dyno summary and testing on early 2.4L & 2.5L

[targa72e]

Hi all, I thought I would share some of my experiences and findings from dyno testing I have done. All the runs were done with the same car, same gear on the same dyno. The test car for these runs is my 73 914-6 conversion. All the runs were done with the same header and exhaust configuration. The exhaust is a 1-1/2 MSDS header with early two in modified to two out early muffler. Previous testing had show this muffler to be very close in power to megaphones on a stock 3.0SC motor.
I have now had 4 different engines in the car over the last 5 years. I will describe the build on each and the results.
The first motor I built and tested was a 2.4L. It started life as a 72T but was rebuilt with the following. 70.4 stroke crank with 84mm pistons for actual displacement of 2.339L. It had factory 2.4 S pistons listed as 8.5 to 1 compression and E cams. The heads were 2.4T with ports slightly opened to 33mm. The induction was MFI with throttles matched to the heads at 33mm. MFI had stock air cleaner system without warm up valve on inlet. I did quite a bit of tuning with the MFI to get good Air fuel mixtures across the RPM range. Dyno below.



The next engine I built was also a 2.4L 70.4 x 84. On this engine I use 73 CIS 2.4 heads. I removed the CIS bungs and bored and ported the heads to 36MM intake 35mm exhaust to match the dimensions of some 2.7S heads I had. This engine used T cast iron cylinders and JE pistons. I CCed the heads and pistons to achieve 9.5 to 1 compression. Cams were factory E cams as previous engine. Induction was a set of modified Zeniths with bored and ported stock manifolds. Air cleaner was stock Porsche with snorkel cut about 4 inches from cover.The chokes were changed to 30MM and the main jets changed to 145. The dyno below is a comparison of the first engine to this.



The big take away from this engine is that the bigger ports will kill low and mid range power. is not true. This engine with big ports made more power and torque everywhere I am sure the extra compression helped as well. Other take away is that E cams made peak power at just over 6000RPM.

The next engine I tested actual a friends that I helped him build and we tested in my car. This engine was a 2.7 built to RS+ specs. It was 70.4mm x 90mm for 2.685L. Pistons were factory RS with 8.5 to 1 compression. Cams were Elgin MOD S and heads were stock 2.7S with 35mm Intake and 35mm exhaust. Induction was Weber 40IDA with PMO manifolds. It used same factory air cleaner as previous 2.4L. This engine made very good power. Dyno below comparing 2.4 to 2.7, no replacement for displacement and hot cams.



The last engine I built is still in the car. It is a long stroke 2.5L 70.4MM stroke with 86MM bore for 2.452L. This engine uses 86MM nikasil cylinders and JE pistons. After CCing the compression ratio is 9.8 to 1. Heads were like previous 2.4L, they started as 73 CIS heads and were bored and ported to match 2.7S heads with 36MM intakes and 35mm exhaust ports. Cams are Elgin MOD S and induction is Zenith carbs on PMO manifolds. Carbs have 36MM venturi with 145 Mains and 110 Air correction jets. I will detail the difficulty getting these carbs to work with this engine in another thread. This used same factory air cleaner as previous engines. So lessons learned on this engine is that more modern cam grinds really help power everywhere over factory E cams. I also did some testing of the air cleaner system that I will detail later. Dyno comparison of 2.4 E motor to 2.5 MOD S motor.



Take away for me iis the MOD S cams are actually less peaky than factory E cams. The E cams made peak power at 6K and the MOD S cams made peak power at 5700 RPM and more torque everywhere. I know some of the torque is due to larger displacement but not all of it. Modern cam profiles just out perform old factory grinds.

I had read that the factory air cleaner used with Zeniths and MFI systems helped mid range power. I wanted to test this assumption. After getting some base line numbers I removed the Air cleaner cover and did another run. I was very surprised to see that removing the air cleaner cover made a big difference in power. Dyno below is with and with out air cleaner cover.



12HP added with air cleaner removed. So now I wanted to see what was causing the loss so I removed the air filter but left the front cover on. Dyno below with and without filter.



So filter cost a couple HP. Next test was to remove the front of the air cleaner. Dyno comparing with and without front cover but no filter.



Result was more power. So even though I had the inlet snorkel cut off making a larger inlet it was still a restriction.

So last was air cleaner with no front cover or filter compared no air cleaner to see if it helps with low end torque.



There is a little bit of gain with the air cleaner on at 3700 RPM and 5000 RPM but I am not sure it makes up for the loss over 5500. What is clear is that if you run the factory air cleaner make the inlet as large as possible.

Last dyno is comparison of current engine in 914 and 911 SC 3.0 CIS engine in my 911 SC race car. These were also tested on the same dyno. The SC was stock class car with 9.3 to 1 factory pistons, CIS and headers. It made the same power as several other stock class similar engines. The 2.5 made more power and torque than the 3.0SC with stock cams.



2.5 makes more power and torque than 3.0 SC at all points about 3400RPM.

john

[stownsen914]

Cool comparisons, thanks very much for compiling and sharing this

[PeteKz]

Excellent data. Thank you.

[Uwon]

John, thank you for your excellent post. I am pretty much a neophyte insofar as early engines are concerned so please bear with me.
I am building an ST out of my ‘71T. I do have a spare ‘73 2.4S motor complete with MFI that I want to rebuild/mod for the ST. The car will only be a country road and highway tourer and will retain the original 911 dog leg transaxle. I would like a bit more power (say 20-30 hp and good highway torque) so I have been advised to aim for a mod to a 2.7. However, your write up on your 2.5 has naturally intrigued me with such great results. I would like to retain the MFI and am open to mods and updates (without going overboard). I would appreciate you opinion whether a 2.5 MFI would come close to the performance that you have achieved with your 2.5. Any additional suggestions would be greatly appreciated.
TIA
Johan

[Discseven]

Impressive work John.

[targa72e]

Hi Johan,
Your 73 S motor should be good starting point. Your 73 engine probably already has the later 7R case used on the 2.7 motors. You could bore the spigots to larger size to make a 2.7 or 2.8 or keep the smaller spigot size and use 86mm or 87.5mm for more displacement with stock bore.
In general MFI should make as much or more power than carbs. The S MFI has the same size throttles and stacks as the 2.7RS so should be fine for what ever you build. The biggest challenge with MFI when building a engine to non-stock configuration is getting the tunning correct. If you go with hotter cams like MOD S you will probably need to get a custom space cam. There are a couple places that work on the MFI pumps and can make you a custom space cam based on your cam selection. There are also some good threads on tuning MFI for non stock applications using Wide band O2 sensors and making adjustment to normally not adjusted areas in the pump. I had to play with the adjustments on the flyweight springs to get my E cam engine with T pump to work correctly.
If you look at my friends 2.7RS + dyno you can see it made very good power. I wish I had known the air cleaner was such a power killer at the time as I think without the air cleaner and a little tuning the 204HP at the wheels would have been more like 214+HP.

I am building another motor for my other 914-6 conversion (this one with flares) and my current plan is 2.8, 10 to 1 compression and ported twin plug heads. It will have ITB and EFI. I will probably run DC43 or DC 60 cams, should be fun.

john

[Rosco_NZ]

Mod-S cams have very similar duration to S .. and work well with 2.0 / 2.2 / 2.4 / 2.7 pumps. The fuel curve just gets moved up and bit using the main rack adjustment. In general AFR’s move around quite a bit with MFI .. tune for worst case … 12.5-13 under hard load and wear the differences at other points. Typically runs rich at idle and low load.

[Rosco_NZ]

215 at wheels is a solid 250 at the crank.

[Uwon]

Thank you John and Rosco for your recommendations. Subject to what I find once I disassemble the 2.4S, I’ll be going for a 2.7. I do have the sources here in Canada to do the required machine work and MFI mod/tuning.
I would appreciate your comments as to idle stability and low/mid range torque from a Mod-S cam. Also, can the cam from the 2.4S be reground to Mod-S specs or is this a completely different animal?
Johan

[targa72e]

Hi Uwon,
My 2.5 with MOD S cams as well as the 2.7 RS+ both idled fine as did the engines with E cams. Idle was set at around 900-1000 RPM. Low end power is good. My 914 has a close ratio gear box with shorter 3rd and 4th gear so it runs thru the revs quickly.
I started most of the dyno runs at 3000 RPM as in normal driving I try and keep the engine above 2500 RPM. I really like the MOD S cams as they have great mid range and a pull that is so nice at the top that makes you want to run to red line on every shift.

john

[lateapex911]

Very cool info!!
My engine is very close to your 2.685L. My builder told me the comp was 9.5. I need to determine the port sizes, but the carbs are PMOs. I was told the cams were "Solexes". I had figured out what that actually meant, I'll have to dig through those notes and remind myself.
I'd be interested in contrasting your Mod-S cams with the old Solexes.

I've never dynoed the engine, the builder felt it should be 200-ish. He didn't specify at the wheels or crank, so I have to assume crank! (LOL)
Your 200 at the wheels is very repectable!

[targa72e]

Below is a Cam spec information from Elgin's web site.



Solex cams look to be somewhere in the middle between E cams and MOD S. They have more lift and duration than E cams but Less of each than MOD S

john

[lateapex911]

Originally Posted by targa72e

Below is a Cam spec information from Elgin's web site.



Solex cams look to be somewhere in the middle between E cams and MOD S. They have more lift and duration than E cams but Less of each than MOD S

john

Thanks, thats great. I should print that out and put it in a binder.
Over the years these cars of ours become more and more unique, and my memory becomes more and more vague, LOL. Like, what was that wiring mod I did 20 yrs ago? Time to be a better documenter, and label more wires. (With a real deal wire label maker)

[Cyberbug007]

what is the I and E mean in that table - 4th column?

[Rostrenner]

Originally Posted by Cyberbug007

what is the I and E mean in that table - 4th column?

I = Inlet valve / side
E = exhaust valve / side

[Cyberbug007]

Thank you

Just spoke to Dema Elgin as well.