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Rb20det Engine With Rb25det Auto

RB120WHY

By RB120WHY,
in Engines & Forced Induction

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RB120WHY Enthusiast

RB120WHY

Posted
Posted

Just a quick question as to what you guys reccomend me to run as my HI-Stall speed. I am thinking of a 3500rpm stall speed. If I get it wrong it will be a pain in the arse to remove transmission as the engine has to come out with it. What do you think??? Has anyone done one with a big turbo??? Specs as follows -

Datsun 120y sedan

RB20DET

RB25DET Auto w/shift kit

Garrett GT35R Ball Bearing turbo. Front a/r 0.7 - exhaust a/r 0.63

GTR Injectors

Remapped ECU - Not done yet

Z32 MAF

High mount manifold

38mm Turbonetics wastegate

3.6 ratio diff

205/50/15 street slicks - 587mm OD

If anyone has an opinion as to what stall they would run, any comments would be used to help in my decision.

Cheers

Steve

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predator Grand Master

predator

Posted
Posted

rb20 auto and rb25 auto are the same so that is no difference. They may have different stall converter -- not sure there.

I think you will definitely need more than 3500 stall speed with that combo.. I would suggest around 4500rpm or possibly even larger. and cams to bring on power sooner. Rb20 needs it, especially with a turbo much larger than factory, where the small factory turbo is designed to give power down low to make up for capacity.

Factory stall on my rb20 R32 is 2500rpm (or close to), and that is shithouse even for a mild turbo setup which I have such as rb25 highflow.. Such a slug off the line, but when gets going it does mojo.

As for 3.6:1 diff ratio -- my thoughts are that will also be too small for that combo with the above done, and you'll be hitting the power band too late for you to get an optimal time. I would suggest an R32 4.3:1 (the factory r32 auto ratio), or even shorter for a drag setup. It seems like this is your main goal?

I would also go larger than 205/50R15's for tyres.. even if that means you have to run 16's to find the right width tyres (i suggest 2x GTR rims if u can fit them)

Will be interested in other people's thoughts on what is required.. the above is probably what I would do if building a proper drag rb20 combo ..but that isn't really my goal.

RB120WHY Enthusiast

RB120WHY

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Posted
rb20 auto and rb25 auto are the same so that is no difference.

I think you will definitely need more than 3500 stall speed with that combo.. I would suggest around 4500rpm, if not even larger.. and cams to bring on power sooner. Rb20 needs it, especially with a turbo much larger than factory, where the small factory turbo is designed to give power down low to make up for capacity.

Factory stall is 2500rpm (or close to) on my rb20 R32, and that is shithouse even for a mild turbo setup which I have such as rb25 highflow.. Such a slug off the line, but when gets going it does mojo.

As for 3.6:1 diff ratio -- my thoughts are that will also be too small for that combo with the above done, and you'll be hitting the power band too late for you to get an optimal time. I would suggest an R32 4.3:1 (the factory r32 auto ratio), or even shorter for a drag setup. It seems like this is your main goal?

I would also go larger than 205/50R15's for tyres.. even if that means you have to run 16's to find the right width tyres (i suggest 2x GTR rims if u can fit them)

Will be interested in other people's thoughts on what is required.. the above is probably what I would do if building a proper drag rb20 combo ..but that isn't really my goal.

Thanks for your opinion mate... I agree with your diff ratio suggestion I have a 5.4 ratio in the garage but thought this would be too short. I guess it doesn't take long to change it back if it doesn't work. I would like to keep it a bit street orientated but yes my main focus is the drags. The reason why such small tyres is they are the largest tyres that i can fit for street legalities and the smallest rim that will clear my brakes is 15". I have a pair of 225/50/15 street slicks which would be great but i need to send QLD DOT a comprehensive list of reasons and how it will effect the performance of handling/braking etc just to run a tyre that is 15mm outside the specs that they allow. I ran this tyre on my coupe and was defected. This time i wont be.

Did you mean just cams or std cams with adjustable gears???

Thanks again for answering mate.

Cheers

Steve

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