Wayne's top engine pick - 2.2 to 2.4 upgrade

[Hotrod911S]

On page 112 of Wayne's book, one of the recommended engine upgrades is using a 2.4 crank in an otherwise 2.2 engine using 9.1 E pistons with the longer 2.2 rods to get a 2.4 with a compression ratio of 10:1. Is this correct? The large journal width of the 2.2 rod is 2mm less than the 2.4 rod. If you use a 2.2 rod on a 2.4 crank, the clearance from the rod to the sidewall will exceed the maximum recommended .2 to .4 mm. Am I missing something here? If not, what needs to be done to use the 2.2 rods on a 2.4 crank?

Rod

[Grady Clay]

No, you must use the 2.4 rods with the 70.4 crankshaft. The 2.4 rods are 2.2 mm shorter than the 2.2 rods and the big end journal went from 57 mm on the 2.2 to 52 mm on the 2.4. Additionally the 2.4 rod big end is wider, 24 mm compared to 22 mm for the 2.2. Not possible to cross fit these parts.

The really good news is the 2.4 rod is about 60 grams lighter than the 2.2 rod.

As I recall there are some clearance issues with the 2.4 crank to the 2.2 piston skirt, 2.4 rod to 2.2 cylinder spigot, and possibly other. All of these can be addressed with judicious grinding.

Best,
Grady

[Hotrod911S]

Grady, thanks for your reply to my inquiry. I have a carbureted 2.0 engine with 2.2S pistons, cylinders, heads and cams that I want to rebuild and upgrade for use in our autocross car. I am planning to use a '72 case with oil squirters and stroke my engine to a 2.4 using as many existing components as possible. I was considering using a set of 2.2E p/c I have with the longer 2.2 rods on a 2.4 crank to get a 10:1 cr, but I didn't think it was easily done and your reply seems to confirm it. If I use the 2.2S pistons with the 2.4 rods/crank, the cr will be lowered to around 9.6 (I think). I may just have the cylinders bored out to 85mm and use new JE 10.5:1 pistons made for a 2.4. Thanks again for the quick reply.

Rod

[Wayne 962]

Right - the key to this upgrade is the piston pin offset in the pistons - not the crank and rods. In general, you need to keep crank and rods together...

-Wayne

[Hotrod911S]

Thanks again for the helpful replys.

Rod

[dtw]

If you want to hit higher CR without incurring the additional expense of buying new JEs and/or boring out your jugs, consider shaving your heads, deleting the base gaskets, or offset boring your rod bushings...

[69911e]

How much compression can be gained on a 2.7 by removing the base gaskets?
Has any had thier rods offset? If so how much did it cost? I have not found anyone local who has ever done this.

[jluetjen]

If I use the 2.2S pistons with the 2.4 rods/crank, the cr will be lowered to around 9.6 (I think).

No. Actually your static CR will be increased because of the longer stroke. The shorter rod just keeps the piston from extending above the cylinder at TDC.

[Grady Clay]

Rod,

Using the 2.2 rods on a 2.4 crank is not just “not easy” – it’s not possible.

I think your 84 mm S P&Cs would work well on the 2.4 keeping the displacement at 2341 cc. I think I recall CR above 11:1 with that configuration.

It sounds like you have a complete 2.4 engine. What type; T, E, S? How complete is it? It might be better and less expensive to build the 2.4 and keep your 2.0-2.2 intact.

What are your goals? How serious of an auto-X car is it? How far will your budget let you go? Is this for strictly track, street, combination, DE, other? Do you have a front cooler? What transmission type? What is the 911 (year,T,E,S, coupe, Targa) ? What is the condition? Any other changes? Is it licensed on the street?

Go search on my prior posts. You will note that I am a proponent of MFI 2808 cc (92x70.4) twin plug, 10.3-10.5:1 CR built on a 2.4 E or S. Properly done, they are outstanding street, auto-X, and DE engines. If treated well (no overheating, no over revving, clean oil, everything kept tight and serviced), they are reasonably reliable.

There are lots of knowledgeable Pelicans on these forums that can help you.

Best,
Grady

[Hotrod911S]

Grady,

We have a '69 911T that my wife and I have recently started to autocross. Because of all the mods to the car and engine, we have to compete in the Zone 8 F Improved class. The car is at the bottom end of the points for the class, so I can make several improvements to the car and be class legal. About 80,000 miles ago I rebuilt the T engine using new 2.2S p/c, 2.2 S heads, new S cams, topped off with PMO intake manifolds and '67S 40 IDS carbs. It has a '67S distributor and an MSD 6A ignition box. The exhaust system is through SSI heater boxes and a Monty dual 3" exhaust muffler. A Mocal front oil cooler system is installed and on a hard run up the mountains the temp stays at about 180 degrees. The car has a 901 trans with a modified 915 shifter, which I prefer, but I may upgrade to a 915 trans in the future. Anyway, I want to freshen up the engine and get more power/torque without going larger than a 2.4 or 2.5. I think the intake and exhaust system is a little too large for a 2.2 and would work better on a 2.4. So with that in mind, and in the hope of getting more torque from the engine, I want to stroke it to a 2.4. Although a lot of machine work has been done on the original 2.0 case, I am planning to base the rebuild on a good '72 2.4 case that was given to me. I need to get a 2.4 crank and rods and figure if I want to reuse the 2.2S p/c or go with something else. I would like to keep it running on pump gas so I don't want to go much above a 10:1 CR. I also have a good set of 9:1 2.2E p/c that I could use. The primary street driving will be in PCA club activities, probably under 2,000 miles a year.

Thanks for any input you can provide to point me in the right direction.

Rod

[Grady Clay]

Rod,

Tell me more about Zone 8 rules. What are the limits for your class?

With those few miles, I don’t think fuel cost is an issue. Let’s see; $2/gal pump premium x 1 gal/12 mi x 2K mi/year = $333/year. $4/gal race fuel x 1 gal/14 mi x 2K mi/year = $571/year. (high compression and twin plugs will get slightly better fuel economy, everything else equal.) With careful street driving and mixing fuel, you almost can’t tell the difference in cost.

If you absolutely want to stay with pump fuel, I would consider using your 2.2 E pistons you have with the 2.4 crank and rods. Use twin plugs and run the clearances as close as possible and you may have about 10:1. The down-side is you have enough intake flow for a nice mild 2.8S.

What does your car weigh?

You may get the best auto-X times by working on the suspension and having the best tires.

Best,
Grady

[Hotrod911S]

Grady,

My 911T weighs 2,380# in street trim with a full roll cage and door bars, power windows, full RS interior (no rear seats), Carrera steel flares, fiberglass '74 IROC Whaletail, '73 RS front and rear fiberglass bumpers, and a 6-stack CD stereo system. The front suspension and all brakes are '88 Carrera and the suspension is fully sorted with 21 mm front and 27 mm rear torsion bars and 19 mm front and rear anti-sway bars. The car has been fully corner balanced and handling and braking are not really a drawback at this time. I could afford the points for increased displacement, a limited-slip diff, and non-stock gearing, but I still want the car to basically be a street car and not a fully dedicated track car. Years ago, I time trialed a '67 911S for the main purpose of winning, but now I'm just interested in having fun with this car, both on and off the street.

I'll weigh my options and let you know how it all works out. I'll be able to get a better idea when I dismantle the engine. The existing 2.0 case has been boat-tailed and the 2.2S cylinders mooned, but I didn't have oil squirters installed when I first built the engine 10 years ago. I may use the 2.0 case again instead of the 2.4 case and just install a 2.4 crank and rods in place of the light weight T crank it now has. A hot 2.8 sounds interesting, but I'd like to keep my 901 trans and I don't think it would last too long with all that torque.

Thanks for taking the time to respond to my questions. Instead of taking up more space on the board with my own issue, can I e-mail you directly if I have more questions?

Rod
porscheixxi@earthlink.net

[jgparker]

Rod,

The 901 trans will handle upto 300 hp without issues. The factory raced with it for a number of years with engines in this HP range. The big problem is the clutch, but there are 215mm clutches available to handle the torque, but bring you wallet. If you are using a '70 or '71 901 it has the larger later cluch anyway. I'm running about 240 hp on my 901 right now. I prefrer the shift pattern on the 901 myself.

Good luck,

JP

[Grady Clay]

Rod,

Cool. Looks like you have a nice street hot rod that you can safely take to track events and have lots of fun.

What is the 2.0 crankcase? Mag, alu, year? What is the 2.4 case - ?R. Have you inspected the 2.4 case? What is the type number of the transmission?

I agree with JP, the 901 will work with a 2.8. I have two 914-6s with 2.5 & 2.8S engines and 901/911 transmissions, have never had a problem. You will need to continue to be careful when auto-Xing. 901s don’t take kindly to even slight abuse in 1st gear. A 915 is far more robust and you can intentionally abuse it in aoto-X with no fear of serious damage. You will want a LSD sooner or later. You do not want a non-differential “spool.”

Don’t ever feel you are taking up space on the forums. There are currently 192 views of people lurking on this thread. Most have something to gain from your information. If Wayne would move the appropriate threads to the “911 Engine Rebuilding Forum” from the “911 Technical Forum” hint, hint.

Best,
Grady

[ber911]

I currently have a 69 motor with 85mm 9.5:1 c.r J.E pistons and S cams.
From what I understand I can swop over my crank and rods with a 2.4
crank and rods in order to increase both the displacement and compression ratio. I am already running twin plugs so the increased
c.r wont be a problem. Is this a straightforward job that will only require
gaskets and bearings and should anything be done to the case while it is apart? Any ideas as to the H.P increase - I currently have 180 BHP.

Thanks
Robert

[Grady Clay]

Robert,

That all sounds right.

I think your critical issue will be proper piston-to-head clearance. There are several good threads on this forum.

What is your twin-plug setup? What has been your experience?

Best,
Grady

[ber911]

Grady

I am running a rsr cap and rotor adapted onto a bosch distributor. Engine runs great all the way to 7300 rpm but I am thinking that another
20 HP would be great , but want to stick with the original motor.

Robert