2.8 question

[Shuie]

I didnt want to hijack Jim's thread, but Ive got a question about building a 2.8. Im not building a 2.8 or anything, but Grady's response in the linked thread has got me curious about this engine.

Grady mentioned building a 2.8 on a 2.4E MFI engine by changing hi-compression 92mm RSR pistons. In Waynes book, he mentions a very hi rev 2.8 using 95mm P&Cs and a shorter 66mm crank. The 2.8 Grady mentions sounds like a streetable motor, the 66mm short stroke sounds like a race motor. Both of these configurations need twin ignition and neither sounds cheap.

questions:
Is there another way to build a 2.8?
Is the 70.4mm crank with 92mm P&Cs the 2.8 RSR motor?
Can the 92mm P&Cs be used on an SC case with the SC 70.4mm crank and rods, or is the rare 930/02 case with a older 70.4mm crank and rods the only way to build the longer throw 2.8 on a aluminum case?


TIA

[Tim Walsh]

The only way to make a 2.8 with an Al case is to use a very early sand cast Al case. The head stud spacing is different with both the 930/02 and any of the other 3.0 and larger cases.

Frankly if you've got the 3.0 case why don't you just slap some JE's in it, run a nice hot cam, put MFI on it and you should be set to go.. nobody but your butt dyno would know any difference (it would be faster and more reliable)

[Grady Clay]

Shuie,
Yes, the 2.8s I was talking about are built on the 2.4/2.7 mag case, preferably the 7R case. It is 92x70.4 = 2808 cc. The P&Cs are from the ’73 2.8 RSR and are about 10.3:1 CR. This makes for a great street engine as an E or S with MFI or carbs.
I agree with Tim.
If you have a 3.0 and want it to go faster, Mahle makes 100 mm Nikasil P&C at 10.3:1, install MFI, S cams, twin plugs and light up your world with a high compression 3.5S. This is a more reliable engine because the SC aluminum case is stronger.

Best,
Grady

[Steve@Rennsport]

A few years ago, we made a "real" 2.8 for PCA racing using an SC bottom end, custom cylinders with steel sleeves and 91.5mm JE pistons.

It had modified 935 heads (early stud spacing) with twin-ignition, 50mm PMO's, and a custom cam. Lots of internal mods, too....

This made 325+ HP at 8000 RPM and was VERY durable. In fact, this engine ran a 1 hour race in August at PIR with no cooling fan when the driver missed a shift on the opening lap and spit the fan belt off. It ran the whole race at 310+ F oil temps and upon teardown, only the lower side of some pistons were a tad scuffed. Mobil 1 15w-50, BTW.
Its still running just great.

[Grady Clay]

Steve,

Absolutely amazing! “VERY durable” is an understatement.

Does this mean you can run a 911 race engine with NO fan, perhaps only some “ram air” cooling? After the belt came off, what direction do you think was the air flow through the engine?

Was this race in the infamous Portland rain? How was it being driven?

Best,
Grady

[304065]

Steve,

I have been thinking a lot about the "935 heads" you mention.

I looked in Bruce's book-- I think there were two-valve and four valve versions? What makes them different than 3.0 heads?

You guys WILL be the eventual cause of my spending $40k on a 2.2 screamer for PCA GT-5R.

[Shuie]

Thanks Grady! Thanks Steve! I'm always interested in learning about the different engine configurations. I appreciate the help and advice.

[Steve@Rennsport]

Originally posted by Grady Clay
Steve,

Absolutely amazing! “VERY durable” is an understatement.

Does this mean you can run a 911 race engine with NO fan, perhaps only some “ram air” cooling? After the belt came off, what direction do you think was the air flow through the engine?

Was this race in the infamous Portland rain? How was it being driven?

Best,
Grady

Hiya Grady:

LOL,...this was an August PCA race here at PIR and ambient temps were in the 90's. Regardless of how this engine came through the ordeal, I cannot recommend disconnecting the fan for more HP,..

The driver is pretty decent and he drove the crap out of it for the whole hour getting second place.

I really don't know what the airflow was on that; it had an 993 3.8 RSR wing so the engine compartment received good ventilation.


John:

No customer 935's had the 935/71 engine: the 4-valve, water-cooled head one.

Almost all of these had air-cooled, 2-valve heads that had some special features such as oil-cooled exhaust guides and REALLY good airflow.

When you are going to do that 2.2 race engine, please give me a call,... There are some neat things we can do.

[Grady Clay]

Steve,

You built a wonderfully engineered and constructed engine to take that kind of thermal abuse and come through intact. Most would have destructed within a half lap. Good for you!

Of course no one in his right mind would intentionally disconnect the fan. However, there is an opportunity here to understand the air flow when the fan isn’t working. That is one powerful heat engine. For the hour there must have been significant air flow to cool the cylinders and heads – the oil couldn’t have done it all. So, where did that heat go? There must have been some air flow through the engine. The basic question is; was the air flow from the bottom up or from the top down? Much depends on your wing configuration.
Knowing the direction of the air flow will tell you if the fan is pushing against a head or working with the flow. There are some serious performance issues there.

John,
Another trick that the air cooled 2-valve 935s used was doubling up the oil flow to the cam boxes. It used both center oiling and the spray bar. I used that on my GT-2 914-6 engines (66x91) with good success. I don’t think that little oil passage from the cam box to the center of the exhaust guide did much for cooling, just some necessary additional lube for a turbo. The finned guide may have done more for keeping the guide cooler. Remember those engines put out 650 HP at normal boost, it felt like it doubled when you cranked it up a little.
Guys, give me a buzz about your race engines, perhaps I can help advise 2c also.

Best,
Grady
gradyclay@hotmail.com

[Jandrews]

Grady,

In the 2808 engine you mention above, what heads and cams are required to use those 10.3:1 pistons? Also, what kind of horsepower would this motor put out? Would the 2.7RS space cam in the MFI pump be sufficient to provide adequate fuel supply?

I have a 2.7RS spec MFI motor right now that is completely torn down and looking for some more horsepower. It is built on an original '73 2.4S motor with a 7R case. Should be putting out somewhere around 210 HP now, but more would be nice if it can be done relatively easily from this base platform.


Thanks,

JA

[911pcars]

This may not apply to every situation, but one of my customers (930 race car) uses this system to "water cool" his cylinder heads. He reports it lowers CHT by about 25ºF.

FWIW,
Sherwood

[Grady Clay]

John,

With your engine it is something slightly more than a bolt-on. The 92 mm RSR P&C will fit everything you have EXCEPT the piston-to-head clearance is critical.

Yes, your 2.7RS pump will work just fine with regular adjustments.

What is your current CR? What is your piston-to-head clearance? Do you have twin plugs? Can you send me an image of the tops of your used pistons? I would like to see the carbon pattern.

I assume you have ‘73S intake stacks, throttle bodies, heads, and cams.

A full point and more in CR with twin plugs will make a large difference in performance. However, you will have to pay much more attention to fuel octane.

Best,
Grady
gradyclay@hotmail.com

[Jandrews]

Thanks for the info Grady!

My 2.7RS has the stock RS Mahle pistons, which I believe are 8.5:1, correct? I don't know what my current piston/head clearance is. Also, since I have been having some persistent performance problems even after a recent top-end job, I don't think you would be able to draw any conclusions from my current carbon pattern. There was only about 300 miles on the top-end of the motor when I tore it down again for the second time. Read more on this issue in this post:

RS MFI - Strange Combustion Problem

Anyway, yes, I have the stock "S" heads, cams, throttle bodies and plastic stacks. I recently had the heads completely redone with machine work, valves, springs, seals, retainers, everything by Ted Robinson at German Precision. I did not have him do twin plugs, but I am sort of wishing I had. Again, the top end has only 300 miles on it.

Any thoughts you might have would be appreciated. By the way, I have paid close attention to your posts here, and look forward to each and every response of yours. I think this board has picked up another expert on the early performance breeds!

JA

[Grady Clay]

John,

Wow, I’m sorry to here of your continuing perplexing problem. I assume you have not yet found a cause for the difference in left bank to right bank. What did you find on disassembly?

Our computer was down (ME died, changed to XP) so I didn’t see your posts in August. Too bad, we came to the Royal for a whole week last fall and I could have used a break from the Kemper Center.

I went back and read all the posts on the problem. You sure are getting good advice.

I’ll reinforce some ideas.
I don’t see any report of swapping mufflers. The Ansa muffler is not OE (or OEM for that matter.) Could there be a restriction in one inlet of the muffler; a shop towel, rodent nest, internal muffler failure? A baffle that has come apart or loose could be the rattle/vibration. Under load the loose baffle could move into a location that would restrict the exhaust flow causing the power loss, yet work OK at idle and part throttle. What does this Ansa muffler look like? Are there two independent mufflers? Is there another MFI Pelican 911 you can swap your muffler on to and see the result? In the overall scheme of things, I recommend going back to the stock OE muffler. I assume you have already inspected the exhaust pipes in the heat exchangers.

Measure the cams. Put a micrometer on the base circle and peak of the cams and verify they are the same S. I can envision the possibility of a T cam being timed to S specs and still sorta work. With the big valve cutout in the RS pistons there might be enough room for it to work. Did the first mechanic have another 911 apart at the same time?

In the 300 miles of running, what diagnostics did you do? I saw your posts, were there any others? How did it idle? Did you balance the air flow at idle?

An important clue is the difference between the two banks but don’t let that put blinders on for other problems.

Best,
Grady

[Wayne 962]

Originally posted by l33t9eek
The only way to make a 2.8 with an Al case is to use a very early sand cast Al case.

100% INCORRECT!!!

If you look at page 112 of the Engine Rebuild book, you can see that you can use the short stroke 66mm crank along with the Euro Carrera 3.0 (early Turbo) case to get an aluminum case 2.8 engine. In fact, this is a very common application for this case, and it is usually why these cases are so sought after...

-Wayne

[rs911t]

uses this system to "water cool" his cylinder heads

Sherwood, my car had a very similar system. The nozzle was setup to spray into the engine fan. The previous owner had removed the pump, but the nozzle was still in place in the engine compartment. The driver would turn it on/off via a toggle switch under the dash.

I don't know if Grady remembers, or even knew about this. His shop built my 2.8 for the original owner, who installed the spray system. They used to race on track in the Rockies. Not much air to keep things cool on hot days.

[Grady Clay]

Greg,

Let’s start a new thread on this subject. I was going to wait until hot weather but now is as good a time as any.

I’ll start it on the “911 Technical Forum” so most will see it. Help keep it alive.

Best,
Grady