I cant really seem to get a whole lot of info on this. Ive gotten a few comments, but I know that there are more out there.

Ive got a 92 3.4DOHC with a T3/T04E turbo, planning 6-10psi boost. I figured stock injectors wouldnt cut it, but not sure.

Injector choice should be based on the amount of HP your engine is going to produce and how much fuel it is going to consume. There is a mathematical formula for figuring this out:

HP / Number of Injectors x BSFC / Duty Cycle

Brake Specific Fuel Consumption (BSFC) factor has to be used in the above formula correctly. A BSFC of .50 means an engine will use .50lbs of fuel per hour for each horsepower it produces. Competition engines with high volumetric efficiency should use a BSFC of .45 while forced induction engines should use a figure of .65. Maximum sustained duty cycle is 0.80 (or 80%) on most fuel injected engines.

So lets plug that formula into the stock 3.4 DOHC engine...

215hp / 6 x .5 / .8 = 22.39lb.hr. To be on the safe side the factory installed 24lb.hr injectors.

Also remember to keep in mind this formula is based on the assumption of 3 bars of fuel pressure (43.5psi). Under boost, assuming your fuel pressure regulator is hooked up to manifold vacuum and will read boost (as it should), the fuel pressure will rise as boost increases therefore the injector flow will increase with the added fuel pressure. Generally, at 10psi of boost pressure to the stock FPR, the fuel pressure on the 3800SC will raise to about 60psi +/- a few PSI. Here is another formula you can use to figure out what flow rate injectors will flow at different fuel pressures:

New Flow = Old Flow X square root of (new pressure/old pressure)

So lets use this formula to figure out how much 36lb.hr @ 43.5psi injectors will flow at 60psi.

36lb.hr x square root of (60psi / 43.5psi) = 42.28lb.hr

Using this new number we can find out how much HP a set of 36lb/hr injectors will support at 10psi of boost (or 60psi of fuel pressure) by reversing the fuel injector hp formula...

42.28lb.hr x .8 duty cycle / .65 BSFC x 6 injectors = 312.22hp.

Now I will give you my opinion of what you should need. We already know the stock 3.4 DOHC injectors are 24 lb/hr. Those were fine for its stock 215hp rating. However, with 6-10psi of boost using that relatively small/ineffecient T3/T04E turbo you will probably only get about 300hp out of a stock 3.4 DOHC engine and should be ok using something on the order of stock L67 36 lb/hr injectors. If you go with a better turbo, you are probably going to need bigger injectors. 36lb/hr units are a dime a dozen because they were used stock on the 96-up 3800 Series II SC engines. You should be able to pick up a good used set for about $50 or so. 42.5lb/hr (@ 43.5psi) injectors are the next step up and can usually be found used for $150/set.

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[This message has been edited by Darth Fiero (edited 09-05-2005).]

i picked up a set of 36 lb 3800sc injectors for about 40$

Where from?!? I cant even seem to find any on ebay

What car is the 3.4 DOHC sourced from, and how much do they usually run at a yard?

-Mulholland

quote Originally posted by Darth Fiero: We already know the stock 3.4 DOHC injectors are 24 lb/hr. Those were fine for its stock 215hp rating.

Darth, where does this information come from? My injectors were flow tested by Cruzin Performance. The results were an average of 21.13 lb/hr (lowest was 20.78 lb/hr highest were three at 21.3). These are the stock injectors.

-Steven

quote Originally posted by 86GT3.4DOHC: Where from?!? I cant even seem to find any on ebay

got em off ebay - but when in doubt http://www.zzperformance.com/products1.php?id=323&PHPSESSID=73aadd76cae124a7c16b07ee6afee77e

The 3.4DOHC was produced from '91 to '97. The 96-97 engines have a re-designed top end and are prefered. They were available in Chevy Lumina (usualy euro and all Z34), Olds Cutlass Supreme, and Pontiac Grand Prix. Though I think some late model grand prixs got the 3.8. Ive heard but never confirmed that they MIGHT be in montecarlos.
Other pertanant info.
In 94 the engine got new cam cogs. Basicaly you can tweak the timing by just removing a bolt, rather than having to remove the belt and pull the cogs. They also got a cam sensor, and I beleive SFI. In ?95 they went to MAF, which is more expensive and harder to tune than the earlyer MAP, in addition to the MAF sensor costing 150+. The newer engines can be converted to MAP with minor wiring and the older computer.

quote Originally posted by Steven Snyder: Darth, where does this information come from? My injectors were flow tested by Cruzin Performance. The results were an average of 21.13 lb/hr (lowest was 20.78 lb/hr highest were three at 21.3). These are the stock injectors. -Steven

Steve, you raise an interesting point. I sent a set of L67 injectors to Cruizin Performance and they only flowed 34 lb/hr. However, in the PCM programming, they are listed as flowing 36 lb/hr. In the 3.4 DOHC stock programming the injector constant is listed at about 24 lb/hr. The actual base fuel pressure (no vac or boost to FPR) on most GM cars is about 45~46psi so this might account for the discrepency.

Where from and how much did you guys get your 3.4L's for?

lol, sorry for the n00b questions

According to Rich from Cruzin Performance, test pressure = 43.5 psi.

My 3.4 DOHC with 89K miles, with ECM and wiring harness was $500 + freight (off ebay). It ended up needing to be rebuilt. I will likely never again buy a used motor unless it was from a friend and I knew it ran great. Its cheaper to buy a crate motor and then a used junk motor just for the accessories, for what you end up paying to rebuild the whole used one...

[This message has been edited by Steven Snyder (edited 09-08-2005).]

ooops, lol wrong thread.

[This message has been edited by 86GT3.4DOHC (edited 11-26-2005).]