I picked up a TBI unit from a salvage yard today and I going to begin the ultimate TBI mods. I have read all the ultimate TBI posts and am ready to go. Any other suggestions from those that have done this. I don't have a dremel but I don have a die grinder and air compressor so I'm going to be using it...shouldn't really make a difference.

 

Why are you doing it when you have a 305? Is there any performance gains, without touching other stuff?

 

Because it needs to be done, ESPECIALLY with the stock intake manifold. The stock intake manifold lacks any signifigant plenum volume. The stock TBI unit on the stock manifold becomes restrictive very quickly. The gain was substantial with my stock head, stock cam 305.

You can see from the log the MAP rising as the RPM increases, down to 93 KPA @ 3,500, it got down to 85 KPA @ 5,000 and choked off power.







The MAP was still falling at high RPM, even with the modified TBI, so I stuck in a 1" open center spacer and went to an open element.



This brought the MAP back to 99 KPA and increased the power above 4,000 rpm. It knocked 2 tenths off my standing 1/8 mile time and added 2 mph to the speed. I was not able to test the acceleration difference in the full 1/4 though.

 

Becuase I want to! Knowledge is power and what better way to gain knowledge then by jumping in and trying something. I eventually want to move to a 350 TBI and this is one thing that will help me with that move.

 

Tim, What did you end up paying at the junk yard for it? Is it a 2" TBI? My local parts yard doesn't currently have any but there looking for one from a 454 application. Just curious on the price to give me an idea so I dont get hosed. Thanks and keep us posted on your progress too would ya!

Brandon

 

Not to get you'll down, but LOOK on the classifieds both here and on Fullsizechevy.com. I recently gladly paid $60.00 shipped for a 2" Marine TBI unit here on this sites classifieds. The Marine TBI engines made between 280HP and 330HP depending on the year model and heads used (193TBI, 083 TPI, L98 113 Aluminum, or Vortecs). The cam remained the same in all engines. The Marine TBIs are FREQUENTLY overlooked on Ebay as well. Even though they have the 28 psi fuel pressure spring, the Marine regulator (vafpr), 2" bore, etc.

 

I payed $20 for it. It is not 2". It is out of a GMC truck...not sure if it is off of a 305 or 350. I have disassembled the entire unit for cleaning and I'm going to try and identify the injectors (flow rate based upon part number) to determine the size. I'll keep you posted.

 

I've been working on this throttle body in my spare time (not much time lately ). I'm using my die grinder and a bit that was in a die grinding kit that I bought from Sears. I've already worn the bit out. The kit said it was for cutting but I'm not sure that is right for this. What type of bits are you guys using? Any pics of the correct bit?

 

Is it a stone bit? the best bits I have found are the metal ones that have like a spiral to them...probably the most useful are the cone shaped ones. I got mine at the local welding supply house but you may have luck at Home Depot or Lowes too.

 

speed is key on the cutting bits. too fast and it will melt the aluminum instead of chip / grind it away and it will gum up the bit. I paid 15 bucks for the dremel carbide cutting drum i used to do my first tbi work. now the same bit is like 4.99 at walmart.

How did I do my last ultimate tbi? ANGLE GRINDER
took like 5 minutes, made a hell of a mess, but thats what the shop vac is for. LOL

 

I took my last TBI down to the local machine shop. For $15 he put it in the flat mill and took the ridges off of it. I then used sanding drums on a dremel to radius the inlets.

 

ya i was thinkin about that too... im sure my machinist friends will prob do it for free or less to nothing. its about 3 miles from my house... But yea, you are right too, people over look the marine TB