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New Motor Making No Power

Huzqld

By Huzqld,
in Engines & Forced Induction

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Huzqld Enthusiast

Huzqld

Posted
Posted

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

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Shoota_77 Veteran

Shoota_77

Posted
Posted

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!

Huzqld Enthusiast

Huzqld

Posted
  • Author
Posted

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

Huzqld Enthusiast

Huzqld

Posted
  • Author
Posted

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?

GTRPSI Mentor

GTRPSI

Posted
Posted

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......

Huzqld Enthusiast

Huzqld

Posted
  • Author
Posted (edited)

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
Huzqld Enthusiast

Huzqld

Posted
  • Author
Posted

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

KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted

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.

Huzqld Enthusiast

Huzqld

Posted
  • Author
Posted

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

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