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so I bought 370cc injectors for my n/a ka24de and a performance chip to tune. obviously it ran way too rich never got it to run. wondering if upgrading stock 250cc injectors to 270cc's will make any difference as far as performance or run it just as bad. Im aware I have to work out the air to fuel ratio. I figured thats where the chip comes into play? what about 270cc with cold air intake, good or bad? can I run 270cc without intake upgrade? or am I wasting my time trying to do all this? new to mechanics just need an opinion
 

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Since you're new, understand that your engine -- any engine -- is basically a glorified air pump. With natural aspiration, there's a maximum amount of air it can suck in and push out based on the engine displacement plus whatever velocity you can create in the intake and exhaust paths to "ram in" a bit of extra charge. Even the latter does a limited amount of good unless you can push the burnt charge out just as quickly using tricks like overlap. Matching cam lift, profile, valve sizes, variable valve timing, plenum tube and exhaust tube sizes is a black art unless you have zillion dollar simulation software like the OEM's use. Those factors all contribute to how many ponies your engine can produce.

The upshot is, slapping in bigger injectors will never do you much good unless you can also increase the amount of air being pushed through your air pump. Fuel doesn't make horsepower, mixture does. The biggest bottleneck to more air in most modern engines is the exhaust, so if you're in a state where you can ditch the cat and put in a freer exhaust, then you can probably make some genuine extra power with larger injectors and some ECM tweaks.

Forget cold air intakes, Nissans already have them. Putting a K&N cone inside the engine box just makes the engine suck hot air coming through the radiator instead of cold air coming under the hood ledge. It'll sound cool, but chances are the dyno will show you horsepower lost and not gained.
 

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so I bought 370cc injectors for my n/a ka24de and a performance chip to tune. obviously it ran way too rich never got it to run. wondering if upgrading stock 250cc injectors to 270cc's will make any difference as far as performance or run it just as bad. Im aware I have to work out the air to fuel ratio. I figured thats where the chip comes into play? what about 270cc with cold air intake, good or bad? can I run 270cc without intake upgrade? or am I wasting my time trying to do all this? new to mechanics just need an opinion
You must have gotten info about the Silvia S14 SR20DET because that engine used 370cc injectors. However you have to remember that engine was a turbo setup that pushed a lot more air into the engine; it also had higher duration cams so the ECU was tuned for that.

The 240SX KA24DE engine used 270cc injectors. However it had a high flow intake system with a larger ported head and higher duration cams compared to your Altima KA24DE with 250's.

Putting 270's on your engine may not give you the results you're looking for. However if you were to install a 1991 - 1994 240SX head with it's high flow intake system and a high flow CAT-back exhaust, then you should get a very noticeable improvement. The stock ECU might be OK with the new setup. I say might; to get a better tune, you probably should use a 240SX ECU.

The 1991 - 1994 cams had the higher duration timing; the later cams were de-tuned due to stricter emission requirements.
 
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