ALFAGTV6.COM

Post by **Zamani** » Fri Feb 09, 2007 5:21 pm

Mats,

Does this have anything to do with the short skirt pistons you showed us a while back?

I heard JimK also likes short skirts, although maybe not on the pistons.

Mats · Post by **Mats** » Sat Feb 10, 2007 1:01 am

Who want short shorts??

WE WANT SHORT SHORTS!!

Micke · Post by **Micke** » Sat Feb 10, 2007 1:24 am

I read in a reputable magazine that short skirts increase CFM at a progressive rate.

Jim K · Post by **Jim K** » Sat Feb 10, 2007 9:29 am

165cfm?? Mats, I'm talking about ONE cylinder, not the sum of all four, heheh! If you have a flowbench showing 165 on an Alfa 2valve head, here are some suggestions: a)read operating manual again, b)calibrate bench, c)plug giant external leaks, d)trash bench, e)stop drinking long enough to measure properly

If you still get 165cfm, call for backup, lock head and head-porter in bank vault and sell both at Sotheby's or Christies for absurd amount!

Any more questions?
Ok, I have to get you off my back, so here's what the Superflow crystal ball says for you:
165cfm for a 500cc cylinder will give you 72hp/cyl at 11krpm.
At 8.5krpm a 500cc cylinder will make 55hp and you need 'only' 128cfm total intake flow. Strangely enough, the extra flow is not useful at this rpm.
Its very curious from all this to see how BTCC engines made 295hp at a rules limit of 8500rpm?? Maybe their tachs were off a couple of thousand rpm...

For that power you need 170cfm which is possible in very good 4valve heads, but the rpm is more than 10k!!Who am I to solve this? The hell with it!
Jim K.

Micke · Post by **Micke** » Sat Feb 10, 2007 10:50 am

I think you answered yourself Jim.

The superflow rough calcs are not the absolute truth maybe?

Do you really believe
a) that more than 128 CFM doesn't help at 8k5?
b) that the BTCC engines revved 2k too high and nobody noticed?

What does the engine analyzer software say?

Micke · Post by **Micke** » Sat Feb 10, 2007 11:41 am

OK, so I did a fast and dirty calc.

TS with 85x88.5 mm, my cams, headers, 12.5 CR, 128 cfm. 209 hp @ 7250 rpm.
Change CR to 10.5. 200 hp same rpm. Knockin changed from likely to not.
CR back to 12.5 and 160 cfm: 225 hp at 7750 rpm
Swapped to small pistons and dry sump: 239 hp at same rpm
Increased ex valve flow from 108 to 130 cfm: 247 hp at 7750 rpm
Exhaust optimization: 254 hp at 8000 rpm
Poked at the cam timing to achieve 256 hp @ 8krpm.

So what do we learn from this? Not much. Probably that more cfm than 128 will do good (the last run which was optimized for max power still gave 239 hp at 7250). Remember this is all theoretical mumbo jumbo and probably not worth a lot. I also didn't change the cams but used the ones I have. I'm sure there are better around.

Now I used the same optimizwed parts but swapped flow back to starting point. 224 hp@7750 rpm and 217 at 7250.

Next shot Jim

Mats · Post by **Mats** » Sat Feb 10, 2007 12:33 pm

Micke, do you use the Bosch simulation software? Read the article in the new Racecar and it's very interesting.

Jim K · Post by **Jim K** » Sat Feb 10, 2007 1:46 pm

The simulation software has pi$$ed me off quite a bit, proving too optimistic compared to real results. I'm trying all kinds of tricks to make it more conservative but its hard going. I haven't input this stuff into it, I just use Superflow nomograms for the quick stuff. Maybe if I have time tomorrow (it'll probably rain, thank God, let's see some winter!) I'll try the simulator.
Jim K.

Maurizio · Post by **Maurizio** » Mon Feb 12, 2007 7:00 am

CR rating versus Cam choice.

A long time ago, I came across this one. Maybe a bit short, my theory, but liked the unhindered by knowledge approach

With the following linked calculator I calculated the cranking pressure off the standard engine. http://not2fast.com/turbo/compression/c ... sure.shtml

Then take the data of the new cam and find the CR with the same cranking pressure. As a start.

So experts.... shoot, what do you think of my simple approach?

Dennis · Post by **Dennis** » Mon Feb 12, 2007 7:14 am

I have had a quick look at the same article in RE. VERY interesting indeed. I haven't had the time to read it completely but the bosch software probably will cost a fortune.

Is there a good free or reasonably priced software package available?

Jim K · Post by **Jim K** » Mon Feb 12, 2007 9:52 am

Micke, 160cfm from the 75 TS head????
Jim K.

Maurizio · Post by **Maurizio** » Mon Feb 12, 2007 11:28 am

ps about simulators:
Anyone ever played with the engine simulator on http://www.lesoft.co.uk/Freeware.html

I've downloaded it two years ago, never took the time to play with it......

Micke · Post by **Micke** » Mon Feb 12, 2007 11:31 am

Nonono,

just wanted to check that more cfm = more power even without 23 zillion rpm. Used something close to Mz's lucky number for this...

Jim K · Post by **Jim K** » Wed Feb 14, 2007 1:28 pm

I did a check on the Lotus engine software...well, looks like a damn serious program at an equally serious price: 1 year subscription costs ~9200Euros, 1 month costs ~1500Euros

I think there's a 1 month free evaluation period, hmmm! The freeware is a one-cylinder model.
Jim K.

Maurizio · Post by **Maurizio** » Wed Feb 14, 2007 1:56 pm

Jim,

installed the program on my pc more then a year ago still starts now. But haven't really played with it........
Anyone around here who can rearrange the freeware in permanent use

More cylinders is interesting for modeling complete intake and exhaust. For a rough guess one cil is ok?

Lotus builds very nice things, love the exige

Saluti,
M