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Join Date: Jun 2009
Location: Socorro, NM
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Lets Build Me a Motor, 914-6

I am looking for some suggestions on what to build for my 914-6 conversion. The car will be mostly a fun car, used for spirited mountain and canyon driving. It will see limited track time. I have a dedicated autocross car so this will not be used for any autocrossing. However, I would like to drive it in a hill climb or two.

The car weighs about 2180 lbs; I have gone through almost everything on the car, including rebuilding the stock side shift transmission 15k miles ago, but I left the gears stock. I have previously built three different four-cylinder engines each being more powerful than the last. I have reached the point where I want to put a six in it. I have bought a magnesium case ’74 2.7, and a pair of 40mm Weber’s. I have an RX-7 oil cooler ducted in the front of the car. I want an engine that makes its maximum power around 7000 to 7200 rpm. I want something that is really fun to ring out all the way to redline. I am not interested in a stump puller. I understand that this type of motor is not the best performing but for me it is more fun, and this is a fun car. And I want it to sound amazing. I would like to keep the 901/914 transmission.

What I am planning right now is:

10.5:1 JE pistons
36mm intake ports
35mm exhaust ports
Twin plug using JB distributor
SC oil pump
Supertech head studs
MSDS headers


Some specific questions are:

Camshafts, I have been debating S, mod S, DC-40, DC-60, and everything in between. I have been leaning towards the mod S cams. My specific questions about choosing a camshaft is, which grind is going to give me what I want, which could I add MFI on in the future, and which is going to sound the best?

Machining, will the stock S ports flow enough for these cams and give me the power band that I want?

Should I have the magnesium case shuffle pinned?


All other comments and suggestions welcome.

Obligatory car pictures





Old 05-04-2011, 02:26 PM
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Location: Arapahoe County, Colorado, USA
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xtrm914,
First, welcome to the Pelican 911 Forum
Even with a 914-6 conversion, you will find a lot of help here.

The first and most basic question is: “What transmission do you want to use?”
If you are willing to use a 915/916 conversion, 930, and later, the sky is the limit for engines.
If you want to use the 914/901/911 transmission, most agree that 2.8 liters is the limit.
Yes, many swear by using 3.0 and 3.2 with the 914 but I won’t.
Your choice with 2.7/2.8, you are at the limit IMHO.
With this stress, an oil pump, filter, cooler extends the transmission life noticeably.

My street hotrod is a ’70 914-6 with a 2.8S, MFI, 11:1 CR and about 1900#, flat sides and still mostly steel.
I use a type 911 side-shift transmission with a ZF LSD and appropriate gears for whatever.
I changed to the big 108 mm CV joints as this has a lot of (potential wheelspin/grab) torque.


I recommend you convert to suitable 911 brakes and 5-bolt hubs.
All the good (mostly 911) suspension is available.


Your proposed 2.7 will be just fine with a 914/901/911 transmission.
There are a lot of subtle mods that will let it live a long and happy life.

I agree, a ‘Mod-S’ or like will be great.
You want to keep your peak hp rpm at or below 7000 - 7300 or so for longevity.
At 10.5:1 CR and twin plugs you will probably be slightly above the limit for pump (93 octane) fuel.
You can make the decision to use race fuel (101-112 octane) as I do but if you do, raise the CR even more.
Above 11:1 is possible and gives stellar performance.
I paid $8/gal last week for 101 octane unleaded for my Max Moritz 3.2 SC.
There is a lot of controversy about fuel and CR but detonation will kill an engine.

It seems like you have a beginning handle on the technical aspects of building a sound 911 engine.
There is a lot of good information available here.
You will find a lot of knowledgeable help.
Be conservative so the engine lasts a good, long time.
Catastrophic failures are unacceptable.

Best,
Grady
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Old 05-04-2011, 04:56 PM
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PFM PFM is offline
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xtrm914,

Yes welcome enjoy the information around here. I too am a 914 guy with a 901 and several type 4 motors in my past. On the questions you asked, the 2.7 does sound like the plan, mag case well light but... I think the aluminum case is a bit more durable, head studs and such. The valves are just big enough to run to 7000 to 7200 the 35 mm intake is a bit large in my opinion, the port speed will be in the 240 feet per second range, a little slow. You will be looking for about 170 CFM @ 28" through the intake side. If you can reach that number at say 80% of your max valve lift it will be a happy motor. If your heads flow much more than this the ports are likely too large and do not help unless you plan to spin the motor more than 7200, this is a place where more can hurt.

I agree with Grady the 10.5 pistons will likely require race gas even with the twin plug. If that fits your budget go for it, premium at the pump will be at $5.00 per gallon here in California soon enough. In this compression area moving down to 9.5 and running premium pump gas will not cost all that much HP. The slight reduction in torque helps keep the 901 box happy. All things to consider.


Get with Camgrinder for cam choice but the MOD S seems like a sweet fit for your driving style and the sound you are looking for.


Last 2 cents consider having the combustion chamber, piston and exhaust port ceramic coated, it helps keep everything cooler, I did see you live in NM yes?

Ok I'm all done now.

Stay tuned,

PFM
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Old 05-04-2011, 05:27 PM
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count on adding 200lbs or so with the conversion
911 motors are HEAVY!
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914/6 2.0S with twin plug
all metal body panels
19quarts of oil
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and 1826 lbs (wet)
Old 05-04-2011, 07:33 PM
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It sounds like the consensus is 10.5:1 compression is too high. In the land of enchantment the highest octane gasoline readily available is 91. With twin plugs how high of a compression ratio can I run with the mod S cams? If I can bring the 10.5:1 pistons down to 10.3:1 or 10:1 will that be enough? Or do I need to use the 9.5:1 pistons?

Also, should I have the magnesium case shuffle pinned?
Old 05-05-2011, 10:08 AM
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I think 10.5:1 on twin plugs with Mod-S cams in a 2.7 is about the safe limit on Pump 91, I might drop it down to 10.2:1 or so and run more timing if you can. Make sure you get a degree wheel and check your cam timing very carefully.

Yes, shuffle pin that mag case.

You will have fun with that motor....
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Last edited by YTNUKLR; 05-05-2011 at 01:22 PM..
Old 05-05-2011, 01:19 PM
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If your car is a "Real" LE, I wouldn't convert it to a -6 as the Values of the LE's seem to be on the rise.

To, your questions, Shuffle Pin & Time-cert your Mag Case. If you are getting JB Racings Twin Dizzy, go ahead and send your Heads to Mike and have JB do the Machining for the 2nd Plug. Also Mike might have some Cams for you too.

T.C.
Old 05-06-2011, 06:12 AM
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Quote:
Originally Posted by carr914 View Post
If your car is a "Real" LE, I wouldn't convert it to a -6 as the Values of the LE's seem to be on the rise.

T.C.

Keep that LE a 4-cyl LE and do a 6-conversion on another car...that's what I'd do, but to each his own...
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Old 05-06-2011, 09:52 AM
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D K D K is offline
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I'm subscribing to this one....

I just picked up a '75 that I plan on converting to a 6 as well. Mine will be more of a track car and I have been kicking around the idea of a 964 or maybe a 3.2 motor (with PMO's).

I'll be following closely and if it's cool - ask a question or two..

D
Old 05-06-2011, 06:51 PM
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Old 05-06-2011, 06:51 PM
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