Jump to content
SAU Community

Recommended Posts

I wouldn't think it would be a set percentage, you'd really need to have provision for EGT sensors in each primary, and monitor all the temps while you adjust the cylinder trim.

I've seen pics of RB26's (may have been one of the big jap drag cars) where the head and/or block is tapped at the back to accept a second coolant hose to better control temperatures. But that may have been due to the RB26 manifold enleanment mentioned above.

Still, if the fundamental problem is heat, and not actually mixtures, then more cooling at the back of the engine may fix the problem, rather than just treating the "symptoms", ie richening the mixtures.

i would have thought that if there was less air getting to the back 2 cylinders (which i presume are no 5 and 6), then they would be running rich, as less air with the same fuel means a richer mixture.... or have i got it all wrong?

GiJOr33, you reasoning is right, however Sydneykid indicated that the airflow in the GTR / GTR Style manifolds was biased *towards* 6 & 5, rather than the other way round, so they run lean.

He also stated that this (air distribution) was not a problem on the 20/25's, so *if* there was going to be a cooling problem at the back of the engine, it would be cooling related, not mixture related, so changing your mixtures would be working against the goal of optimum tuning.

IF testing with EGT probes (not lambda in this case) or similar indicated that there was a problem with cooling, then you would be better off tapping in a coolant line to the back of the block to better distribute the coolant.

And upgrading the water pump and radiator on any high po engine, esp a turbo one, is never a bad idea. Provided your thermostat works properly, then you can't have too much cooling : )

aaaahhhhh.... i was thinking that the first 4 cylinders were using up most of the air in the plenum before it reached the back 2. What must be happening is that the velocity of the air means if flows fast enough so that most of it hits the back of the plenum, meaning cylinder 5 and 6 get the most air and run lean.

If you bow air into a tube from one end and block the other end, then most of the air will be where the tube is blocked, so feeds better into the rear cylinders that the front ones - this would explain the tapering off of the plenum at the rear too. If the plenum was sealed pressure would be equal on all surfaces, but once you open an inlet vavle, the flow dynamics of the entire plenum change - this is why it takes so much time to design any plenum properly, and the flow of each runner must be measured individually - to ensure they are matched as closely as possible.

haveing said that, it would follow that the stock RB20/25 plenum would be biased towards 3 and 4, perhaps they just got the design spot on? From Corky Bells books on forced induction, the plenum design for the RB20/25 is better than a front mounted throttle body.

Interesting subject.

Hi Steve, you asked "As far as cooling for rear cylinders, could it be overheating on 5 and 6 because they are running a bit leaner?"

It's a bit of a circle, 5 & 6 run hotter so they lean out and they lean out so they run hotter. And around it goes.

As for the percentage leaner, I haven't seen any more than 5% and ours is between 2% and 3%. That's at 1.5 bar, at less than 1.3 bar it is hardly anything at all, less than 1%. More important than boost, we are running over 65 lbs of air per minute. That amount of airflow really backs up at the back of the plenum as Steve said in a previous post.

Hope that clarifies

by lifting the rear of the bonnet you would be cooling the rear cylinders more by allowing external airflow.

how effective is it to reduce engine temps from the exterior of an engine (venting the bonnet or raising it) compared to cooling the internals (coolant/fuel) ?

  • 8 months later...

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

    • The car/ECU will have all the sensor that it needs and expect to have. I think i do not have to explain to you how the Link is way better specialy if you have swapped engine   I just do not want to deal with any "problems" cuz i have only Nistune which i learned is not that great and in my case cant even deal with that speed problem (Link can) And of course it will be way more easier to tune and diagnose and safe. And for the ECU/speed problem...i dont know.
    • Per Mark Roberts of Sonictune: Mark Robert Author At this time, no. No ETA either 2016-17 models. You will be able to purchase and install a 2018.5+ TCU though   TCU purchasing and pricing info! As we near the release of TCU tuning, I am going to answer some questions I get asked often.   What do I need for TCU tuning? At this time, you will need a 2018.5+ TCU to be able to tune. If you have a 2016-to early 2018, you will need to replace your TCU with the newer version. One good way to know if your TCU is good is if you have auto upshift in manual mode in 1st gear around 6500 rpms. If your manual 1st gear goes to 7k rpm and will hit the rev limiter unless you shift, you have the older TCU.   Why do I need to buy another ecu license/phone flash if I already have it on my ECU tune? The TCU is its own computer module. It is completely separate from the ECU. Because of this, you will be required to purchase a TCU license and, if your tuner has it, the phone flash license required to tune it via phone/bluetooth.   Do I need TCU tuning? TCU tuning is NOT required. However, the faster your setup, the more it will assist in track and dragy time consistency.   If I’m ECU tuned by (tuner A) can I get my TCU tuned by (Tuner ? Yes, since it’s a different module and a completely separate flash, you can have two different tuners. However, it is highly recommend that you have both tuned by the same tuner. For me, my TCU tuning will directly complement my ECU tuning style and features and running my ECU and another TCU or vice versa MIGHT cause some issues. At this time and for the foreseeable future, I will only be tuning my current ECU tuned customers TCUs.     I have a SYVECS AWD controller. Do I still need it? Yes! The AWD controllers main job is to control your AWD system. However, with TCU tuning, you will no longer need the auto-shift function as that will be done through the TCU. The AWD controller will still be very beneficial for racers looking to maximize traction on the launch.     Shift schedule changes: holding gears longer at lower pedal input as well as max shift rpm changes. Please note, the new ECU race rom coming out will address 90% of the shitty drivability issues these cars have through custom maps from myself and Racebox—as well as others I am sure.   Increase shift speeds: as seen in the videos I’ve been posting, the TCU shifts much faster once tuned.   Increased shift pressures: as also seen in the videos, much firmer full throttle shifts.      
    • Per Mark Roberts of Sonictune:     Mark Robert Author At this time, no. No ETA either 2016-17 models. You will be able to purchase and install a 2018.5+ TCU though   TCU purchasing and pricing info! As we near the release of TCU tuning, I am going to answer some questions I get asked often.   What do I need for TCU tuning? At this time, you will need a 2018.5+ TCU to be able to tune. If you have a 2016-to early 2018, you will need to replace your TCU with the newer version. One good way to know if your TCU is good is if you have auto upshift in manual mode in 1st gear around 6500 rpms. If your manual 1st gear goes to 7k rpm and will hit the rev limiter unless you shift, you have the older TCU.   Why do I need to buy another ecu license/phone flash if I already have it on my ECU tune? The TCU is its own computer module. It is completely separate from the ECU. Because of this, you will be required to purchase a TCU license and, if your tuner has it, the phone flash license required to tune it via phone/bluetooth.   Do I need TCU tuning? TCU tuning is NOT required. However, the faster your setup, the more it will assist in track and dragy time consistency.   If I’m ECU tuned by (tuner A) can I get my TCU tuned by (Tuner ? Yes, since it’s a different module and a completely separate flash, you can have two different tuners. However, it is highly recommend that you have both tuned by the same tuner. For me, my TCU tuning will directly complement my ECU tuning style and features and running my ECU and another TCU or vice versa MIGHT cause some issues. At this time and for the foreseeable future, I will only be tuning my current ECU tuned customers TCUs.     I have a SYVECS AWD controller. Do I still need it? Yes! The AWD controllers main job is to control your AWD system. However, with TCU tuning, you will no longer need the auto-shift function as that will be done through the TCU. The AWD controller will still be very beneficial for racers looking to maximize traction on the launch.     Shift schedule changes: holding gears longer at lower pedal input as well as max shift rpm changes. Please note, the new ECU race rom coming out will address 90% of the shitty drivability issues these cars have through custom maps from myself and Racebox—as well as others I am sure.   Increase shift speeds: as seen in the videos I’ve been posting, the TCU shifts much faster once tuned.   Increased shift pressures: as also seen in the videos, much firmer full throttle shifts.      
    • The fancy pants red shock tower brace is finally incoming from MX5 Mania, getting it shipped from 'Merica has been a long and problematic process, and GWR, the 'Merican supplier will not ship directly to consumers outside of the US, Mania basically had to order a heap of them, the colour choice was silver, or red, and we all know anything red adds 5 killerwasps of dynotorques..... Whilst it does fit over a 2.5, and I've seen a few photos and videos of it being installed and fitting, google also says it might get real close to the FAB9 intake front runner, people in the US says it does fit with the FAB9 intake, except for one person who said it slightly touched.......so there is that.....LOL..... As it seems that I am the first in AU to have this combination of parts there's no local knowledge about fitment, so I'm just a willing guinea pig in this endeavour, I'll cross my fingers and toes and hope for the best In other news, I ordered stuff from China  on the same day I ordered the 23° silicone bend from Victoria, the stuff from China arrived a day ago, the 23° silicone bend is still travelling around Australia thanks to Australia Post, and "may" be here next week
    • Very good news...I contacted Racebox about it last night. My car is a 2016 so remains to be seen if it is compatible, requires a TCU swap, or is impossible.
×
×
  • Create New...