2.2 to 2.4 Conversion?

[hasaramat]

First time post in the engine rebuild forum. I have a complete 2.2T engine and I want to convert it to 2.4. I have a 70.4 crank and rods out of a 911/84 2.7 engine that was parted out years and years ago. This engine would be for a 914/6 conversion in a norrow body car with no front oil cooler. Can I use this crank and rods in the 2.2T case? Was thinking 2.4 with Zenith carbs, E cams, and 2.2 E pistons on the longer stroke for alittle more C/R. What do you think?

[Flat6pac]

You have to clear the crank counterbalancers with the piston skirts..at least you do with S 2.2 pistons on this application.
Bruce

[super9064]

This is exactly the engine I just had built by TRE. I had a 2.2 T engine that had been upgraded to 2.2E Ps&Cs, and Webbers. I pu in E cams, and a E distributer.

I just had the engine rebuilt using a 2.7 crank and rods. The heads were recuilt to S spec. So it's basically a 2.4 but with high compression pistons. I think the ratio is about 10 to 1, but have been told that may be high. Runs fine on pump gas.

What a blast!!! It's a fun engine, lots of torque through out the rev range. I would highly recommend it, and it's not a very expensive build. 2.4,2.7 cranks and rods are not very expensive.

[Henry Schmidt]

I just built a similar engine for a customer with a few light changes.

We used the matching numbers case, 2.4 crank and rods, 84 mm cast iron cylinders with 8.0:1 forged pistons with 2.2 T heads ported to 36 and stock T cams.
The engine made 177hp @ 6,000 on regular gas. No cooler and heating issues.
This engine although relatively mind made a very fun car to drive.

I built the E engine in the OP description for my 914-6 some 15 years ago and had issue after issue with detonation on hot days. I had to stop and drastically retard the timing on the way to Vegas on a hot summer day just to make it up the grade leaving Baker.

These days, with the crappy gas (and getting crappier) I limit my compression to 9.5:1 on street gas and twin plug anything higher.

[super9064]

Henry, what would be the compression ratio of a engine using 2.2E P&Cs, with E cams, and 2.7 crank and rods? and what would you estimate the HP assuming carbs, distributor re curved, heads ported and polished with a MK exhaust.

Thanks

[Henry Schmidt]

Originally Posted by super9064

Henry, what would be the compression ratio of a engine using 2.2E P&Cs, with E cams, and 2.7 crank and rods? and what would you estimate the HP assuming carbs, distributor re curved, heads ported and polished with a MK exhaust.

Thanks

Horse power numbers seem to exist in an ever floating universe but I'll take a WAG.

Horse power increases based on compression alone are like every other performance enhancement. There is a law of diminishing returns. Compression increases in the lower end (let's say 7:1 to 9:1) will yield a higher return by percent than say 9:1 to 10:1. My experience says that increases from 7-8 and 8-9 will yield 7 to 10% where increases from 9 to 10 will yield only 3 or 4 %.
With the 911 engine you have an inherent propensity to detonate under higher compression ratios. With the compression limited by both fuel and chamber configuration, the more aggressive the compression the more conservative the ignition advance must be.
I believe that is why Porsche limited their compression ratios in their earlier (non fuel management) engines. Remember the 2.7RS engine only ran 8.5:1 and yet was a great performer on street gas. Even the racing engines of that era were limited to around 10.4 :1 with twin plug.
That said, I would guess that a 2.4 E engine running 2.2E pistons (9.6 :1 comp) will yield a horse power increase of less than 4% over a stock 2.4 E. The ports may help but at a loss of lower end cylinder filling yielding lower torque readings at 2-4 thousand RPM.

Of course all of these compression numbers being bandied about are static compression numbers and the only numbers that really matter are dynamic compression.

The difference between STATIC COMPRESSION RATIO and DYNAMIC COMPRESSION RATIO is where the piston is in the cylinder when the valves close and the piston can actually start compressing the remaining volume in the cylinder vs the static compression ratio that assumes the pistons starts making compression the instant it leaves bottom dead center and starts upward on the compression stroke.

Old school Porsche cams were generally designed with low lift and high duration creating relatively low dynamic compression.

I like M&K mufflers but they are not a bolt on item on every engine. Quite often you must tune the specific engine to realize the performance increase.

I know that really doesn't answer your question but perhaps it will add some insight.

[super9064]

Thanks Henry, good info. So I can assume it would be about 160Hp.

[Henry Schmidt]

Originally Posted by super9064

Thanks Henry, good info. So I can assume it would be about 160Hp.

If I remember correctly, the standard 2.4 E has a compression ratio of 8.0:1 and your new engine has a compresion ratio of 9.6:1. That should yield an increase of something like 10 to14%.
WAG, if you started with stock 2.4E you had 155 and with a 10% increase that would yield horse power around 170.