2.7 Rebuild – To bore or not to bore and other questions

[911 SLANT]

Nice work on your case. Did you decide to port your heads? A couple of details I forgot to mention was I went with 39mm in. 35mm exh. On my heads. I Also run a 7:31 R&P in transmission. My car is very quick and great torque off the line. I need to get it on a dyno.

[draw]

Originally Posted by 911 SLANT

Nice work on your case. Did you decide to port your heads? A couple of details I forgot to mention was I went with 39mm ex. 35mm in. On my heads. I Also run a 7:31 R&P in transmission. My car is very quick and great torque off the line. I need to get it on a dyno.

Thanks! I debated porting the heads for quite a while. When I dropped the case off at Ollie's we talked about it for a bit, too. Their advice was if 36mm intakes and 35mm exhausts was good enough for the 2.7 RS then it would be good enough for my motor. When I bought the DC43x-102 cams from John Dougherty, he thought 37mm intakes would work good for my application. So, I decided to go with 37mm intakes and 35mm exhausts. Craig Garrett rebuilt the heads and did the porting.



Now, I'm prepping various parts for the rebuild. Here, a previous mechanic decided to RTV the rocker shaft nuts in. Tried several ways to get these out, but finally settled on heat from a propane torch.

[chrismorse]

Originally Posted by draw

Thanks! I debated porting the heads for quite a while. When I dropped the case off at Ollie's we talked about it for a bit, too. Their advice was if 36mm intakes and 35mm exhausts was good enough for the 2.7 RS then it would be good enough for my motor. When I bought the DC43x-102 cams from John Dougherty, he thought 37mm intakes would work good for my application. So, I decided to go with 37mm intakes and 35mm exhausts. Craig Garrett rebuilt the heads and did the porting.



Now, I'm prepping various parts for the rebuild. Here, a previous mechanic decided to RTV the rocker shaft nuts in. Tried several ways to get these out, but finally settled on heat from a propane torch.

Hi Ward,
My Dad's old 74 started out with 32/35 porting and i bumped it to 37/35 after settling on DC 43-102 cams. Cgar opened it up while doing the valves and guides. Probably the same Ti retainers and springs, (aasco springs and retainers, IIRC), It didn't seem to make sense opening up the exhaust more than 35, because that is the inlet diameter of the SSI's. and the car isn't a race car.
I too had the case line bored, and the spigots trued, after line boring, 4 bar pump, bypass mod, alum PP and RSR wheel, with .050 deck, the CR was 10.3, which i was ok with - looking for engine life.
X Factory PMO intake, Megasquirt, Twin-plug EDIS - what a lot of work $$$.

Almost done, got a glitch or two in the wiring harness before it will fire - first i have to get the wife's benz head gasket fixed, (after putting in a rebuilt tranny)!!!!!
Chit, I'm 75 and running outta steam - (but still want to track the 2.8)
HAMMER down,
chris

I know the proper proceedure would have been to develop the heads and select the cam in conjunction with flow testing, but this is a bump up hot rod

[detroit]

I'm glad to see there's someone out there that works nearly as slow as me...

[PeteKz]

There's plenty of competition for that title, including me.

[draw]

Slowly plugging away on the minutiae that people don't talk about a lot...buggered case studs and built-up gunk meant pulling every stud...thanks to age and prior mechanics, many will need to be replaced.

The chain housing mating surface needed some love, so I wrapped some fine emery paper around a 1-2-3 machinist's block...





Took a couple of minutes of light sanding to get it pretty flat again. Not perfect, but close enough...



I've seen various homemade contraptions for holding up the rods and timing chain during assembly. After trying some different versions myself, I decided that I was going to get the "real" tools. The genuine Porsche P221 Connecting Rod Straps and the P222 Timing Chain Strap are available for $270 from Rose Passion in France.

[draw]

Originally Posted by chrismorse

Hi Ward,
My Dad's old 74 started out with 32/35 porting and i bumped it to 37/35 after settling on DC 43-102 cams. Cgar opened it up while doing the valves and guides. Probably the same Ti retainers and springs, (aasco springs and retainers, IIRC), It didn't seem to make sense opening up the exhaust more than 35, because that is the inlet diameter of the SSI's. and the car isn't a race car.
I too had the case line bored, and the spigots trued, after line boring, 4 bar pump, bypass mod, alum PP and RSR wheel, with .050 deck, the CR was 10.3, which i was ok with - looking for engine life.
X Factory PMO intake, Megasquirt, Twin-plug EDIS - what a lot of work $$$.

Almost done, got a glitch or two in the wiring harness before it will fire - first i have to get the wife's benz head gasket fixed, (after putting in a rebuilt tranny)!!!!!
Chit, I'm 75 and running outta steam - (but still want to track the 2.8)
HAMMER down,
chris

I know the proper proceedure would have been to develop the heads and select the cam in conjunction with flow testing, but this is a bump up hot rod

Thanks for sharing Chris! I'm 55 and I'm feeling the pressure from Father Time to get this done!

Originally Posted by detroit

I'm glad to see there's someone out there that works nearly as slow as me...

Originally Posted by PeteKz

There's plenty of competition for that title, including me.

Yes, "analysis paralysis" is my main problem...I keep telling myself that the journey is more important than the destination, but Father Time is tapping his watch and giving me the look like "now or never buddy."

[draw]

Time to measure, Part A...

With all the machine work that's been done to the case, heads, and the new LN/Mahle cylinders and pistons, I needed to measure the components to calculate "deck height."

First, the case half height...



I was able to fit the case half on my granite block, so I measured it that way, too...



Next, the LN cylinder...



Confirming the wrist pin...



On to compression height (plus wrist pin x 0.5) of the Mahle piston...



Then, I rewrote the "piston to deck clearance" equation to my liking and entered the measurements into Excel...



LN's website says they can make custom cylinder base shims in 0.050" (1.27mm) so I used that in my calculation.

Looks like I'm right where I need to be with the 1.06 mm deck height. Now, I need to cc the heads/pistons to make sure the compression ratio is acceptable. The heads were flycut 0.25 mm, so I'm curious to see where everything turns out. If it's too high, I'm thinking a 0.060" shim might be needed, which would put the deck height around 1.31 mm.

With all this measuring and calculating going on, I'm finally using "in real life" what I learned in my college physics and chemistry classes.

[Old H2S]

Good, good..

[draw]

Time to measure, Part B...

I bought the COMP Cams cc kit that came with the plexiglass plate, burette tube, stand, and holder.

The plate was square and it needed to be cut into a circle...



I couldn't find my compass anywhere, so I used the old "roll of tape" method to find the correct circumference...



Traced, then cut out with a jigsaw...



After fiddling with the clogged burette for 30 minutes, I was able to cc the head...



It came out to 68.4 cc's...



Moved on to the piston...



Enough measuring, time to calculate...



The advertised compression ratio for these pistons is 10.3 at a 1.0 mm deck height. The heads have been twin plugged and chamfered for the larger pistons, so that probably contributed to the lower compression ratio. I'm also going to use a 0.050" base shim, which will up my deck height to 1.06 mm.

Overall, I'm pretty happy where this all calc'd out. Especially considering that I'm using California gas, the slightly lower compression ratio is probably a good thing. Displacement calculated out to 2,869.32 cc's.

[rennzeit]

Your Ollie's invoice has a line item for "6 barrel shims 1mm". Mine only needed .5mm. They were stuffed inside the chain area between a pair of cardboard squares. Hopefully you didnt discard it when you unpacked it.

[Uwon]

Following with great interest. I’m about a year behind you.
Happy Holidays,
Johan

[PeteKz]

I went with .75mm deck clearance, not to increase CR, but to improve squish and chamber turbulence. If you went with .25mm base gaskets, you would end up with 0.81mm deck. Tighter, but not too tight.

[draw]

Originally Posted by rennzeit

Your Ollie's invoice has a line item for "6 barrel shims 1mm". Mine only needed .5mm. They were stuffed inside the chain area between a pair of cardboard squares. Hopefully you didnt discard it when you unpacked it.

Thanks for pointing that out! I did find them, but it looks like I won't be using them because I'm going to be using a 0.050" or 1.27mm shim from LN.

Originally Posted by Uwon

Following with great interest. I’m about a year behind you.
Happy Holidays,
Johan

Thanks, Johan. I think we took Tony's engine building class together a while back...

Originally Posted by PeteKz

I went with .75mm deck clearance, not to increase CR, but to improve squish and chamber turbulence. If you went with .25mm base gaskets, you would end up with 0.81mm deck. Tighter, but not too tight.

After taking my measurements and doing the calculations, a 1.27mm base gasket will give me a deck clearance of 1.06mm. If I went with the 1.0mm base gasket, my deck clearance would be 0.79mm, resulting in a 10.4:1 compression ratio. If I used a 0.25mm base gasket as suggested, it would result in a deck clearance of 0.04mm and a compression ratio of 11.44:1. I crosschecked my calcs three different ways, so I'm pretty sure they're correct.

But to your point, I could go with a 1.0mm base gasket to improve squish, etc., however, I'm concerned about too high a compression ratio for California pump gas. I'm also concerned about shortening the deck height too much, which will affect the timing chain slack and location of the camshaft relative to the chain housings.

[PeteKz]

Draw: I confused some of your measurements. I meant that a .25mm reduction in the deck height won't change the CR appreciably (maybe 0.1 or so). However, if you are concerned about California pump gas and want to keep the CR where it is, then ignore me.

The timing chain would be affected even less, because a .25mm change in cam gear centerline to cam would effectively "lengthen" the chain by .5mm. If the tensioners can't take up that little additional slack, something else is wrong.

[Rostrenner]

Zq

[draw]

Time to measure, Part C...

I had Ollie's balance the rods along with the other machine work. I don't have a rod balancing fixture to check big end vs. small end, but I wanted to confirm total wieght...

The min. was 674.0g and the max was 675.0g, for a difference of 1g. I probably could futz around with these a little bit to get them closer, but I think I'm going to call it good.



Stock wrist pin weighs in at about 116.1g...



The Mahle wrist pins weigh in at a min. of 101.6g and a max of 101.7g. I'll match the heaviest pins with the lightest pistons to reduce the amount of balancing that needs to be done...



The stock CIS piston (with a little extra carbon buildup and piston rings) weighs in at 473.15g...



The Mahle pistons weigh in with a min. of 442.9g and a max of 443.5g.



I'm going to balance the total weight of piston/wrist pin combination down to 0.1g. So, one piston needs to lose 0.5g, one piston 0.3g, and three pistons need to lose 0.1g.

When I bought the pistons, I wasn't really thinking about the weight difference compared to stock, but I was pleasantly surprised when the piston/wrist pin combo came in at about 44g lighter. Should help make for a snappy revving motor!!!

[chrismorse]

I might have missed it, but what are you using for the Flywheel and Pressure Plate??
I think the Fenlane version of the RSR wheel comes in at about 6.5 pounds, vs the stock wheel at a bit over 11.
Similarly, KEP's aluminum PP is good for 400 hp and comes in at about 7-8 pounds vs almost 18 for the stocker.
It has been a while since i installed them and i haven't had it running yet - LIFE,
But, if you're looking for a snappy motor these two would really help.
chris

I had a shaved wheel and an all-aluminum 2.2 S clutch on a hotrod 914 and it was VERY responsive - I did occasionally stall it taking off.

[draw]

Originally Posted by PeteKz

Draw: I confused some of your measurements. I meant that a .25mm reduction in the deck height won't change the CR appreciably (maybe 0.1 or so). However, if you are concerned about California pump gas and want to keep the CR where it is, then ignore me...

I appreciate the input! Definitely good to hear other perspectives...

Originally Posted by chrismorse

I might have missed it, but what are you using for the Flywheel and Pressure Plate??...

I've thought about going with a lighter setup, but I haven't made any decisions yet. At the rate I work, I have a couple of years to figure it out...

[draw]

Balancing the pistons and wrist pins...

My target total weight for the piston/wrist pin combination is 544.6g. Unfortunately, the pistons don't have a lot of meat to shave off unlike the stock pistons. I watched a great Youtube video from High Performance Academy about balancing pistons and where to shave off weight. I practiced on an old CIS piston, then went for it...

This piston needed the most weight removed at 0.5g. Chamfered the web a little bit with the die grinder and carbide burr...



Grind, measure, grind, measure, etc., and "bob's your uncle"...