Carrera vs SC head difference

[joetiii]

Besides the size of the intake opening, what else is different between the early SC heads with 39mm intake and the 40mm intake carrera heads?

[Flat6pac]

The intake boss is shorter and needs to be shimmed up but the carrera shims that the factory uses only works with the Motronic runners. If youre using CIS you need the shims like PMO sells with their carbs to block off the injector notch on the head..
Bruce

[jcge]

SC exhaust ports have air injection holes
Carrera head has boss machined for temperature sensor

[joetiii]

I read in BAs book that the Carrera heads exhaust port is 4mm larger than the early SCs. Would this size necessitate a larger exhaust to make more power?


I have SSis now and they make a good strong mid range which is nice. I hear that the next step up is the 993 heat exchangers which make better top end but offer a less crisp mid range.

I guess my question is, does the Carrera exhaust port make size make a difference if you're going through SSIs and want to maintain a stronger midrange for streetability?

[James Brown]

If it does, get the die grinder out and start moving metal. Not that much of a mystery to port heads. You just have to have the wavos to do it.

[911nut]

Originally Posted by jcge

SC exhaust ports have air injection holes

Some do, some don't. I think '78 to '80 used it.
My '81 SC had a cat and no air injection.

[prschmn]

We'd need a bunch more information on just what your engine configuration is to make judgements on what exhaust/head combo might be best suited. Remember that port velocity is very important in both intake and exhaust so I'm inclined to respectfully disagree with James statement that "it's not much of a mystery to port heads"

[tcar]

Originally Posted by 911nut

Some do, some don't. I think '78 to '80 used it.
My '81 SC had a cat and no air injection.

Only 78 and 79 SC's had air injection in the US.

Also, only 78-79 have the larger ports (and intake runners) than the 80-83 SC's (in the US).

[James Brown]

I understand that port velocity is important and people/shops spend tons of research on head flow numbers however, running a high speed die grinder on aluminum is not very hard. experimenting on these engines is relatively cheap as heads are easy to find. Making a whole bigger is not rocket science. There are several pictures and discussions on what and how to remove metal. I opened my mag intake manifolds for the Zenith vent mods. Seems to be working quite well.

[RWebb]

I thought you were talking about matching the ports to the manifold - that is easy.

But, I agree with prschmn - there is a LOT more to "porting a head" than just "Making a []hole bigger" -- the world is full of screwed up motors where somebody just hogged out the heads w/o knowing what they were doing.

Fluid flow is big medicine.

[joetiii]

Originally Posted by prschmn

We'd need a bunch more information on just what your engine configuration is to make judgements on what exhaust/head combo might be best suited. Remember that port velocity is very important in both intake and exhaust so I'm inclined to respectfully disagree with James statement that "it's not much of a mystery to port heads"

OK so here we go.... 1969 Targa is 75% Street/25% AutoX, DEs

Currently a stock 82 3.0 engine with PMO 40s, SSIs & ElectroMotive crankfire
74 915 trans w/ 7.31 CWP & GT TB diff.

Plans are to upgrade to
98mm JEs @ 10.5:1
Second EM coilpack for twinplug
DC24 or GTII on 106 LSA
PMO 46s

Engine pulls strong from 3500 to 5500 then flattens primarily due to the ports and cam. I am looking to keep that low rpm response and move power peak to 6300 giving me some overrun to 7k.

I spent some time on this Boards discussions about port velocity and developed a spread sheet that says a 38mm - 39mm intake will get me to that range.

Which brings me to my original thought. Either I can have my small intakes opened up to early SC size or go with the Carrera heads. If the larger exhaust ports in the Carrera heads will add to high rpm performance at 6500+, then I'd opt for using my current heads. If they have a lower rpm benefit, then I'd consider them.

[RWebb]

why not call up Steve Weiner, discuss your plans and send some heads to him or buy modified heads from him

I'm told, by people whom should know, that the 3.2L heads flow pretty well already and need little work. But that was for my hotrod 3.2L motor.

[joetiii]

Oh yes. I've spent some time on the phone with Steve. Great guy with loads of experience & advice.

He would do wonders to my heads!

[prschmn]

My quick thought would be have your heads opened up some to accomadate your potential
cams and and a bit bigger set of headers. Save ya a bunch of money versus buying a set of 3.2 heads that will probably need work anyway. I've spent a LOT of time on my flow bench
and in the end the rules keep changing- the relationships between C.S.A., V.C.A and bowl volume vs velocity is still not completely understood.

[joetiii]

Mark,

Are you up in New Hampshire? I see ads in Excellence about Exotech....