Acceleration Question

[SrS13]

Im goint to attemp to explain this as clearly as possible, please bare with me:

This is on a 1990 240 with a red top Sr20, HKS FMIC, Walboro Fuel Pump, HKS air filter, 3 inch downpipe, KA exhaust, stock T25 other than that everything else is stock. Spark plugs gaped at .028

Normal driving my car runs perfectno problems, it is when i rev first gear up to 5,000 rpms and quickly shift into 2nd drop the clutch stomp on the throttle my car boggs up and down almost like i was on a mechanical bull.

also like if i were to let of the throttle and then push it down, thats is similar to the effect as well.

Could this be a MAfs problem? or is my exhaust to blame? or am I not shifting correctly? these are the culprits I've come up with.

sorry so long thanks for reviewing :help :help

[nlzmo400r]

sounds like your injectors arent getting enough fuel to the car, check all fuel lines and such, another problem is your stock KA exhaust, def not made for turbo, even a small t25 will generate problems

[Siddhartha]

Also check all vacuum lines, that could be causing a stumble.

[SrS13]

thanks would these be my only problems?? do you guys think the things I mentioned above are messed up as well or do they not have anything to do with my problem?

[SpeedRacer1]

Does it seem like the car bogs and makes a noise?

Or do you floor it, then it speeds up, then all of a sudden slows down, then starts to speed up again, but not at the same speed as before?

Do you have a BOv or are you using the stock recirc valve?

The KA exhaust is the same size as the SR exhaust, however with an exhaust that small, you will not accelerate quickly, in other words, you will probably not be thrown back in your seat much. But I dont think the exhaust is your issue.

How old is the clutch?

[haddixracing]

Sounds typical of incorrect spark timing. Have you checked and reset your cam sensor?

Also, if the turbo bearing are going out the turbo will stumble at the point between VAC and Boost around 0 in-hg.

If your BOV isn't working properly you could also be forcing the turbo to surge on shifts when you lift the throttle suddenly.

[UsedToOwn240SX]

Yeah, I would think it's BOV problem. The bog that you feel maybe as a result of the turbo has to spin back up after being forcefully slowed down by closing of the throttle body. Don't run the car in boost for now if it's the problem. Need more info on your BOV and check the vacuum line going to the BOV too. That line has to be the one from upper right corner of your TB.

[SrS13]

Sounds typical of incorrect spark timing. Have you checked and reset your cam sensor?

how do i reset the cam sensor?

I have a Atm BOV but it makes the swoosh sound inbetween shifts dosent that mean it is working correctly??

as soon as I shift from 1st to 2nd(this on a quick shift) and floor it the car bounces pushes me back and forth as if i were to have let off the throttle then stomp down again. Only i dont do dat my foot is pressing the pedal down all the way. Hope thats a better explanation

thanks for the help so far

[GodzillaFan]

how do i reset the cam sensor?

I have a Atm BOV but it makes the swoosh sound inbetween shifts dosent that mean it is working correctly??

as soon as I shift from 1st to 2nd(this on a quick shift) and floor it the car bounces pushes me back and forth as if i were to have let off the throttle then stomp down again. Only i dont do dat my foot is pressing the pedal down all the way. Hope thats a better explanation

thanks for the help so far

except your motor is not designed to run an ATM BOV... it needs to be recirculated.

[Cyberkreig]

except that you can easily run an ATM bov, many of us do.

I know the problem you are describing.. The car 'bounces' front to back. This can be a sign of drivetrain slack and worn shocks.

[GodzillaFan]

TIGHTEN or recirculate the bov... then report back..i think this is your problem.

[SrS13]

TIGHTEN or recirculate the bov... then report back..i think this is your problem.

what do you mean tighten or recirculate??

[Phax]

...another problem is your stock KA exhaust, def not made for turbo, even a small t25 will generate problems

I have a T25, running through an HKS downpipe into a stock KA exhaust and the car runs great.

[Cyberkreig]

I also ran stock exhaust for a few months with no real problems.. I didnt really notice too much improvment with the N1's either.. *shrug*

[nlzmo400r]

usually to get the full potential of the exhuast, u have to couple it with an intake and headers for best results

[SpeedRacer1]

what do you mean tighten or recirculate??

The SR as with most Nissan engines in stock trim run engine management with a MAFS (Mass Air Flow Sensor). This senses how much air has passed through the intake pipe and adds fuel to the combustion accordingly. When you use a recirculating valve on a turbo car, the air that has been "metered" by the MAFS is recirculated back into the intake system after the MAFS so that it is not metered again. This allows the computer to not get tripped up and add fuel for re-metered air. On an atmospheric blow off valve, the air is not recirculated. This creates an issue when it comes to metered air because the MAFS has metered the air and the BOV has now ejected it during a shift or dropping into neutral. When this occurs, the combustion becomes rich because the ECU sent fuel for air that has just been ejected from the intake. The result is a fireball if you do not have a cat (under certain conditions), backfiring (aka a popping sound) for those with and without cats, and depending on the idle setting of the engine and the level of tuning, a loss in power between shifts because you are trying to go fast while the engine is stalling. Some BOV's are made so that they can have a recirculation hose fitted to them (HKS SSQV, Blitz DD, Greddy valves, etc). This would be the wisest choice for driveability sake, however the "cool swoosh sounds are muffled."

The blow off valve has two principle designs, the regular single valve and the dual valve. The single valve is less useful since it has to be used in tandem with a recirc for the most part. The reason for this is because at low RPM's the recirc will be good for releasing low amounts of boost without producing compressor shock; at higher boosts the single BOV will release higher boost. The dual action systems allow you to get rid of the recirc valve completely because they will release at low and high boost without damaging the turbo. They will not leak at idle and are tuned perfectly when you are not leaking boost at full boost at high RPM in 5th gear, however they release air under nearly all conditions. If the BOV is too loose it will leak boost under less than WOT conditions. This can result in metered air escaping while the ECU is delivering fuel for that air. Thus causing rich conditions and loss of boost which can easily be spotted with a boost gauge. Tightening the screw will keep the BOV shut longer and release under higher levels of boost.

Atmospheric BOV's are not as driveable as recirc valves because they can cause stuttering, and richness. There are concepts and devices that can compensate for the lost metered air. One concept is the blow through MAFS where the MAFS is relocated between the throttle plate and the BOV. In this case the air that is being ejected into the air has yet to be metered, thus no stuttering, bogging, stalling or richness. Another idea is the fuel computer which can come in the form of a rechipped stock ECU (aftermarket ECU, etc), fuel piggyback computer (ApexI SAFC low end; ApexI Power FC, HKS FCon high end, etc), or standalone computer (Haltech, etc) to completely get rid of the stock MAFS device. There are other devices that are not fuel computers such as an HKS Vein Pressure Converter (VPC) that completely gets rid of the MAFS style system in favor of its own metering system that is more accurate. All these are expensive.

In reality a BOV is nothing more than a noisemaker at stock boost and serves no superior purpose over a recirculation valve. The recirc valve has its limits and will start leaking boost levels above what it was intended for, since it cannot be tuned. That is where BOV's actually become more of a necessity.

On your car if you have a grippy clutch and a fully tuned BOV the bogging should disappear between shifts since the clutch should snap the engine, telling it to go forward and forcing the engine to keep going. On bad tuning, vacuum leaks, or a weak clutch the car will do what it wants to naturally do with atmospheric BOV's and no compensation, stall and/or DIE. My only advice if you do not know how to tune the BOV properly is to raise the idle to about 1300-1600 RPM's that way even when the car does run rich for the moment and wants to stall, it will not get into the danger zone (sub 500 RPM's), or should be able to recover faster.

For personal referance my setup is an ApexI dual chamber BOV on the stock turbo at stock 0.5 bar. I have my idle set to 800 RPM's with a switch that activates my auxiliary air control valve (AAC). When the switch is off I am at 800 RPM's, when the switch is on the idle is at roughly 1300-1700 RPM's while moving and 800 when stopped. This way I can drive with the BOV but never have to worry about stalling.

[Cyberkreig]

usually to get the full potential of the exhuast, u have to couple it with an intake and headers for best results

i dont think that applies to turbo motors

[nlzmo400r]

it does to a certain extent, but with a turbo, you're right, the intake doesnt have that much of an effect, however larger headers does help with power gains with the exhuast

[Cyberkreig]

anything that helps spool time & reduces back pressure is good for a turbo.. but then the HP gains are as much from the added boost as from the new parts.

[nlzmo400r]

well yea, ubt the higher boost you run, the more exhaust flow capability you need

[SWIFT_DRIFT]

it does to a certain extent, but with a turbo, you're right, the intake doesnt have that much of an effect, however larger headers does help with power gains with the exhuast

You do realize that SR's filters are not referred to as an "intake" nor is the exhaust manifold referred to as "headers." Do you even have any experience working on an SR, or a turbo motor in general?

[SrS13]

The SR as with most Nissan engines in stock trim run engine management with a MAFS (Mass Air Flow Sensor). This senses how much air has passed through the intake pipe and adds fuel to the combustion accordingly. When you use a recirculating valve on a turbo car, the air that has been "metered" by the MAFS is recirculated back into the intake system after the MAFS so that it is not metered again. This allows the computer to not get tripped up and add fuel for re-metered air. On an atmospheric blow off valve, the air is not recirculated. This creates an issue when it comes to metered air because the MAFS has metered the air and the BOV has now ejected it during a shift or dropping into neutral. When this occurs, the combustion becomes rich because the ECU sent fuel for air that has just been ejected from the intake. The result is a fireball if you do not have a cat (under certain conditions), backfiring (aka a popping sound) for those with and without cats, and depending on the idle setting of the engine and the level of tuning, a loss in power between shifts because you are trying to go fast while the engine is stalling. Some BOV's are made so that they can have a recirculation hose fitted to them (HKS SSQV, Blitz DD, Greddy valves, etc). This would be the wisest choice for driveability sake, however the "cool swoosh sounds are muffled."

The blow off valve has two principle designs, the regular single valve and the dual valve. The single valve is less useful since it has to be used in tandem with a recirc for the most part. The reason for this is because at low RPM's the recirc will be good for releasing low amounts of boost without producing compressor shock; at higher boosts the single BOV will release higher boost. The dual action systems allow you to get rid of the recirc valve completely because they will release at low and high boost without damaging the turbo. They will not leak at idle and are tuned perfectly when you are not leaking boost at full boost at high RPM in 5th gear, however they release air under nearly all conditions. If the BOV is too loose it will leak boost under less than WOT conditions. This can result in metered air escaping while the ECU is delivering fuel for that air. Thus causing rich conditions and loss of boost which can easily be spotted with a boost gauge. Tightening the screw will keep the BOV shut longer and release under higher levels of boost.

Atmospheric BOV's are not as driveable as recirc valves because they can cause stuttering, and richness. There are concepts and devices that can compensate for the lost metered air. One concept is the blow through MAFS where the MAFS is relocated between the throttle plate and the BOV. In this case the air that is being ejected into the air has yet to be metered, thus no stuttering, bogging, stalling or richness. Another idea is the fuel computer which can come in the form of a rechipped stock ECU (aftermarket ECU, etc), fuel piggyback computer (ApexI SAFC low end; ApexI Power FC, HKS FCon high end, etc), or standalone computer (Haltech, etc) to completely get rid of the stock MAFS device. There are other devices that are not fuel computers such as an HKS Vein Pressure Converter (VPC) that completely gets rid of the MAFS style system in favor of its own metering system that is more accurate. All these are expensive.

In reality a BOV is nothing more than a noisemaker at stock boost and serves no superior purpose over a recirculation valve. The recirc valve has its limits and will start leaking boost levels above what it was intended for, since it cannot be tuned. That is where BOV's actually become more of a necessity.

On your car if you have a grippy clutch and a fully tuned BOV the bogging should disappear between shifts since the clutch should snap the engine, telling it to go forward and forcing the engine to keep going. On bad tuning, vacuum leaks, or a weak clutch the car will do what it wants to naturally do with atmospheric BOV's and no compensation, stall and/or DIE. My only advice if you do not know how to tune the BOV properly is to raise the idle to about 1300-1600 RPM's that way even when the car does run rich for the moment and wants to stall, it will not get into the danger zone (sub 500 RPM's), or should be able to recover faster.

For personal referance my setup is an ApexI dual chamber BOV on the stock turbo at stock 0.5 bar. I have my idle set to 800 RPM's with a switch that activates my auxiliary air control valve (AAC). When the switch is off I am at 800 RPM's, when the switch is on the idle is at roughly 1300-1700 RPM's while moving and 800 when stopped. This way I can drive with the BOV but never have to worry about stalling.

This is all alot of info and I greatly appreciate it. Im assuming I must have some serious traction problems causing this? My shocks are blown I know that for a fact and my clutch is most likely on its last grabs. Ill see what happens after I install new shocks and a new clutch.

Thanks

[nlzmo400r]

You do realize that SR's filters are not referred to as an "intake" nor is the exhaust manifold referred to as "headers." Do you even have any experience working on an SR, or a turbo motor in general?

yes i know they're not liteerally called that, hoewver its much easier for the average person to understand when it is reffered to in a more common name. And in all reality, the 'headers' are still there, and serve basically the same purpose as on a normally aspirated car, but thanks for once again doubting my knowledge, i am not trying to say i know everything by any means, however i think you give me less credit because of my age, but its cool, everyone is entiteld to their own opinion.

[SWIFT_DRIFT]

yes i know they're not liteerally called that, hoewver its much easier for the average person to understand when it is reffered to in a more common name.

Well your version of the "common" name is incorrect regardless.

And in all reality, the 'headers' are still there, and serve basically the same purpose as on a normally aspirated car,

I'm glad you think so. The exhuast manifold on NA connects directly to the downpipe. So this must be the same for turbo cars according to your common name usage and knowledge...

but thanks for once again doubting my knowledge, i am not trying to say i know everything by any means, however i think you give me less credit because of my age,

You sir are correct. You are what, 17, couldn't even find the clutch reservior without posting here lol. Your profile says you post over 16 times a day, so post count must equal knowledge. We all know how that ended up with you know who. How about you install an SR in your car before you even post in this section, kthx.

[nlzmo400r]

yes the common term is 'incorrect, however on a turbo car ARE THE HEADERS/exhaust manifold NOT THERE? yes they are, and so what of my age, that doesnt mean im not knowledgable, and who said post count equals knowledge? And wtf does it matter if i havent installed an SR into *my* car before i even post in this section, seems to me that im younger , yet seem soo much more mature than you when it comes to helping people. So are you going to tell Fred that he can't post here simply because he's never installed an SR into a car before? NO , why you ask, because he's older, and therefore u respect him much more than you do me (not that you do at all). I may not know everything about SRs, but i could sure as hell hold my own, its not like anything you've said has been at all helpful to anyone on the board. Trust me, im much more intelligent than you think i am, probably more intelligent than yourself, so think twice about putting someone down simply because of their age

[SWIFT_DRIFT]

hahahah mr.16postsaday. you obviously have no life other then the internet to defend yourself so heartedly...bahbahhaha!!

[BaliLover]

Turbo vehicles do not have headers, they have Manifolds. Plain and simple. I have never seen one company sell turbo headers because they do not exist.

Maturity mean knowing when you are wrong and being able to admit it.

[Cyberkreig]

http://search.ebaymotors.com/s...eader

I am not taking sides in this.

Exhaust manifolds are often refered to as "turbo headers"

[SWIFT_DRIFT]

Lol cyber. I will not include you, but I do have to comment on your post. I really don't think ebay is a worthwhile link in this case. Think about the typical import consumer...if you were one of those would you rather buy a turbo manifold (correct name) or a turbo "header." Seems more like a marketing tactic because "header" sounds more powerful, when it really makes absolutely no difference, just causing misinformation on what it's really called.

[SrS13]

For personal referance my setup is an ApexI dual chamber BOV on the stock turbo at stock 0.5 bar. I have my idle set to 800 RPM's with a switch that activates my auxiliary air control valve (AAC). When the switch is off I am at 800 RPM's, when the switch is on the idle is at roughly 1300-1700 RPM's while moving and 800 when stopped. This way I can drive with the BOV but never have to worry about stalling.

That is very interesting I'd like to know how you did this if that is ok with you