Increase Horsepower for 1967 Porsche 912

[Billthdg]

I have a 1967 912, with the straight 1,600 CC engine and the normal ~90 HP. I AM NOT a mechanic, but would like to increase the horsepower power by 10-15 percent without major modifications.

I have been told that by adding a new exhaust and setting up the carbs, I can add another 10-plus horsepower.

Any thoughts from this rogues gallery, would be appreciated.

Doug

[Prsh356]

Big bore kit , mild cam !

[ejboyd5]

Ask yourself if it is really worth the cost and effort if the present configuration is running well. Find someone who has installed the larger P & C, drive their car and see if it is worth it to you. If you are facing a complete rebuild for some other reason, my answer might be different, but if all is presently good, I'd leave well enough alone. A complete tune up by a reputable shop would be a lot less expensive than the improvements you are asking about and might well surprise you with the results.

[peter leinberge]

Agreed^^^ !!
to add to the sense of wonderment when driving the car (any car)
all you have to do is WASH IT.

[cmpski]

Where do you live. Maybe someone can refer a good shop near by. 10 hp might be a reach, If you gain 10 hp on the top end it will more than likely come at the expense of low and mid range torque.
Beyond a new exhaust things will get expensive quickly. Hopefully all you need is a proper tune. These cars when stock are about handling and momentum,

[wkrtsm]

External to the engine, probably add exhaust headers, Weber carbs (40 IDF) and velocity stacks, MSD ignition. Certainly add header wrap on the headers, since that can boost performance as well. MSD can add mid-range torque, which equates to performance. Internally, add a big bore piston kit, erratic camshaft, etc.

[jess p]

I’m in the same boat. If you have some money I would
go with a big bore kit. Mild cam, and an exhaust. Weber’s or
Delorto and ignition setup. You could be looking at a 25-30 hp
gain. Since you have to split the case, for cam make sure everything
looks good. Boattailing the crank will get you 5-10 hp.

[Joehand1]

That's exactly what I have in my restoration 912 I am working on. If that is true, the HP is close to the 911 of that era correct?

[cmpski]

I consider the real hp of the 912 616 engine to be 90 not 102 at sea level. I believe it's overly optimistic to expect 110 hp with a 1720 or 1750 and a ever so slightly warmed over cam. A big cam might give you another 5 to 10 hp in a very narrow power band at the cost of useful street driving torque. HP is for bragging rights. It's torque that does the work and puts a smile on your face out of a corner. A 1.9 to 2.1 liter will cost big $ and have a much shorter life span to get that 125 to 140 hp. The scrawny little 3 main bearing mag case was never designed for long term life with 125 plus hp. It would have helped if it was an aluminum case but they're heavier. I called ALL the top 616 engine builders 10 years ago and realized if I wanted 125 plus long term hp I better look for an alternative.
The best 616 engine builder of the top 616 vintage race engines here in Denver just laughs at the claimed hp numbers people throw out.
The 912 616 engine is a detuned 95 hp 356 SC engine. They dropped it to 90 and tuned it for more torque so it would be easier to drive in city traffic as the 912 weighed more. My 1959 356 super had 75 hp a normal had 60. The later B had a Super 90. The 64/65 SC 95. If Porsche thought they could get 110 plus long term reliable very drivable hp they would have done it.
The boy racers always want hp. I was there once. After a while power in the 4500 to 6000 rpm range with little torque under those reeves in places like LA and Denver gets really tiering.

[cmpski]

912's have a history of breaking cranks. It's obivious just looking at the case. Two rods together without a bearing, then a bearing and two more rods without a bearing. The cranks flex! This is why Porsche limited the hp to 95 on the 356 SC's. Yes race engines can make a fair amount of power but they usually only run a few seasons (one or two thousand miles) before disasembly. If you want strengh get a forged crank. Expensive. https://lnengineering.com/scat-billet-74mm-crankshaft-for-porsche-356-912.html

Here is my case. Four cylinders like the 616 but it has 5 main bearings. The bottom end is like a tank and can handle seven to eight thousand rpms. I run mine to 7200 and know of others who run to 7500. I also run 14 quarts not 4. In 3000 miles the oil sees the inside of the engine only 1/3 as often as a 4 or 5 quart fill. Unfortunitly it's just too pricey for most folks.

All I can say is if you want a modistly priced 616 build be realistic on your hp expectations. Don't overstress the wiggly mag case and stock crank. Going from 90 to 110 hp DIN isn't an easy ask. That's over 20%.

[NICE 69 S]

cmpski, the 912 case is certainly not Magnesium. All aluminum. Pretty sure the crank is forged also, just not as well made as the Scat.
Your engine is a Polo, and from what I hear about 20 K+?
Bob B

[cmpski]

Bob,
If aluminum I stand corrected. The case is still old and wiggley. I still believe 125 hp out of a 1720 or 1750 is a big ask. Maybe 105 or 110. Can you build up a 150 hp race engine or medium term hand grenade. Yes. There have been many 912 stock broken cranks over the years. I suspect many were in built up engines. I had a long conversation with Jeff Trask (RIP) some years ago. A well know 912er with a licence plate that read NO911NV. He ran dozens of 912 tours. He told me the reason he never built his 912's to over 1750 (and kept many of them to 1600) was that the cars on his tours (many in the desert) that were 1.9 and bigger would run too hot. Power is heat and too much power for an engine that was never designed for it is at risk.
My engine makes power therefore it makes a lot of heat. How do I keep it cool? By running two custom triple loop front coolers and 14 quarts of oil. My goal is to keep the oil out of tha case for as long as possible. Even when blasting around on a 100 degree day with single digit humidity here in Colorado the oil never goes over 200 degrees. Plus my case is made of the latest aluminum alloys. Not 50 plus year old material that has been heat cycled a zillion times. Be kind to your 616 engines.
These days $20K will probably buy a POLO kit. A very nice Willhoit 2.1 616 is well over $20K and probably $30K plus. As far as prices of a POLO motor you would have to ask Dean who builds them.
www.polomotor.com

[ejboyd5]

If HP is what you're looking for, why not sell the 912 and buy a 911.

[Brad912]

John Wilhoit does a stroker kit to make a 2.2 4 cylinder out of the factory case. Think it’s around 145 hp. Might look into that

[Rdkc01]

I would highly recommend reading through the development “white papers” that John Willhoit has written. He has many iterations of the 912 motor he has assembled and Dyno tested. You can lean a lot here. http://www.willhoitautorestoration.com/documents/WR-Dyno%20Tests%202010.pdf

From a cost standpoint this can become a slippery slope very quickly. Your getting some sage advice in this thread already.
1. If you take the plunge to a big bore kit make sure you buy a proven combination of parts. IE a proper cam and carbs along with the pistons and cylinders.
2. Assembly- proper and detailed attention here makes the difference.
3. For the street driven car torque in the drivable RPM range is king.

Stepping up from a 1720-1750 kit gets pricey quick. Case prep for 90mm plus bore can run north of $2K alone. John Willhoit’s 2.2L kit is just under $17K and his 1925 S kit is just under $13K. There are several top quality engine builders and some shady ones too. Claims of “seat of the pants”torque and HP numbers are just not something to rely on. Dyno readouts with AFRs are.

Chris mentioned his due diligence in regards to checking out viable options. This is very good advice.

Good luck with your quest and happy motoring.