I'm an lurker here, but I'm looking for all the help I can get. A trip to the dyno yesterday revealed some very low numbers for the given setup.

JDM B18C (GSR)
- Blox B's
- stock pistons
- JDM ITR header
- 2.5" Magnaflow spun cat
- RSR Ex-Mag
- 3" short ram
- Neptune RTP

I was on a Dyno Dynamics at ProFunction Automotive in Burr Ridge, IL.

The car didn't make over 90 ft/lb of torque, and made less than 140 WHP. Obviously this is truly disappointing.

We were baffled at the output because the car drives and sounds great. There are no leaks from the motor, and it doesn't smoke or burn oil.

After trying to find some power through tuning, with little improvement, we threw the compression tester on.

All cylinders pressures were even at 118 psi. Super low for a JDM GSR, so we busted out the leakdown tester.

We only checked cylinder 1 because of the even readings from the compression test. The leakdown was less than 10%. Even if there was 10% leakage, it doesn't account for the missing compression (IMHO).

So now I'm really looking for all suggestions that people may have.

Graph (sorry it's a little dark):



Video:

http://www.youtube.com/watch?v=f2wPfRkx9vU

 

Someone changed the pistons before you got the engine...

 

yeah im thinking the engine was built for boost at some point with lower compression pistons.....or maybe a thicker head gasket(or both).

and yes 10% leakage is a bit high.........as painful as it is......id say you need to pull the pistons out and head off, re-hone, new rings, and at least stock pistons........but since you are in there you might as well get a good set of higher compression pistons. maybe 11:1

 

I personally know the previous owner. He owned the car for 7 years, used it strictly as a weekend autocross car. He provided me with every receipt possible and I trust him 100%.

Tearing the motor down is my last resort, but of course my first thoughts were that the pistons had been replaced. After scoping the pistons through the spark plug holes, they do appear to be cast pistons, so they are OEM. Whether or not they are LS/B16/GSR cannot be determined unless the head is pulled.

As a mechanical engineering student, I can't even think of any other reasons for such low compression other than piston size/cylinder leakage. I'm going out of my mind!

 

how was the compression test performed, was the fuel system disabled? Also, it's always a good idea to do all four cylinders when performing a leak down or compression test.

 

Yes, the fuel system was disabled. The tester was a digital Matco, so I don't doubt the integrity of the tool.

I know its not good practice to "assume" that all the cylinders were the same as cyl. 1, but we were tight on time.

As of right now, I'm just getting my commute on. I'm just going to drive it until I can go 2 liter. Thanks for all the replies.

 

Updated with graph and video.

Some insight from the tuner:

#1. Compression test maxxed out at 119 and went as low as 113. Not enough of a differential to cause any alert.

#2. Leakdown test proved to be within the 10% range, which is good. As a matter of fact it leaked out to about 6-7 percent. Mint.

#3. Usually you can tell the compression's strength and output from the first number read on the first stroke of your compressions test. For example: A JDM ITR B will usually stroke about 120-140 on its first hit. And jump up to the 200 range from the following hits. Your engine only gave me about 60-70 on the initial stroke and only provided 10-15psi hits from there on out.

#4. No leaking, No burning, No excessive(if any)crankcase pressure. That combined with the leakdown figures allows the assumption of good rings.

#5. All relevance of your valve job's quality would show in a leakdown test. It passed with flying colors.

At this point it would warrant a teardown to see what the deal is. When i test drove the car it did seem like it was very underpowered. Bleeding compression from the cams is a possibility, but not enough in my mind to cause something like this. I almost feel like at this point a smaller cam wont bring back the full life of this motor.

 

camshaft timing?
properly degreed in?

 

Intake is advanced 2 degrees as suggested by Blox.

Head has never been milled, and the timing is dead on.

 

Any chance since you're running a cat that it got clogged or the honeycomb is screwed up in anyway? I know when mine got busted up the power difference was huge.


That compression is weird.. I know i had 205 across the board on a completely stock b17 (9.7:1 stock pistons I believe?)

 

IMO I would get some rs pistons thinner headgasket ITR intake mani mild sized injectors and retune on dyno if you were going to stay 1.8 for a while.........

 

I don't think a clogged cat would produce such low compression numbers.

However, I'm running a 2.5" Magnaflow spun cat. It's not even 3 months old.

Already running a Skunk2 intake manifold as well. Stock injectors should be fine for sub 200 WHP.

 

wow thats a disturbing dyno result... even more disturbing is the compression test results. i just had my gsr dynoed on a dyno dynamics yesterday. the owner said dyno dynamics read lower numbers than dynapacks and dynojets.

my setup was: aem ca, dc4-1, bc spec3+ cams, bloxs s/r, itr pistons(81.5), hi-flo cat
-stock cat-back
-itr ecu w/apexi safc neo
-pulled 176.8whp and 123fttq hopefully i will get the dyno graph uploaded later.

anyways ur compression is whats holding u back. u should pull a lil more than i did ,my stock exhaust was keeping me from hitting 180whp and i think blox Bs are a lil more agressive profile than bc spec3+ cams. sounds like ur best option to really figure out whats going on is to break down ur motor and see whats up with those pistons

 

I'm aware that Dyno Dynamics read lower than Dynojet/Dynapack.

How does posting your setup/numbers help me?

I'm looking for insight on MY specific problem not comparisons to others. Feel free to make your own thread about your setup.

 

with ls pistons compression should be 9:6.1 your compression even still seems lower then that. thats crazy man i have no other ideas then it having diffrent pistons unless it has b16 rods but would it even run like that

 

Yeah, if it had a B16 crank and rods the bastard wouldn't even run.

With those compression readings, it's like the car has sub 9:1 compression. I'm surprised it runs as nicely as it does.

I've pretty much given up all hope of finding a "fix" for the low compression.

My path as of right now is to pick up a B20B from a local shop, and throw the GSR under the microscope.

I will definitely update with my findings .

 

u did a leak down and its fine
ur compression gauge is probaby off
-try checking compression with same gauge on a stock or known healthy car
-does the car feels strong?
-run it against a stock gsr..................
a dyno dynamic is unpredicable just use it as a tool and not for numbers...................

 

A digital Matco is probably one of the best compression testers you could use.

The car does not feel as "strong" as a cammed B18C should. It can't even break the tires loose if you punch it in first gear.

The Quaiffe might have something to do with that though .

And I would have to disagree with the Dyno Dynamics being unpredictable.

 

And for the record, this is not the first setup I've put together.

I chose all these parts because I know they work.

All my builds have been GSR motors w/Blox B's or Skunk2 Stage 2's.

They have all been professionally tuned and assembled by me.

This is the only motor that I did not assemble (besides the cams). Even though I trust the previous owner when he says he did not replace the pistons, I will not know for sure until I pull the head.

As stated before, a teardown is in order and will most likely reveal what is causing the power loss.

 

matco ,snap-on ,mac it doesn t matter a tool is a tool
calibration and user eror may play a big roll

 

go back and see if u dyno the same................
don t be surprise............
if the correction factor is off your numbers will maybe off
call and ask what correction factor they used when u dyno........

dyno dynamic is an adjustable dyno period.........
a dynojet can t change so numbers r more reliable...........

 

If you think a tuner will mess with the correction factor to fudge numbers, I don't wanna go wherever you're going.

What I care about in a dyno is how well it works when tuning! So I agree, I use it solely as a tool, not for the numbers.

But I didn't make the thread because I was disappointed with my numbers. That's not entirely true because I AM disappointed, but it's not the dyno's fault. The numbers are what caused us to find the real issue I need to address, the low compression.

With 118 psi of cylinder pressure, I will read low on ANY dyno. Sorry, but I don't doubt the integrity of the tool, dyno, or my tuner.

The Dyno Dynamics gives much better real world results when tuning, and quicker too. That's reliable in my book.

I'll take an eddy current (loading) dyno over an inertia roller any day.

And yes, I've used both before in the past.

 

I couldn't help but notice you advertise a shop in your sig, so I had to check the credibility.

What's this all about? Is this the same place you work at?

I'm not jumping to any conclusions as it looks like this was over a year ago, so it might be under new management. But why keep the same name?

http://www.fresnobee.com/2009/10/16/...esno-auto.html

http://www.kmj580.com/pages/landing_...364&feedID=806

 

Hahaha ownage, I'll take a $20 bag and 2 hot B18Cs please
Whats up with that Datsun stolen 30+ years ago?

 

here i ll help u out
-there s way more coverage that
-the orignal video of the shop raid has been removed by the news station and they won t release it(they have to cover up)

http://abclocal.go.com/kfsn/story?se...cal&id=7069114

action news 2

http://www.kmph.com/Global/story.asp...enttype=mobile
kmph written news

http://www.fresnobee.com/local/crime/story/1676201.html
fresno bee

http://www.kmj580.com/pages/landing?blockID=81364
radio station kmj

http://abclocal.go.com/kfsn/story?se...cal&id=7069114
action news onlline written paper

http://www.pebhmong.com/forum/index.php?topic=146051.0
hmong forum

http://topics.treehugger.com/article...uel+economy%22
tree huger forum

http://www.localxxl.com/us/local_new...ed-1255746278/
local xx forum

http://www.newstin.com/tag/us/151247291
another forum

http://www.datsuncr.com/
nissan forum

http://www.fcoe.org/index.php?n=7
f something news

http://news.surfwax.com/general-news...chop_shop.html
some news