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Ok-
This was probably covered before, but here goes.
What are the advantages of PI over TBI, I assume thottle response is part of it(charge gets there faster). But other than that, what due you gain for the added complexity?
I am considering the MegaSquirt, and the TBI seems to be WAY simpler.

Any input would be appreciated.

Thanx,
Casey Brown

Sombody--anybody ??

Surely the great fi minds on this forum could point out the basic advantages of a injector for every cylinder vs. the much simpler single injector in the thottle body.
I am all about doing it right, but if the advantages don't apply to my application I would go the simpler route.

OK, I'll byte.. Usually when someone doesn't get a reply then everyone who has read it doesn't know the answer or figures it has been covered and you should search the archives. That said. I'll try.
TBI is more like a carb, but better. Benfits, simpler, cost less.
PI more tuneable, cost more, more complex.

Some may argue one will get you more HP or something else and that may be true, but where and how much. $$$ to get 5% more or ?
Read, Read, Read, and ask questions. Join the Megasquirt forum, the DIY-EFI forum or at least read as much as you can. Read Ray Greenwoods and Brad Anders (panders) ? post. They know a whole lot on the early VW-Bosch EFI and CIS systems... find Brads website (check archives here too) Tons of good info/
No flame, but no single person can say what is right or will be perfect for you, but you.
Happy Squirting


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Richard
Lost in Texas
68 Chopped Top Squareback (wasserboxer conversion)
69 Fastback Auto (MegaSquirt EFI)

[This message has been edited by PapaG (edited 04-10-2002).]

[This message has been edited by PapaG (edited 04-10-2002).]

Thanx PaPa G for responding..I DID search the archives to no avail, and I do realize that there is no "one size fits all" solution. It seems to me that there would be some reason the vast majority of aftermarket and performance oem efi went the multiple injector route. I am hoping someone here would lay out the basic pros and cons. I agree that a tbi would be like a single carb in a lot of ways, and as such, would favor low to med rpm range compared to a duel carb setup. Is that the only reason ? What would be the rpm cutoff for a TBI ?

I am far from being the expert on this stuff, but I'll try.
You have a engine size of 2.0l 4cyl (sample)
Now you have TBI with 2 injectors.(injector size dug out my A@# not real just a example) These 2 injectors have to be small enough to let the engine idle, and take it through max power-rpm. Injectors can run at 80% max duty cycle or they burn up, Meaning the must be off 20% of the time. So max fuel per hr x 80% = total
25x2x.80 = 40lbs TBI
20x4x.80 = 64lbs PI
smaller injectors will idle( too big they will flood) but you still have more fuel to make more HP-RPM
There is really a lot more than that, but I hope this gives you what you are looking for.. If not ask away. Maybe somelse will chime in too

------------------
Richard
Lost in Texas
68 Chopped Top Squareback (wasserboxer conversion)
69 Fastback Auto (MegaSquirt EFI)




[This message has been edited by PapaG (edited 04-10-2002).]

Generally, TBI injectors are peak and hold to allow the small pulsewidth at idle. If you use this type of induction, make sure your ECU has injector drivers which can handle P&H injectors.

The TBI systems I have seen are on V8s. If you have a V8 and carb manifold with Holley bolt pattern, TBI is easy to install.

You may realize the same drawbacks between using a single carb and TBI on a flat four engine. Due to the runner length and horizontal run required for a flat four engine, fuel may puddle and not stay in suspension.

I do not know what your application is, but can you not find stock FI hardware to install. This will provide you with port injection and having the hardware eliminates any simplicity you gain with TBI. Otherwise, if you are fabricating from scratch, it will take similar labor to fabricate port injection induction as TBI.

I agree with PapaG. You can always tweak to gain more power or drivability, but you must be willing to spend the dollars or time to gain that extra performance. It's easy to talk about optimum systems, but you must be willing to work for it. For me, simplicity is important, since it gives me a better chance to complete the project. To each his own.

Jay

Another plus for port injection on an aircooled Type 1 is that fuel vaporization all occurs at the head, helping with cooling!

I think every aftermarket injection system uses 4 injectors on a 4 cylinder. THe whole term TBI and PI is kind of mute with a air-cooled vw. Alot of the throttle bodies you can buy have the injector bosses in them and the fuel does spray out of the throttebody but it isn't really throttlebody injection because it has a seperate runner and injector for each port.
Most fuel injection systems can't run just two injectors on a 4 cylinder motor.
Also you would need two very big injectors to make any power unless it is on like a stock motor or something.
I really don't see any practicality to running just two injectors versus 4 injectors. Why put injection on the car and not use all it's advantages especially the advantage of more power.