Jump to content
SAU Community

Recommended Posts

Hey guys.

Went for the tune of my 25/30. We cant get it to make hardly any power. And compared to my old slap together SOHC setup, it makes less power less torque and it all happens later, Also its starting to knock up high at anything over 19psi (98ron).

We suspected cam timing so degreed the cams in again, (found the exhaust cam 15 degrees retarded). intake cam is 4deg retarded but cant adjust that with out pulling the gear off.

Set the exhaust back to 115 deg *standard cams. It made it better but not a whole lot better.

Motor specs

Rb25/30 Neo 9:1 comp (old motor was in the 7s)

forged pistons, rods

CPC plenum

steam pipe manifold gt35

3inch exhaust 1 muffler no cat

660cc injectors

vipec v88

Standard head with upgraded springs and retainers

still has vct but didnt turn it on yet.

Exhaust, turbo and intercooler plumbing is exactly as it was on old motor.

Here's a pic of the run in comparison to the old sohc.

Any ideas?

post-78438-0-27124000-1429354860_thumb.jpg

Link to comment
https://www.sau.com.au/forums/topic/455838-new-motor-making-no-power/
Share on other sites

Hate that! I'm tipping you had mentally prepared yourself for a big increase! Not that a forged engine will necessarily make more power, just stay together for a bit longer.

I would presume they have checked spark timing?

How confident are you of the compression ratio?

How long has the car been sitting during rebuild- not old stale fuel?

Not sure if it's possible but VCT not locked over advanced seeing not connected?

I'm sure there are other possibilities but that's all I can think of. The knock is a concern and hopefully leads to the diagnosis. It shouldn't be pinging on 98 with 9:1 comp.

Good luck!

Well yeah I was looking for at least an extra 30-50 hp. Going from a single cam head to a twin cam head.. The single cam head only had a baby cam. I expected the boost and power to be on earlier and make more torque and power in general.

Yeah we double checked ignition timing. Pretty confident on the comp, its a tad higher then 9:1 i have it here somewhere.

Fresh fuel. And Ive done over 1000ks on the motor with a soft tune.

Not sure on the vct one but I thought if off its just normal and energized it will advance? Even being advanced you would think the power would be on alot sooner

Ok not sure where to go next with this thing.

Got the cams set at In 121. Ex113

Gets to about 5000rpm and starts detonating even with only 13 degrees timing on only 17-18psi, still making no power or torque.

Afr are good

Compression is 170-165 across all 6.

It has around 2.5 psi exhaust back pressure

And 2.5psi pressure drop from hot side to manifold

Head was decked down to 46cc to get the comp up a bit.

To much compression?

Is it possible the vct gear is stuffed and causing the cam timing to move around?

Is it me just getting old but are those pistons dished in the picture?

I hope not because if they are i can assure you your not getting 9:1 compression.

For some reason i see a 5-9mm ring at deck height around the piston, then they dip down lower.

Is that right?

If so then i can see lots of Det causing pockets right under the quench pads.

Did you round off the valve relief edges on the pistons?

Its a really weird piston shape for those heads, what pistons are they? Part number?

Maybe they are domed, im seeing dished, could be the way the pic was taken......

Cam's can only go one way due to the VCT gear on inlet.

Yeah you are seeing correctly, they are dished. 9cc. (Dished because neo chamber is alot smaller than the normal 25-26 head

They are a wiseco piston, here is a close up. Did not do anything with the pistons...

It's seeming more likely these are the issue with the knock.

post-78438-0-18039900-1430036937_thumb.jpg

Edited by Huzqld

I'm pretty confident on the compression, calculated while we were building.

Is there anything I could get done to the head to fix the issue?

Really don't want to have to pull the motor back out to replace Pistons and get it all balanced again. I think if I have to go that far I'll put a 26 head on it while it's out.

post-78438-0-85664600-1430043134_thumb.jpg

How sure are you about the 9:1 compression? You planed the head to get the compression up and then dished the pistons to get it down? Do a compression reading and see what you get

I don't know what your cam settings are - they seem a prime suspect.

I already had the pistons as I bought all the parts off a guy that didn't go ahead with a build. I was going to just run somewhere in the 8:1 range compression but was advised against it, so decked the head to get to 9:1.

Did a compression test and got 170-165 PSI across all 6

Cam settings are. Inlet 121deg- Exhaust 113deg

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

    • Might also needs a stronger actuator with the right preloading. With older 2019 built bush G3 units, BB upgrade or 21U housing down size makes a pretty decent gain in response as well. 
    • Hey lads  so im finally putting together my rb30 forged bottom end and ran into an issue. I measured my main bearing clearance with arp main studs torqued to 60 ft-lbs using ACL H series STD size bearings and standard, un-ground crank shaft journals and got an oil clearance reading of about 1.3 thou measuring straight up and down and about 2.8 thou measuring at a 45 degree angle (just above and below the parting line). My machine shop said they measured the main tunnel and it was all within spec (they didnt say the actual measurement) and to go with a standard size bearing, which i have done and the clearance is too tight, I'm guessing because of the extra clamping force from the arp studs distorting the main tunnel. I was wanting to run about 2.5 thou main bearing clearance.  My questions are: 1. could i just use the HX extra 1 thou clearance ACL bearings? that would fix my straight up and down clearance making it about 2.3 thou, but then would the side to side clearance be too big at around 3.8 thou? 2. what actually is the recommended main bearing clearance for measuring near the parting line / side to side. i know its supposed to be bigger as the bearing has some eccentricity built into it but how much more clearance should there be compared to the straight up and down measurement? at the moment there is about 1.5thou difference, is that acceptable or should it be less? 3. If i took the engine block + girdle back to the machine shop and got them to line bore the main tunnel (like i told them to do the first time, but they said it didnt need it) what bearing size would i buy? the STD size bearing shells already slide in fairly easily with no real resistance, some even falling out if i tip the girdle up-side-down. If im taking material out of the main tunnel would i need a bearing with extra material on the back side to make up for it? this is probably confusing af to read so if something doesn't make sense let me know and ill try explaining in a different way. My machine shop doesn't come back from christmas break until mid January, hence why i'm asking these questions here. TIA for any help or info 
    • I bought the model back in Japan in Feb. I realised I could never build it, looked around for people who could build it, turns out there's some very skilled people out there that will make copies of 1:1 cars or near enough. I'm not really a photo guy... but people were dragging me in a group chat for the choice of bumper as someone else saw the car before it was finished as they are also a customer of that shop. I took the photo in the above post because I was pretty confident that the lip would work wonders for it. Here's some more in-progress and almost-done pics. It gives a good enough idea as to what the rear looks like!   I have also booked in a track day at the end of January. Lets all hope that is nothing but pure fun and games. If it's not pure fun and games, well, I've already got half an engine spare in the cupboard 
    • Well, do ya, punk? Seriously though, let's fu<king go! The colour and kit looks amazing on the car. Do you have any shots from the rear? I don't quite follow how the model came around. You bought the white kit and he modified it to match your car? Looks nuts either way!
    • So my car is finally back from paint! This took an absolutely insane amount of work and should get it's own build thread - but I didn't build it. It was completed by Troy @ https://scalekustoms.com.au/ I originally bought the AOSHIMA URAS Type R kit while I was in Japan, it's supposed to look like this when assembled: Now, I thought that was cool enough until I opened the box with Dismay, as there's no way I could possibly have completed it. The thing is 1/24 and has details down to the steering wheel horn button, which is a 2mm diameter sticker. I originally wondered if someone could make it at all, as is - But then things got a little carried away. It's worth noting that the model does not have an openable bonne, let alone engine bay, OR an openable boot. - Troy has worked wonders with 3D printer and presumably better eyes than I will ever have. My photos suck, so I will post up some of his in-progress ones he sent to me during the way. Unsuprisingly, he is very detailed. A lot of these are out of order. But he: 1) Made a LS engine and an engine bay appear out of thin air 2) Made the bonnet removable 3) Printed the rims I will buy in the future (or any rim you want) 4) Printed and added the wing that is going on 5) Tinted my back windows as this is what my car has IRL (privacy glass) 6) Added a licence plate. 7) Somehow did the interior 8) 3D Printed my actual seats 9) Made the exhaust under the car connect even though this is likely invisible. 10) Created a boot with my fking battery box, power steering reservoir, subwoofer and toolboxes back there. To say it's insane is an understatement. And I f**ked it all up because when I was re-mounting the wing (it broke in transit) I spilled glue everywhere and ripped paint up and Gregged the rear half of the car. Which about makes sense. Also, this arrived on the same day. Quite the change from: I spent 16 hours per day over the next 3 days pre-christmas putting the interior back together, mounting lip, fixing various bodykit problems with window mouldings, etc. and servicing, rebuilding my 370z brakes to go on the car 'soon', messing with heights to check clearances for new wheels, etc. I also had a foray into mounting wiper-mounted washer jets which was an absolute disaster. The bodyshop has welded (and painted) over the stock jet locations for reasons unknown to everybody (i.e they forgot) I also wanted to wire in the oil pressure sensor on Christmas Eve which was a BAD IDEA. You do not know terror like pulling your ECU apart, pinning in half-fitting pins that aren't the right ones, but trying anyway because it's Christmas eve, putting your ECU back together and having a no-start condition with a fuel pump not priming. Then you undo all your work and the fuel pump still doesn't prime. So after all that terror and horror and pain and tedious disassembly, the issue was the relay in the boot which seems to have died/stuck when I was turning the car off and on about 700 times testing shitty washer jets. I also re-wired the fuel pump power plug which fell apart in my hands. I am very happy I had 3 extra pre-made ones from a few posts/last Christmas's breakdown. https://bluewireautomotive.com/products/10-x-pcm-ecm-ecu-terminals I have put an order for these in, so I can actually add the pins to the ECU properly. The commodore ECU does not have the pins for Oil Pressure via ODB2. However the ECU can support it if you create the pins and wire them in. So for round two, and somehow attempting to route that into the engine bay through my impossible engine bay grommet is a fight for another day. It's 40C in Melbourne tomorrow, I am half tempted to drive the car with the aircon on to deliver presents to my partner's family and see if it helps with the overheating-on-40C-days-in-traffic-with-aircon-on-only issue that the vents were intended to solve. Do I feel lucky?
×
×
  • Create New...