PMO carbs or slide valve injection for 83 SC ?
 

Just want some input on this idea. I have stock engine in my 83SC , but have some bolt ons (including an exhaust system I fab'd up myself using ideas from info found here. I do track days, DE's and also drive on the street. I see so much verbal bashing of the stock CIS system and would like to update the performance and clean-up the overall look. What would you suggest--Webers , PMO's , slide-valve injection ??? Would there even be any gain with the stock cams ? Let me hear you opinions and experience !!!

Thanks much

MFI and slide valve

Michael

Go for one of Tony Bitz's EFI kits using Megasquirt. Better than both of them and probably cheaper too...

http://www.bitzracing.com/products/Complete_kit/index.html

http://forums.pelicanparts.com/porsche-911-technical-forum/139422-cis-efi-kit.html

ianc

Or....maybe a set of cool MFI or slide stacks ...but using the megasuirt could be VERY cool, and really easy. An advantage over MFI would be easy retuning in the future if you decide to go with a different cam or whatever.

I agree, MFI and Slide Valves would look the coolest and have people staring at your engine for hours.

But, having driven a few slide valve motors, they are not really all that great for street use. They are pretty much on or off and while that can work on the track, it's not great for traffic.

Besides, if you have a bone stock 3.0L motor it would be a waste of money anyway. Do you have any idea what a set of original slide valves or even reproduced versions cost? It's not cheap.;)

I drove a GTI with a touring car 6-speed sequential ($20,000+) for 3 months and while I was the envy of just about everyone and was constantly taking people for rides, I couldn't wait to get rid of it. It's a race part that is just not practical for street use, just like slide valves.

Good luck with your decision.

Ralph

C-3.5L said it all. But you should do it just to be contrary and different. After all, it isn't my money...

OR... Maybe we should back up ... what is your goal for the car/engine?

without a cam change an induction change is a waste of $.

That Bitz kit is a sccreanibg deal.

OK....slides are filled with drivability issues...but a set of RS or S (Probably not big enough) stacks would look really cool as well. I still think the Megasquirt has the flexibility for the task, and room to grow down the road.

MFI with slide valves will cost more than the entire car. I stick with the CIS unless you're changing pistons and cams...

-Wayne

Take Randy, 3.5's and Wayne's advice, and especially give a second thought as to what you'll use the car for. CIS is fine - it just doesn't have the throttle response of PMOs and whatever else is out there. The key that I've found to making CIS responsive is to simply stay in the powerband.

As for improvements, a less expensive, yet still effective improvement on an '83 CIS 3.0 is to find yourself some '78 or '79 3.0 heads and CIS, swap in some 20/21 or 964 cams and a pair of SSI heat exchangers. You can probably pick up a good two-thirds of these parts from the classifieds section for much less than the $3K cost of PMOs. The heads might be harder to locate, but Wayne and Pelican can help you with that. If you choose to build up a motor like this, you won't have that sexy carbureted sound, but you'll have a big port, high compression CIS motor that will be quite powerful and cost effective at the same time.

Thanks for all the replys--I will take your advice and steer away from all show / no go mods-----ie...slide valves wont do much on a stock 3.0. Think I'll lean towards cams and carbs with velocity stacks for both looks and performance.

Go with a set of PMO carbs with ITG filters, and short stacks.

They work excellent out-of-the-box, can support future upgrades, and are much less (1/2) expensive than a aftermarket FI setup... and they look really nice installed!

I've got a set on my '82 SC. I love 'em.

TonyG

Yep, nothing is cooler than MFI on a 3.0+ motor. Budget as follows:

core MFI stacks, throttle bodies, & pump - $1k minimum
rebore stacks & throttle bodies - $2k
re-calibrate pump - $1k
tap heads - $300
injectors - $600
mod cam for drive pulley - $150
lines - $50
airbox - $50
engine tin - $50
fuel filter console - $50
pump bracket - $50
fuel pump - $300 min
---------------------------------------
so at least $5600

Im probably forgetting something, but those are conservative numbers.

As far as slide valves go, you are getting into prices that cannot be easliy documented. There was a set of 3.0SCRS slide valves that were sold here less than a year ago for under $2k. I have obsessingly shopped this stuff for the last year and this was the absolute best deal I have ever seen anywhere on MFI parts. Ive only seen high butterflies for sale for $10k from one source. The conventional MFI stuff is getting more expensive everyday.

On the other hand:

Carbs = $3k max = DONE! ****ty gas mileage, but still DONE!

Running and healthy 3.2 Carrera motors are dropping below $5k these days. DONE!

OTOH, Tony's EFI = $1600 = DONE! Better gas mileage than stock as well...

Tough choice...

ianc

Maybe so. Im still waiting for an actual review on the tbitz system. Ive PM'ed people who have openly posted about buying this system in the past for their impressions and have received no response. No problem, I understand if it is still being tweaked and I anxiously wait for a good affordable FI system. It sounds very promising, but I'll believe EFI for $1600 when I see it. Anyone have any real experience to post?

I'm working on a slide valve carb that should be less than PMO. I've yet to test it as my schedule is a bit crazy right now.

We're also working on individual throttle body EFI using TWM throttle bodies and Megasquirt. That system should also be competitive with the PMO setup. The ITB EFI is a lot further along than the carbs. The carbs are aimed at the racers who have to apply "available technology" for compliance, while the ITB EFI has a much wider range of applications....even forced induction!

Here's a pic of my PMO setup:

Oh.. .and BTW, my PMO setup has zero drivability issues and easily compares with my euro 3.2 Carrera FI setup with resepct to smoothness, throttle response (better), and hot start.

The only place the carb setup lacks is cold starting. It takes about 20 seconds, when cold (overnight) for the engine to warm up enough to drive without hesitation.

The mileage has only gone down about 4 mpg from that of the CIS setup.

On another note... the engine runs MUCH cooler due to the fact that it runs richer. PMO's vs CIS


http://www.tonygarcia.org/911SC/TG_PMO.jpg

Carbs v MFI the debate wages

Go with what makes you happy

Michael

oh, Im not debating. I absolutely love the idea of 3.0+ MFI motors. Given a $15k budget for an engine, Id be happy to spend $7.5k on the perfect MFI system. Problem is that I dont have that kind of budget for my entire drivetrain right now. My favorite thing about MFI (other than the intake sound and throttle response, of course) is that the parts can be sold easily to fund other stuff that I can afford to implement.