Jump to content
SAU Community

Recommended Posts

Hey guys,

I am after some help from any tuners on here, but all advice welcome.

Specs on engine:

rb30det

rb26 head with Trust 272 cams, 10.5 lift, ported on in and ex, HKS step 2 springs

Bottem end is 9:1 CP's, forged rods, standard 26 pump with long nose drive

Intake is a yum cha but one of the better ones, still uses factory 26 intermediate plate for injectors

1000CC ID injectors

PowerFC

Borg Warner S366, 66mm comp, 91 AR, T4 footprint

T4 HKS exhaust mani

3.5 exhaust

50mm synchronic gate

Now the issue is the car has no low down torque. It's just rediculously bad. Once it hits boost it's pretty good, but anything below 4000 is shit.

Last tune they told me it was down on torque quite alot, and a dyno graph comparing a standard 26 it beat me for low down torque. Mechanically I can't think of anything that could be causing it.

Where should I start?

The tuner couldn't tell me why it was like that.

Cheers.

Link to comment
https://www.sau.com.au/forums/topic/412557-rb30det-down-on-torque/
Share on other sites

Big cams are not the thing to make strong low to mid range torque with , they are all about opening the valves further and for longer to make upper end power .

That inlet manifold isn't going to be the thing of low to mid range torque if its a large plenum single throttle job either . They actually make an engine worse in this area that has big cams .

You call but I'd be refitting the whole stardard RB26 inlet manifold inc plenum and using a pair of mild cams . I tink the difference would be night and day .

A .

Here's mine with stock bottom end and stock R33 head (estimated 8.2:1CR) and Greddy copy FF plenum and GT35/40 (max revs about 6800) - it feels like it has heaps of off boost torque to me but not enough power so I am getting some custom cams (high lift but not too much overlap) and a very thorough tune.

20120621EHD341.jpg

How about you post up your chart for a start?!

Settle down champ, I don't have a graph to post up.

Yes pistons are 9:1 with the 26 head. I am thinking it is the large plenum to be honest, and I was actually thinking of re-fitting the ITB setup. It had standard cams before, and it feels exactly the same. Both sets of cams were dialled in.

Yeah I realize there was going to be sacrifice down low for the 272's, but I didn't think it would be this bad. But then again going from standard to 272's has done nothing, which leads me to believe it could be plenum instead.

It's running a Nissan Q45 throttle.

Large throttle doesn't really change the torque characteristic of the engine, just the ability to control throttle opening at low angles.

When I hear "ported" with respect to RB26 heads, I always end up wondering;

  1. Who ported it?
  2. Do they know what they're doing?
  3. Was the desired outcome of the porting explained to them?
  4. Was the porting done to work with the cylinder capacity resulting from sitting the head on a 3L bottom end?
  5. Was the porting done to work with the chosen cams?
  6. Or was it just hogged out with the result that there is now a lower than good port velocity through the important working range of the engine?

Large throttle doesn't really change the torque characteristic of the engine, just the ability to control throttle opening at low angles.

When I hear "ported" with respect to RB26 heads, I always end up wondering;

  • Who ported it?
  • Do they know what they're doing?
  • Was the desired outcome of the porting explained to them?
  • Was the porting done to work with the cylinder capacity resulting from sitting the head on a 3L bottom end?
  • Was the porting done to work with the chosen cams?
  • Or was it just hogged out with the result that there is now a lower than good port velocity through the important working range of the engine?

All valid points, most of which I can't answer as I just don't know the history.

I bought the head from Japan already ported with the cams and springs in it, so I would have to assume the porting was done to suit cams. Not too sure what it came off, but I was told who ever did it knew what they were doing, they had dropped the guides out properly and replaced with tomei bronze phosphorous guides etc. Basically I was just trying to get the 3L breathing a bit better, which is why I opted for a ported head with the 272's. Maybe this was a mistake on my part.

I think a lot of has to do with the fact that I still remember how responsive a standard 26 is, and I might had to come to terms with the fact that I have built a motor to be the complete opposite lol.

That's why I went the 91 rear with the S366 as I thought this would help the mid a bit.

Anyway cheers for everyone's help.

Are you going to share a dyno plot comparison with the stock RB26? With a boost curve overlay would be ideal! Or alternatively do you have more info on how they compared? When do you get "full boost"?

The way you communicate it (and the fact that you are subsequently on a forum asking randoms for opinions) sounds like the tuner was a bit dismissive of your concern, which suggests to me that either it is clear to them that the turbo/something is not suited to making respectable down low torque - or that you might need a new tuner who will ensure everything is working as it should be

Yeah the tuner is fine, he did recognize that it should have been doing a lot better and showed me a graph of another 26 tune side by side on his computer, at this stage I hadn't even driven it yet he just pulled me aside when tuning and flagged it with me. He just didn't have the time to investigate and/or do a proper overlay.

I do realize it's never going to be super responsive ala stock 26 set-up, but you can literally plant your foot to the floor and there is nothing there before 4000 or so.

I think I will take it back and have the cams checked again, failing that I'll just have to deal with it.

Ah ok rereading it I see that, when you resolve it please let us know what the issue is (assuming the solution doesn't come from this thread). Will be good to see how it goes, keen to see a healthy S366 RB30 result :) Would definitely expect an RB30 to have something, even if it is laggy

S

Ah ok rereading it I see that, when you resolve it please let us know what the issue is (assuming the solution doesn't come from this thread). Will be good to see how it goes, keen to see a healthy S366 RB30 result :) Would definitely expect an RB30 to have something, even if it is laggy

Seen this car (not an RB30 but)?

http://www.trademe.c...px?id=520124510

The feeling I get is that large single throttle plenum inlet manifolds are all about getting the maximum airflow through the system for high rev only

drag race apps . They are simpler cheaper and have 1/3 of the setup issues the original RB26 throttles have .

I don't aim to put words in peoples mouths , but it often sounds to me like there is a myth that RB30s are huge and the tamer of long cams and big turbos .

They are really just a squarer version of the 25 or 26 with a taller block and longer rods . I don't look at RB30s as a long stroke motor - more that 25s and 26s are short stroke ones .

Having ~ 20% more capacity than the short stroke motors should in theory give up to 20% more torque at the same revs , but if they (30s) have long period cams with more overlap timing the cylinder pressures tend to be lower and the torque can be less - at the same revs . It obviously can be a self defeating exercise if what the user wanted is more low to medium rev grunt (torque) in the first place .

Years ago there was a boy racer cam profile for the old L Series engines which basically had significantly more valve lift but not much more duration than a warm road cam and it worked really well . It b reathed better because it opened the valves further but didn't have them opened terribly long . The result is high volumetric efficiency and good trapping ability because the valve open time wasn't long nor the overlap timing very wide . It is harder on the valve train because the valves have to open very quickly and close the same but it works performance wise . If it can work well on a daggy old two valve SOHC rocker engine in can work as well or better on a four valve cam lobe on bucket valve train .

With a single throttle manifold all the inlet ports obviously communicate with the same plenum area , if long cams are used you will get reversion issues because the valves open too early and close to late to give good cylinder "trapping efficiency" at low to meduim revs and part throttle openings . Most long period cams are timed to have a fair bit of overlap valve timing because the aim is to spin to high revs and have the thing scavange the cylinders in the overlap phase - at high revs .

What ITBs do is block the reversion pressure waves at part throttle so they tame down camminess noticably at lower revs .

I think it was SK that quoted years ago that the std RB26 inlet system was good for ~ 600-650 Hp and better plenums on the std throttles push this up to I think 700 plus ? Thats possibly as much or more than the OP wants and theory suggests should give a better all round result in a car thats often driven at normal speeds and not just a WOT drag car .

Just my thoughts , cheers A .

Edited by discopotato03

Thanks for all the info guys I appreciate the help.

I spoke to a tuner yesterday, and they advised that it could be the PFC and AFM's causing it. He said it would be better with a MAP based ECU, what do people think?

Also the camshafts are currently 0 in and 0 ex. I was also advised that JAP cams are often best left at this, I don't have the cam card as I bought the head with cams already in it. They said they can play around with the cam timing on the dyno through trial and error, but this will be the only way without the card.

What's people's opinion on it? Is it worth going down this route?

I was quoted roughly $1000 to look at the cam timing and another tune. I know it will be a PITA for someone as the CAS will need to come off each time to play with the ex side.

Edited by James_03

I doubt that its the PFC and AFMs although if you have money to burn by all means get a Link!

I have been told by lots of people (see also Guilt Toy) including my local RB guru that adjusting the cam timing is critical on the RB30s and that dramatic improvements are to be had. That is why I too will be spending about $1000 on a comprehensive tune by a very respected tuner who knows RBs backwards and I am confident of a good result. he won't be using a degree card as he has done this many many times.

If your tuner is good and you are prepared to give them the time I am sure you will get an improvement - whether it is enough to get it to where you want with the low down torque remains to be seen. What was the max kw that you were seeing?

+1

I went through similar issues on my motor about a year ago.

Built RB25/30 + GT3076R + Cams. Should have been making 260+ RWKW on OEM cams and was only making 220RWKW whilst wanting to ping. Threw the cams at it and re-timed + adjusted the base cam gear timing etc. Ended up making ~250 RWKW with no explanation of why it wouldnt make anything more. Was making the torque/power/response under 5000 RPM, just wouldn't make power!

With literally nothing changed, I took it to a well respected tuner - made some adjustments to the tune. Walked out of there with 281 RWKW on a "lower" reading Mainline dyno.

From my (and others) experience, since these motors do not maintain an OEM timing setup (taller block + DOHC), they are very sensitive to the timing being correct.

My advise is to re-check timing. AFM and computer is not the issue. Plenty of others have had no problems with PFC + Nissan AFM's. Won't matter whether you have a MAP/MAF or Link/PFC, if the thing isn't timed properly it will never make decent power/torque.

Edited by R32Abuser

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


  • Similar Content

  • Latest Posts

    • Update 3: Hi all It's been a while. Quite a lot of things happened in the meantime, among other things the car is (almost) back together and ready to be started again. Things that I fixed or changed: Full turbo removal, fitting back the OEM turbo oil hardlines. Had to do quite a bit of research and parts shopping to get every last piece that I need and make it work with the GT2860 turbos, but it does work and is not hard to do. Proves that the previous owner(s) just did not want to. While I was there I set the preload for the wastegates to 0,9bar to hopefully make it easier for the tuner to hit the 370hp I need for the legal inspections that will follow later on. Boost can always go up if necessary. Fitted a AN10 line from the catch can to the intake hose to make the catchcan and hopefully the cam covers a slight vacuum to have less restrictive oil returns from the head and not have mud build up as harshly in the lines and catch can. Removed the entire front interior just shy of the dashboard itself to clean up some of the absolutely horrendous wiring, (hopefully) fix the bumpy tacho and put in LED bulbs while I was there. Also put in bulbs where there was none before, like the airbag one. I also used that chance to remove the LED rpm gauge on the steering column, which was also wired in absolute horror show fashion. Moved the 4in1 Prosport gauge from sitting in front of the OEM oil pressure gauge to the center console vents, I used a 3D printed vent piece to hold that gauge there. The HKB steering wheel boss was likely on incorrectly as I sometimes noticed the indicator reset being uneven for left vs. right. In the meantime also installed an airbag delete resistor, as one should. Installed Cube Speed premium short shifter. Feels pretty nice, hope it'll work great too when I actually get to drive. Also put on a fancy Dragon Ball shift knob, cause why not. My buddy was kind enough to weld the rust hole in the back, it was basically rusted through in the lowermost corner of the passenger side trunk area where the wheel arch, trunk panel and rear quarter all meet. Obviously there is still a lot of crustiness in various areas but as long as it's not rusted out I'll just treat and isolate the corrosion and pretend it's not there. Also had to put down a new ground wire for the rear subframe as the original one was BARELY there. Probably a bit controversial depending on who you ask about this... but I ended up just covering the crack in the side of the engine block, the one above the oil feed, with JB Weld. I used a generous amount and roughed up the whole area with a Dremel before, so I hope this will hold the coolant where it should be for the foreseeable future. Did a cam cover gasket job as the half moons were a bit leaky, and there too one could see the people who worked on this car before me were absolute tools. The same half moons were probably used like 3 times without even cleaning the old RTV off. Dremeled out the inside of the flange where the turbine housing mates onto the exhaust manifolds so the diameter matches, as the OEM exhaust manifolds are even narrower than the turbine housings as we all know. Even if this doesn't do much, I had them out anyways, so can't harm. Ideally one would port-match both the turbo and the manifold to the gasket size but I really didn't feel up to disassembling the turbine housings. Wrapped turbo outlet dumps in heat wrap band. Will do the frontpipe again as well as now the oil leak which promted me to tear apart half the engine in the first place is hopefully fixed. Fitted an ATI super damper to get rid of the worn old harmonic balancer. Surely one of the easiest and most worth to do mods. But torquing that ARP bolt to spec was a bitch without being able to lock the flywheel. Did some minor adjustments in the ECU tables to change some things I didn't like, like the launch control that was ALWAYS active. Treated rusty spots and surface corrosion on places I could get to and on many spots under the car, not pretty or ideal but good enough for now. Removed the N1 rear spats and the carbon surrounding for the tailpipe to put them back on with new adhesive as the old one was lifting in many spots, not pretty. Took out the passenger rear lamp housing... what do you know. Amateur work screwed me again here as they were glued in hard and removing it took a lot of force, so I broke one of the housing bolts off. And when removing the adhesive from the chassis the paint came right off too. Thankfully all the damaged area won't be visible later, but whoever did the very limited bodywork on this car needs to have their limbs chopped off piece by piece.   Quite a list if I do say so myself, but a lot of time was spent just discovering new shit that is wrong with the car and finding a solution or parts to fix it. My last problem that I now have the headache of dealing with is that the exhaust studs on the turbo outlets are M10x1.25 threaded, but the previous owner already put on regular M10 nuts so the threads are... weird. I only found this out the hard way. So now I will just try if I can in any way fit the front pipe regardless, if not I'll have to redo the studs with the turbos installed. Lesson learned for the future: Redo ALL studs you put your hands on, especially if they are old and the previous owners were inept maniacs. Thanks for reading if you did, will update when the engine runs again. Hope nothing breaks or leaks and I can do a test drive.
    • No those pads are DBA too  but they have colors too. I look at the and imo the green "street" are the best.
    • I’m not sure what happened I told them about sonic tunes free OTS tune and the next the I know .. I was booted..   To funny 
    • Yea - I mean I've seen my fuel pump which is decades old and uh, while I'm not saying this with real knowledge... but I sure get the ick at using anything in the fuel system that produced the state of that pump. Many years ago I went through multiple pumps (and strainers) before I dropped the tank to clean it out with extreme violence. I'm talking the car would do maybe 50km before coming to a halt, which resulted in me cleaning out the filter with some brake cleaner and going on my way. None of my stuff ever looked like what came out of your fuel tank. I don't think I'd be happy with it unless every single component was replaced (or at least checked/cleaned/confirmed to be clean here).
    • I'm not going to recommend an EBC pad. I don't like them. Just about anything else would suit me better. I've been using Intima pads for a while now.
×
×
  • Create New...