Here are some of my tried and tested TBI mods. These work well in a 5 part upgrade. I have done this same mod on 4 TBIs in the last year and it worked very well on all of them. The mid-upper RPM power improved and throttle response was much sharper. I would say around 20 HP @ peak and about the same torque down low.

A.) Bump timing to about 4*
B.) TBI spacer (cheap Ebay 2 hole converted to open center, left rough)
C.) Ultimate TBI mods (double stacked pod gasket, unshrouded, left rough)
D.) Drop base open element air cleaner(this being my Van it is a flat base).
E.) AFPR set for 12.5-13.25 PSI (fine tweak it to match your setup)

Not necessary, but I recomeend a 180* thermostat. It is hot enough not to coroperate with the ECM calibration, yet cooler than stock. The cooler heads allow for slightly more timing and more dense air/fuel mixture and therefore more cylinder pressure making more power.

I always leave everything rough to help promote atomization.

These would be good in combination with 1.6:1 roller rockers, headers, full exhaust, and chip tuning.

 

instead of that tbi spacer you have id recomend a helix power tower. the one needed for a tbi engine is the one for the jimmy/blazer with the 4.3/5.7 tbi engine found here http://onestoptruckshop.com/ONLineOr...VYHelix.htm.th
i used this on my 91 rs along with all your other mods accept the timing advance.. with this added after the other mods i noticed a little better throttle response and pick up as well as 60 miles more per tank full.

 

I think the website is down being worked on.

 

I strongly recomeend that you stick with the one I posted. I picked it up as a cheap 2 hole off ebay, 30 minutes with my saber saw and dremel produced what you see. Works EXTREMLY well. The TBI setup needs ALOT more plenum volume to make a good top-end charge. The stock intake lacks it. The open center allows each side of the intake to breathe through the opposite throttle body bore. It is essentially like giving it a much bigger carb. On carb engines you can equate this to needing a larger carb with a dual plane manifold than with a single plane. I noticed an improvement of 1-2 MPG on my 1994 G10 vans 305 when combined with the other mods. The stock throttle body and intake combo on that beast generated a sizeable vacuum @ WOT. The 2 hold design does nothing for this. Without the spacer with the ultimate TBI mods, I was at 90 KPA and dropping at around 3,500. With the spacer it stays at 98-99 KPA all the way to 5,600 even with the factory air cleaner in place. It also has a hypertech powercharger on it. It further boosted power.

 

sorry heres the page again

Helix Power Tower Plus - Throttle Body Spacer - Chevy

and i forgot to addt that the picture posted is a generic one it does infact have dual bores that are spiral drilled to spin the air and fuel together to improve atomization of the air/fuel mixture.

it does infact look similar to the one in your pic accept that it is not just open in the middle.

i just want to be clear im not knocking your choice of spacer. i am only speaking from my experience with this,, the only throttle spacer i have tried.

 

Not trying to knock yours either, but the swirl ports already have plenty of swirl to them. The rough finish that I left on my spacer, IMO is better than being smooth.



Mine started out as a two hole $15.00 ebay special. I ran it for a while, pulled it off, then I cut the middle out of it. Worked well to begin with, but works even better when I cut the divider out.

 

if i still had a tbi car i would get one of yours and swtich them out and see which one i like better but since i dont i cant. i must say that whichever one someone may choose it would provide a boost over not having one at all.

 

I can agree with that. I will also say that you will never know which one compliments your driving style until you have experimented with them. Some people may like the extra grunt on the bottem that the 2 hole gives. I myself think that the TBI engine has plenty of off-the-line grunt but needs more top-end. In the end it all boils down to if you are satisfied with the end results. Some of us never are.

 

Fast, have you ever tried cutting the plenum dividing wall out of the manifold?

 

Also I dont even see a cheap spacer on ebay anymore, they are all the same price as the ones in summit.

 

the one in my lfost (if you choose to go with the one i reccomend that is) is 69 dollars

the one that works is for the 87-95 blazer/jimmy 4.3/5.0/5.7 tbi

 

How high can you go with a spacer because I want to lift my airfilter into my cowl and was considering spacing it to make for minimal shroudage around my cleaner.

 

when i used a spacer on a stock irock hood i had to remove the airfilter housing spacer ring in order for my proflow open air element to allow the hood to close. dont know if that helps.

lol prolly not.

 

No what I am wondering is can I space my TBI way way up into the cowl i am getting? or is the 1in spacer the limit?

 

i havent seen a bigger one but do some google searches you just might find one.

also you could always use 2 just get extra gaskets and longer bolts. but that may just be a stupid idea.

sorry im not more helpful.

 

Its alright I am trying to figure this out myself... My hole idea is to seal my aircleaner into my cowl so its all nice fresh cool air instead of the hot air its sucking in right now. Just wondering how much I can raise it w/o having to fab up a shroud.

 

My neighbor has. He then smoothed the gap area and had the coolant chamber holes (two small ones) welded closed. So he gained the more-open plenum without needing a spacer.

It's difficult to say precisely what the performance gain was from doing this mod, because he also did stamped 1.6 rockers, full duals and low-restriction cats, and a Caddy elbow/sewerpipe/cone airfilter.... and some ECM work. Those mods together resulted in mid 7 second 0-60 mph, as compared to high 9s in a fullsize 4000+ lb TBI LO3 Caprice. FWIW.