CIS to Webers Question... on a RoW 3.0SC

[Jesset100]

Don't you have to readjust the distributor? Something about advancing...

[ianc]

my carbs & cams get around 2/3 of what I previously had with CIS. My carbs are very adjusted.

Lessee, I average around 15 with my SC with CIS, so that would put it around 10.

Is it worth the extra 10 HP BA quotes? Torque figures not quoted...

Gas here just hit $3\gallon! Good luck!

ianc

[randywebb]

10 hp? Yup that's what BA says & JW confirmed that to me a few years ago.

Above, SW said there would be a "nice power gain" iff... you set up the carb just right. So maybe it's more than 10 hp -- that's why I aksed him to respond.

Also, they changed intake port sizes on the SC's at some point didn't they? That might make a difference in power gain & prob. for mileage too.

ANyway, the induction noise & feel (engine response) I thought was worth it.

[ianc]

Yeah, I think the earlier SC had larger intake valves. Can't recall how much larger or what the cutoff was. Don't really know if this would contribute to more HP or not...

It seems to me that for a street-driven car, torque is much more important than HP anyway. You don't often run for extended periods at 5-6K RPM+ on the street. You'll want the torque for pulling away from stop lights, squirting in and out of traffic, etc., and the torque gains are less clear with carbs.

Even if the torque figures are slightly better with carbs (and we don't know this), the ease of troubleshooting, instant starts, ability to pass smog (for those of us in such states), and much better fuel economy are well worth it to keep the FI.

I don't honestly know about throttle response; never having driven a later model FI car converted to carbs. Compared to my Carrera, my SC's throttle response feels pretty much instant though...

ianc

[RoninLB]

All above is great replys. Then there appears to be two thoughts going on. I may be nuts so don't take me serious.

Carbs is like pouring gas into a hole connected to a combustion chamber. Guys who've run carbed engines by actually pouring gas out of a coke bottle know about this first hand. Either you like it or you don't.. and the cost of the gas is really insignificant to total cost of operation, unless its a commuter car.

The bottom line is to create combustion with power. The only monitoring of this power that I know of is EGT heat. You need the most efficient envelope for creating this desired EGT as the engine goes through all its gyrations that are constantly changing. With nice carbs a good tuner can create more power than the CIS and Motronic inductions imo. It's not a matter of pouring in more gas than necessary because this would only cool combustion and retard flame speed which leads to less power. It's the delivery of the correct amounts of air and fuel for power. So if you're into owning the greatest toy created use tuned carbs.

FI is great for its purpose. Don't buy carbs unless you really really want them.

[ianc]

FI is great for its purpose. Don't buy carbs unless you really really want them.

I think that carbs can actually do a good job, but they are inherently less versatile than FI. If the car is a track car, you spend most of your time at high RPM's and temperature\throttle variations are not that great. Carbs can shine in this application.

For a street car that needs to (possibly) sit for a few days, start easily, idle well, pull smoothly no matter what the temperature, pass smog, and hold resale value, FI can't be beat.

ITB FI would be best, but barring that, the application should determine the method of induction,

ianc

[RoninLB]

Originally posted by dd74
Do a search. There was a thread about this last year, where someone posted the dynoed hp on their rebuilt stock 3.0 with PMO/Webers. TRE added some insight as well, which was quite enlightening.

I read a few of Tyson's replys awhile ago. Is this what you mean?

[RoninLB]

Originally posted by ianc


I think that carbs can actually do a good job, but they are inherently less versatile than FI. If the car is a track car, you spend most of your time at high RPM's and temperature\throttle variations are not that great. Carbs can shine in this application.
------ Good point. It's a package deal. If you have a high rpm cam you adjust for high rpms. If it's a street cam you tune for the street. If your cam is a little of both you tune for a little of both. My act is waiting for speed racer bear bait to come up so he can escort me and my V-1. My carbs are tuned to pull 4th gear between 65-100mph quickly. He passes and I'm pacing the mother almost instantly. My brother's stock '88 911 took noticeably longer which meant that the '88 had to finally reach very high speeds before I could pace him. I've spent weeks living in his car traveling solo so I know how much power it has. Can you imagine if I had a carbed 3.2 and compared it my bro's car? There is a gearing issue between the cars when viewing the total package though.

And for bonus coupons my engine combustion runs about 25-50 deg cooler at 4.5-5k than at 3.5k in 5th so no way is it even close to detonation the higher the rpms become.. up to a point I figure humbly as I haven't pushed the edge yet.

I can go on forever about this.


ITB FI would be best, but barring that, the application should determine the method of induction,
-------- if you can tune the ignition and fuel flow on the fly it'd be a nice FI. You can apply nice FI or carbs to anything you want. It's what do you want and what do you want to play with?

all above is a prejudicial rant

[RoninLB]

Originally posted by Jesset100
Don't you have to readjust the distributor? Something about advancing...

distributor curves can be adjusted.

[RoninLB]

Originally posted by randywebb


SW said there would be a "nice power gain" iff... you set up the carb just right. So maybe it's more than 10 hp -- that's why I aksed him to respond.

He helped me dial in my carbs.

God bless America.

[ianc]

if you can tune the ignition and fuel flow on the fly it'd be a nice FI.

3.2 and larger do this,

ianc

[RoninLB]

Originally posted by ianc
3.2 and larger do this,

in a simplistic way. You can't be dialing the flow and curve to your liking. If you want more injection for a particular reason you're stuck with other consequences afaik.

[ianc]

You can't be dialing the flow and curve to your liking.

No, there is a basic fuel-air map. This is modified according to 'weighting factors', which are signals received from various sensors. These increase or decrease injection time (pulse width) according to temperature, load, etc. As the FI gets more sophisticated, the better it is able to make these decisions.

Timing is also adjusted as necessary by the ECU, with knock-sensing available in later iterations.

So you really can dial the curve; if not to your liking, then at least to prevailing conditions.

ianc

[dd74]

Originally posted by RoninLB
I read a few of Tyson's replys awhile ago. Is this what you mean?

IIRC, 220-230 hp was what someone at TRE quoted as the gain with Webers on a stock 3.0. I don't know who at TRE made this comment, but those numbers are what I recall. As well, I cannot recall if this increase was in conjunction with SSIs and other exhaust changes.

The person who had his rebuilt stock 3.0 with PMOs dynoed, made close to 240 hp; again to my recollection.

As for intakes, in '81, Porsche changed intake sizes for at least the US 3.0s, lessening their diameter from 39mm to 34mm, yet raised compression .8 pts. The horsepower from a late 3.0 is the same, however the engine develops a bit more torque.

To be certain, it must be considered that not all 180, 200, 220 or even 250 hp is alike on different engines. Sure, I believe 240 hp is obtainable with Webers on a stock 3.0. I believe 240 hp is obtainable with a CIS 3.0. The caveat is how efficiently is that power coming on, and where.

The other caveat about 3.0 engines and Webers is to just throw them on is fairly much a waste of effort, money and engineering, particularly when it is considered that when built in a rather radical street/race form, a 3.0 with Webers that has had its pistons and cams changed, can develop over 300 hp.

[Halm]

Since you are in MA, you might want to send the Webers over to Matt at Eurometrix. He can make sure that there is no hidden damage like a crack in a bloat bowl, refurbish them so they look and act new, and he can rejet them for your exact engine setup. Not cheap, but it might be worth it in the long haul.