Questions for Those With Low Compression Piston - Help!

[NSXROC]

I am hoping to get some feedback in order to figure out what the problems might be with my car. I have a new engine with low compression pistons. The car is not performing well. The problems that I am currently experiencing:

My current setup:
NSX 3.0 rebuilt engine
JE low compression pistons
6 speed tranny
Comptech Autorotor supercharger, low boost
HKS exhaust
Topspeed headers
K&N Filer
The injectors have been checked and they are fine

The problems:

The car hesitates at low speed and low RPM (2000-3000). It also hesitates during acceleration in 2nd gear. If I step on the gas harder, the hesitation goes away. I feel that I have to step on the gas pedal hard to make the car go.

There’s surging at low RPM (2000-3000). For example, when I cruise on the highway in 5th or 6th gear at 60 mph, I feel the car pulling back and forth. I experience similar situation when driving on local streets in 4th gear at 40 mph.

Questions:

Does the car drive different when you have low compression pistons?

For those of you with low compression pistons, could you please describe the difference?

What are the problems with my car?

I appreciate any feedback that you have. Thanks

 

[jmp]

Re: Questions for Those With Low Compression Piston - Help!!!

What are you doing re engine management (oem ECU w/ comptech mod, piggyback, AEM, other) and fuel delivery (stock injectors or other, stock fuel pump or walbro)?

 

[ffffanman]

Re: Questions for Those With Low Compression Piston - Help!!!

What do you mean by low compression?
What is your spec?
Trev

 

[NSXROC]

Re: Questions for Those With Low Compression Piston - Help!!!

What are you doing re engine management (oem ECU w/ comptech mod, piggyback, AEM, other) and fuel delivery (stock injectors or other, stock fuel pump or walbro)?

I use OEM ECU, everything is stock.

 

[J-RnsxT]

Re: Questions for Those With Low Compression Piston - Help!!!

Running low compression pistons on stock ecu will run erradic. You should have it retune with an EMS and should run better.

Its good to see you back on the game..:biggrin:

 

[Elite]

Re: Questions for Those With Low Compression Piston - Help!!!

Low compression pistons "drive" the same as higher compression.. relatively. Meaning your symptoms are not from low compression pistons, but from the need of a tune. When you say you are on the stock ecu, I'm assuming you mean, stock ecu, plus the Comptech stuff. Which wasn't designed/tuned for low compression. You need to pick your choice of tuning tools and get the car tuned, you will be happy with the driveability and power after you do so. You may want to look into the AEM F/IC unit.

 

[ffffanman]

Re: Questions for Those With Low Compression Piston - Help!!!

Who built your engine?
What pistons where purchase and what are the specs?
What is your compression?
Trev

 

[jmp]

Re: Questions for Those With Low Compression Piston - Help!!!

That is where I was going with my questions. Elite is right on the money. The CTSC has an adjustable fuel regulator which should be adjusted while on a dyno to see where your A/F's are and if they can be gotten in-line. If that is not enough you could try the AEM piggyback setup. Get on a dyno and go from there.

 

[Swift]

Re: Questions for Those With Low Compression Piston - Help!!!

This is some scary stuff...damn. Driving a new engine with SC totally untuned for the new engine..wow!

 

[01blacks4]

Re: Questions for Those With Low Compression Piston - Help!!!

its not THAT scary,
the rising rate will rise, dumping more fuel, the SC will heat up the intake air temp, causing the factory ECU to pull timing.....it just will not run as well as it could, but i doubt if he will see any detonation issues

 

[jmp]

Re: Questions for Those With Low Compression Piston - Help!!!

Odds are you are right that he won't experience detonation, ... but if that unlikely situation arises...

No peace of mind. I would run out and get on the dyno.

 

[nuccaJB]

Re: Questions for Those With Low Compression Piston - Help!!!

As long as he is not getting into the boost while breaking in the motor he should have no problem. You need to have a tuner and a wideband so you can see what it is doing. The difference in the compression should not make a huge difference. You actually want to run the motor a little lean and out of the boost while breaking it in.

 

[David]

Re: Questions for Those With Low Compression Piston - Help!!!

1) The pistons are not the problem.

2) To find the real problem, put the car on a dyno (preferred) or drive it (if no other choice) with a wide-band on it so you can see if it is a fuel issue or a timing issue.

If it is a minor fuel issue, you can use the adjustments in the FPR to get the fuel increase trimmed out as close as you can. I have used "piggy-back" systems like the Neo on a couple of blower cars and they work great, since the fuel trim rarely needs to be altered more than 10-15% - much better and more accurate than monkeying around with the FPR. On some cars you have to periodically reset the ECU, as may try to return to factory setting over time, but its easy to do.

For a timing issue, you will have to use something more sophisticated like the AEM piggy-back.

Its also possible you may just have an ignition issue not related to the blower, such as a bad coil, bad plug, vacuum leak, etc. Take a quick look at the ignition system to rule out something basic like that. Then check your air/fuel ratio with a wide-band.

Best of luck with your project.

 

[ffffanman]

Re: Questions for Those With Low Compression Piston - Help!!!

Did you change your plugs up to run cooler, so one number larger!
Trev

 

[nuccaJB]

Re: Questions for Those With Low Compression Piston - Help!!!

Like David said you may want to pull a few plugs and see how they look. Make sure they are not fowled or too light looking. Also have you changed the gap on your plugs to account for the boost?

 

[NSXROC]

Re: Questions for Those With Low Compression Piston - Help!!!

First of all, I like to thank you all for providing me with all the valuable information. I am slowly learning everything about engine and tuning.

Running low compression pistons on stock ecu will run erradic. You should have it retune with an EMS and should run better.

Low compression pistons "drive" the same as higher compression.. relatively. Meaning your symptoms are not from low compression pistons, but from the need of a tune. When you say you are on the stock ecu, I'm assuming you mean, stock ecu, plus the Comptech stuff. Which wasn't designed/tuned for low compression. You need to pick your choice of tuning tools and get the car tuned, you will be happy with the driveability and power after you do so. You may want to look into the AEM F/IC unit.

Is there anyone out there running low compression pistons with stock ECU and not experience any issues? Is a stand alone engine management system an absolute must to solve the problems that I have? Should I look into AEM F/IC unit or AEM EMS?

Who built your engine?
What pistons where purchase and what are the specs?
What is your compression?
Trev

I bought the rebuilt engine from a Prime member. The engine was rebuilt by RacerX-21. The engine came with JE pistons with 9.5:1 compression ratio.

As long as he is not getting into the boost while breaking in the motor he should have no problem. You need to have a tuner and a wideband so you can see what it is doing. The difference in the compression should not make a huge difference. You actually want to run the motor a little lean and out of the boost while breaking it in.

I am in the process of breaking in the engine (first 1,000 miles). This is one of the reasons why I have not obtain a dyno. I did get a wideband AF gauge installed and a data logger installed. I will try to retrieve some data this weekend for analysis.

1) The pistons are not the problem.
Its also possible you may just have an ignition issue not related to the blower, such as a bad coil, bad plug, vacuum leak, etc. Take a quick look at the ignition system to rule out something basic like that. Then check your air/fuel ratio with a wide-band.
Best of luck with your project.

My mechanic did find an ignition issue. One of the plugs was bad. Since replacement of the plug, the car has been driving better, but still with the symptoms I had stated in the earlier post.

My mechanic Zahntech will be available later this week. I will talk to him about what all of you have suggested and continue the journey of getting my car back to normal. It’s been more than six months since I first ran into the engine problem,

http://www.nsxprime.com/forums/showthread.php?t=95448

I can’t wait to get everything finished.

 

[Elite]

Re: Questions for Those With Low Compression Piston - Help!!!

Considering you are running the CTSC, you are technically not representing your fuel setup entirely correctly. You should have the fuel adjusting stuff that comes with the CTSC installed, thus when you say you are running the stock ECU(while technically correct), doesn't give the full picture.

In any case, yes, people run the stock ecu, with the CTSC stuff on low compression pistons. Once again, the low compression pistons are not your issue.

For break in miles, you should still have a decent base map in general. In your case because your car is running rough, I would have definitely made at least a pull(maybe not even a full pull depending on what the results were) on a dyno to see what your a/f curve looks like. Then made any changes that may have been needed.

With a good tuner(and maybe some help from Devin), you should be good with either AEM product. However, what year is your car? I know the F/IC works better with the '95 and later cars(OBD2).

 

[David]

Re: Questions for Those With Low Compression Piston - Help!!!

Again, if it is a fuel issue and not a timing issue, something simple like a Neo will work fine. If you can get the AEM piggy-back installed and tuned for about the same money, then it is a better option, but is generally more expensive.

 

[NSXROC]

Re: Questions for Those With Low Compression Piston - Help!!!

Considering you are running the CTSC, you are technically not representing your fuel setup entirely correctly. You should have the fuel adjusting stuff that comes with the CTSC installed, thus when you say you are running the stock ECU(while technically correct), doesn't give the full picture.

In any case, yes, people run the stock ecu, with the CTSC stuff on low compression pistons. Once again, the low compression pistons are not your issue.

For break in miles, you should still have a decent base map in general. In your case because your car is running rough, I would have definitely made at least a pull(maybe not even a full pull depending on what the results were) on a dyno to see what your a/f curve looks like. Then made any changes that may have been needed.

With a good tuner(and maybe some help from Devin), you should be good with either AEM product. However, what year is your car? I know the F/IC works better with the '95 and later cars(OBD2).

My car is a 92. I will talk to my tech and discuss about the AEM products. The problem is, we really haven't figure out what exactly is the problem yet. It could be timing or fuel or ignition.

 

[nuccaJB]

Re: Questions for Those With Low Compression Piston - Help!!!

Honestly, if you are running stock injectors and no fuel tuner, if you stay out of the boost and run the car in the lower RPM ranges to break it in you should be fine. Let the stock ecu think there is no blower and drive it like an Accord until you seat the rings properly. Once that is done the motor should be able to handle a bunch more abuse without as many worries. Then you can mess with tuning and timing.

 

[NSXROC]

Re: Questions for Those With Low Compression Piston - Help!!!

Honestly, if you are running stock injectors and no fuel tuner, if you stay out of the boost and run the car in the lower RPM ranges to break it in you should be fine. Let the stock ecu think there is no blower and drive it like an Accord until you seat the rings properly. Once that is done the motor should be able to handle a bunch more abuse without as many worries. Then you can mess with tuning and timing.

Thanks for the note. I have been doing just this; staying out of boost. I tried to drive the car like there's not supercharger, and that's why i was able to distinguish the difference in the performance from the last engine. I was able to identify the problmes that I am having.

 

[David]

Re: Questions for Those With Low Compression Piston - Help!!!

Let the stock ecu think there is no blower and drive it like an Accord until you seat the rings properly.

If the rings have not seated properly by now, they are not going to.

What is it about the symptoms that makes you think its the rings? Unless they are complete junk, they should not affect how smoothly the motor runs, just how much power it makes and how much smoke it pukes out.

 

[nuccaJB]

Re: Questions for Those With Low Compression Piston - Help!!!

I was not totally sure how many miles he had on it yet. I was talking from the standpoint of zero mile break in.

 

[NSXROC]

Re: Questions for Those With Low Compression Piston - Help!!!

For break in miles, you should still have a decent base map in general.

Could someone please send me a base map?

 

[ffffanman]

Re: Questions for Those With Low Compression Piston - Help!!!

Correct me if I am wrong.
Maps are used when you have an aftermarket add on computor system which you add onto you car to manually set fuel pressures, spark, timing, injector pulse and all that stuff.
If you are running a stock system, then you have what you need.
Nothing to load or invent or tune.
So, if you bought an aem system and knew someone who had the same exact engine and accessories, then you could get their map and load it into your aem and tune your car from there. Each car is going to be different and location and temperature will cause different settings to be had.
Hope I'm right, I hate to be wrong.
Have you not had your car to your mechanic?
He should be able to solve this.
Did you install a new fuel pump, filter, fuel pressure gauge to see your fuel pressure? Hows the plugs.
Trev