Rb30Det Down On Torque

[James_03]

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.

[urtwhistle]

well the first thing I would think to check is the big cam's your running. 2nd are the pistons 9:1 with a 26 head? 2nd are the cams dialled in perfectly? has any porting of the chamber been done. cos that would lower the compression a fair bit.

[KiwiRS4T]

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

[black bnr32]

compression test and degree your cams

[discopotato03]

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 .

[KiwiRS4T]

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.

[James_03]

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.

[James_03]

Also comp test I was going to do, I think I will do one tonight and post results.

[GTSBoy]

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?
   

[KiwiRS4T]

Your turbo is good for around 450awkw so probably doesn't do a lot low down.

[James_03]

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.

[Lithium]

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

[James_03]

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.

[Lithium]

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

[KiwiRS4T]

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

[discopotato03]

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 October 29, 2012 by discopotato03

[STATUS]

not the plenum we did back to back on cats car with the big greddy one and it made bugger all difference to bottom end torque even on a small 26 @ 400-420rwkw

[James_03]

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 October 31, 2012 by James_03

[KiwiRS4T]

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?

[R32Abuser]

+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 October 31, 2012 by R32Abuser