Carbs vs Aftermarket FI

Porsche_monkey · 06-17-2003, 07:20 AM

Can't a properly set up and tuned aftermarket fuel injection system make just as much power and be more reliable than a carb set-up?

I am thinking of adding megasquirt FI to replace the CIS on my 2.7. Everyone seems to suggest that carbs provide the most horsepower, why?

Tim Walsh · Tim Walsh's Garage

I think everyone says carbs since they're easy to bolt on and dial in. FI requires lots of work tuning something on the order of 5hours vs 30 hours from what I've heard.

FI does make a little bit more power since it can be tuned almost exactly. Sometimes it will make alittle bit more top end HP but in general I think it makes more power throughout the whole RPM band when compared to carbs.

I'm a FI guy myself and if I ever own a 911 that doesn't have MFI or motronic I'll probably go megasquirt.

Just my $0.02 from a desktop porsche junkie

Porsche_monkey · 06-17-2003, 07:30 AM

l33t: You might want to check out

http://www.geocities.com/tbitz/cis_to_efi.html

Tim Walsh · Tim Walsh's Garage

yep yep I've read through it at least twice. I've got MFI on my car right now so I'm more than happy with it. If I end up getting a CIS car, I'm definitly switching to megasquirt and then run some hotter cams.

Edit: Woaw.. where'd my signature go?

1fastredsc · 06-17-2003, 08:01 AM

It's also a money thing, FI if properly setup, is very expensive. But the benefits are definitely there, just depends on whether it's worth it to you. The other thing to is that carbs get horrible gas mileage, so if that's a determining factor then you should keep it in mind.

Porsche_monkey · 06-17-2003, 08:03 AM

I think FI an be very reasonable (as opposed to carbs) if you about it the right way. Megasquirt can be done for about $500.

1fastredsc · 06-17-2003, 10:03 AM

I just read through that whole link and that gentleman is my hero.

Porsche_monkey · 06-17-2003, 10:20 AM

I was thinking the same thing but too embarassed to say so...

Tim Walsh · Tim Walsh's Garage

I'm still wondering though. Can you run wilder cams with this? I know the CIS itself is a major restriction for running wild cams but is it possible to run S cams with the CIS bodies converted to megasquirt?

1fastredsc · 06-17-2003, 10:33 AM

Yes, the only thing that makes the cis restricted from wild cams is the sensor plate is sensitive to pulsation which is created when running high overlap cams at low engine speed. This "megasquirt" uses map, or manifold absolute pressure to determine load and atmosphere temp to assume realitive air density. So a simple change in fuel map and wild cams are your best friend.

Porsche_monkey · 06-17-2003, 10:36 AM

What are S cams worth and how hard are they to swap?

Tim Walsh · Tim Walsh's Garage

They're worth about $300 I think and they're easy to swap depending on the motor.

I don't belive they're work in the Al cased engines (3.0 and higher) but they're great for smaller displacement engines. The big thing to watch out when using them is clearance between the pistons and valves. If you don't have S pistons or custom pistions the pistions very well may hit the valves.