2.4 Build

[Phoenix]

Hello All,
It‘s been quite a while since I‘ve posted. Life has gotten in the way of my Porsche pursuits.

I‘m now ready to focus a bit on increasing the torque on my 2.4 Motor.

Aside from the odd Autocross or PCA track day, the car will not be tracked. My core objective is a reliable motor with strong low end torque pulling well from ca 1500rpm.

Current setup:
- [ ] PMO carbs 40
- [ ] Bore: 74mm OEM Mahle 911s piston and cylinder
- [ ] Stroke: 70.4mm
- [ ] Compression Ratio: 8.8:1
- [ ] Valve sizes: 46mm intake / 49mm exhaust
- [ ] Port sized: 32mm intake / 32mm exhaust
- [ ] Camshaft specs:
- [ ] intake duration 270/ exhaust duration 254
- [ ] Exhaust opens at 36ABC/ closes at 20ATC

I‘m considering a PMO EFI system to improve everyday useability; meaning sure cold starts, minimum sputtering across rpm range, slight increase in fuel mileage, etc...

What would you build with these objectives and current setup in mind?

Many thanks in advance for your thoughts!

Best... Oliver

[Trackrash]

It's always how far you want to take it and of course your budget.

If it was me I would go to a 92 or 93mm bore for a 2,8 or 2.9 with a CR around 9.5 - 1 and a mod S cam.

Easy to open up the ports to 36mm

Next step would be more compression and dual plugs....

[Phoenix]

Thank you Trackrash. From my perspective the build to achieve reliability and strong torque at the wheel (225+?) starting at around 1500 will dictate the cost. Would a 92/93 bore and mod S cams get me there? Would E cams be better given their mid range capabilities?

[Trackrash]

A local mechanic I know has a 2,9 and he claims it is bullet proof. Maybe others will have info on the latest cylinders that are available in that size.

As far as cams go, I would use a mod S. If you want more midrange, go with a mod solex grind or something like a DC 35. The trick is to match all of your components. More compression likes more cam, for example. I'm running a custom GT-2 102. Similar to a DC 35 in my 3,0. Starts pulling around 3,000 RPM. IMO, you will want more cam than the factory E grind.

Look here for good cam choices. Dougherty Racing Cams Porsche 911, 930 and 964 camshaft profiles

My last motor was a SS2,5 with E cams. I originally had T cams then went to the E grind, due to my car's classing. I would have liked to have even more cam than the E even in that motor.

[cmcfaul]

What Trackrash said. Higher compression with Mod S or DC 30 cams is a bullet proof application. Don't know why Porsche did not make it.

I had a 73 E... ran out of breath at redline 7300 RPM.
Upped the compression to 9.5....big difference
reground the E cams to DC30's....holy cow...screamer.

Combination of compression and cam with the right VE is the recipe you want.
9.5 CR and DC 30 cams on MFI 2.4 was an amazing engine.

Chris
73 E

[Neil Harvey]

""Aside from the odd Autocross or PCA track day, the car will not be tracked"".

Some of the most dangerous words you could have chosen.

If you will use the car for any sort of off road event, chose the one that will put the engine at its greatest demand and build the engine to this. Even if its a 1 time use only. The number of times a customer has said to me, ""if only I had built my engine for ...……. It is my fault, I was at the track and wouldn't slow down""!!!

My advice is to go EFI. Don't bother with anything else. A well tuned EFI system will be hands down better all around. Most EFI systems today are all very good offering control well above that of any mechanical system or Carburetors. I hate carburetors. If only they would remain in tune and change for different conditions???

We are currently building the first of our 2.9L kit with new rods and Pistons and newly designed camshaft. A more modern take on these older engine upgrades. Budget will be your limiter here. Figure out exactly what you want to spend in total and work backwards from there.

[Phoenix]

Thank you Neil, Chris and Trashrash. Sound advice on building for track/ autocross. I will work to that.

I am currently thinking PMO‘s EFI system for the exact reason you mention plus the reliable/ sure starting.

So I’ hearing:
- EFI
- DC 30 or similar cams (what is the list here?)
- 9.5 CR

Which P&C’s should I opt for here?

Rough budget would be $20k max.

Am I in the Range?

[Trackrash]

Are you doing the work?

As far as P&C go, look here https://lnengineering.com/products/aircooled-cylinders-pistons/porsche-911-1965-77.html?p=3

and here https://www.pelicanparts.com/cgi-bin/ksearch/PEL_search_2016.cgi?command=DWsearch&description=cylinders

Boring out a set of 2,7 cylinders may be an option, but I'm not experienced there.

BTW, this ^ is why I started with an SC motor for my last build. I found a COMPLETE 3,0 SC motor with MAHLE cylinders. All I needed, beside a basic refresh was JE pistons and Doughtery cams to build my new motor.

[cmcfaul]

I liked the JE pistons, they are lighter and have deep valve pockets. Your heads will likely be milled as part of the rebuild process. This will add a little compression. It's important to keep temps down and fuel mixture not too lean to avoid detonation. A fender mounted cooler would be recommended.

Chris

[Phoenix]

Thank you for your input.

My builder is recommending boring the case spigots and going with 93 mm pistons and cylinders and 10.3 –1 compression ratio. This will require twin plug, which I‘m told will help with low speed response.
The heads will need to be modified for the twin plug, and the port sizes would be 36 intake and 35 exhaust with GE30 cams. Front mounted cooler will also be needed.

Is the added expense of twin plugging and boring the case spigots worth it in terms of low end performance?

Would a 9.5:1 CR and one plug per cylinder be close to his recommendation?

That high a CR seems to me may stress the motor too much?

Am I off base here?

I‘m looking for a reliable bullet proof motor with good low end torque.

[cmcfaul]

9.5 CR is about the max for single plug.

93mm, 10+ CR and twin plug is a race motor. Will need highest octane gas and a cooler to limit detonation (not an option). NOt the direction I would go, just too far from stock in my opinion.

Chris

[Phoenix]

Thank you Chris.
I‘m not looking for a race motor rather good low end torque for a fun spirited driving car.
Perhaps the brief I‘m giving them is too tall for my needs.

Do I really need 190/200 ft lbs for this?

... Oliver

[cmcfaul]

Ask anyone who builds these for a living. The motor you want is a 9.5 (below 10) CR with DR 30 cam. It's the engine Porsche should have built. Will pull harder down low than an S and scream past redline unlike an E.

I had an 73 E with this set up and got there incomentally. Only change I would make is it wants to rev beyond the 7300 RPM redline (its full on powerband at redline). If you can lighten the top end to allow more revs before floating the valves I don't know where it will run out of breath. On the track the only cars faster were turbos. Very reliable setup as well.

As part of the process I did Case Savers (7R case), ARP rod bolts, JP pistons (deep valve pockets and lighter), ARP flywheel bolts and the rests of the stock stuff. None of these mods are budget busters but recommended.

Good Luck and enjoy the process

Chris
73 E

[Phoenix]

Thank you Chris,
I‘m on a steep learning curve with this build. I understand the some of the basics though get lost in the details.
What are the benefits of ARP rod and flywheel bolts?
Is there a lightweight flywheel I should be looking at?
What about the clutch?
Did you mean JE pistons? I haven’t heard of JP pistons for Porsche motors.
Can your set up with with a 7O.4 stroke?

Apologies for the myriad of question. I want to make sure I get this right.

Many thanks... Oliver

[Phoenix]

Also... what would you estimate the max torque be for the engine you describe with EFI?

[cmcfaul]

Sorry. JE pistons. The ARP bolts are just stronger than stock. My research told me with increased HP and RPM's to go with the stronger bolts in these two locations.

Chris

[Phoenix]

Thank you all.
I too believe twin plug may be overkill.

What are the board‘s thoughts on:
- PMO EFI w/ Clewett mgt.
- 93mm bore w/ JE p&c‘s
- keep 70.4 stroke
- GE 30 cams
- remain Single Plug

What torque would this motor generate in the 1500-4000/ 5000 rpm range?
Would this be a cost effective build?

Best... Oliver

[lvporschepilot]

You're definitely in territory where an outside oil cooler would be needed to handle this rig. Overall BHP as described would likely be in the 230-240bhp range. Great street engine. PMO w/EFI is $$$. If you're doing the build yourself you're in the $10-12k range for parts, but I am probably a bit low.

[Wellwood]

Great thread for a fellow Noob - thanks to the OP for starting - and thanks to the collective brain trust for responding.

[cmcfaul]

There is some harmonic issue with the flywheel bolts and it is recommended to upgrade those to the ARP. I look at as why not...Cheap insurance. Same goes for the rod bolts....why not.

These magnesium cases get brittle with age and heat cycles. Recommend casesavers all around. Again cheap insurance.

With more HP comes more heat. Heat and higher CR is a bad combination (detonation). Now or down the road an external oil cooler could not hurt.

Chris
73 E