Hi-comp 2.4S or 3.x????

[pieterk]

The one out here is for ME and Sherwood and Bert and Dan and a few others!

Like I said, I'm pretty sure there are others scattered in the valley. Dave B named a couple, but I don't remember where. I'm sure there's one or two not too far from you. Maybe try Google or call Dave tomorrow. He mentioned a list somewhere--I can't remember where that is either.

Oh my brain.

[dd74]

Yeah - I found a couple already. One in Van Nuys, and the one in Sun Valley. There are others who "deliver" race fuel by "ground only" (not by air - LOL).

Can you imagine having a 55-gallon drum of 104 Octane in your garage?

I once had a near empty five-gallon can of race fuel for about a week on the side yard of my house, and the fumes were...um...invigorating. One probably wouldn't want to light their Lucky Strike around that stuff, either.

[Grady Clay]

Guys,

I’ll add some opinion.

More displacement is better almost regardless. Higher compression is better IF you use appropriate octane fuel. Very high revs reduce engine longevity. Keeping the heads & cylinders cool makes power and longevity. Lighter weight is better for almost everything.

Pelican peterfranz has a signature I modified:
“If you don’t have the time (money) to do it right the first time, how are you going to find the time (money) to do it again.”
The point is to do it right the first time.

For early engines I like the 2.8S because it is very powerful, light weight, and reliable. To emulate a 2.8RSR (with the 8000+ cams) makes for unacceptable performance and reliability unless it is a dedicated race engine rebuilt at 25 hour intervals. In original form the 2.8RSR was far less reliable racing than the later and more powerful 3.0RSR and 935 engines.

A 2.8S has a practical redline (peak performance) of about 7300 or less. The 911S cams are basically responsible. The S cams also have acceptable street performance in the 3000-5000 range. The peak performance rpm range is also appropriate with street (stock) gearing. This engine approaches the longevity of a stock 2.4S or 2.7RS.

While a 2.8RSR (911/72) engine is possible to be driven on the street, it has less performance in most (street) situations. When “on the cam” 6000-8300, it is great fun. These cams barely run below 4500 rpm and certainly not at full throttle at those low rpm. The price is less drivability and very high maintenance (25 hr rebuilds).

I had a great personal comparison when Bob I and I drove to the ’73 Parade in Monterrey. We went Denver-LV-LA-Willow-PCH-Monterrey. Bob in his ‘73S with a new Factory 2.8 RSR and me in my ’68 with a 2.5S. The difference between S and RSR cams was dramatic on the street. I’ll never recommend race cams on the street unless someone wants to show how slow they are.

All of the above assumes race gasoline with 102+ octane depending on CR. For use with pump fuel, the current most economical way to go is to use the 90 mm 2.7RS Mahle Nikasil P&Cs.

I would like to see someone argue the point for suitability of JE and other aftermarket P&Cs. I agree the price consideration is compelling. My friend Steve Werner has been able to successfully make them work within some limitations. I’m sure he can offer more insight.


Starting with a 3.0+ engine is a whole another world of consideration. They can make more power and can be larger displacement but are heavier. Few were MFI and none original for longhoods.


dd74 makes a good point about temperature. I will speculate he is on the limit with detonation where low revs lead to less cooling, high head/cylinder temperatures and consequent detonation.

Pieter (Pelican pieterk), “I suppose that if the project were to take as long as I imagine (two years plus or minus?), that would make it more possible to purchase and install as light as possible parts, where the choices exist. Things like titanium rods would no doubt be just too expensive, but little things like titanium fasteners for a glass shroud and other such things are doable.”
I agree.

”I don't recall seeing the idea of a 13:1 CR in all of your previous posts. Wow. That would be something else!”
There is a good explanation of this in Bruce Anderson’s book. (pp 138-143). When he & I (and Jerry Woods) started doing this in about ’73. The diagram on p. 139 is close. Depending on which head you start with and the care with machining you can end up with less than the 68.1 cc that Bruce specs. That results in very high CR even with a relatively wide deck clearance (0.050”). The 2.2 and 2.4 heads are best to start with for being able to finesse the combustion chamber shape. All but the OE 911S heads will need the intake runner enlarged.
Check ”2.8 Short Stroke Compression Ratio fine-tuning“

Another advantage to starting with a complete 2.4 engine is you get all of the MFI parts. It is increasingly difficult to assemble a complete set.

Much of the extra time and effort in building one of these engines is in measuring and setting the CR, piston-to-head and valve-to-piston clearances.

Bobboloo is correct. I will second (with emphasis) the recommendation to NOT use the 93 mm (2.9) P&Cs. There isn’t enough material. The 92s seem to last almost forever, the 93s are too short lived. The cost of the Mahle Nikasil 92s isn’t too bad if you shop carefully and do a group buy. I’ll participate.

”To re-address a point of yours from previous posts, can you confirm that even with a CR as high as 13:1, as long as you were to keep the revs limited at say 7,300-7,500, could you reasonably expect such a motor to have a long life without requiring frequent refreshing? If 7,300 is too high, what would be the highest you recommend? I pick that number only because that's where my 2.7RS revs to, and so far it's fine.”
It is high revs that necessitate more frequent rebuild interval and not very high CR (IF there isn’t any detonation issue). Using 7300 as a limit will allow the 2.8S to approach the longevity of a 2.7RS. With a 2.8S using stock MFI intake and exhaust, the peak hp is closer to 7000.

”Finally, I think the Rubbermaid Solution is starting to sink in! I'm going to think about pulling that together early next year or in the spring, when it starts to get hot here again.”
Yes, it really works – in spades. Too often some dismiss this because it is so simple and inexpensive.

”Are you on a PC? If it's a Mac, I might be able to help. Let me know.”
PC. Pelicans kobaltblau, joefrantz and jpinkert are helping specify a lan for me with my old desktop, a new desktop and a new laptop. Aside from better utility, I want future failure recovery to be seamless. Reinstalling and configuring to my preferences is a pita. I’ll post OT for help reviewing what I come up with. If anyone has advice, please email me; gradyclayathotmaildotcom.

Randy, all that water is going to snow in the High Rockies. We are warm and dry (should be in the high 70s today.) We get our big Denver snowfalls (30” blizzards) from Gulf moisture.


I want to be clear about storing fuel. It should be in a sealed steel container and kept in a cool, dry location, not in the sun. I purge the space over the fuel with nitrogen. My next iteration will be a N2 powered pump and two dry-break connectors for the fuel delivery and vapor return. This topic deserves its own thread but I have a few detailed prior posts.

Best,
Grady

[dd74]

Grady - as always, thanks very much for the information. You make a compelling point about driving WOT below 4500. This is something I've lately tried to avoid doing this. Interestingly enough, my car does not detonate - if that's what it is doing - if I avoid WOT below 4,500 RPM, no matter if I've been driving in stop and go or on the track. More a gradual push down on the accelerator up to 7,300, and the engine reacts fine.

Still in all, I do believe twin plugging might be in my future. Until then, I'll probably use a high octane/race octane blend, and give a serious look, once again, into the Rubbermaid solution.

[YTNUKLR]

'nuther thing..this all depends on what your application is. (missed that first time around )

I personally don't think it makes much sense to build a 2.8 Short-stroke on DC80 race cams for the street. There is no advantage to the short stroke in this case, 8000+ rpm on the street has no real use.

A hot-rodded 2.7 will come very close to the performance of a 2.8, everything equal (c/r, cams, induction, etc.) except displacement.

In my experience, JE pistons are not all bad. You do get what you pay for--they are not as "good" as Mahle all-around, but they are quality racing pistons, which is what they are marketed as. They have very low Silicon content, thus they have a high coefficient of expansion, and that's why they can knock around when cold. JE pistons do have significant taper from crown to skirt (something like .028" diameter difference from top to bottom), this is why they "flop" around. Once they expand, the crown effectively matches the clearance at the skirts and they work great.

From this standpoint they are not the best choice for a street piston (however, can work well for a while). In a race car, once they get hot, they are as good as Mahle, and I might imagine stronger because they have very little Silicon--they are almost pure forged 2618Al. I've heard of people ordering off-the-shelf pistons from JE, often clearances were ridiculous, ~.005-.007". On this 2.8SS, I have set the clearance to .002", right on par with Mahles...

Best regards
Scott