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Old 10-28-2017, 12:51 PM   #1
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Throttle Body and Injectors

Working on an LX9 3500 swap on an 02 GA. I am having trouble finding information on throttle body sizing and what will work with our 3x00 engines. I am looking for a set of junk yard injectors to pull from a car as well as a throttle body. Thinking somewhere in the 60-70mm range for the throttle body and 36#injectors. What can I get those parts out of ?

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Old 10-29-2017, 03:45 AM   #2
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Fuel Injector Upgrades

Some modification of the 36's, or the fuel rail bracket, or changing the fuel rails may be needed. I cut new mounting slots in the injectors....
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Old 10-29-2017, 11:10 AM   #3
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Wow, That was exactly what I was looking for. Thank you so much! Now if anyone has the same info for the throttle body ill be set

Thanks,

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Old 10-29-2017, 11:31 AM   #4
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Just fyi, if you are leaving the 3500 mostly stock, you don't need larger injectors. That will do absolutely nothing for you (except give more tuning headaches). The stock 3400 injectors have plenty of room for a 100cc increase in displacement, and even a cam and headers. A bigger TB won't really do a lot for you either, without other mods.
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Old 10-30-2017, 12:59 AM   #5
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Originally Posted by AaronGTR View Post
Just fyi, if you are leaving the 3500 mostly stock, you don't need larger injectors. That will do absolutely nothing for you (except give more tuning headaches). The stock 3400 injectors have plenty of room for a 100cc increase in displacement, and even a cam and headers. A bigger TB won't really do a lot for you either, without other mods.
My plan is to take advantage of a couple of other air flow mods and then tune the vehicle. I will be creating two tune files... one for 93 octane and one for E85.

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Old 10-30-2017, 11:51 AM   #6
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Most people still don't need bigger injectors unless you are adding boost. You need heads/cam/headers along with full intake, exhaust, TB, and ported intake manifolds to even approach the limit of the stock injectors. You need to do the mods first, then log some data and see where the injectors duty cycle lands. Most people with those mods find it sufficient to upgrade to 28# trailblazer injectors, and those don't require any mods to the injectors or fuel rail. They are plug and play, other than the need to scale the injector size in the tune.
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Old 10-30-2017, 12:08 PM   #7
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Quote:
Originally Posted by AaronGTR View Post
Most people still don't need bigger injectors unless you are adding boost. You need heads/cam/headers along with full intake, exhaust, TB, and ported intake manifolds to even approach the limit of the stock injectors. You need to do the mods first, then log some data and see where the injectors duty cycle lands. Most people with those mods find it sufficient to upgrade to 28# trailblazer injectors, and those don't require any mods to the injectors or fuel rail. They are plug and play, other than the need to scale the injector size in the tune.
Ok, that sounds like good advice.. so Ill take it. I can get a set of trailblazer injectors for about $20 total so Ill make the swap. You are correct about data logging first. I'm just trying to leave myself some room. I can't imagine GM left too much room. E85 takes away about 30% of my duty cycle. Why have a duty cycle at 90% when you can have room at 50-60 at WOT on a larger injector? Scaling is not a problem, I will be using HPTuners. E85 is about a $1.94 right now in my local area. 93 is over $3.00 a gallon. On a 3500 ill pickup maybe 4-6 horsepower moving from 93 to E85 and turning the timing up, but Ill be saving money on the fuel, and practicing my tuning skills on something cheap before I start working on my other project.... the Turbo LQ4 I am building and the 454 Chevelle I have converted to a flex fuel standalone 0411 ECU.


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Old 10-30-2017, 12:14 PM   #8
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Old 11-01-2017, 11:22 AM   #9
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Well, most people's first instinct is just to go to way bigger injectors than they need to have plenty of room available, but that can cause tuning and idle issues. The stock injectors actually have a decent amount of capacity in them over stock power levels.

If you are going to run E85, well yeah... then you are going to need more injector. You'll also need a bunch of other mods though too. The stock fuel system isn't designed to accommodate that much alcohol. Plus there is the fact that in northern states, E85 isn't actually 85% alcohol year round. Alcohol is difficult to get to burn in cold temps, so in winter they switch to something closer to E65, and in summer it's E85. That means if you have a static tune, your fueling will be off when it switches. If you tune for E85, you'll be running rich in winter.

Factory vehicles use a fuel sensor to detect the alcohol content (about $400 from GM for the sensor). I read a good article a while back in a magazine where the converted an R33 Skyline in Las Vages to run E85 so they could up the boost and increase timing. They had to upgrade the fuel pump and replace most of the fuel lines and fittings to handle the extra flow and resist the alcohol, get special injectors, the GM fuel sensor, and a standalone engine management system that was capable of adjusting the fuel and timing mapping based on the fuel content (like the factory ECU on a flex fuel car). Not cheap or easy. You can do it without some of that stuff... but it won't be as safe or last as long. Not worth it for 4-6 HP in my opinion.
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Old 12-07-2017, 06:20 AM   #10
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Skip the E85, go with a Snow meth injection kit. Majority of cost is right up front and will effectively turn 93oct into around 106. Kits are available for both NA and Boosted applications now. I've installed three of these so far and they are fantastic. One vehicle that I work on(this one's boosted)sees cooler head temps at the end of the track than what I get in the burn out box in a 10second V6. E85 isn't worth the hassle imo either. Stay the hell away from the stuff. Unless built for corn, I'd never use it. Even NA sees big gains from meth. And my goodness a bottle last a long time. You won't go broke keeping that tank full. And I like the snow kit as it monitors Meth level and has a warning lamp you mount in your dash. If the system did run out of Meth, or if it failed for some reason, it'll even protect you and pull timing. Great system, and for what you get, it really is a cheap mod. You won't run out of injector with Meth in there and you don't need to go looking for those 85 pumps. And a real nice bonus, clean intake and intake valves...forever. You will never clean an intake or top end again. When you set this up right, your combustion chamber will NEVER carbon up either. The only problem I have with Meth is someone trying to spray it through a blower. Big no no there. It will destroy the rotors over time. Has to be injected after a blower if you install one of those down the road.
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Old 12-07-2017, 11:55 PM   #11
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I hear ya. I'm a throttle body away from having this thing up and running with 28lb Vortec 4200 injectors. Ill get it dialed in on 87 first and then we will see how it feels. I use meth all the time, just looking to experiment with something different.

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Old Yesterday, 02:01 PM   #12
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Quote:
Originally Posted by AaronGTR View Post
Most people still don't need bigger injectors unless you are adding boost. You need heads/cam/headers along with full intake, exhaust, TB, and ported intake manifolds to even approach the limit of the stock injectors. You need to do the mods first, then log some data and see where the injectors duty cycle lands. Most people with those mods find it sufficient to upgrade to 28# trailblazer injectors, and those don't require any mods to the injectors or fuel rail. They are plug and play, other than the need to scale the injector size in the tune.
Actually, anyone who does a 3500 swap along with some bolt-ons should probably get larger injectors. Ideally to keep the injectors lasting a long long time, you should run them at a max duty cycle of about 70% when the engine is at wide-open-throttle, and the injectors are at their max operating level. If you start pushing this value above that, the injector life starts dropping. Above 90%, and they won't last long at all. Well at 180hp, the stock injectors are sitting around 62%, but when we combine a 3500 with our tune, 68mm throttle body, plugs, t-stat, and 2.5" downpipe, it's making about 230 crank hp, and now those injectors are around 82% duty cycle. For me, that's just too high. A lot of people do 28's. I tend to do 36's. With 28's, 230hp is about 66% duty cycle, which technically is sufficient, but there's just no more room to grow if you add more mods., which is why I typically use 36's. With the 36's, you can do anything you want to do naturally aspirated and never run out of injector (320 crank hp would be 71%). Running a 36lb injector or even a 60 for that matter when you don't need that much flow won't actually tuning issues. Modern injectors if made by good reputable companies like Bosch and Siemens, or some others, are much more accurate than injectors used to be, and as long as the injector tables in the pcm are tuned correctly, there is no harm in running an injector larger than actually needed. High impedence injectors have come a long way recently, and there are many more options for high flowing high impedence injectors than there used to be. When I put 95 lbers in my grand am, I had to run low impedence ones to get that flow when I built the car about 10 years ago, and then run an injector driver to manage them, with limited results, but now you can just buy high impedence ones that do the same thing, do a better job, and no extra headaches.

We sell 36lb injector kits on my site, and we also sell the brackets a la carte if you want to supply your own injectors.
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Old Today, 05:57 AM   #13
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What do you mean by "not last long at all"? Wear isn't the issue with injectors at this point. Its about accurate timing and spray pattern, both of which are fine at 80% for the injectors being discussed. Lucas slider type injectors are supposed to be good just past 90% but we don't have those from the factory. If its a road course setup, then lower % is better for heat, but street and drag race use is such short interval that you aren't wearing anything out.
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Old Today, 09:56 AM   #14
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Quote:
Originally Posted by MilzyZ34 View Post
Actually, anyone who does a 3500 swap along with some bolt-ons should probably get larger injectors. Ideally to keep the injectors lasting a long long time, you should run them at a max duty cycle of about 70% when the engine is at wide-open-throttle, and the injectors are at their max operating level. If you start pushing this value above that, the injector life starts dropping. Above 90%, and they won't last long at all. Well at 180hp, the stock injectors are sitting around 62%, but when we combine a 3500 with our tune, 68mm throttle body, plugs, t-stat, and 2.5" downpipe, it's making about 230 crank hp, and now those injectors are around 82% duty cycle. For me, that's just too high. A lot of people do 28's. I tend to do 36's. With 28's, 230hp is about 66% duty cycle, which technically is sufficient, but there's just no more room to grow if you add more mods., which is why I typically use 36's. With the 36's, you can do anything you want to do naturally aspirated and never run out of injector (320 crank hp would be 71%). Running a 36lb injector or even a 60 for that matter when you don't need that much flow won't actually tuning issues. Modern injectors if made by good reputable companies like Bosch and Siemens, or some others, are much more accurate than injectors used to be, and as long as the injector tables in the pcm are tuned correctly, there is no harm in running an injector larger than actually needed. High impedence injectors have come a long way recently, and there are many more options for high flowing high impedence injectors than there used to be. When I put 95 lbers in my grand am, I had to run low impedence ones to get that flow when I built the car about 10 years ago, and then run an injector driver to manage them, with limited results, but now you can just buy high impedence ones that do the same thing, do a better job, and no extra headaches.

We sell 36lb injector kits on my site, and we also sell the brackets a la carte if you want to supply your own injectors.
Ah yes... always trying to sell something, right Mike?

Bullsh!t. I made 230 HP at the wheels with my stock injectors before they hit 90% duty cycle. The stock injectors have plenty of room available to handle the rated 25 hp increase from the 3400 to the 3500. Throwing a bigger TB on an otherwise stock engine doesn't net a lot more airflow either. Now, if he's doing other mods as well, like an intake and exhaust and a tune, then yeah he might benefit from a bump in injector size. He does not need 36 lb injectors though, that's overkill. The 28 lb trailblazer injectors would be plenty, they are plug and play which simplifies installation, and they keep a similar spray pattern to stock which should improve idle and part throttle tuning. Better fuel atomization, better burn and fuel economy.
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Old Today, 11:34 AM   #15
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Quote:
Originally Posted by AaronGTR View Post
Ah yes... always trying to sell something, right Mike?

Bullsh!t. I made 230 HP at the wheels with my stock injectors before they hit 90% duty cycle. The stock injectors have plenty of room available to handle the rated 25 hp increase from the 3400 to the 3500. Throwing a bigger TB on an otherwise stock engine doesn't net a lot more airflow either. Now, if he's doing other mods as well, like an intake and exhaust and a tune, then yeah he might benefit from a bump in injector size. He does not need 36 lb injectors though, that's overkill. The 28 lb trailblazer injectors would be plenty, they are plug and play which simplifies installation, and they keep a similar spray pattern to stock which should improve idle and part throttle tuning. Better fuel atomization, better burn and fuel economy.
what mods did you have when you made "230whp"?

according to my tables which are based off of scans I've done over the years, the stock 22.5's are maxed at around 200-210whp on the dyno we use. Perhaps your dyno reads differently?
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Old Today, 11:48 AM   #16
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Quote:
Originally Posted by Vegeta View Post
What do you mean by "not last long at all"? Wear isn't the issue with injectors at this point. Its about accurate timing and spray pattern, both of which are fine at 80% for the injectors being discussed. Lucas slider type injectors are supposed to be good just past 90% but we don't have those from the factory. If its a road course setup, then lower % is better for heat, but street and drag race use is such short interval that you aren't wearing anything out.
What I mean is at 70% the injectors will last almost forever because they're not working as hard. The more duty cycle, the harder the injectors have to work, and they wear out exponentially faster as you go up in duty cycle. As they wear out, performance drops off and they can flow less fuel consistently, making the problem even worse. Also you get the effect where the hotter they get the less dense the fuel is, so the more fuel they have to flow to meet the air fuel ratio commanded in the pcm, again making the problem worse. If you ran a car at 90 something % on a dyno for a while making one pass after another, I wouldn't be surprised if you wore them out that day.

So the rule of thumb I was taught and have used forever is 70% to avoid all these issues, but if you'd rather tempt fate and run more, that's up to you. I have to warranty my work, and to me I don't see the justification to risk going lean and risk blowing an engine because of it. So are 36's overkill? Yes, and we make them overkill on purpose. I don't see the reasoning to buying slightly larger injectors over and over and over each time you add a couple parts to a car, and then have to retune the PCM every time when you can just put 36's in there and never have to change injectors again with any mod you want to install naturally aspirated, and you only have to go up if you go boost and turn it up.
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Old Today, 05:16 PM   #17
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Originally Posted by MilzyZ34 View Post
...So are 36's overkill? Yes, and we make them overkill on purpose. I don't see the reasoning to buying slightly larger injectors over and over and over each time you add a couple parts to a car, and then have to retune the PCM every time when you can just put 36's in there and never have to change injectors again with any mod you want to install naturally aspirated, and you only have to go up if you go boost and turn it up.

This says a lot right here. Tuning for an injector swap isn't that hard. If you are adding parts to an NA car like cam, heads, etc. then you should be retuning the car anyway.

Quote:
Originally Posted by MilzyZ34 View Post
what mods did you have when you made "230whp"?

according to my tables which are based off of scans I've done over the years, the stock 22.5's are maxed at around 200-210whp on the dyno we use. Perhaps your dyno reads differently?
Stock heads and cam. S/C with 2.5" pulley. Random tech 2.5" downpipe and SLP 2.5" exhaust. Stock airbox with K&N filter.

Yeah, blame it on the dyno.
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