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-   -   2.5SS - Will This Work? (http://forums.pelicanparts.com/911-engine-rebuilding-forum/983936-2-5ss-will-work.html)

wertygrog 01-12-2018 07:18 PM

2.5SS - Will This Work?
 
Hi all,

I am thinking about putting together a 2.5 Short Stroke from a 2.7L that suffered a rod bearing failure. I have built a few big/turbo Type IV engines but this will be my first 911 engine. Here's what I have in terms of major components:

-2.0L case and bearings, bored for 90mm jugs. Oil bypass mod, case savers, no squirters. Measured/checked and is ready to go
-2.0L (66mm) Counterweight crank and bearings ready to go
-2.7L (70.4mm?) crank with damaged/undersized rod journal
-2.7L and 2.0L rods
-2.0L heads, rebuilt
-Worn 90mm Alusil jugs, good matching CIS pistons
-Worn cams which will be sent to Dougherty for a new grind
-4 rib oil pump
-Set of Weber 40IDAs
-Wayne's book

Plus all of the other parts needed to assemble the engine (minus hydraulic tensioners). Will replace all parts suggested in Wayne's book for sure.

I was thinking about using what I have (plus reconditioned Alusil jugs) to make a 2.5SS. However, I am concerned that my CR will be unmanageably low. But will it work OK for a street engine? My other thought was 9.5:1 JE pistons with Nikasil jugs but I'd rather find a less expensive solution. I am very much on a budget due to a second baby on the way. Essentially, I am looking for the cheapest way to build a no-frills, reliable engine with minimal shortcuts. This beats the alternative of selling the car or letting it sit around the garage for a few more years!!

Engine will be for my 914/6 conversion and the goal is a fun weekend driver, no racing.

Cheers and I appreciate your two cents, it's all I can afford at this time! I love lurking on this forum btw. :)

Brenthttp://forums.pelicanparts.com/uploa...1515816860.JPG

targa72e 01-12-2018 09:57 PM

Here are some quick thoughts. 2.0 heads not the best (has to do with shape) maybe sell and get some later heads. The aluminum cylinders need piston squirters. So add squirters, plate cylinders and get some JE's then you can pick a good compression ratio. Then you just have to decide 2.5 or 2.7.

Fyi
I am in the middle of a 914-6 conversion. Built short gearbox and going 2.7RS spec for engine.
.

john

stownsen914 01-13-2018 05:19 AM

Agree with the comments above.

The 2.0 case is magnesium? The 2.0 mag cases were the worst ones for strength, and don't have any of the updates like squirters, the oil bypass mod, and need to have case savers installed for the head studs, or you'll get pulled studs for sure. The mag cases also warp and wear in key places, so need to have all the critical dimensions checked and often require machining.

Sounds like a cool project!

(Edited a couple comments after realizing this won't be a turbo motor.)

Scott

JackMan 01-13-2018 08:09 AM

Good luck w the engine build. Fantastic 914! More pixs, subscribed.

Trackrash 01-13-2018 05:23 PM

I think you are on the right track.

As mentioned the 2.0 heads are probably not your best choice, especially with the larger cylinders. Also there are different versions of the 2.0 heads, I am guessing that you have the T heads. Again, I would look to find a set of 2,2 or later heads as they have bigger valves and are a better match to the larger cylinders.

You are right about the pistons, again not a good choice, for a couple of reasons.

You have an awesome opportunity to go bigger than 90 mm on your bore. Since you need to have the cylinders re-furbished anyway why not have them bored to 92 and get the proper JE pistons to match.

Those 2,0 cases aren't as much of a problem compared to the later 2,7 cases, so I would imagine you would be OK there.

A 2,5 or 2,6 SS will be a great match for your 914.

wertygrog 01-13-2018 06:51 PM

Good input guys. Sounds like the consensus is that the CIS pistons is a NO-GO for 2.5SS due to low compression. Also the heads are not great. I think they are 2.0L heads because of what appears to be a '68 date code in the casting. Is there a way to identify them more confidently?

Where could I find 92mm JE pistons? I don't think I saw them for sale here on Pelican.

See attached for another pic. We all love pics! That's my '64 13-window deluxe.


http://forums.pelicanparts.com/uploa...1515901848.JPG

Matt Monson 01-13-2018 07:21 PM

Brent,

I've been considering a similar engine. I've got a cam thread here where we are talking about it. I bought a set of 90mm RS 8.5 MFI P&Cs recently. They are new. I'm probably going to get some higher compression JEs. Want to buy just my slugs? I'm keeping the jugs. PM me if you want to chat.

Trackrash 01-13-2018 08:02 PM

Do the heads have a provision for MFI? You can also measure the valve size. They could have 39mm, 42mm, or possibly 45mm intake valve size. The 2,2 and later heads all had 46mm intakes and the included angle of the valves is less, which will be a benefit with the larger cylinders.

I have the 2,7 RS P&C set in my SS2,5. Even with cutting the heads and leaving out the base gasket I was only able to get 8.4 to 1 CR. Probably not what you would want.

I am guessing JE has or can easily make 92mm pistons. The thing would be to do the math and figure out what CR you want and from that what compression distance (I think that is what it is called), and the dome volume you need. I am sure this has been done, so it should not be a huge deal to figure it out.
Here is an example.
http://forums.pelicanparts.com/uploa...1515906148.jpg

targa72e 01-13-2018 11:43 PM

Ok, second round of 2 cent advice, Realizing you have limited money to spend and want a 911 engine for your 914.

Do you have the oil tank, hoses, mount etc, to put a 6 in your existing car?
Oil tank $700
Hoses $350
Mount $$300 Plus install
If you do a 2.5 or 2.7 you probably need a additional cooler and hoses $350;

2.0L case and bearings, bored for 90mm jugs. Oil bypass mod, case savers, no squirters.

The way the case is set up its really only good for T cast iron cylinders but has been bored for 90mm Aluminum cylinders. Adding piston squirters this is $440 from Ollies. sell case or get squirters installed. If you had a case for 2.2/2.4 cylinders cast iron T P&C a good used set is less expensive.

Measured/checked and is ready to go
-2.0L (66mm) Counterweight crank and bearings ready to go
Worth some money sell to fund project. Displacement will get you more on limited budget.

-2.7L (70.4mm?) crank with damaged/undersized rod journal
Not worth much but 1st under rod bearings are same cost as standard. Keep and use.

-2.7L and 2.0L rods
Sell 2.0 rods with crank or separate
-2.0L heads, rebuilt
Sell and buy later heads. The set you have will probably require machine work to use with 90mm Cylinders. Factor this in vs selling and purchasing later that need rebuild

-Worn 90mm Alusil jugs, good matching CIS pistons
Cylinders Worth about $200 in credit with EBS so that's about market value. Either need to re-plate for around $1200 (and still need pistons) or find a set of NiKasil in spec if you want to reuse with aftermarket pistons I got a set of good Nikasil in the last year for $500 but looked for about 6 months. Still need pistons the ones you have are not very usable.
Set of Je pistons is about $1000. Might get lucky and find are usable set of stock use 2.7 P&C but will be limited on cam selection

-Worn cams which will be sent to Dougherty for a new grind
You might be able to go next most aggressive cam, grind around $400
-4 rib oil pump
good
-Set of Weber 40IDAs
If in good shape and set up for your eventual engine configuration really nice.

In the end no inexpensive way to do what you want. Might look into building a 4 cyl for now if funds are limited as you could build/buy a 4 for the cost of the supporting hardware for a 6 swap.

john

Matt Monson 01-14-2018 10:52 AM

Last time I spoke to him Tom had a couple decent used sets.

http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/956119-fs-nos-mahle-2-7-rs-piston-cylinder-set.html

Carbster09 11-14-2018 06:31 PM

Hello,

I am considering a 2.5 SS for my '71T. Question is ... should I or could I use the stock '71T motor for this? Or should I really save the OEM engine and start hunting for parts? If so, what case, crank and heads do I want?

Chris

Trackrash 11-15-2018 11:28 AM

Quote:

Originally Posted by Carbster09 (Post 10252201)
Hello,

I am considering a 2.5 SS for my '71T. Question is ... should I or could I use the stock '71T motor for this? Or should I really save the OEM engine and start hunting for parts? If so, what case, crank and heads do I want?

Chris

These motors are all about choices and $$$. Do you have Wayne's book?

I built a SS2,5 out of my old '71 T motor. No problems for 30 years, hundreds of auto crosses, dozens of DEs, 90K miles. 190+ HP.


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