Help, advises needed - Page 2

beepbeep · 06-13-2003, 02:23 AM

What happened? Looks like moderate overrev? Why not go for EFI? ... carbs are hard to tune.

phe · 03:50 AM

beepbeep,

Overrev??, as everybody is telling me that, I guess it is. I am driving at high rpm from time to time, but I do not remember any overrev.

EFI was the reason choice, but I always wanted carbs I am building my dream car which will not be the reference 911 3.0, but simply the one I wanted. I hope that new carbs will not create to much problem (My dream will comes true in a few days.... 10-9-8-..)

Philippe

Wayne 962 · Wayne 962's Garage

Looks good!

-Wayne

snowman · 06-16-2003, 08:26 PM

Carbs are NOT hard to tune. It takes about 1/2 hour max and is very straight forward ( as long as the engine, carbs, and linkage are in good condition). They will stay tuned for a very very long time.

phe · 06-18-2003, 03:40 AM

Jack,

God bless you and your words....

phe

jluetjen · jluetjen's Garage

Swapping the CIS for Carbs opens up a whole new realm of tuning possibilities for improving the HP. I'd take a look at some cams with more duration and overlap like an early S or a GE60 grind, neither of which will work with CIS, but work great with carbs. You may need to open your intake ports up to about 38 or 39 mm's if they are not that large already. The result will be an engine which will generate peak torque at around 4500 RPM and generates peak HP at about 6500 RPM and will rev to 7000 - 7500 RPM. Just make sure that your engine builder is aware of your intended rev range since he may recommend some additional modifications to support those sorts of engine speeds.

If you really want to go all out you can go for "Full Race" cams like the 906, RSR or GE80, but then you're talking about rebuilding the engine as an 8000+ RPM engine which is a whole new can of worms.

phe · 06-18-2003, 07:38 AM

Ok not really engine, but parts are arriving...

8 days to wait....

beepbeep · 06-18-2003, 07:57 AM

Quote:

Originally posted by snowman
Carbs are NOT hard to tune. It takes about 1/2 hour max and is very straight forward ( as long as the engine, carbs, and linkage are in good condition). They will stay tuned for a very very long time.

Errr....carbs are pre-historic wide-a**ed way of guesstimating how much fuel engine needs. You can "tune" them to be right on one load segment but they will certainly be off-tune on another.

So even if it might be easy to "tune" them in such sense that you fiddle them to make car run (w/o belching black smoke) they have nothing to do in modern high performance engines.

EFI can and should be mapped for all loads and revs and will result in cleaner running, stronger and more fuel efficient engine.

I think you are still stuck in Chevy-land tough...

Doug Zielke · 06-18-2003, 08:27 AM

Wayne has a good primer on EFI systems in the rebuild book. After reading it, I would never consider carbs as an alternative to my CIS.

Groesbeck Hurricane · 06-18-2003, 09:35 AM

Phe,

Je me bien regardez le garage !! Tu vas d’avoir une bonne journée ou track.

jgparker · jgparker's Garage

I'd gladly trade an old CIS system for a set of Webbers. Anyone want to take that deal? I think a good EFI system and CIS (K-jetronic) are two different things.

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by Doug Zielke
Wayne has a good primer on EFI systems in the rebuild book. After reading it, I would never consider carbs as an alternative to my CIS.

Funny, I'm going to be running carbs on my short stroke 3.2. EFI is great, but you gotta have the bucks to play the game, especially when you're twin-plugging and running a hot cam (you need the individual throttle boddies). $500 set of carbs (yes I got a good deal on them) versus about $5K in throttle boddies and computers. The EFI can wait for me...

-Wayne

jluetjen · jluetjen's Garage

Quote:

EFI is great, but you gotta have the bucks to play the game,

Nor has anyone mentioned the dyno time needed to properly dial in a fully mapped EFI system. I've heard that it takes a good two solid days of dyno time to fill in the map assuming that you know what you're doing. Sure a rough cut map can be made in a couple of hours, but in order to really get the benefit of the system compared to carbs, the detail work takes a lot longer. What's dyno time going for?

Now if you happen to have a library of maps for similar engines, that's a different story.

Tommy P · Tommy P's Garage

Hey Phe
just been reading your posting. Looks like the same thing happened to me. I've not started tearing the engine down yet, but I have a broken rocker arm. I'm expecting to find more damage (similar to yours) when I do.
So a rebuild will be on the way, though I expect mine will take longer to do than yours (circumstances in time and money).
The post has come up with some interesting issues that I have been considering during my own rebuild. I have some 40's on mine and would also like to increase to 3.2. I would also like to do some work on the gearbox, so keep us informed of how things work out.
Wayne, your project sounds interesting too, are you intending to give out some details of this one?
Good Luck
Tom

beepbeep · 06-18-2003, 05:14 PM

I don't want to make this thread into some carbs vs. EFI flame war but I believe that people are afraid of all this "EFI-thing" as something strange, complicated and expensive.

I understand that it isn't as straight-forward as carbs or CIS but it really isn't that complicated (or expensive) at all, especially compared to MFI.

You basically measure air-pressure in plenum, revs and squirt enough fuel...that's about it!

EFI systems are cheap and new ones can be mapped on the road with pretty good results, especially if using wideband lambda.

I believe that biggest obstacle is in people's minds...(on the other hand, I designed electronic devices for living so i probably find it easier/less frightening)