RB20DET is a terrible autocross engine. And pretty shit overall.

"Kanaric" (Kanaric1) 05/21/2018 at 10:48 • Filed to: None

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What’s an engine that has terrible mid range, laggy, while also having no top end power? RB20.

When I got this Skyline GTST I had intended to in part yse it for autocross. People said it was a terrible engine but I totally see it now.

With the stock turbo it felt ok. I usually had power when I needed it in autocross. The stock turbo is also terrible, can make no power, and uses ceramic wheels.

On this engine if you do any upgrades at all, including just upgrading te internals on that stock turbo, it moves all your power over 4000rpm at least.

I got a slightly larger turbo than I should, because I wanted stock mount, and I am paying for it. The problem is even if I got something like a 16g I would be in the same situation. This turbo is like an 18g.

Basically the entire course I am off boost in 2nd gear. The turbo only just coming on as I reach a decent speed, which at that point in autocross you are already stopping. The problem is in this car 1st is an an extremely short gear, more than on most cars, so it’s totally unusable.

Whats really bad about this engine is even though this turbo makes 16 psi to redline power drops off because of the tiny ports on this engine. It’s all around garbage.

There are solutions to my problems. One is to go twin scroll turbo. Which is very expensive. Engine swap, again. I could do both together and be in a perfect situation. Meanwhile if I ever get this rx7 it will be good out of the box and make as much power as this on the stock turbos. That’s what’s shitty, other cars already do it right.

Ill have to decide what I’m going to do going forward. . RB25 + twin scroll is something idk if I want to do.

Jake - Has Bad Luck So You Don't Have To > Kanaric 05/21/2018 at 11:07

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So... it’s a Mazdaspeed Miata? The worst autox car that shouldn’t be so utter shit but somehow manages anyways?

LOREM IPSUM > Kanaric 05/21/2018 at 11:14

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Need a fancy progressive nitrous setup to spool that beyotch.

...or something.

Biggus Dickus (RevsBro) > Kanaric 05/21/2018 at 11:22

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It’s AutoX, seat time goes waaaay further than engine mods.

Edit: Shit this goes for all racing. Learning this one first hand racing motorcycles by watching guys on 300s run faster lap times many people are capable of on a liter bike.

ITA97, now with more Jag @ opposite-lock.com > Jake - Has Bad Luck So You Don't Have To 05/21/2018 at 11:23

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A 5-speed swap makes Mazdaspeed Miatas so much better.

Textured Soy Protein > Kanaric 05/21/2018 at 11:36

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Seems like the head flow on the RB20 means that even an only-slightly too large turbo gives bad results. What about something based on a Garrett GT2860R? Wouldn’t make crazy top end but should do more of the power band you’re looking for. I’m not sure what all is involved in adapting it.

Jake - Has Bad Luck So You Don't Have To > ITA97, now with more Jag @ opposite-lock.com 05/21/2018 at 11:40

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5 speed swap makes all stock Miatas better. Aisins just aren’t as nice to use.

RX7 6 speed is a solid choice though.

Kanaric > Textured Soy Protein 05/21/2018 at 11:54

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Ya I can try that. The problem though is I need a turbo that hits power like 1000 rpm earlier than now and I don’t think even that can do it. I’d have to spend money on an experiment since nobody really has put that or it’s gt28rs equivalent on a rb 20 from what I’ve seen. Most people just swap to rb25

Edit. Thought you said gtx28

Kanaric > Biggus Dickus (RevsBro) 05/21/2018 at 11:55

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If this was for track it would be fine. I am doing a track day with this car in June and I won’t have these problems there.

Kanaric > LOREM IPSUM 05/21/2018 at 11:55

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Lol a friend of mine has antilag on his.

random001 > Kanaric 05/21/2018 at 11:56

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Swap in an LSx. Love life.

Kanaric > Jake - Has Bad Luck So You Don't Have To 05/21/2018 at 11:57

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At least in this car I can engine swap it. I wouldn’t see the point in doing that in a msm. Might as well buy a regular Miata at that point lol. That’s how useless the msm is lol.

In this car engine swaps are basically expected, I unfortunately didn’t take those suggestions seriously......

Biggus Dickus (RevsBro) > Kanaric 05/21/2018 at 12:56

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I think you missed my point, carrying corner speed is far more important than having power. Especially in something as corner speed centric as autocross. Best way to learn how to carry maximum corner speed is seat time.

Neil drives a beetle and a fancy beetle > Kanaric 05/21/2018 at 13:11

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Im going to show some of my R32 ignorance here but lots of E30 BMW people swap differentials to get better gearing for their uses; any chance that is an option?

Kanaric > Neil drives a beetle and a fancy beetle 05/21/2018 at 14:16

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It’s possible I could do that, if I went really long diff and use up 1st gear, i’d have to see what 1st would top out at and I don’t think there is any way it would be at the the speed I need. That isn’t ideal though.

As far as a shorter 2nd it’s not possible, I already have the shortest diff available. I would have to change transmissions.

Kanaric > Biggus Dickus (RevsBro) 05/21/2018 at 14:20

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I get that, I actually do well at autocross. I compete well in ASP with my Audi S3 and won my class (XP) at this event but I wasn’t going up against anything that would be nationally competitive.

Power really was a problem though. This was a slow course where I had to accelerate often, if it was a faster course I wouldn’t have had this issue.

The problem was when I needed power I didn’t have it, except at the very beginning when I was getting up to speed.

At the end there was a very tight corner then a straight that in my Audi I wouldn’t have had to downshift on. On this car shifting to first is what I should have done but really I was going at too high of a speed for that, it would have really unsettled things.

Kanaric > random001 05/21/2018 at 14:24

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There is someone who makes mounts for that so that is an option. It seems weird to me to have this car just to put in a LS though.

The ideal option I want is a RB26/30 naturally aspirated with forged internals. Tommy Kaira made an engine like that and it was equal to Euro E36 M3 power and sounded awesome. However it’s expensive. I could get the mounts and swap in an all aluminum, so much lighter, LS engine in and make the power I want even if it was just a 5.3.

On this car the “proper” tried and true setup would be RB25DET with a twin scroll turbo. I should have done this as soon as I blew my headgasket all those months ago.

Kanaric > Textured Soy Protein 05/21/2018 at 14:26

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I did some reading and apparently less than a year ago people with a GTX2860R with a twin scroll setup get the results I wanted. I wish that info was out when I bought this stuff.....

daender > Kanaric 05/21/2018 at 18:02

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Would a VQ swap have any potential? I imagine a healthy motor out of a 350Z/G35 or newer coupe would have a jump in power over a stock or lightly modified RB20 while improving weight balance. Pictured: Top Secret’s R32 with a 3.5L block and 3.0L internals to make a 3.2L V6 .