Upgrades to the D15b SOHC engine?

**je.tansengco** · February 6th, 2011 11:40 AM

sir, the car is all stock except for the intake which i upgraded to a K&N short ram. the original engine is a 1.5L D15b SOHC, and the car is a 1998 Honda Capa. Pansin ko lang kasi na smooth ung acceleration up to around 80km/hr, tapos biglang parang nahihirapan na ung engine to accelerate any further. so, ask ko lang if baka may sira ung ECU or un talaga ung max ng engine? and kung ano kailangan ko gawin?

**ghosthunter** · February 6th, 2011 12:11 PM

Originally Posted by je.tansengco

sir, the car is all stock except for the intake which i upgraded to a K&N short ram. the original engine is a 1.5L D15b SOHC, and the car is a 1998 Honda Capa. Pansin ko lang kasi na smooth ung acceleration up to around 80km/hr, tapos biglang parang nahihirapan na ung engine to accelerate any further. so, ask ko lang if baka may sira ung ECU or un talaga ung max ng engine? and kung ano kailangan ko gawin?

Have you checked the usual stuff like fuel filter (both the inline and intank) and the fuel pump? Is the ignition timing adjusted to factory setting?

IS the exhaust smoky or clear?

**je.tansengco** · February 6th, 2011 01:39 PM

Originally Posted by ghosthunter

Have you checked the usual stuff like fuel filter (both the inline and intank) and the fuel pump? Is the ignition timing adjusted to factory setting?

IS the exhaust smoky or clear?

the exhaust is pretty normal as far as i can tell. the fuel filter is brand new. the ignition timing is adjusted to factory setting. if i did an ignition timing advance, what will that do to the car performance? also, will a better exhaust system help increase the top speed?

i have a few theories although i may be wrong since i'm a noob at cars.
1. exhaust system sucks
2. fuel pump not applying enough pressure at high speeds
3. ECU not working properly

what do you think?

**ghosthunter** · February 6th, 2011 02:37 PM

Originally Posted by je.tansengco

the exhaust is pretty normal as far as i can tell. the fuel filter is brand new. the ignition timing is adjusted to factory setting. if i did an ignition timing advance, what will that do to the car performance? also, will a better exhaust system help increase the top speed?

i have a few theories although i may be wrong since i'm a noob at cars.
1. exhaust system sucks
2. fuel pump not applying enough pressure at high speeds
3. ECU not working properly

what do you think?

Given it's an old car, have you checked the in-tank fuel filter? Also check if the fuel pump is giving out the right pressure & flow rate. While there, the fuel line between the tank & engine should also be checked if it's clogged with built-up dirt.

Regarding ignition timing advance, assuming your car is working right, advancing the timing slightly will increase power output. Do it too much, detonation/pinging will happen. To avoid that (while keeping the advanced timing) you will need to use high octane gasoline. Downside, advanced timing will result in increased fuel consumption.

**je.tansengco** · February 6th, 2011 03:12 PM

sir, is the fuel line the same as a fuel rail? and if yes, would aftermarket fuel rails increase the performance if i decide to replace the old one? thanks.

**ghosthunter** · February 6th, 2011 03:22 PM

Originally Posted by je.tansengco

sir, is the fuel line the same as a fuel rail? and if yes, would aftermarket fuel rails increase the performance if i decide to replace the old one? thanks.

No, they are different.

Changing the stock fuel rail to an aftermarket version without changing the support stuff (fuel pump & fuel pressure regulator) will not give additional performance because the amount of fuel going into the cylinders will be the same.

An adjustable fuel pressure regulator or bigger fuel injectors will increase the amount of fuel to the cylinders.

**je.tansengco** · February 6th, 2011 09:25 PM

thank you. i've been looking through the forum and can't find a dealer of high pressure fuel injectors. any suggestions? so, this will definitely make the car go faster right? along with proper exhaust?

**ghosthunter** · February 7th, 2011 09:13 AM

Originally Posted by je.tansengco

thank you. i've been looking through the forum and can't find a dealer of high pressure fuel injectors. any suggestions? so, this will definitely make the car go faster right? along with proper exhaust?

I think you combined what I said.

Either an adjustable fuel regulator OR a set of bigger fuel injectors.

BTW, these mods will require a degree of tuning on your engine's ECU so you will definitely need something like a APEXi S-AFC (Air Flow Converter). This device tricks the engine to add more or less fuel by adjusting the signals from the airflow meter. And along with this, you will need some dyno time to tune/adjust the settings properly.

Do note that these mods will only work IF the engine is working 100% to start with. Given your engine gets your car to barely 100kph indicates that there is something wrong. I strongly suggest visiting a shop to have the source of your problem diagnosed before doing any mods.

**je.tansengco** · February 7th, 2011 10:06 AM

okay thank you for the help. i also did some research and found out that some if not all cars have speed limiters. maybe this is something worth looking into. thank you.

**ghosthunter** · February 7th, 2011 11:42 AM

Originally Posted by je.tansengco

okay thank you for the help. i also did some research and found out that some if not all cars have speed limiters. maybe this is something worth looking into. thank you.

Most cars with EFI engines have speed limiters but typical limit would be at least 180 or 185 kph for japanese cars.