What size injectors shoould be used for a 35r, i searched and found people using everything from 750cc injectors to 1600cc injectors.

Whats the recomended size?

 

1000cc

 

thats a good question, but i think people jump to 1000cc right away to be safe. I have seen log maps from a 35r equipped car at 25 psi only using like 60% duty cycle with 1000cc injectors. Jarrod from Buschur Racing was only at 80% duty cycle at 23 psi with 780cc's and a 3065(similar to a 35r). So my guess is that 880's would be perfect

 

This is actually pretty easy to figure out. You just need to use a little math and two things: (1) airflow of turbo and (2) AFR you will be running.

The GT35r is just a generic term for many different turbos. Let's take one that has a compressor that can flow 75lb/min.

Then, you need to know the AFR that you are going to be tuned for. Let's do two calclutations at the max airflow of 75 lb/min. One for a 11:1 AFR and one for a 12.5:1 AFR.

11:1

For every 75lbs air, you will need 75/11 lbs fuel. Or, 6.82 lbs fuel. We have four injectors, so you need 6.82/4=1.71 lbs fuel per injector. Injectors for imports are commonly measured in CCs, so we have to convert to 1.71lb to CCs. You need the specific gravity of the gas that you are going to be running.

Pump gas has about .76 specific gravity. Specific gravity is a relation to that of water. Water has a density of 1g/ml or 1g/CC. The same amount of pump gas will be .76g/cc

So, 1.71lb(454g/1lb)(1/.76)=1021.5 CC injector needed

12.5:1

75lbs fuel/12.5 = 6 lb fuel divided by 4 = 1.5 lb fuel per injector

1.5 lb *(454g/1 lb)(1/.76)=896 CC injector needed


So, you can see that it depends on your AFR (the leaner the less injector you need) and the max airflow of your turbo or the air that you are going to be flowing.)

Also, since you see that the specific gravity of the gas is invloved, that matters, too. For example, C16 (a popular race gas) has a specific gravity of .73. So, using the same calculations above, we get the following results:

75 lb/min compressor

AFR pump gas C16
11:1 1022 CC 1064 CC
12.5:1 896 CC 933 CC

So, you need bigger injectors if you (1) are flowing more air, (2) are using a richer AFR, (3) are using a race gas with a lower specific gravity.


Eric

 

Perfection,

thats all i needed was the formula, thanks.