Building a 2.8
 

OK,

so I have read how to build a 2.8 from the pages of Wayne's book.

I will go that way if anyone can point me at a reasonably priced early 930 motor.

What are my other options.

I know I can get 2.8L cylinders for a 2.7L motor. That will give me a 92x70.4 bore and stroke motor. The bad thing about this is using the 2.7L case.

I figure I can get replacement cylinders that underbore a 3.0L motor. Basicly take a sc motor and have cylinders made that fit this motor, but are 92mm instead of the stock 95mm from CMW or the like (someone out there make these for stock ?) Drawback being the cost of the 92mm cylinders.

Option 3? replicate the 930 setup with an sc case. Use the 95mm cylinders and pistons and a 2.2L crank. Special bearings? sleeves in the case of some sort ? Anyone doing this or have heard of this?

Give me some more ideas. I will take them.

Thanks

Ed

You can get to 2.8 at least two different ways.

92mm RSR P&Cs with a 6 bolt 70.4mm 2.4/2.7 crank & rods and case. These P&Cs are going to give a compression ratio of well over 10:1. Probably over 11:1. Plan on twin plugs, blending race gas, 250hp, and big torque. excellant motor for a really lightweight car since its built on a mag case

95mm P&Cs with a 66mm crank & rods on an early aluminum turbo/C3 case (type 930/02 or 930/52) also gives you short stroke a 2.8. The engine case is key here. You cant do this with an SC case unless you have a 959 (obviously not feasible or easy to obtain) crank. It must be an early turbo or a Carrera 3.0 case to use a 2.0 or 2.2 crank. I think you also have to go with J&E pistons to get a suitable compression ratio in this config. This gives you an engine that should spin to 8000+RPM and make big power all day long.

either way its big money. Search old posts from Pelicanites Grady Clay and Henry Schmidt for the details on each version of the above mentioned 2.8s. Both of these guys have built a bunch of these engines and know all of the tricks for each.

good luck.

I realize at 2.8 is sexy, but what about a high CR 2.7? Not sure what you are starting with, but seems a little easier to build.

Jeff

So that you understand.

I currently run gt4s. The limit of gt4s is 2.8L.

My current motor is a 2.7L high compression motor.

I am doing very well with the setup (2k lb car, all the suspension tricks that can be had, big tires, pleanty of grip)

I am looking for the extra boost that my competitors have. I am being out run down long straights and I want to fight back.

My 2.7 could be hotter than it is I understand, but if I am going to build another motor I want to do it right.

Here is what I would like to know.

With the 3.0L case with the short stroke. What rods do I use. Basicly stock size for the 3.0 turbo (is the 3.0 na rods the same)

What about the cyliders. are they the stock 3.0 turbo to use ? are the 3.0 na the same.

The pistons. I want high comp. Something from J&E ? are there other options. Ross racing, Wiseco ...

who has the best headwork for this setup.


Thanks

Ed

Early turbo/3.0 Carrera cases are EXPENSIVE if you can find one; I have seen them for as little as $1600 for the case only. I'd use an early aluminum case, which is about half the price and just as bullet proof. Of course you'll still have to do the requisite machine work (squirters, shuffle pins, etc.)

Kenik:

You are right that these early Turbo 3.0 cases are hard to find and command a price premium but the older 2.0 aluminum cases, while much better than the magnesium ones, are nowhere near as strong as the 3.0 Turbo cases.

Just open both of them up side-by-side and look at the main bearing webs to see for yourself. There is a reason why Porsche homologated that whole new design for the 934/935 cars,....:)

Steve,

Good, you jumped in.

I saw an earlier post that you built a long stroke (for lack of a better distinction) for a customer.

Given the choices, would you build the 2.8 short stroke or another long stroke.

Given my purpose is a dedicated gt4s racer weighing in at 2k lbs.

Based on the long stroke motor. What about a later 3.0L case with special made 92mm cylinders. I figure cmw or us chrome could come up with a set if asked.

Thanks

Ed

I wasn't trying to say the older aluminum case was as strong as the 3.0L case, merely strong enough to be bullet proof for a 70.4mm stroke 2.8L. My dream is still a 2.8L w/ 66mm crank.

:)......Yessir, I knew that but I felt the clarification was necessary for the others who might read this thread.

Hi Ed:

We've done a LOT of 2.8's over the past 28 years,...:) Its an awesome combination for several reasons and I'm quite fond of them.

I'm a believer in "area under the curve" and for that reason, a long stroke engine produces a more useful and wider spread of torque over a short stroke version, all things being equal. Its the kind of performance that gets a car out of a corner,....:)

One of the 2.8 race motors we did was built on an SC case & crank (with a LOT of custom preparation), Pauter rods, GT-3 R oil pump, special 91.5mm cylinders with steel liners, twin-ignition, custom cams, 935 heads that received airflow enhancements and bigger Ti valves, and 50mm PMO's on raised, PMO tall manifolds.

This motor made 327 HP at 7900 RPM. Without question, this was NOT cheap, but was very strong & reliable since the owner was very hard on equipment and we wanted maximum durability as well as competitive performance.

Ultimately, it depends on one's budget and expection for how long it should last. :)

[92mm RSR P&Cs with a 6 bolt 70.4mm 2.4/2.7 crank & rods and case. These P&Cs are going to give a compression ratio of well over 10:1. Probably over 11:1. Plan on twin plugs, blending race gas, 250hp, and big torque. excellant motor for a really lightweight car since its built on a mag case ]
How would this combo work using the 92mm flat top slip in pistons I read about in another post. Wouldn't that keep the c/r ratio lower?

Gumba:

The final CR with Mahle 92mm RSR P/C's depends on head volumes. 2.8 RSR heads had a 72cc chamber that yielded around 10.2 to 10.4:1.

Since that varies according to whether one uses 2.4 heads or 2.7 heads and whether they have been resurfaced or not helps determine final CR. These heads range between 64cc and 67cc and since one will need them machined for the lower plugs, that helps reduce it a bit.

Final real world CR is usually between 10.5:1 and 11.2:1, depending on the heads and whether any creative work is done to lower it down a bit. :)

Without question, a custom set of JE's can be sourced to get whatever CR you wish, but one should be aware that these do NOT last anywhere near as long as Mahles.