Nistune Forums

Guys I'm completely at a loss here.

I rebuilt my RB26/30 due to spun bearings. Put it all back with stock components. While apart I changed/did the following:

-New ACL big end and mains
-Had the injectors cleaned and tested
-Cleaned the head with new seals / lightly lapped the valves
-New plenum gaskets
-Greddy adjustable cam gears in the stock position

I think that's it. This thing made north of 400 whp when it ran. It feels like it's making about half of that now. It idles fine and feels normal at light and part throttle. It builds boost normally but it is VERY sluggish and feels bogged down when in boost.

Things I've ruled out:
-Timing, 15* BTDC
-Knock, it is not accessing the knock maps.
-Cam angles, the dots are slightly misaligned (half a tooth or so) but this is only from me slacking the belt off as I had it too tight (damn RB30 conversions). It's been this way the last time it ran well.
-MAF voltage appears to be normal in nistune, however I haven't cleaned it this season.

In nistune, when comparing old logs, TP (load) ramped up exponentially when boost was built. Now it just goes up linearly and to a max of about 30-40% of what it was before. I seriously have no idea.

I can liken it to the difference in power when I changed from a terribly designed intercooler to a great one, except this is the reverse. Which is why I almost feel the next step is to check for rags in my pipes although I never put them in in the first place.

Anyone else have any ideas before I start to go down a rabbit hole?

Thanks.

have you tested for vacuum/boost leaks ?

Have you checked the turbo is OK?

I'm certain it's fine. It's building boost fast and holding 15 psi.

Guys I cannot figure this out. Cleaned the MAF, checked for unusual boost leaks. Nothing. It builds boost and power ramps up till about 3500 or so, feels like its gonna go like stink and then boom power just hits a wall. It's also quite dangerous because load isn't going to where it's supposed to so AFRs are in the 13 range at full boost. Soon I'll be forced to scale the TP until I figure this out. . Very frustrating.

Gonna rip the bumper off and tear the IC pipes apart in a last ditch effort to hopefully find a blockage. Short of that, I'm open to suggestions.

Did You put new piston rings? And brake engine properly? What compression and engine leak test result are?

I reused them. I only replaced the bearings. I suppose I can do a comp test but the symptoms are not indicative of low compression. This is the 3rd time I've reused the rings. Every other time compression has been 150 across the board.

ST240 wrote:It's also quite dangerous because load isn't going to where it's supposed to so AFRs are in the 13 range at full boost.

if the tune is good, it shouldnt be anyway. Check fuel pres on the load, fuel filter, fuel pump. Maybe you have problems with fueling.

unex wrote:

ST240 wrote:It's also quite dangerous because load isn't going to where it's supposed to so AFRs are in the 13 range at full boost.

if the tune is good, it shouldnt be anyway. Check fuel pres on the load, fuel filter, fuel pump. Maybe you have problems with fueling.

I don't understand what you mean. If I scale TP back down to a max of say 70 (accessing last column) from 120 my AFRs make it into the 11s. However you are not comparing apples to apples. The load and therefore one can only assume power, if we're talking about the same engine, has dropped. This whole issue screams air restriction somewhere. Checking the IC pipes tomorrow.

oh, sorry, I wanted to say "it shouldnt be that way, anyway". Because, I think, even if everything would be ok with your engine, you could access these cells with the same boost at least for a short time. I just wanted to say, if this does not have anything with fueling, maybe your these cells was left too lean, but you never saw that. Of course its not related with your problem.
In that case I would start checking timing belt, cams, and ignition.

what technique have you been using to check TDC when doing the cam gears?

if you use the Pulley timing mark, that could be your problem.

That is the "method" I was using lol. Not to mention that to get the dots on the cam gears to line up the belt has to be horribly tight (RB26/30 conversion). So I've slacked it off and the exhaust cam is out by about half a tooth. Think that could do it? I'm thinking that may be the next culprit. I'm going to get a mag base w/ dial gauge and degree wheel and do it right.

That's wrong, don't line it up with the belt tension or you'll smash a valve or piston when belt breaks.

The belt tension is the belt tension get it right using preset spring and lock it up. 20kg/on the spec sheet. must not exceed this.
Cam timing is cam timing, the two aren't related apart from the dayco belt that joins them.

Do you have a dial indicator gauge? if not, it's hard to get the cams right, maybe close but not right.
same goes for if you deck the block or head with a rb26 or rb20, 25 what ever it is, need adjustable gears.

One of your cams sounds like it is a tooth out, probably exhaust cam.
There is a step count between cams for when the piston is at TDC don't go off timing pulley or harmonic balancer mark just yet until its confirmed as correct reference

First, you dial the engine up at TDC using the piston, (as it spun a bearing previously can I assume the engine locked up?)
check if harmonic balancer timing mark is sitting on TDC timing mark on lower belt cover.
if it is TDC and marks line up then you can assume the balancer is a correct reference.

The cam/crank marks will be off using the belt step count because of the 152 -141 = 11 extra teeth rb30/26 and the non-standard location of the idlers, you have to use a dial indicator to align the cams @ .050 lift. there really is no other way. Afterwards you can mark the block and head with alignment dots for future belt replacements.

sorry for the late edit, I though it updated last night.

Thanks for the info. Unfortunately with RB30 conversions the belt tension is not the belt tension due to the fact that you have two tensioners :/. What do you mean by they will be 10 belt steps apart from each other?

Your symptoms sound like a classic case of retarded IGN timing to me. Yes, I know you checked it but I'd be re-checking. The acid test would be run run it up and try adding some timing in NIStune. If your base IGN timing is right then you'll run into detonation pretty quickly. If you find that you can add lots of timing then your power will improve before detonation starts - and you'll have found your problem.

Just my 2c worth!
PL