This week I removed all the valve guides and I clean preliminary the heads. Also the machine shop removed all the rusty exhaust studs. Only 3 of them came out, the others ones broke and have inserts installed.

And now I have a question about the heads porting size. Would be ok to port the intake side to 36mm and how much I need to port the exhaust side?

Also what headers would be the best for this combination: the 1 1/2" ones or the1 5/8" ones?

comp. ratio?
hp wanted? (vs. low end torque to give up)
use of engine?
induction system?
cam?

compression ratio: 9.5:1
hp wanted: daily driver and highway use
induction system: PMO 40mm carbs
Cam: DC40 Mod S

almost identical to my motor... :) you'll be happy with that set-up

1.5 inch headers will be best with that engine.

-Andy

I would be conservative with the ports. Probably the #1 mistake people make is to hog out the ports to be too large for the intended usage... also don't bother polishing much. The motor is just not going to be spending a lot of time near redline. That is the fact with any street motor - no matter how much you thrash it, it mostly lives in the mid-range.

More specific recommendations might be had in the engine building forum. I'd pay attention to comments from "SuperTec" and Steve Weiner.

RWebb is right, easy on the porting and polishing...

all I did with my heads was to match port the PMO manifolds and some slight polishing

thanks guys. I read the Performance Hadbook by Bruce Anderson and find the port specs for the 911 RS. The only difference was the increased size of the intake port: 36mm vs 35mm. The valve size are the same and the exhaust port are the same too. With that info I port the intake to 36mm and the exhaust still have the 35mm. I only do a rough polishing into the intake to help the fuel atomization because the carbs and to remove a light carbon deposit that was there. In the exhaust side, I polish it to a smooth finish to help reduce the carbon deposits. There was a lot of carbon. Also I do a mirror polish in the combustion chamber. This take a lot of work but looks great. I'm exhausted. I only do one head today. I think I will do 1 head per day.

jtkkz, what headers size do you have?

This is a slightly off topic post but 2.7 folks may be interested:

In the near future I'll be offering for sale a running '77 2.7 CIS core engine w/ 84k miles. It's a non thermal reactor 2.7 with some nice upgrades and runs well. Please send me a PM if interested and I apologize for the off topic post!

:)

I am using SSI, may need that heat on a early morning drive :)

atomization is power


it's a Carb eat MFI world.. in my opinion :D

-Scott -- take a video of it running to help w/ the sale.

Hello again.

After a few christmas hollydays I return to work in the engine. After the machine shop remove all rusted exhaust studs (only 2 came out with out problem, the others are drilled and have a threaded inserts installed). I still working in the cylinder heads ports opening to 36mm on the intake and doing a rough polishing. In the exhaust side I'm trying smooth surface to avoid a lot of carbon build up. I have already one cylinder head done with the mirror polish on the combustion chamber. The other are in process. This take to much time. I also have the wrist pin bearings con the rods already installed and waiting to have been bore to the stock specs.

I still thinking about the 92mm pistons and cylinders and I have a few questions.

I know that the 92mm cylinders are bored only on the inside and not on the outside were they insert into the engine case. The question is: With the 92mm cylinders I need to buy a 92mm CE ring (cylinder head gasket ring) or I can still use the stock 90mm ring gasket?

The other question is that with Alusil cylinders I can use the JE pistons without problems?

There is no difference in the CE ring size. It is the same. Ideally 92mm cylinders would be best if they didn't have a CE ring groove because the ring groove results in a very thin cylinder wall at the area of highest compression on the cylinder. Not an ideal situation.

You could weld the groove shut and then machine the top of the cylinder flat but then your machine costs go up substantially.

Alusil 90mm cylinders will be good donors for a 92mm cylinder mod. After they are bored out they can be nickel plated to turn them into Nickisil.

Before you commit to boring Alusil add up your total costs of boring and plating and then compare that to buying some aftermarket QSC cylinders. It might end up being cheaper in the long run to just buy new QSC cylinders. The QSC cylinder sets do not have a CE ring groove.

http://qscusa.com/porsche.htm

I didn't notice that the QSC cylinders don't have the CE ring. Without that ring, they would seal perfectly with the stock cylinder heads? Or I need to have that groove made on the cylinders to accept the CE ring?

sweet Jesus that is wonderful!

With the QSC cylinders no CE ring is needed. They will seal without a CE ring/groove to the stock heads.

New Mahle 2.8 RSR cylinders also do not have a CE ring groove. As matter of fact all the 3.2 Carrera motors never used CE ring grooves.

You can still bore some 90mm cylinders to 92mm and use them with the CE ring but you need to be extra careful that no detonation occurs. Detonation when it occurs usually occurs at the edge when the piston is at TDC. This is the point where the cylinder is thinnest due to the CE ring. That's probably why Porsche did away with the CE ring on the high compression 2.8RSR P+C sets.

Depending on what compression ratio you go with you should take this into consideration. It would probably be a good idea to leave an additional safe margin for error when choosing a compression ratio to use when using bored out 90mm cylinders.

2.7 homebrew street motor
 

Here is my homebrew 2.7S, JE 9.5:1, E-cams, SSI's, Dansk 2/1 sport, Weber 40IDA's, etc. Just dialed in the Webers last weekend. Goes good and makes very nice sounds. you can do it.

http://forums.pelicanparts.com/uploa...1199856858.jpg

Ok now I'm catching up.

This thread is answering a lot of my questions.

The 2.7L I've been running in my 72T is suppose to have "E"cams. It does have a lot of pull starting at around 35-4000 rpm. I have pulled a turbo 944 on the straight at Portland.

I also have 40mm webers rebuilt by Harry Beiker in Oregon. I'm running Pertronix and MSD ignition through a rebuilt distributor but it sounds like I may need to have it recurved or at least put on the machine and checked.

I'm also running European headers into Ben's 2 in 2 out sport muffler.

I've always had the hyd chain tensioner as well.

Now I have reduced the weight down to 2200 lbs with a one battery conversion, fiberglass ducktail and hood, recaro seats and the headers and sport muffler. Reducing the weight is a lot cheaper than adding horsepower.

I talked to J & E and it looks like I'll be going with the 9.5 pistons

Question: Mod S and solex cams, where do I get info on them. Also could I send my cams out and have them reground or would it be cheaper to pick up some new cams?

I would use the JE 9.5:1 pistons.

I need to modify the cylinder heads sealing surface to accept the non ring seal cylinders like the QSC?

I contacted QSC and they dont have in stock right now any 90mm aluminum Nikasil cylinders. But I see that they have a cast iron cylinders. The cast iron ones would be not a good choice for the 2.7?