Rb27 Tunning Problems, And Issues.

[Shockster0429]

Okay guys, heres the deal, yesterday was tuning day for me and my freshly built rb25/26 hybrid. Well we had serious problems getting down there non car related it was a long day...

I'll cut to the chase, car started out AMAZING, 500 rpm increment pulls with the microtech lt12s slowly but surely adding fuel with 14psi through the gt35r. We were making 300ftlbs at 3000 rpm.... We made 387rwhp and 345 ft lbs at 5500 rpm loads at 14 psi. Never got to make a full sweep yet... At that point we were running out of fuel. The nismo FPR cant handle the dual pumps or something, and is not raising its pressure properly. So I ran down to Jegs and got an aeromotive. Hooked it in cant get the base FP down any lower than 55-56 with vac, it just wont go any lower... So tuning was compensated for that.

Now heres were it gets weird. Our numbers started falling off, yet the motor sounds extremely strong, no different then it was before. So after a few ramps at 4000 we are only at 200 is ft lbs now about a 1/3rd or a bit less than before... we decided to check the plugs. They were fine, A/F's are 11.1-11.3 the entire time, with little timing seeing around 16-17 degrees the coming back down as boost was added which was now around 16-18 psi (we didn't touch the MBC). Super super conservative tune, but no power now? So we do a compression check and leak down test cylinders are all 150+ish, leak down test is 95-100% across the board.....

We are coming to the conclusion the valves are leaking under pressure. Or they just arnt opening enough. Some of my lifers were squishy.. right after we shut it off and some are rock hard how they should be and others were soft. Theres no lifter tap however. You guys think the lifters are preventing my valves from getting proper lift thus the drop in HP? Or it could be the springs being weak and leaking off? I'm only at 8.5mm lift and 264in-268ex duration...

Anyone ever seen a similar problem such as this? They car is drivable, it sounds like a ****ing animal, holy **** the added displacement and modifications makes it sound so scary.... I've got footage and **** I need a buddy to send it to me so I can show some of the pulls. But right now shes a total dog. It idles great, No boost leaks nothing of that, we checked everything....

Also the injectors are re flowed to 740cc's they are from a reputable company who has been proven and known for their injectors.

lets hear some other opinions on the matter... I'd really like to know what the deal is. I'm leaning towards a valve related issue.

[crack]

what pressure were you running with the nismo fpr? how was the tune "compensated"? wouldn't you need a retune for a different base pressure.

how were the injectors re-flowed? i know you said they were done by a reputable company and thats great if you trust them, but i was of the assumption that they flow what they flow from the factory. correct me if i'm wrong.

[-_-StRyDeR-_-]

nah you can get injectors highflowed. but some companys dont like this idea, they say it doesnt give as good of a spray pattern as a injector already built for XXX about of CC.

personally i havnt had personal dealings with highflow injectors...so i cant comment if they are good or bad.

[Sydneykid]

My 20 cents;

Compression and leak down tests would show up leaking valves due to insufficient valve spring seat pressure. Although it won't show up oil pressure leak down of the followers. But leaking followers usually means rattling on start up, which you report isn't there. So I doubt it's a valve issue.

Did you check (with a timing light) that the ignition timing actually agrees with what you have mapped?

Have you tried dropping the exhaust? We had a flexible joint fail on a car on the dyno recently and it blocked the exhaust flow. All the numbers (A/F ratio, knock etc) looked OK, but it just dropped power by 25%. I tried the usual drop the exhaust at the first joint and it picked up the lost power straight away, some examination with a torch showed up the restricted exhaust flow.

You may also want to check the inlet pipework for a similar collapsing problem, although that generally shows up in a loss of boost.

Cheers

Gary

[Shockster0429]

My 20 cents;

Compression and leak down tests would show up leaking valves due to insufficient valve spring seat pressure. Although it won't show up oil pressure leak down of the followers. But leaking followers usually means rattling on start up, which you report isn't there. So I doubt it's a valve issue.

Did you check (with a timing light) that the ignition timing actually agrees with what you have mapped?

Have you tried dropping the exhaust? We had a flexible joint fail on a car on the dyno recently and it blocked the exhaust flow. All the numbers (A/F ratio, knock etc) looked OK, but it just dropped power by 25%. I tried the usual drop the exhaust at the first joint and it picked up the lost power straight away, some examination with a torch showed up the restricted exhaust flow.

You may also want to check the inlet pipework for a similar collapsing problem, although that generally shows up in a loss of boost.

Cheers

Gary

Gary,

I see what your saying with the valves being shown leaking in a leakdown/compression check. However wouldnt they just get pushed up and closed from the cylinder pressure and not leak? I'm thinking when the boost is coming on. On the intake side port when the valves should be closed the boost pressure in the plenum runners is forcing them to open due to weak springs?

I have a reason the springs could be possible weak. When I rebuilt a few of the hydro lifters that were squishy before reinstalling them. However I re-installed the bleeder valve upside down, causing the lifter to be to tall and incompressible. This made the valves leak. So I had to remove them all and install lifters I had laying around from another motor. But the motor was cranked with these lifters installed wrong a hundred or so times... now I'm not sure what type of lift I would have been putting on these springs but I feel like I might have fatigued them. It seems so strange that the power we were making went away after our best pull when the numbers were starting to get up there. Possibly just finishing my springs off?

After we ran into this hp issue the boost was actually higher than it was before even though the MBC wasn't touched. (from 14 psi to 17-18psi)

Also 3000rpm had the same hp/tq basically as 4500rpm.... There were no gains like there was before (172hp/300ftlbs@3000 to 282hp/330ftlbs@4500)

I can check my exhaust, its just pretty much a straight pipe. 2 mufflers and one connection. Its possible the gasket for that broke and is hanging in the pipe? I'm doubting it but I know you are saying. I've seen a bad cat absolutely turn a truck into a dog due to being clogged just killing the power.

thanks, any more ideas insight would be greatly appreciated.

-Cory

[Shockster0429]

****UPDATE!!****

I found a big boost leak after I was working on my car... fixed it took the car out for a drive and it felt a LOT better however...

Well it appears as if my ***-Dyno is off by over 50%. We got back on the dyno today, only to see my issue did not go away. The boost leak fixed spool times and response, but didn't fix ANY numbers...

We are making 200ft-lbs at 2000 and at 4000 with 14 psi. Fuel pressure is all straightened out now. Holding 45psi vac off at idle. Didn't change at all day. The car just has no balls. Dont get me wrong, its not slow, but its no where near what it should be.

Everything is basically perfect. Air intake temps, water temps, a/f ratio (11.1-11.3 at WOT), timing is spot on as well, plugs are great, good equal burn pattern and no missing..., muffler is not clogged by any means.

I drove down with my buddy who owns and EVO 8, my car is basically as fast as his bolt on EVO.... to give you an idea, but its not making numbers of what it should be.

We really are thinking that its something with the valves/lifters/springs.

Springs possibly weak and when boosting begins they start leaking at the intake ports that are supposed to be closed. (so the back of the closed valve stem is being pressed down by the 14-15 psi in the plenum)... even if it is just a little bit, its enough...

Or I have some bad lifters, but I'm doubting that since we have no lifter tick. Even this morning I turned my car on it was 32 degrees outside and no tick....

opinions would be greatly appreciated. As nice as it is to drive my car now, I feel like I have wasted xx,xxx dollars just to make it as fast as it was before...

The head I'm using is not my old head but rather someone elses...so I'll I know about it is that the valves hold cylinder pressure... but I don't know about boost...

I'd really appreciate ideas, I'm getting very stumped...

-Cory

[Adriano]

Are they stock valve springs, if so upgrade them, it can be done without pulling the head off.

[Shockster0429]

Are they stock valve springs, if so upgrade them, it can be done without pulling the head off.

Yeah they are stockers, tomei valve springs? Can they be used with stock Hyrdo lifters w/o over powering them?

[NYTSKY]

The Tomei type A springs will be good.Up to 9.0mm lift and will rev to 8500rpm.

Im not saying this will fix your problem,couldnt hurt though considering you will eventually be putting big power through it.

[Shockster0429]

The Tomei type A springs will be good.Up to 9.0mm lift and will rev to 8500rpm.

Im not saying this will fix your problem,couldnt hurt though considering you will eventually be putting big power through it.

Yeah it is a good idea, how do you know which washers to pick?

http://www.tomei-p.co.jp/_2003web-catalogue/efr_index.html

[NYTSKY]

Hmmm good question. I think a set will come with the springs(cant be sure until mine arrive this week)

[Shockster0429]

Pretty sure I found my problem!!

owned times infinity.

thank you boys for all your help! Its much appreciated!

[Swiper the Fox]

far too much retard on that exhaust cam...hehe

who forgot to check the bolts for tension??

[Guilt-Toy]

they are not bolts, they are allen keys that are weak as piss, you cant do them up without stripping them.

I have the exact same cam gear and i replaced 4 of them with 10mm bolts, which so fit in the grooves.

I am going to pull my cover off and check mine to make sure they have not moved.

its a cheap cam gear so this is what you get i spose.

[NYTSKY]

But doesnt it feel good to know that you have found the problem!?

FYI: My Tomei valve springs arrived and they did not have the washers with them.

[rb26s13]

The Tomei type A springs will be good.Up to 9.0mm lift and will rev to 8500rpm.

Im not saying this will fix your problem,couldnt hurt though considering you will eventually be putting big power through it.

the type A's are rated up to 10.85mm lift and 8500rpm rpm

[Shockster0429]

But doesnt it feel good to know that you have found the problem!?

FYI: My Tomei valve springs arrived and they did not have the washers with them.

It feels amazing.

thanks for the tip Guilt Toy, I'll go look for some new hardware to tighten this gear better.

I cant wait to get back on the dyno to lay down so good numbers hopefully.

This car makes me wise and wiser with every issue.

[NYTSKY]

the type A's are rated up to 10.85mm lift and 8500rpm rpm

Im thinking about my ones(RB25)

Yeh 26s are 10.85mm.

[rb26s13]

Im thinking about my ones(RB25)

Yeh 26s are 10.85mm.

ahh yep.. i saw rb27 and assume it was 26 head.. however another quick read thru im unsure?

[R31Nismoid]

they are not bolts, they are allen keys that are weak as piss, you cant do them up without stripping them.

I have the exact same cam gear and i replaced 4 of them with 10mm bolts, which so fit in the grooves.

I am going to pull my cover off and check mine to make sure they have not moved.

its a cheap cam gear so this is what you get i spose.

Hence people should just mod the factory cam gear and make that adjustable

Never fails, cheap as chips