to get this work done and also get more out of the Shockworks as I felt like I wasn't getting the full use out of them.  To cut a very long story short, it ended up being the case the passenger side castor arm wouldn't accept the brand new bush as the sleeve had worn badly enough to the point you could push the new bush in by hand and completely through. Trying a pair of TRD bushes didn't fix the issue either (I had originally gone with Hardrace bushes). We needed to urgently source another castor arm, and thankfully this was sourced and the guys at the shop worked on my car until 7pm on a Saturday to get everything done. The car rides a lot nicer now with the suspension dialled in properly. Lowered the car a little as well to suit the lower profile front tyres, and just bring the car down generally. Eternally thankful for the guys down at the shop to get the car sorted, we both pulled big favours from our contacts to get it done on the Saturday.  Also plugged in the new Stedi foglights into the S15, and even from a quick test in the garage I'm keen to see how they look out on the road. I had some concerns about the length of the LED body and whether it'd fit in the foglight housing but it's fine.  I've got a small window coming up next month where I'll likely get a little paint work done on the 110 to remove the rear wing, add a boot wing and roof wing, get the side skirt fixed up and colour match the little panel on the tail lights so that I can install some badges that I've kept in storage. I'm also tempted to put in a new pair of headlights on the 110.  Until then, here's some more pictures from Easter this year. 
    • joshuaho96
      R32 GTS (RB20DE) Injectors Replacement

      By joshuaho96 · Posted

      I would put a fuel pressure gauge between the filter and the fuel rail, see if it's maintaining good fuel pressure at idle going up to the point when it stalls. Do you see any strange behavior in commanded fuel leading up to the point when it stalls? You might have to start going through the service manual and doing a long list of sensor tests if it's not the fuel system for whatever reason.
×
×
  • Create New...