2.0 -> 2.5 Ss?

SigmundF · 12-08-2006, 12:40 AM

Hi, I need some help/advise.

I have a -67 2.0 L engine with a broken piston and cylinder and now I am planning to rebuild this engine. I have been reading quit a lot on the forum about short stroke engines and I would like to try to put together one of these engines based on my 2.0. This engine has original Webber that I am planning/hoping to use.

So the question is what parts do I need to replace, in order to end up with a 2.5 SS? As far as I have figured out I need:

A set of 2.7 L cylinders and pistons (I am not sure what pistons to use, based on compression rate)
The 2.0 heads are not the best, so I am also planning to get a set of 2.7 heads.

What else do I need?

andrew15 · 12-08-2006, 07:26 AM

A few things come to mind:
- Case needs to be bored for bigger cylinder spigots
- 90mm P&Cs
- 2.7 Heads
- 2.2 Rods - Some say they are beefier than the 2.0 and should be used with the larger piston
- Different jets and venturies for carbs

AM

tctnd · 12-08-2006, 09:46 AM

A couple of years ago Bruce Anderson covered this in some detail in his Excellence column. I don't remember which issue, but if you search you'll find it.
regards,
Phil

911pcars · 12-08-2006, 10:29 AM

"A couple of years ago Bruce Anderson covered this in some detail in his Excellence column."

Anderson's 911 Performance book or Wayne's book should provide all details. Typically, RS piston/cylinder kit, but there are many variations depending on your wallet. The S heads are doable, but the cylinder sealing surfaces must be machined to accomodate the 90mm cylinders (same as later heads).

Sherwood

tadd · 12-08-2006, 11:10 AM

Are you going to up the compression and cam? 2.2 heads are a better starting point if you want more CR as they have the non-peaunt plug holes. I't not a lot but every cc helps. IMHO there is nothing wrong with the 2.0 heads once twin plugged other than the smaller valve sizes. They actually bore out nicer (less material to blend in) to 38 mm than the 2.x heads because the valve angle is steeper.

Might I suggest that instead of cutting the case that you just go with a 70.4 crank and rods. They are pretty cheap and are a drop in. Then you could have a longstroke 2.5 and save some machining costs let alone the wait time. (this is assuming you will stick with the S cams. If you use more cam that needs more revs, C6, RSR, GE80 or what have you, I'd cut the case and use the 66 crank as it is more robust at higher revs since it doesn't have that nasty 4th harmonic from the huge 'push' of the power stroke.

Another option you might consider is a 2.1 long stroke, actually 2173 with 81 mm pistons (2.2?). You could bore your birals to 81 and bore your heads (or use supertec 906 type barrels with 2.x heads - they are made for the larger spigot bore). The rennsport web page says you can get 235hp out of this motor choice and was (is?) one of my rebuild choices. More bottom torque for the corners but still small enough to rev the crap out of with an S or modS cam. I've also heard really great things about this set of parts from a pretty respected engine builder. It's also nice if with the stock heads and barrels no one would be the wiser

.

tadd

shbop · 12-08-2006, 11:37 AM

Another option you might consider is a 2.1 long stroke, actually 2173 with 81 mm pistons (2.2?). You could bore your birals to 81 and bore your heads (or use supertec 906 type barrels with 2.x heads - they are made for the larger spigot bore). The rennsport web page says you can get 235hp out of this motor choice and was (is?) one of my rebuild choices. More bottom torque for the corners but still small enough to rev the crap out of with an S or modS cam. I've also heard really great things about this set of parts from a pretty respected engine builder. It's also nice if with the stock heads and barrels no one would be the wiser .

tadd

I remember a discussion about this motor before. Seems, you were very enthusiastic. It was infectious. What happened?

tadd · 12-08-2006, 01:48 PM

shbop:
I still think the 2.1LS is a great motor... no make that a really great motor the more I read about this stuff. What happened was I gave into an impulse buy. There was a set of NOS 92 mm L&N nickies and NOS 92 mahles for sale from two differnent folks on this board. The price combo was far cheaper than a new set of 906 mahles and L&N cylinders to pass up so I 'leaped' onto the 2.8 bandwagon. I should have done more research before I bought as you just can't get the RSR heads anymore. In a nutshell, I think the 92 will sit on a shelf and I'm going to go back to the 2.1. The problem is that I waffle depending on who I've been talking to

.

tadd

shbop · 12-08-2006, 01:55 PM

Thanks for the up-date Tadd! I don't want to veer to far off the trail of this post, so I'll end by saying that I hope you'll post the details, when it unfolds.

Vintage911Racer · 12-08-2006, 02:41 PM

If this is just going to be a Street 2.5SS then 2.0L "S" rods are OK. The "S" rods are Nitrated and stronger then standard 2.0L rods. A lot of the guys I race with use 2.0L "S" rods on their 2.5SS race motors reving up to 7800 rpm.. Using 90mm Pistions. They have had no problems. I just built my new 2.5SS race motor and opted for the Pauter rods.

Choices:

2.0L "S" Rods (Light)
2.2 Rods (Heavier, stronger then stock 2.0 rods, not sure about "S" rods)
Pauter rods (Very light, strong)
Carillo rods (more expensive then Pauter (not neccasarily better)

SigmundF · 12-10-2006, 04:23 AM

Thanks for all the input.

I forgot to mention that the engine is for street use. I was also planning to get new cams, maybe S cams or something like that, and I think I will go with the 66 crank option.

Since the 2.0 heads I have is not a good starting point and therefore I need some new ones anyway. I was thinking a set of standard 2.7 heads might be easier with a set of 2.7 cylinders. Then I don't need to machine the heads to fit the cylinders. Is the there any difference in the 2.7 heads from 74 - 76 (ports/valves), except for the RS and RSR?

As far as I have figured out regular 90mm pistons with a 66 crank would give a low CR. I am going for a setup that uses standard fuel and does not need twin plugs. What kind of pistons would be the best? And could I use the rods I have from the 2.0l?

Tadd:
The 2.1 long stroke sounded interesting, is that with a 70.4 crank? I was looking at Rennsport's web-page for some more information, but I could not find anything about this. Do you have link or some more info.

tadd · 12-10-2006, 12:50 PM

Here ya go... it's buried in the 2L stuff.

http://www.rennsportsystems.com/engines%202.0-2.4.html

You should have an email as well.

tadd

Vintage911Racer · 12-11-2006, 12:02 PM

It dependson what pistons you are using. If you cc the heads and have the pistons custom made to that cc you can get a pretty high compression ratio. I am using the 90MM pistons with 66mm crank. the pistons are J&E 10.5 : 1.. It actually ended up being 10.7 :1 when it was all said and done. I am not twin plugged. You are not going to need to worry about twin plugging that engine. At least I dont think so.

SigmundF · 12-12-2006, 05:39 AM

Mark

What type of heads and cams are you using, do you use the standard 2.0S? I was also planning to go for JE pistons.

Vintage911Racer · 12-12-2006, 09:18 AM

I am running GE80 Cams.
I am using 1970-77 heads. They have 46mm intake valves, 40mm Exhaust and the ports are 39 intake and 37 exhaust using 1 5/8 headers.

SigmundF · 12-13-2006, 01:16 AM

Mark

It sounds like you have the same setup as I am going for, more or less. You said you use the 90 mm PE pistons 10.5:1, are those custom made so that's the CR you end up with using the 66 crank? And where would you recommend to get the pistons, I see that our host only have 95mm and up? And where did you get the GE80 Cams?

Vintage911Racer · 12-13-2006, 06:17 AM

I had my heads CC'd and then had the pistons custom made at J&E to match those specs. The CR came in just a tad higher then 10.5:1 9more like 10.7:1). The cams came from my old 2.0L Motor. I had them maged and polished. I got them from Frank Beck in Phoenix AZ. He is the guy that built my 2.0L.

Sounds like you are going to have a stout motor as well.

SigmundF · 12:33 AM

Thanks for all the response.

I think I will go for JE pistons with CR around 10:1 with standard 2.7 heads and 66 crank, but when it comes to camshafts I am not sure which way to go.

Anyone have a link or some information on the difference between GE-40, GE-60, GE- 80 and S cams? Or is there any other options to be recommended? I am still planning to use my carbs (Weber)

SigmundF · 01-02-2007, 05:46 AM

Hi Happy New Year

Is there anyone how can help me out with some information/advise on camshafts?

tadd · 01-02-2007, 06:36 AM

Call John Dougherty, camgrinder on this board, or visit his web page. He will set you up. He even whipped up a cool set of custom cams for kenikh. he KNOWS his stuff.

tadd

SigmundF · 11-01-2007, 03:47 AM

Hi The winter is getting closer and it is time to pick up this project again...

I have two sets of heads, one set with 35 mm ports ('75-77 911S with air injection (CIS)) and another set with 30/33 mm ports ('73.5 911T (CIS)).

Which port size would be best for a 2,5 SS with Weber's?