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Old 02-14-2011, 03:55 PM
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What is the correct TBI injectors for 383 stroker

I just installed a new GM Performance HT383 stroker. I had the GM intake mainfold bored out to 2" from the stock 1&11/16. I also installed a 454 throttle body by SPR. I installed new 454 injectors, The fuel flow is too much for the engine: black smoke, etc. What is the cfm that this engine needs to run efficiently. I heard a holly 650 would be about right, which injectors would be the best match for this set-up.
The camshaft that came with the GM crate 383 is:
Valve diameter (intake/exhaust) 1.94"/1.50"
LIFT .431 intake .451 exhaust
Duration:196 intake 206 exhaust
Centerline: 108 ATDC intake, 116 BTDC exhaust
The compression is 9.1:1
The axle ratio is 373
the tires are 245/75R16
HP 340 Torque 425

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Old 02-14-2011, 05:12 PM
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I heard the "cop car" injectors are the way to go @ 65lbs/Hr. Here is a quote from a pretty useful site:
Quote:
GM released 5 sizes of TBI injectors (actually more but those are the important ones) 40lb/hr for the 4.3L and 5L engines, 55lb/hr for 350 engines, 65lb/hr for cop car 350 engines and (80lb/hr and 90lb/hr) for 454 engines.
I'm not sure how old the info is but there is a lot for what you are doing. Read the whole page if you get a chance: http://www.tbichips.com/truckmods.htm
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Old 02-14-2011, 05:24 PM
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Thanks, I'll go with the cop injectors. I knew I needed something less than 454 injectors but wasn't sure what.
Jeramiah
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Old 02-14-2011, 05:48 PM
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One more thing you can try is reducing the fuel pressure going to the injectors. What is your pressure now?
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Old 02-14-2011, 06:21 PM
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Quote:
Originally Posted by satdiver1
I just installed a new GM Performance HT383 stroker. I had the GM intake mainfold bored out to 2" from the stock 1&11/16. I also installed a 454 throttle body by SPR. I installed new 454 injectors, The fuel flow is too much for the engine: black smoke, etc. What is the cfm that this engine needs to run efficiently. I heard a holly 650 would be about right, which injectors would be the best match for this set-up.
The camshaft that came with the GM crate 383 is:
Valve diameter (intake/exhaust) 1.94"/1.50"
LIFT .431 intake .451 exhaust
Duration:196 intake 206 exhaust
Centerline: 108 ATDC intake, 116 BTDC exhaust
The compression is 9.1:1
The axle ratio is 373
the tires are 245/75R16
HP 340 Torque 425
You need to replace the chip in the computer. With EFI, unlike a carb, the air and fuel flows are separate functions. The computer connects them with function maps where sensor information of RPM, throttle position, and manifold vacuum are used to compute the air flow through the engine to which the proper fuel is added by controlling the injector's on to off time. But this is done for each specific engine configuration where the cam greatly influences the relationship of manifold vacuum to the other two functions and displacement establishes the air flow requirement at any throttle opening.

You have larger cam than what comes from the factory and you added 33 more cubes above a 350 and 78 more if the original engine was a 305. The cam has changed the manifold vacuum relationship to the throttle position and RPMs while the 383 increased the air demand. The computer has no way of knowing. It just takes the variable relationships and tries to find the place on the map that appears to be the correct look up number for the injector on time.

Part of the problem is the larger 454 injector which will deliver more fuel than a 350 injector for the same on time. The use of a smaller injector may solve the low and mid cruise richness but risks going lean on the upper end.

Reprogramming the chip can deal with the large 454 injectors you have by reducing on time for feeding the 383. Or you can go to a smaller injector but you still have to correct the on time to get them to feed the engine correctly because of the cam and displacement changes. Pick an injector and have someone like TBI Chips at http://www.tbichips.com/ program what you need. The smaller injector will be switched on more of the time than the larger injector. More on time begets a hotter injector operating temp, generally it is accepted that on time of the Duty Cycle shouldn't exceed 80% of the time at max flow requirement. The TBI Chips people will be helpful in this area when you talk to them. The problem you'll have is at WOT the typical 454 injectors cannot put enough fuel into the engine and keep from cooking themselves from excessive on time to feed 340 horses. This power level is getting to, or is slightly beyond, what they can comfortably do in pounds of fuel delivered per hour. So while the air flow from the 670 CFM unit is more than sufficient for 340 hp from a 383 the 454 injectors are right at their upper ability to supply enough fuel which comes close to nullifying the cop car injector idea.

Bogie
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Old 02-14-2011, 07:29 PM
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I have the upgraded chip from TBIchips.com, but the engine still is to rich, black exhaust smoke etc. That is why I was looking at a smaller injector with better flow than stock for a 350. The engine is in a '95 suburbanI wanted the extra power for towing and because the stock 5.7 with 190 hp was pitiful. I don't plan on running anywhere the 6,000 rpm the stroker is capeable of. I just don't want to throw unburned fuel out the back. Does this make any difference in the full flow time you were tgalking about?
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Old 02-15-2011, 05:24 AM
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Is the Chip you have matched to the Injector you have? That engine should look for 630-710 CFM a stock GM SB TB only flows around 490. My guess is you have 454 Injectors in a stock body. They are overpowering the air and thus leaving with a rich run situation.

I would either send out your stock TB to be bored to a 650 or buy a 454, or Holley 670. Then take the truck to a good chassis dyno and run it for a couple of tunes, "power" Streeability" and "economy". A good aftermarket tuner can get it close but no matter what a Chassis tune is far better.

Here is this to calculate what you need for CFM and injector poundage.

TBI Fueling

Introduction:

Second only to the stock TBI ECM, the stock TBI fuel delivery system leaves a lot to be desired. Starting at the tank the fuel pump is a turbine pump. Quiet and long lasting, but weak fuel delivery. The fuel pressure regulator is set for approximately 12 psi (30 psi on '94 & '95 trucks). With a service range of 9 to 13 psi being considered good. This equates to a 17% to 20% change in injector flow rate over the service range. Then the stock injectors are just large enough for the engine they were on top of.

From all of this, it is obvious that GM never put a TBI unit on anything but a low performance engine. The largest GM TBI unit was provided on the BBC 7.4l trucks. This is a 2-bbl unit with 2" bores.

Even though in stock form TBI setups were never used on a performance engine, it doesn't mean that they can't be used on a high performance engine.


All is Not Lost:

There are several ways to increase the flow capacity of the TBI unit and the injectors. The TBI units can be bored out larger for more airflow. Two 2-bbl units may be placed on a dual-quad intake manifold. Holley and Accel make 4-bbl TBI units. For additional fuel larger injectors and/or high fuel pressure can be used.

The first thing to do is to start with a decent estimation of engine horsepower. For the best results be reasonable in this estimate. From this we calculate the required fuel for that horsepower. Then work toward the required injector flow rating. Selecting the injector and fuel pressure that delivers the required amount of fuel as the final step.


Calculating Fuel Requirements:

You knew there had to be some math. Can either use your Windows calculator or open a spreadsheet, then follow along.

An important parameter in engine performance is known as Brake Specific Fuel Consumption (BSFC). It is the pounds of fuel required to generate one (1) crankshaft HP for one hour. The lower the number the more efficient the engine. Engines using gasoline with forced induction (turbo/supercharger) run between .55 and .60 BSFC. That is it takes between .55 and .60 pounds of fuel to generate one horsepower for one hour. An engine with moderate compression ratio and so-so heads the BSFC will be about .50. An engine with higher compression ratio and a decent chamber runs about .45 BSFC. With ultra high performance engines running .35 BSFC and lower. If you have the engine dyno'd (not the car) the BSFC can be measured.

For your basic high performance street engine with decent heads a value of .45 is typical. Let's say that the engine is making 400 HP peak. How much injector is required?

First calculate the amount of fuel required to produce 400 HP at a BSFC of .45:


400 * .45 = 180 pounds of fuel per hour (#/hr).


Then factor in a maximum of 85% duty cycle for the injectors:


180 / .85 = 212 #/hr


The duty cycle of the injector is the ratio of on time to off time. Note that this is not the best method. The required 'off' time is really tied to RPM, not a duty cycle.

OK, now we know that the engine requires 212 pounds of fuel per hour to produce the rated 400 HP. To do this with two injectors each needs to provide half that amount.


212 / 2 = 106 #/hr per injector.


As of writing this there are no 106 #/hr TBI injectors available. However, by using BBC 81 #/hr injectors and increasing the fuel pressure the 106 #/hr delivery can be achieved. To calculate the required fuel pressure we will use the square of the ratio of the injector flow rates (the 13 is the stock fuel pressure in psi for the rated 81 #/hr):


SQ(106 / 81) * 13 = 22.3 psi (To do this with the Windows calc put it into scientific mode: View->Scientific. Then use the x^2 function for SQ).


By using two 81 #/hr injectors at 22.3 psi they will provide 106 pounds of fuel per hour per injector. This is enough for the 400 HP. And by running the fuel pressure above 18 psi it is a perfect candidate for a Vacuum Referenced Fuel Pressure Regulator (VRFPR). See further along for information on the VRFPR.


Fuel Delivery

So now how do we get 22.3 psi of fuel pressure. First thing is to install a high pressure pump. Second is to install an external FPR or modify the stock one.

For a fuel pump be careful to not purchase the biggest baddest pump there is. High pressure pumps move a lot of fuel at 43 psi (port fuel pressures). And deliver even more fuel at 22.5 psi. The TBI unit, regulator, and return fuel line need to pass back to the tank any fuel that isn't used by the engine. A pump that is too large can cause the fuel pressure to increase above the set point.

Injector & TBI Unit Information

GM produced TBI units in both 1-bbl and 2-bbl configurations. Single 1-bbl units were used on 4 cylinder engines. Dual 1-bbl units were used on the Corvette and Camaro Crossfire injection setups.

In the 2-bbl TBI series the popular units are found in three sizes:


2.8l and 3.1l engines:
◦have 1-3/8" bores and flow about ?? CFM
4.3l, 5.0l, and 5.7l engines:
◦have 1-11/16" bores and flow about 490 CFM
7.4l engines:
◦have 2" bores and flow about 645 CFM

The flow ratings are approximate and are at 1.5" Hg. This is the same pressure that 4-bbl carburetors are rated at.


For injectors they come in various flow rates. The common injectors that are found in the above TBI units are:

2.8l and 3.1l engines: 33 #/hr
4.3l engine: 45 #/hr (note: some units have different flow rate injectors. This is done to help with fuel distribution.)
5.0l engine: 55 #/hr
5.7l engine: 61, 65, & 68 #/hr
7.4l engine: 46*, 75 & 81 #/hr.
*Just watch for the '94 - '95 BBC truck units as the injectors only flow 46 #/hr at 13 psi. Which is 74 #/hr at the 30 psi these TBI units use. On the up side they come with a 30 psi FPR. The down side is that the injectors are small.



Good Luck....
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Old 02-15-2011, 07:01 AM
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Wow,
That is a lot of info. I appreciate that. I have a new throttle body from spr that was also bored to 2 inches to match the manifold, along with that I received a stronger spring and a higher pressure fuel pump. This is why I thought the 454 injectors were wrongI am getting too much fuel. I will try the formulae you sent and see what I end up with. Thanks again.
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Old 02-15-2011, 08:25 AM
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its possible to much fuel pressure or a bad reg. is causing it to dump extra fuel. Spec from GM on a 454 is 9-13. If you are at 15+ thats a good place to start. Try to tie in a T fitting on the TB to measure actual pressure.


Keep me posted, also just double check with the chip programmer a Generic plug in chip won't be able to compensate for a new injector, they most likely widen pulse time which in your case would also cause a flood/rich condition, does it suffer any other problems IE stumbles, poor start, gas wash?
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Old 02-15-2011, 09:06 AM
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Quote:
Originally Posted by satdiver1
I have the upgraded chip from TBIchips.com, but the engine still is to rich, black exhaust smoke etc. That is why I was looking at a smaller injector with better flow than stock for a 350. The engine is in a '95 suburbanI wanted the extra power for towing and because the stock 5.7 with 190 hp was pitiful. I don't plan on running anywhere the 6,000 rpm the stroker is capeable of. I just don't want to throw unburned fuel out the back. Does this make any difference in the full flow time you were tgalking about?
I'd recommend you talk with them if you haven't. In the mean time run a pressure test to be sure the regulator is keeping things in the proper range, you can tune a bit if you install a variable pressure regulator. Another thing to be looking for is whether the computer recognizes when the engine is warmed up and comes out of choke mode. I don't know what TBI set your chip for, the factory requires the engine coolant be above 176 degrees F, many custom chips lower than to 160 but you need the specific spec. If the choke mode is at the OEM setting and you're using a 160 thermostat the computer will not come out of cold start mode.Another thing is the quality or condition of the injectors, if these are old used injectors it is possible that the valving leaks.

Certainly this needs to get fixed not just from a fuel burn standpoint but also the excess fuel is washing the upper cylinder lube away which increases top end wear by a lot.

Bogie
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Old 02-15-2011, 09:49 AM
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I went to TBIchips, if you didn't tell him what injector and TB you were running and he programmed it thats the basis of your problem.

I agree with Bogie too, if its programmed for 176 choke turn off you'll be full rich all the time.

All kinds of problems with over fueling, and those are over emphasized on a new engine.

Ultimately 200 spent at a good GM chassis Dyno will be the best money spent I'll bet you a dinner.


"personal note"
98' Mustang with BBK Long tubes, TB, X pipe, PI head upgrade and a 5.1 Stroker kit light weight flywheel, underdrives and 29lbs injectors . I had a custom chip flashed and the programmer promise me that it would work fine and any Dyno time wasn't worth it.

I took my car to Steen Racing in VA beach, they put it on the Chassis and at 115' in the shop and high humidity they got another 21HP took care of my off idle stumble and WOT hesitation. Also Cold start up was much better and they car all in all drove 100 times smoother ran better and got 2MPG better.

they did 4 different tunes, 2 for performance 1 for Economy and 1 for Juice.

All told it cost me 220 dollars and they did at least a 12 pulls plus waited for me to replcae the plugs on it.

I would go straight to a good dyno after checking the injectors and the Key on Engine off Fuel pressure.
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Old 02-15-2011, 09:49 AM
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First off any time you make an engine change your going to need a new chip burnt depending on what year the truck is. Thats just to start off with. You need to do a little reading and fine a tuner in your area if you have on because the can give you a better tune. If you don't have a tunner in your area fine the close chip guy to you Fast chips, Pcmsforless, Wester garage. Tbichips.
Tunning: www.thirgen.org
Trucks: www.fullsizechevy.com
There more out there Just depend on what your plans are.

Craig
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Old 02-15-2011, 03:19 PM
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Try at howell-efi.com
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