Ahriman

is anybody over here running the 10:1 pistons and the GM stage injectors? I have had nothing but problems since i installed the 60#ers, even fell victim to the cooked cylinder 4 fiasco. when i rebuilt i still had bigger plans for the car and went with 10:1 pistons. I have since decided that i dont really want to go any bigger with this car and would like to get away from the 60's if possible. i already switched from a 2.7" pully up to a 3". I know the 42.5's are just fine on stock compression with a 3" pully, but i was hoping i would be able to get away with them w/ the 10:1 pistons as well. anybody got any input here?

blown06

i believe in the 300hp build gm used the 10:1 and 42's with the head work and stage 3 pcm

Ahriman

thats what has me confused man... the build book never references the injectors in #'s, iirc it references them in gps, which i am assuming is grams per second but ill be damned if i know for sure.

handyjoe

Normally thats gallons per second, I believe.

What are the build book injectors rated at?

Ahriman

whats up joe? figured id post this over here since only two or three of us on the RLF are running anything other than stock pistons.

im not sure what exactly the books says, im at work right now, but i know it doesnt say 42.5's or anything close to that.

blown06

they are 5.64 gallons per second (gps), they look just like the stage two 42.5's

Ahriman

i have even seen Intense claim that with the ceramic coated top, and molly coated side skirts, you can run a higher compression w/ the same boost and timing as you did previously due to the reduction in heat caused by friction and what not.... i dont know how true any of that is though.

but if it is true, than you would think i would be just fine on the stage 2 injectors AND an unmolested stage 2 tune without issue. not to mention the 3" exhaust reduces cylinder pressure wich i would think would somewhat help balance the higher cylinder pressure caused by higher compression pistons... or am i over thinking it and perhaps wishfull thinking?


well ****, im gonna give it a try then and see how it works out.


still though, is there anybody else already running the 10:1's with the 42.5's?

blown06

i am in the same boat i installed 10:1 have 60's but going to go to 42's instead with a bigger pulley

Ahriman

ya man, in my opinion its just not worth it to run injectors that are twice as big as our fueling system was designed to suply, just so you can run a puly that makes to much heat and takes the blower out of its efficiancy range. unless of course you want to dive into modifying the whole fueling system, and i just dont want to go there.

beamSS

is it true that if you up the compression you need to run 100 octane all the time to eliminate knock

bc3tech

you are exiled for starting a thread here... *lol*

Witt

If you are using a 3 inch pulley, the 42.5s will work fine. The increase in compression has no effect on incoming airflow. Only when incoming airflow increases will the injectors need upgraded to match the ratio. Other than maybe a loss in the amount of timing, you'll find the tune will basically stay the same as well.

shabodah

Ben, Ben, Ben, Ben, Ben.......

*shakes head*

Ahriman

hey man, give me a break, nobody on RLF other than alpha is running after market pistons, and when i ask questions about em over there, i dont get much info back. there are more peeps over here running similar setups so i figured id post LOL. dont be disapointed in me.


thats what i figured


thanks for all the help guys.

Witt

Mr. Premo Member.

handyjoe

5.64 gallons per second?!

Thats a crazy amount of flow. That would make them flow 125884.8 (using 6.2 lb as the weight of 1 gallon of gas (thank you google)) lb/hr.

I think its supposed to be 5.64 gph, but that may not be right as well because that would make them stock injectors (36#).

BUT

if it was grams per second, that would make them 44.76lb/hr injectors, which would probably make them 42# with round off errors.

...which makes you still correct.

Witt

Its a misprint. Its definetly grams per second.

handyjoe

Ok, cool. Just makin sure.

blown06

This is copy and pasted straight from the build book:

The factory fuel injectors need to be replaced
with performance units. In general, if you’re
making more than 240 hp, you’ll need injectors
that flow at least 5.64 gallons per second
(gps). To swap the injectors, lift the tang
locking the electrical connector on the fuel
injector and pull the connector off. Then, pop
this clip off the injector body and pull up on
the injector. Make sure to apply a light dab of
fuel injector lube or vaseline on the new
injector O-ring before pushing it into the body
to minimize the chances of the O-ring folding
over and causing a leak when it seats in the
injector bore.

Ahriman

in case anybody was wondering. did the swap yesterday. the 42.5's, a 3" pully, and a straight stock GM stage 2 tune(minus cat codes), work great with the 10:1 pistons.

LopsidedJester

how is it performance wise? a big difference between 3" pulley gm stage 2 and 9.5:1 compression? I was wondering about 10:1 pistons for future build plans and whether or not it would be ok to run a 2.9" pulley with the 42.5's still.

M88ArRamadi

I was thinking about that too. I wonder if it would benifit me if I switched to 42's.

I was also looking into getting the walboro 255 pump and set up a return line. Not sure which route to go now.....

blown06

i have been running 10:1, 42's and 2.9 pulley, runs great but at 7k the injectors are maxed

M88ArRamadi

then I'm not going w 42's......I plan on running to 8000.

InfinityzeN

Don't go with 60#. A set of 50# should be more then enough and less likely to make you blow piston 4 up.