Lowering the 10:2:1 rb20de ratio?

[Nismo_Boy]

Hey guys, I'm after some info on lowering the stock rb20de 10:2:1? Ratio, to something a little closer to what the rb20det 8:5:1? Ratio is.

I was thinking of calling up some engine builders and seeing if a custom head gasket could be made, but this may prove a little expensive for this conversion, as its just a muck around motor until I get a hold of something else.. I was thinking maybe the likes of a Tomie head gasket (or other) would lower the ratio enough for the motor to live a little longer then what it would with 10:2:1 with 1bar+ of boost. Any thoughts on this?

Note* this is a muck around motor, I would like too see it last atleast 6 months with a turbo slapped on. Please don’t tell me it’s not worth it, as its just a silly project mates an I are doing.

Cheers, Josh.

[rsx84]

is there any difference in pistons between de and det?

[Nismo_Boy]

is there any difference in pistons between de and det?

No idea. One would asume that there was a little difference, but that isn't a real big deal with me. Squizz's N/A+t lastest over year with the stock ratio. Im sure I could atleast get 6 months with a ratio closer to the DET version.

[rsx84]

it was just i'm about to put the rb25de head on my rb30e bottom (staying N/A) and if i use the rb25 N/A pistons in to rb30 block the compression is raised from 8.6-1 to 10.5-1 so perhaps different pistons is the go.....GREX have metal head caskets for the rb20det offering 8.6-1 or 8.3-1 for around $350

[Nismo_Boy]

it was just i'm about to put the rb25de head on my rb30e bottom (staying N/A) and if i use the rb25 N/A pistons in to rb30 block the compression is raised from 8.6-1 to 10.5-1 so perhaps different pistons is the go.....GREX have metal head caskets for the rb20det offering 8.6-1 or 8.3-1 for around $350

I’m not that knowledgeable with motor’s an such, but could “decking” your head work? I have been told when you deck a head the compression is raised a tad.

If I were to buy one of these GREX items, and place it onto an rb20de, what would be the rough compression ratio? I don’t think I would achieve the 8.6-1 or 8.3-1, as I’m starting out with a higher ratio to begin with.

[Cubes]

Nismo Boy,

Simply buy a RB25 turbo bolt it on and run it at stock actuator pressures with a good ecu tune running 11.6:1 afr's.

It will make excellent power. Similiar to an RB20DET running 1bar.

[rsx84]

If I were to buy one of these GREX items, and place it onto an rb20de, what would be the rough compression ratio? I don’t think I would achieve the 8.6-1 or 8.3-1, as I’m starting out with a higher ratio to begin with.

the standard rb20det compression is 8.5-1 so by the sounds of these, one will drop compression by .2-1 so not that much difference.. for an extra $200 or so you could probibly get your hands on an rb20det motor??? its one of those things!

[gaki]

I don't know about boosting it up to that high using a stock piston. I don't think your piston and conrod gonna stand up to it for very long. If 6mths is what your after, probably it will.

I'm sure that if you keep the boost to 7psi as what the factory spec on the turbo motors are, it would last a long way.

To lower the compression, I think you will either need to get a custom made head gasket, or to change the piston with lower compression ratio.

[Cubes]

You will be suprised the power you will make with the stock RB25 turbo & rb25 actuator.

[Nismo_Boy]

I don't know about boosting it up to that high using a stock piston. I don't think your piston and conrod gonna stand up to it for very long.  If 6mths is what your after, probably it will.

I'm sure that if you keep the boost to 7psi as what the factory spec on the turbo motors are, it would last a long way.

To lower the compression, I think you will either need to get a custom made head gasket, or to change the piston with lower compression ratio.

As I said in my 1st post, I have zero respect for this motor as its comming out in 6 or so months, This is just a back yard job my mates an I will do, I was just hoping for it to last the time untill it came out, If not so be it.

Thanks for all the info guy's. I'll be giving the rb25 turbo some real thought.

[666DAN]

It should last Josh, my one has been going for a year now...that's about 40K of driving so far.

[Nismo_Boy]

It should last Josh, my one has been going for a year now...that's about 40K of driving so far.

I'm very impressed with how long your conversion has lasted!

Another question, as my car will stay auto until I find the founds to buy a manual. Would the n/a ECU work if I ran a SAFC II and the Apexi SITC? Obviously being budget wise I'd be looking at buying this second hand. Or would getting the E-mange be a better option?

Dan, I believe you run the E-mange? What’s your thought on this?

Josh.

[666DAN]

The E-manage hmmmmm Well I think it's a very sound unit...provided you actually get the boost sensor harness too.

I've seen an N/A Supra converted to turbo without much trouble using the e-manage + ignition/injector/boost harness...without the boost harness to indicate exact engine load...the tune ends up being a bit rich and too much timing pulled.

You may find that switching your ECU to the turbo unit...in combination with the SAFC may be all you need.

[StraightSix]

High compression + lowish boost = an engine that's a lot of fun to drive

[180bfj20det]

Nismo Boy,

 

Simply buy a RB25 turbo bolt it on and run it at stock actuator pressures with a good ecu tune running 11.6:1 afr's.

 

It will make excellent power. Similiar to an RB20DET running 1bar.

Yep, this is the way to go. High compression low boost. Its awesome. You always feel like your car is powerful because of the power delivery. Change your compression later when you want it to go faster but suffer the typical off boost doughyness.

[Cubes]

If you want more power/boost fit big cams to help bleed off a bit of that compression.

[LeeGTS]

Hmmm was thinking about a cam as the next step for my one

[meggala]

you might need to change injectors cause the de has smaler ones I think.

also pull back the timing a bit in the begining rb25 or vg 30 should do the job nicely.

I'm still deciding whether to turbo my rb25de I want to run a 14 first then i will decide.

I get it back in a week or so

meggala

[666DAN]

you might need to change injectors cause the de has smaler ones I think.

also pull back the timing a bit in the begining rb25 or vg 30 should do the job nicely

You'll need bigger injectors for sure. As for the timing, it's best to get some proper timing control. The RB25DE seems to spool the turbo a lot quicker than the DET so areas of the factory tune have timing too far advanced in the 1800-2500 rpm range. The problem is if you pull timing over the whole range the car bogs badly off the line and has a few 'holes' in the most of the range, but hammers from 4500-redline.

Something to consider.

[Nismo_Boy]

Thanks for you help guys.

Steve, bigger injectors were on the list for sure.