grady 2.8s

pizzy · 09-26-2006, 05:27 PM

alright, i've heard grady talk about this 2.8s motor. what is it? who's going to build me one? and how much will it cost me?thanks
steve
57 coupe
71 targa
84 coupe

rs911t · 09-26-2006, 05:56 PM

Well, here's what Grady had to say about my engine ...

"The original engine was converted to 2.8 L with the addition of 92 mm factory RSR Nicisyl pistons and cylinders. The case and heads were cut to accomplish this. The cylinders were shimmed to get a compression ratio of 10.3:1 with proper squish. The cams are standard 911S factory cams. I am sure that the stock valves and springs were retained as was the original crank and rods. It obviously still is single plug."

In my case, the original was a 2.4T. But, it received S heads along with the S cams. It was originally built with Webers. I've since replaced the carbs with a S MFI and a pump modified to RS spec. Cost to have someone build it? $15k? More?

Grady Clay · 09-27-2006, 07:09 AM

Steve,

Do a Pelican search on my username and keywords like 2.8S and Nikasil. I have discussed this quite a bit.

I like the configuration for long hoods for several reasons. First it is a very powerful street engine – usually around 275 hp. It has neck-snapping throttle response to the point where you could injure an unprepared passenger. It is light weight, particularly with carburetors. It is period correct – you can have what absolutely appears to be a stock 140 hp 2.4 911T and there is a 2.8S lurking inside.

The down-side is that it is a relatively expensive engine to build (all good engines are). The biggest issue today is finding a good crankcase and then applying all the tricks to gain longevity. The case on Pelican rs911t’s 2.8S has never been split since the original build in 1974.

Building one today, I would go to the effort to have access to very high octane fuel and have the CR as high as possible; ~11.5:1. The availability of (relatively) inexpensive twin plug today allows that for a significant benefit. MFI can easily handle the large displacement. The cooling issues are easily addressed with the 1.82:1 engine fan and front cooler.

There isn’t any mystery getting a powerful 911 to connect to the road with current suspension and ZF LSD.

There is nothing like the intake resonance of an MFI 911S pulling from 6000 to 7000, WOT.

All this fits under a flat-sided 911. A true “Wolf in sheep’s clothing.” Pelican rs911t’s 911T came originally with the rare 6x15 chrome steel wheels. With those it is a real sleeper.

If you want to build one (or have one built), I’ll be glad to offer my help so you end up with a successful project. While it isn’t easy, it is straightforward if you address every single “little” issue. Sorry, I don’t build engines.

Best,
Grady

Steve@Rennsport · 09-27-2006, 08:29 AM

I'd affirm what the illustrious Mr. Clay spoke about the ubiquitous 2.8S engines,...they REALLY rock if done properly.

We've done quite of few of these over the past 30 years and its one of my all-time favorites for cars under 2400 lbs, especially with a good close-ratio gearset.

I'd only offer that pump gasolines are not what they used to be and I try to maintain a 10.25:1 CR when using 92-93 premium gas. IMHO, these things require twin-ignition, too.

As Grady said, these are not cheap to do but they have neck-snapping throttle response (carbs or MFI) thats really hard to beat.

pieterk · 09-27-2006, 08:38 AM

Grady, this is an interesting option. I currently have a 2.7RS which I'm extremely pleased with, but I've been talking with TRE and others about the possibility of rebuilding it as a 2.8RSR once it requires a rebuild anyway (it's currently only got about 5k miles on a rebuild, so this is down the line). The car is primarily a track car.

However, it's been made clear to me that a full 2.8 RSR build will require refreshing every 50 or so hours, especially if I'm running it as high as 8,300 rpm. It sounds to me like your version of the 2.8 wouldn't require that kind of attention, while producing only about 30 bhp less than a full RSR.

Since the basic specs you mentioned seem superficially close to an RSR, what about this build you're suggesting is different from an RSR that helps keep it durable?

This could be a very interesting direction to go in. Thanks Grady! Awesome input as always.

Grady Clay · 09-27-2006, 10:11 AM

Steve,

Good to see you back in the saddle again. I have one more day of these double-dose antihistamines so I can actually wake up tomorrow.

Steve and I have agreed for 30+ years about the need for twin plugs on these engines.

Pieter, The difference is rpm. If you keep any of the Porsche engines to about 7000 rpm, they last for a very long time. That is practical with “S” cams. Now if you use 906/935/sprint cams (GE80?) and turn 8300 every time with occasional excursions above, prudence dictates very frequent “maintenance rebuilds”. You usually don’t find anything wrong at 40-50 hours but the purpose is to keep everything inspected and new. The cost of regularly replacing rings, bearings, rod hardware, gaskets, etc. is insignificant when compared to a blow-up.

A “real” 2.8 RSR engine is probably impractical to reproduce today. They had titanium rods, ti lay-shaft, non-adjustable rockers, alu cam sprockets and much more. A 2.8 RSR wasn’t nearly as reliable as the 3.0 RSR. The 2.8 had ongoing issues with the light steel flywheel resonating and loosening the bolts.

Over the past few years I have helped several Pelicans organize their fuel. Depending on where you live it is practical to use race gasoline in the range of 108 to 114 octane. I have 112 octane VP race gas at home. Several guys here keep the fuel at their businesses. We are fortunate here. There are local drive-up gas pumps that dispense up to 114 octane.

You can buy race gas in 55 gal containers. You pay a drum deposit and then just exchange drums each time. You have two drums, one sealed and full and one you are using. When one is empty and you start on the spare, you order a new spare. They exchange for the empty. The gas costs in the range of $4-$6/gal. For a non-daily use hotrod that falls in the acceptable annual cost for many.

Having this fuel access allows running CR in the 12:1 range unique to a 2.8 built using stock (non-RSR) heads. This is what gets the most energy out of the fuel.

There are nitrogen powered pumps for the fuel drum. This puts N2 gas above the gasoline for safety. The drums need to be in a cool (or refrigerated) well ventilated place. They need to be sealed when not in use.

While all this may seem like a lot of trouble, it solves the fuel octane issue. It is particularly desirable because you control the quality of your fuel.

Pieter, you should also consider the rules for the class(es) you intend to run. Your choice will be dependent on class, performance, longevity, serviceability, cost and many other criteria.

I have three race engines that are 91x66 that I’m converting to 92x70.4 for my son. They were 8300+ engines but I expect the additional displacement will bring the peak down to around 8000. They were 10.5:1 single plug and will be 12:1 twin plug. They will still get serious over maintenance.

The time seems about right for Mahle to make another batch of 92 mm RSR P&Cs. I’ll ask.

Best,
Grady

randywebb · 09-27-2006, 11:08 AM

I'll add that, if you need to detune an engine to run on the gas you can find (say, while driving across the state) then the 'solution' is to increse the displacement...

rs911t · 09-27-2006, 11:14 AM

My "T" still has those chrome wheels, and the case is still unopened. But, I've come to believe the latter is inevitable ... sooner than later. Unfortunately I bent the exhaust valves on the race car and had to flip the coin. The "T" lost, at least for the time being.

Steve@Rennsport · 09-27-2006, 11:32 AM

Hi Grady:

LOL,..Glad to hear that you'll be "back" soon,...

FWIW, I still have one new set of 92mm Mahles here I bought from the last production run.

pieterk · 09-27-2006, 11:33 AM

Tremendous Grady, thank you.

I suspected that a large part of the longevity was keeping the revs closer to stock redline, but I wasn't sure.

This really is a very intriguing option for me. One reason it is, is that I have a gas station an easy ten minutes from my house that sells 100 octane. At our local tracks, I can purchase up to 110 I believe. However, I'd probably tune for 100. I'm already comfortable with that, as I'm considering using 100 with the 2.7 anyway, and playing with the timing a little, so it would be no stretch to use 100 with a 2.8.

I've considered the class ramifications as well. It would bump me up out of Prepared in POC into V. The plus side to that is that I can then lighten the car even more aggressively. Right now, I'm class limited to a lowest weight of 2,324. If I end up in V anyway, I might as well take the four points per 100 less pounds and aim for say 2,100-2,200 lbs. I still have a lot of work to do as a driver, and would be hopelessly outclassed in V--I'm outclassed right now anyway, but that's fine. There's time to drive and keep learning.

This is all quite a way down the road though, but I'm so thrilled with this 2.7RS that I can't help but imagine how even more viscerally beautiful a higher performing MFI engine built along the same principles would be.

I'll keep an eye out too to see what you discover about a new run of 92mm Mahle P&Cs.

Thanks again! I'm filing this idea away in the long term projects folder!

blue72s · 09-28-2006, 06:20 PM

Quote:

Originally posted by Steve@Rennsport
We've done quite of few of these over the past 30 years and its one of my all-time favorites for cars under 2400 lbs, especially with a good close-ratio gearset.

If 92 x 70.4 is one of the best, I'm surprised nobody has tried a very similar configuration, if not identical, but easier to get parts:

95 x 70.4
95mm Mahle 10.3:1 RSR p+c's but with 86mm stud spacing
70.4mm SC crankshaft
SC case
SC heads (valves are bigger thus more air!)
twin plug
S cams
carbs or MFI

propricer · 09-28-2006, 07:10 PM

The 2.8L I had built for my stock 914-6 with 40's and GE80's was an unbelievable engine and lasted almost 60K miles. Street only, I never found anything that could beat it - or even come close !!!

That same engine will, in the not too distant future, be built as a twin-plug and dropped into my 914-6 race car.

GREAT engine ... the GE80 cams really wake the engine up and the 40's give low end pump for the street rather than hi-end race track stuff.

And yes, expensive ... but worth it !

Steve@Rennsport · 09-28-2006, 10:30 PM

Quote:

Originally posted by blue72s
If 92 x 70.4 is one of the best, I'm surprised nobody has tried a very similar configuration, if not identical, but easier to get parts:

95 x 70.4
95mm Mahle 10.3:1 RSR p+c's but with 86mm stud spacing
70.4mm SC crankshaft
SC case
SC heads (valves are bigger thus more air!)
twin plug
S cams
carbs or MFI

Actually, thats been done and it too, is a dandy.

The SC's 9-bolt crank does a far better job of retaining the flywheel near 8K (for race apps) but this engine is 25 lbs heavier than the mag-cased version. The $$$ difference lies only in the machine work & prep required for a magnesium cased version and thats about $ 2K.

With the early large-port SC heads, this one can make big power if everything is done right.

Joeaksa · 09-29-2006, 10:59 AM

Guys, pls do not forget that 100 octane is available everywhere. Everywhere that is at your local airport. Its called 100LL and used in almost every airplane flying today with a piston engine.

Nice thread and makes me miss my '72 911.

randywebb · 09-29-2006, 11:05 AM

Is it legal to dispense that into a car? I thought it wasn't.

And, remember, there are lots of places w/o airports w/in 200 miles.

Steve@Rennsport · 09-29-2006, 02:05 PM

FWIW,.....Be aware that 100LL aviation gas is totally different in octane, Reid Vapor Pressure and specific gravity than 100 octane unleaded race gasolines.

Further, race gas "lights off" quicker than Av gas and you feel that in the throttle response. Jetting requirements (and float settings) are also very different between these fuels so Caveat Emptor when using that stuff.