Rod Ratio vs. Displacement. Is there a choice to be made?

[eurotrash]

[eurotrash]

121 head and 635 CSI pistons..which are installed at 1mm over the deck due to a 3.4mm cut to the deck.. I was going to go with either a 1.8 or e12 head and custom pistons with 10.5 CR.. hm. 

 

 

Edited October 10, 2018 by eurotrash

[Preyupy]

I have built 3 race engines using S14 Evo 87mm stroke crank,M10 blocks at 92mm bore,  2313cc,  146mm rods, Single cam M10 heads, Schrick 336 cam, 47mm intake valve, 39mm exhaust valve,  13:1 compression ratio, dry sump oil system, .  50DCO carburetors with 42mm chokes. 

Peak HP 249.2 @7900 rpm    Peak Torque 195 lb/ft @ 5600 rpm

Average HP 4500-8000 rpm 219.3 HP     Average Torque 4500-8000 rpm  184.4 lb/ft

148.5HP @ 4500 rpm    173.3 lb/ft @ 4500 rpm

 

I am in the process of converting one of these engines to EFI with 45mm ITBs.  I'll post the dyno sheets when I actually get it on the dyno (don't hold your breath it is going to be a while, this is my project and the customer engines come first) 

 

For comparison a equally prepared 2 liter with 146mm rods

Peak HP 225@ 8100 rpm   Peak Torque 171.9 lb/ft @ 5900 rpm 

Average 199.2 HP 4500-8300 rpm   Average 163.5 lb/ft 4500-8200 rpm

 

I have not used a S14 block for one of these engines yet,  I sonic check the cylinder wall thickness and have found a few M10 blocks that I decided NOT to bore over 91mm for race use.  I have not felt comfortable going over 92mm on any of the M10 blocks. One problem with going over 94mm with the S14 block is the space between the cylinders gets so thin it is hard to keep head gaskets alive between the cylinders. 

[eurotrash]

So, @Preyupy, have you ever chased torque vs. HP, for a quick street car? (Not that those numbers are bad.. but those kind of revs are why I sold the s14 top end off to begin with.  Well, that, and I wanted a period look as the finished product.)  I currently have, and am planning for 45mm carbs, but have been pricing/specing out the Jenvey Heritage TBs and EFI bit for later improvements.  I had the e30 and early e21 m10 intakes as well, but sold them off when I decided to stay with carbs. 

Edited October 10, 2018 by eurotrash

[AceAndrew]

Fun race builds all around then.

 

It would be interesting to see what a non-stressed full-torque-range 91-octane street stroker would put out.  I'm guessing around 170-185whp.

Edited October 9, 2018 by AceAndrew

[Preyupy]

You have to remember that torque is the force that is being applied to the input shaft of the transmission.  Horsepower is how much work can be done in a given amount of time.  A really good normally aspirated gasoline engine with 1 spark plug and 2 valves per cylinder with all things designed for maximum torque (cam, compression ratio, combustion chamber design, bore/stroke ratio, intake runner length, header design etc) will produce 1.35-1.42 lb/ft of torque for each Cubic inch of displacement ( or 16.3cc's). This is all the torque you are going to make and unless you are willing to run very high compression ratios you will be lucky if you can make 1.25-1.3 lb/ft per Cubic inch.  If you want a torque engine you want to make that number as low in the RPM range as you can, this means you will fall off the top of that curve as the RPMs go up. If you want more HP you need to make that torque number at a higher engine speed, this means you will LOOSE torque at lower engine speeds.  If you build an engine that only needs to turn a specific RPM you can optimize everything and possibly make as much as 1.48-1.52 lb/ft per Cubic inch but you will pay a huge penalty for deviating from that RPM by more than a very small % (they do this for engines used in generators, pumps, tractors, conveyers etc)  .   

 

To calculate your horsepower you  Torque X RPM and divide by 5252. 

If you have a engine that makes 140 lb/ft of torque at 2000 rpm you are making 53.3 HP.  move that torque peak up to 4000 rpm and you are at 106.6 HP.  Move it up to 6000 rpm and you are suddenly at 159.9 HP.  Increase it to 7000 rpm and you have a snorting 186.6 HP engine.  A 2 liter BMW engine with a streetable compression ratio of 10:1 is lucky to make 140-145 lb/ft at peak so if you want a really good street engine with lots of low/midrange torque you will be lucky to make 150 HP because as soon as you go past the peak torque RPM the torque starts to fall away so if you have 140 lb/ft at 3500 rpm you will be lucky to have 125 or so at 6000 (142 HP)  and it might fall off to around 115 by 7000 (153.3 hp). 

 

Modern engines use variable valve timing to broaden the peak torque output of the engines.  By changing the cam timing (and in some cases valve lift) they can make that peak torque number over a much wider RPM range which gives you the advantage of low/mid range torque and top end HP.    

 

 

[irdave]

My limited understanding is that the 1.8i head flows well (could have just been what I was told so I'd feel better about buying the head...)  And then the people I got my engine parts from had JE pistons made to go with the head at the compression ratio given the rod length...

[eurotrash]

@Preyupy

 

Interestingly, I decoded that build sheet from Germany.

1. It says that they used an M3 head gasket, and added cooling passages to the head. 

I asked and he said that he indeed had the head drilled for the cooling holes between the bores. As well as filled the s14 hole at the back of the block with aluminum. 

2. I also found that the sheet says that they "drilled the the oil gallery to 2mm"..?

I asked, and that was just for more oiling.

3. They also decked the block 3.4mm. I asked, and that was so it would work with the s38 pistons with stock 144mm s14 rods and a 1mm deck height.

4. 121 head was used, I asked.  

 

For an off the shelf build, it sounds like:

 

2.3-2.4L  to keep the bore size in the s14 block down.

1.8mm (MLS..?) head gasket for 1mm deck height (guesstimate for now)

1.8 head with mild work including big valves

292 (maybe 300) cam

46mm rods/m10 coated bearings

10.5:1 CR custom pistons, just add dome shape for head of choice. 

s14 oil pump with m10 pickup

8.5" intake runners tuned for 2.4L, 292 cam and max torque at 6000.  

Cut the crank snout to accept the m10 crank pulley

M10 timing cover

Block the coolant passage in the block

Drill head for s14 water passages between the bores. 

 

Edited October 10, 2018 by eurotrash

[xr4tic]

What is the advantage of the S14 block over the M10 block if you're not using the S14 head?

[allbim]

The S14 crank uses a different damper and I'm sure BMW has a reason for that. Cutting the snout will not let you use that damper.

Machining the timing cover to accept the larger S14 seal takes 30 minutes or less on a CNC mill.

[Preyupy]

I agree, if this is going to be a street engine I would run the S14 front pulley/damper.  Race engines never sit at one RPM for very long but street engines get set a one RPM and cruise for long distances and harmonic vibrations become a huge issue.  I also don't lighten street cranks. 

 

As far as having Maximum torque at 6000 rpm you are not going to do that with a 292 or 300 deg cam. More than likely max torque will happen closer to 4000 rpm.  Depending on your intake and exhaust you might be making max HP about there.  336 deg cams usually make max torque around 5800-6000 rpm. 

 

The advantage of the S14 block is the cylinder walls are designed with the larger bore in mind and you can run at 93-94mm without worrying about wall thickness. 

[xr4tic]

27 minutes ago, Preyupy said:

The advantage of the S14 block is the cylinder walls are designed with the larger bore in mind and you can run at 93-94mm without worrying about wall thickness. 

 

Can an M10 block be sleeved?  Seems like with the amount of work it takes to make an M10 head fit an S14 block, you could just sleeve an M10.  Plus if it blows up, M10 blocks can be had for cheap.

[Doug Riparetti]

On 10/9/2018 at 11:23 AM, Preyupy said:

I have built 3 race engines using S14 Evo 87mm stroke crank,M10 blocks at 92mm bore,  2313cc,  146mm rods, Single cam M10 heads, Schrick 336 cam, 47mm intake valve, 39mm exhaust valve,  13:1 compression ratio, dry sump oil system, .  50DCO carburetors with 42mm chokes. 

Peak HP 249.2 @7900 rpm    Peak Torque 195 lb/ft @ 5600 rpm

Average HP 4500-8000 rpm 219.3 HP     Average Torque 4500-8000 rpm  184.4 lb/ft

148.5HP @ 4500 rpm    173.3 lb/ft @ 4500 rpm

 

I am in the process of converting one of these engines to EFI with 45mm ITBs.  I'll post the dyno sheets when I actually get it on the dyno (don't hold your breath it is going to be a while, this is my project and the customer engines come first) 

 

For comparison a equally prepared 2 liter with 146mm rods

Peak HP 225@ 8100 rpm   Peak Torque 171.9 lb/ft @ 5900 rpm 

Average 199.2 HP 4500-8300 rpm   Average 163.5 lb/ft 4500-8200 rpm

 

I have not used a S14 block for one of these engines yet,  I sonic check the cylinder wall thickness and have found a few M10 blocks that I decided NOT to bore over 91mm for race use.  I have not felt comfortable going over 92mm on any of the M10 blocks. One problem with going over 94mm with the S14 block is the space between the cylinders gets so thin it is hard to keep head gaskets alive between the cylinders. 

Are those "hp" numbers to the rear wheels or crank?

[Preyupy]

Crank

[Preyupy]

14 hours ago, xr4tic said:

 

Can an M10 block be sleeved?  Seems like with the amount of work it takes to make an M10 head fit an S14 block, you could just sleeve an M10.  Plus if it blows up, M10 blocks can be had for cheap.

 I do not believe you can effectively sleeve a M10 block to take a 94mm bore. With a bore spacing of 100mm that only leaves you 6 mm between the bores or a wall thickness of 3mm in each cylinder.  The S14 bock uses a siamese cylinder wall design (this is why they use the small water passages between the head and block to move some water around that part of the cylinders. The M10 has some space between the cylinders)