http://cgi.ebay.com/ebaymotors/ws/eB...m=170207702511

Thats the one I won on ebay!

What yall think?

 

you don't need it. I hope you didn't spend to much. Your stocker with the ultimate tbi mods is good for 300+ HP. I have a 46mm xtremefi tbi and I'm thinking about selling it for that same fact.

 

Well im not putting it on for at least 1 or 2 months when I get my heads, and other stuff.

And if its so unnecessary then why does everyone get it?

 

some of us are using them for strokers or

<------Big blocks.

just teasing. The 454 unit really needs to be tuned for and will

cause drivability problems on engines that are near stock. Even full "bolt on cars"
using the stock tbi unit on a better intake manifold would be a better choice. Properly maching cam,and headslets you select the proper manifold to target the rpms you want to run/make power in. Then diy tuning.

 

Looks like you got a good buy. It should be good when you go to the hotcam and zz4 heads. But yes be prepared for doing the tuning.

 

Thanks guys.

Yeh I know I will def have to tune it. Should the car be drivable when I get the heads, cam, TB, intake manifold on?

I plan on getting it tuned at a local tuning shop, they said 400$ I think or 450$ and they would tune it, and they said they have done a few cars with TBI, so should be running great after I take it there. They are also going to give me a copy of the BIN, so if I change anything in the future I can modify it.

 

Probably will not be drivable with the stock 305 chip. it will be extremely rich. You may have a bit better luck with 350 injectors to get it running. It will still be rich but will probably run. Just don't get on it hard. May run well enough to get it to the shop. Then put the 454 injectors back in to get it tuned.

 

Well ive got the EBL Flash already in my car. So maybe I can just set it leaner when I get it all put in so i can drive it to get tuned. And actually just by doing a bunch of VE learns it leaned out on its own I think.

 

If you got Ebl then no problem. Set the BPC for the injector size. Do some ve tuning and it will probably be drivable.

 

The only way I would use one of those is if I was planning on 350+ RWHP I think that using one of those requires serious tuning. I tried running the 46mm tbi with my TBIchips tune and it ran "ok" but it lost a bit of down low torque and it pinged at WOT. I had to put the stocker back on.

 

Actually, its more like 250+rwhp where one should start to think about a larger TB. But since you are no where near that level stock is probably your best bet.

Timothayyy on the other hand will be in that area and will see gains from the larger TB. Yes, tuning will be more difficult, but nobody said HP was easy. The more you want the more time and money you will spend.

 

Well said but I'm not completely clueless. If I wanted to play with getting alittle more air I would first use the 46mm. If I wanted to go higher after the fact, such as a larger motor or what not ofcourse I would use the 50mm. But the way I see it the max I think you would ever need FOR A 305 would be the 46mm. IMHO.

 

Yeah, my set up is going to be very difficult to tune, but I just gotta get it to the shop for them to tune it, after that its all on them to tune it.

I should be having a very potent 305 TBI system going, hopefully it will be done by Third Gen Nationals or The East Coast F-Body Nationals. And hopefully ill have some impressive hp and torque numbers.

 

Timothy, you got a smokin' deal on the BB throttle body, but even with your planned upgrades its probably too much flow for your 305 engine. What this means is not only will it be hard to tune but you'll make less horsepower than with a better matched unit.

Here's a common formula used to size carbs that also gets you in the ball park on the size of your TBI unit:

CFM = ((Displacement * RPM) / 3456)

Some recommend scaling this down by .85 for "street" applications or up by 1.1 for "drag" applications.

Lets say your going to hit the drags with your engine, so we'll scale it up. With the cam you're talking about, I'll guess it will make peak HP around 5200 RPM, correct this in the formula if I'm wrong.

CFM = ((305 * 5200)/3456) * 1.1 = 505 cfm

This is pretty close to the 490 cfm of your stock 305/350 TBI (the units are exactly the same). With the "ultimate" mods you can get it up to 500 cfm.

What happens when you go larger is the velocity of the air thru the unit gets too low, and your cylinders don't get filled with as much air/fuel and your engine makes less horsepower. This is definitely a situation where bigger isn't always better.

Off the top of my head, I believe the stock BB units flow around 620 cfm, too much for your 305 at the RPM range you are planning to run it.

I'd hang on the BB unit and use it when you go to a 350.

Another rule of thumb that gets you close on carb/TBI sizing is to multiply a good (and realistic) estimate of the max flywheel HP your engine will make times 1.62 .

Lets say your 305 with the new heads and cam will make 300 HP.

cfm = 300 * 1.62 = 486 cfm

Again, very close to the 490 cfm of your stock TBI unit.

Paul T.

 

Hmm, yeh it was a good deal. But all the guides here say to get the 454TB, lol.

What about if I get on the bottle? Because ive been thinking about getting maybe a 75 shot. Would that affect the needed cfm?

I dont think im going to get a 350 in this car unless this motor like blows up. As long as the motor is good I see no reason to replace it.

Well when I get it tuned they will tell me the peak hp and torque numbers, so if they seem too low, I may try to just modify my stock 305TB and see if that helps.

 

The specs on the LT4 hot cam are more aggressive than I realized, they show it capable of making 394 HP at 5500 RPM, so if your heads and exhaust system are up to it you should be able to match those numbers scaled down by the displacement difference:

HP = 394 * (305/350) = 343 HP

The HP rule of thumb is now cfm = 343 * 1.62 = 555 cfm

and a recalc of the other rule of thumb shows:

CFM = ((305 * 5500)/3456) * 1.1 = 533 cfm

I still think you'll go faster with the stock 305/350 TBI versus the stock BB one, but the stock 350 one may be limiting your HP a little, what might be the best way to go is a bored out 350 unit, they end up around 590 cfm.

Unless you have a really good tuning shop that has a lot of TBI experience you'll definitely be better off learning to tune yourself, especially if you plan further upgrades down the line, those trips back to the dyno will add up fast.

Dyno tunes are also compromised by the limited time they can spend on your car, they might get it close but to get it perfect requires driving it for a while and making some refinements.

If you can scrounge a laptop the $500. you're planning to spend at the dyno shop is enough to pay for either the slick EBL system from www.dynamicefi.com or a tuning setup from www.moates.net .

Learning to tune does take some effort, and to be honest, some studying of the info on these forums, but there are a lot of sharp guys on here that will help you over the tough spots.

Paul T.

 

The shop said they had done several TBI.

Also I already have the EBL Flash system and plan on adding a wideband sensor to that set up soon.

I mostly just want to take it to a shop so that I can just start driving it in perfect or near perfect conditions without any downtime.