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Waste of time and money... Turbo TBI

kc8ksg

Active member
Joined
May 21, 2020
Member Number
1066
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27
So I bought a 91 Roadmaster a few years ago that had been sitting for 8 or so years before that from a guy for scrap price.
Finally got around to messing with it and with a little tinkering it runs and drives great, everything works including the AC.
Unfortunately 91 was the only year that got the 305, it's pretty underwhelming.

I've got a couple 5.3s and a couple 6.0s (lq4 and lq9) which it will eventually get one of, but right now I want to see how much I can squeeze out of the 305 before it let's go.

I thought about nitrous but the wet kits only go up to 125 for the TBI so I started looking into ebay/Amazon turbo kits. Again the TBI is the limiting factor with getting more fuel when you add air.

From my research I've found you can do an LT1 pump then turn up the fuel pressure and put bigger injectors in the TBI so it will fuel more, just not sure if it will be enough depending on the amount of boost.

I know it's a waste to do anything to the 305 and the LS swap makes more sense. I figure I can use the turbo stuff on another small block later. Just looking for comments from the peanut gallery if anyone has any experience with the tbi stuff.
 
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Add a throttle body spacer with an extra fuel injector or two. Use a pressure switch to "turn on" the extra injector(s) when you hit a certain PSI. Tune by adjusting fuel pressure or the size of the injector.

Edit: or do it with water/methanol injection, with the added benefit of cooling the incoming air charge and effectively increasing the octane "rating" of the incoming fuel charge.

The original water/meth injection kits just used an RV water pump. Use the windshield washer tank as long as you don't go over 50/50 methanol/water. Injection nozzles are fairly inexpensive.

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Last edited:
I bought an adjustable fuel psi regulator for my 454, havent installed it yet.

You dont need a "lt1" pump. Most aftermarket pumps will make more than enough psi/gpm. You only need about 19lbs before the tbi starts getting wonky.
 
MadScientist said:
Just following because I’m curious as well. Also in before every LS swap it comment.
Click to expand...
It'll get that eventually, but for now just wanting to see how cheap I can make power until it goes boom.
Tooheysmax said:
Click to expand...

I like the lowered sleek look but the faded woodgrain vinyl white trashyness of mine is growing on me, especially if it is ever actually somewhat quick.
MChat said:
Add a throttle body spacer with an extra fuel injector or two. Use a pressure switch to "turn on" the extra injector(s) when you hit a certain PSI. Tune by adjusting fuel pressure or the size of the injector.
Click to expand...
Good idea, I hadn't thought of that.
total newb said:
I bought an adjustable fuel psi regulator for my 454, havent installed it yet.

You dont need a "lt1" pump. Most aftermarket pumps will make more than enough psi/gpm. You only need about 19lbs before the tbi starts getting wonky.
Click to expand...
Yeah I read the lt1 thing in a forum researching, it just got a new pump a few weeks ago to try to get it running, so good to know.
 
A rising rate fuel pressure regulator would extend the capacity of the TBI injectors as well.
 
MChat said:
A rising rate fuel pressure regulator would extend the capacity of the TBI injectors as well.
Click to expand...
I found this on the YouTubes and he tapped into his temp sensor to adjust the fuel.

The 305 has the smallest injectors, 350 has a little bigger and 350 police the biggest that fit in the same throttle body. From what I've read you upgrade to the 454 throttle body after that.
I was thinking the biggest injector in my current TBI with higher fuel pressure and watch my AFR and see where that gets me as a starting point.
 
This is the question of the century.
The $$$ spent to go Terminator/FAST/etc. easily exceeds the LS swap.
Gen 1/2 sbc is really lacking a affordable induction system.
If I had a milling machine I might think about putting bungs in a Aluminum intake.
 
kc8ksg said:
I found this on the YouTubes and he tapped into his temp sensor to adjust the fuel.
Click to expand...
That's an interesting idea to tune AFR, the piggy-back computer I used on my old SRT-4 did something similar with the MAP sensor voltage. I noticed he mentioned using a RRFPR a couple of times.

Depending on how much boost you're running, water injection can make up for not having an intercooler. Or, if you have both, water injection can make up for not using better gas. While most guys were running 20 psi on premium gas, I was running 24 psi. I also saw a temperature drop of about 40 degrees at the AIT sensor. Ambient temperature on the day I was tuning was 116 degrees. AIT without the water/methanol injection read 122 degrees, AIT with water/methanol injection showed 84 degrees. I ran a 60/40 mix (60% water) and a water/methanol injector that was sized to about 20% of the total of the fuel injectors I was using.
 
CarterKraft said:
This is the question of the century.
The $$$ spent to go Terminator/FAST/etc. easily exceeds the LS swap.
Gen 1/2 sbc is really lacking a affordable induction system.
If I had a milling machine I might think about putting bungs in a Aluminum intake.
Click to expand...
I looked at a few different EFI setups but your right, at that point it's really not worth messing with but it would make tuning easier. That's why I'm leaning towards trying to make the TBI work as best it can until it doesn't.
MChat said:
That's an interesting idea to tune AFR, the piggy-back computer I used on my old SRT-4 did something similar with the MAP sensor voltage. I noticed he mentioned using a RRFPR a couple of times.

Depending on how much boost you're running, water injection can make up for not having an intercooler. Or, if you have both, water injection can make up for not using better gas. While most guys were running 20 psi on premium gas, I was running 24 psi. I also saw a temperature drop of about 40 degrees at the AIT sensor. Ambient temperature on the day I was tuning was 116 degrees. AIT without the water/methanol injection read 122 degrees, AIT with water/methanol injection showed 84 degrees. I ran a 60/40 mix (60% water) and a water/methanol injector that was sized to about 20% of the total of the fuel injectors I was using.
Click to expand...
I considered water/meth but figured I'd get it all in and then see where I'm at.
 
CarterKraft said:
This is the question of the century.
The $$$ spent to go Terminator/FAST/etc. easily exceeds the LS swap.
Gen 1/2 sbc is really lacking a affordable induction system.
If I had a milling machine I might think about putting bungs in a Aluminum intake.
Click to expand...

You can make more power for cheap than you could ever want out of a 23° 400+ ci small block Chevy with a single 750 carburetor and twin turbos. You don't even have to intercool it if you run methanol. Why you need EFI?
 
SLOWPOKE693 said:
You can make more power for cheap than you could ever want out of a 23° 400+ ci small block Chevy with a single 750 carburetor and twin turbos. You don't even have to intercool it if you run methanol. Why you need EFI?
Click to expand...
This. Fucking with old EFI is just not worth it for how tune-able they aren't. Even when you can tune them it's an expensive kludge.
 
arse_sidewards said:
This. Fucking with old EFI is just not worth it for how tune-able they aren't. Even when you can tune them it's an expensive kludge.
Click to expand...

Kid from Street Race Chanel on YouTube has a 434" SBC with AFR heads, a super Victor intake and a single ATM 750 blow through carb with twin 67mm turbos on it that makes more than 1200hp to the wheels on methanol. He uses a big electric fuel pump, an MSD ignition/distributor with a programmable MSD retard box and a digital A/F ratio gauge that's mounted to the dash. His "data acquisition system" is a gopro mounted to the back window that looks at the gauges and A/F readings during a run. :laughing:
 
I was always under the impression that the biggest limit for TBI was what the PCM could tolerate short of complete custom programming. I though magic number was ~10% more hp.:confused:

Watching because I like off the wall.:homer:
 
Well if you wanna wake it up.

  • Long Tubes and custom 2 1/2" exhaust with chambered mufflers (if you are resourceful 96-97 F body LT1 manifold and Y pipe. You ant the one with the huge assed driver side cat. Keep it or gut it. But that wont become a restriction on a 305 until you make 375 HP)
  • Duct tape or cleanly plumb in a 4" dryer duct with a home depot rectangle floor register for a cold air intake.
  • 1.6 ratio rockers on the exhaust and 1.5s on the intake.
  • Bump the fuel pressure a lb or two.
  • Remove the charcoal filter in the air cleaner if it has one, swap in a K & N or spectre equivalent.
  • Throttle body spacer.
  • 454 throttle body with injectors if you can find them. IIRC 2 of the BBC injectors are the cost of a holley sniper alone.
  • Loosen the knock sensor and hand tighten it with about 10 wraps of stainless steel pvc tape.
  • 160 degree thermostat, colder plugs and set the base timing around 17 degrees. Octane boost or some race mix for fuel.
  • Find a stock used 4L60E converter from a vortec 4.3L S series Suv. That should be 2300-2450 stall in the heavier car.
  • Transgo shift kit in the trans
  • 4.10 gears, trust me it will help with the struggling 305 and may help fuel milage
  • Some sorta limited slip torsen or locker.
  • Stocky rear tires.
When you get serious just slap a holley sniper on the 305. That's something that can be reused on a 350 or 400 or whatever. And can handle boost

That should get that car into the low 15s in the 1/4. Maybe low 16s if your up in elevation. That's the 80s Cadillac recipe to wake em up. Its basically the same car. I have seen it run a 13.70 in a 5.7 L TBI with a tiny cam and vortec heads.

Good luck and keep us posted.
 
turbo shit is waaaaaaay too much effort for blowing up a gen 1 small block

get you some proper port nozzles for your nitrous shit and tap them into the intake with the intake on the car
leaf blower combobulated onto the intake to keep the chips blowing outtta the holes you're drilling
 
I thought that would have an electronic quadrajet? Maybe that ended in 1990?
 
SLOWPOKE693 said:
Kid from Street Race Chanel on YouTube has a 434" SBC with AFR heads, a super Victor intake and a single ATM 750 blow through carb with twin 67mm turbos on it that makes more than 1200hp to the wheels on methanol. He uses a big electric fuel pump, an MSD ignition/distributor with a programmable MSD retard box and a digital A/F ratio gauge that's mounted to the dash. His "data acquisition system" is a gopro mounted to the back window that looks at the gauges and A/F readings during a run. :laughing:
Click to expand...

Lil'John said:
I was always under the impression that the biggest limit for TBI was what the PCM could tolerate short of complete custom programming. I though magic number was ~10% more hp.:confused:

Watching because I like off the wall.:homer:
Click to expand...

Will12785 said:
When I did my turbo s10 I slapped a blow through carb on it.
Click to expand...
I don't want to throw a lot into the TBI, just kind of figuring trying some cheap YouTube/forum tricks to squeeze more fuel out of the TBI and if that isn't enough go with a blow through carb or Holley Sniper. From what I've found a blow through carb is close to the cost of the Sniper unless you build your own, plus an intake and whatever other odds and ends I'd need.
 
ANGRYBLACK said:
Well if you wanna wake it up.

  • Long Tubes and custom 2 1/2" exhaust with chambered mufflers (if you are resourceful 96-97 F body LT1 manifold and Y pipe. You ant the one with the huge assed driver side cat. Keep it or gut it. But that wont become a restriction on a 305 until you make 375 HP)
  • Duct tape or cleanly plumb in a 4" dryer duct with a home depot rectangle floor register for a cold air intake.
  • 1.6 ratio rockers on the exhaust and 1.5s on the intake.
  • Bump the fuel pressure a lb or two.
  • Remove the charcoal filter in the air cleaner if it has one, swap in a K & N or spectre equivalent.
  • Throttle body spacer.
  • 454 throttle body with injectors if you can find them. IIRC 2 of the BBC injectors are the cost of a holley sniper alone.
  • Loosen the knock sensor and hand tighten it with about 10 wraps of stainless steel pvc tape.
  • 160 degree thermostat, colder plugs and set the base timing around 17 degrees. Octane boost or some race mix for fuel.
  • Find a stock used 4L60E converter from a vortec 4.3L S series Suv. That should be 2300-2450 stall in the heavier car.
  • Transgo shift kit in the trans
  • 4.10 gears, trust me it will help with the struggling 305 and may help fuel milage
  • Some sorta limited slip torsen or locker.
  • Stocky rear tires.
When you get serious just slap a holley sniper on the 305. That's something that can be reused on a 350 or 400 or whatever. And can handle boost

That should get that car into the low 15s in the 1/4. Maybe low 16s if your up in elevation. That's the 80s Cadillac recipe to wake em up. Its basically the same car. I have seen it run a 13.70 in a 5.7 L TBI with a tiny cam and vortec heads.

Good luck and keep us posted.
Click to expand...
I've looked at the Sniper and might go that way if I can't get the fuel I need from the TBI. Thanks for the advice on the other stuff I might tinker with some of it and see what helps.
[486] said:
turbo shit is waaaaaaay too much effort for blowing up a gen 1 small block

get you some proper port nozzles for your nitrous shit and tap them into the intake with the intake on the car
leaf blower combobulated onto the intake to keep the chips blowing outtta the holes you're drilling
Click to expand...
I was right with you when I started this, throw some nitrous and see how much it would take. Then the more I looked into it, I found I'd need a wet kit to actually have it make power. Plus the cost of the bottle and the cost to fill the bottle would have me at $1k or so. The ebay headers and turbo will be under $500, odds and ends another few hundred and I'll have a turbo and won't have to drive an hour and a half to fill a bottle.
6 one or half dozen of the other, I'm not married to the turbo, but am drawn to the cheap Chinese ebay garbage.
 
kc8ksg said:
I don't want to throw a lot into the TBI, just kind of figuring trying some cheap YouTube/forum tricks to squeeze more fuel out of the TBI and if that isn't enough go with a blow through carb or Holley Sniper. From what I've found a blow through carb is close to the cost of the Sniper unless you build your own, plus an intake and whatever other odds and ends I'd need.
Click to expand...
I built mine from one of those old 390 cfm holly carbs. I don't think I had much money into it at all. Piped it with one of those 4" spectre air rams.
 
Stock 305 injectors are 55lb/hr and 454 injectors are 90lb/hr and they aren't that much on rockauto. I'm wondering if the 454 injectors combined with a little higher fuel pressure would be enough fuel for the boost.

I don't mind trying the injectors and putting the turbo on it and if it's still running to lean then going blow through carb or sniper.

Just thinking out loud here so people who are smarter than me can poke holes in my logic.

In thoery... if the TBI with 454 injectors isn't enough fuel I would just adjust the wastegate down until I had enough fuel for the right amount of boost to get the correct AFR right?

Then I could decide if I want to go blow through carb or Sniper.
 
SLOWPOKE693 said:
Kid from Street Race Chanel on YouTube has a 434" SBC with AFR heads, a super Victor intake and a single ATM 750 blow through carb with twin 67mm turbos on it that makes more than 1200hp to the wheels on methanol. He uses a big electric fuel pump, an MSD ignition/distributor with a programmable MSD retard box and a digital A/F ratio gauge that's mounted to the dash. His "data acquisition system" is a gopro mounted to the back window that looks at the gauges and A/F readings during a run. :laughing:
Click to expand...
So Ill continue this in my own thread but I'm curious how much cash it takes to get to the same spot.

I have zero blow through carb knowledge, I know there are some diy style guides but I don't have the time or money to dump into "learning blow through".
The idea is interesting if you could do it cheap ish.
 
Out of all of the headers I like these for space and doesn't look like it'll affect my AC compressor.

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Chinese ebay turbo

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I can get an oil feed from the oil pressure sensor and the return can go in the fuel pump block off plate.
 
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