la_strega_nera
Platinum
Platinum
Posts: 494
Joined: Tue Feb 21, 2006 10:05 pm
Location: Sunny Euro-Brisney

Post by la_strega_nera »

JimGreek wrote:If I finally go for 115* lobe centers in/ex, HC should be very reasonable.
115*????
why? trying to stop the valves thumping the bloody piston?
Any good reason for not running something like a 110 or 108* lc? Genuinely curious (and not curious about "Greek style"!)
Jim K
Verde
Verde
Posts: 1751
Joined: Tue Nov 30, 2004 12:10 am
Location: Athens,Greece

Post by Jim K »

Ok, I wanna redeem myself on account of the injector screw-up. Approx. max engine hp for a given injector in the V6 is found by multiplying the max.delivery at 3bar pressure (cc)x1.21 and by 0.81 in the 4cylinder. Therefore, the Motronic 190cc injectors are good for ~230hp and the 24v 240cc ones for up to 290. This is taking a BSFC of 296cc/hp/hr (.47lb/hp/hr).
Ben,correct, 115* will not foul pistons. Strange timing I admit, but hear this: I built a 2liter for a racer 4 months ago and the guy insisted on getting some Godzilla 13mm cams. These cams were specified for 104* LC's. Well, we put them at 106* because of v/p clearance and it didn't run as expected. Iinput all engine data in the engine simulator softwareand it gave 114*/110* (in/ex) You wouldn't believe the difference! I asked another engine builer here and he said he has seen comparable results. Now, I do have a problem with my piston clearance, but chain calculations come up with comparable numbers, along with a 725mm header (doable by shortening the existing CSC system) Believe me I have run countless simulations in the last 4 months and there is a definite trait. There is almost no loss in the range with these LC's. I wouldn't have thought of this before, but I'm learning! My mechanic's 105 historic 2liter had Godzilla cams also (believe 320* duration) and they were timed at ~102-106. We switched to 115-109 and the beast came alive! Of course, a prerequisite for all this is CR over ~12:1 if you expect to see anything over 210psi on the hot compression test (retarding intake LC really kills compression) I don't know what negative side-effects this move can have, as the racers don't run for more than 20 minutes or so. Anyway, I'm working on a method to deepen piston pockets also, so we'll see.
Jim K.
la_strega_nera
Platinum
Platinum
Posts: 494
Joined: Tue Feb 21, 2006 10:05 pm
Location: Sunny Euro-Brisney

Post by la_strega_nera »

Yeah, i was going to say, you'd need monster compression. Something else I thought of is the big lobe centres will let you get a better idle and maybe have a hope in hell of getting it to run on a factory managemenet system. But hell, if it works!
Jim K
Verde
Verde
Posts: 1751
Joined: Tue Nov 30, 2004 12:10 am
Location: Athens,Greece

Post by Jim K »

Hey, all you 2.5ers! Today I finally got around to measuring flow on a stock 2.5 head! Well, the intake flows less than the std 2liter 105 (41 vs 44mm valves) but the exhaust is way better albeit with a smaller valve (36.5 vs 40mm). However this is an unfair comparison as cylinder size is not equal (415 vs 492cc) Theoretically, the 2.5 can make a max of 216hp with the std runners at 7300rpm and 227 with 39mm ones at 7600rpm (all this in very high spec, max CR, banzai cams, headers). This are numbers for a stock head mind you!
I'll see if I can make an excel table, and post it as jpeg, with std 2.5 and 3liter flows. I shall return! 8)
Jim K.
Jim K
Verde
Verde
Posts: 1751
Joined: Tue Nov 30, 2004 12:10 am
Location: Athens,Greece

Post by Jim K »

Here I is again with the stock 2.5/3.0 head showdown (although unfair because of the displacement difference). Note surprising high-lift flow superiority of 2.5 with smaller valve. Low and mid lift gain of 3.0 is normal due to larger valve.
Jim K.
Attachments
Std 2.5-3.jpg
Std 2.5-3.jpg (101.88 KiB) Viewed 9399 times
Greg Gordon
Verde
Verde
Posts: 1552
Joined: Mon Nov 29, 2004 7:06 pm

Post by Greg Gordon »

Jim this is very good information. I don't quite understand why the 2.5 exhaust flows better, nor do I understand why the displacement difference matters. CFM is CFM right?

By the way, I am ordering your 4 cyl book. I have a lot to learn about these Nord engines for my SuperSpider build up.
Jim K
Verde
Verde
Posts: 1751
Joined: Tue Nov 30, 2004 12:10 am
Location: Athens,Greece

Post by Jim K »

Maybe the port geometry is better with the smaller 2.5 valve. As a matter of fact, the ideal exhaust port outlet (ex. gasket surface) should be Vx1.25. in this respect, they're both off, but the 2.5 fares a bit better. As I point out, lower lifts have higher flow with the larger valve (larger opening area)but at higher lifts port dynamics take over.
CFMx0.43 will give you the approx. hp potential for a given cylinder, so if a std 2.5 can make 38.5hp from 415cc and a 3.0 can make 45, guess what? They're both making ~91hp/liter!! Amazing,isn't it?? I think if the std 2.5 had 44mm valves it would be a killer mill! My comment about 'unfair' is more about the much larger valve size of the 3.0. Interim trick solution: 3liter bore, 2.5 stroke...but then you've heard this a lot! OR, 3liter with big valves.
Jim K.
Jim K
Verde
Verde
Posts: 1751
Joined: Tue Nov 30, 2004 12:10 am
Location: Athens,Greece

Post by Jim K »

Hey Greg,
You are a confirmed boost-lover, so maybe you'd like this curve for your super-Spider: its a bog-stock TS engine with a turbo,intercooler and EMS management. And this is only the preliminary result...before serious map and hardware fiddling!Oh, CR is the std 10:1!!
Jim K.
Attachments
TS Turbo1.jpg
TS Turbo1.jpg (120.65 KiB) Viewed 9387 times
User avatar
Mats
Verde
Verde
Posts: 4059
Joined: Mon Nov 29, 2004 12:26 am
Location: Gothenburg, Sweden
Contact:

Post by Mats »

I just measured a V6 cam in the garage and what do I find here? Great info! :D

Good stuff as always Jim! I'll hit you with an e-mail with some cam-data when I have done something useful with it.
Mats Strandberg
-Scuderia Rosso- Now burned to the ground...
-onemanracing.com-
-Strandberg.photography-

GTV 2000 -77 - Died in the fire.
155 V6 Sport -96 - Sold!
User avatar
fedezyl
Verde
Verde
Posts: 645
Joined: Wed Jun 01, 2005 2:45 pm
Location: Montevideo, Uruguay

Post by fedezyl »

Great info Jim, how does the 24v head flow? how big is the difference? I have both a 12v and a 24v 3liter but i'm waiting for some parts to do the conversion, I don't know how much harder it is to put the 24v instead of the 12v
Greg Gordon
Verde
Verde
Posts: 1552
Joined: Mon Nov 29, 2004 7:06 pm

Post by Greg Gordon »

That's impressive power from the Turbo Twin Spark. I wish we had those engines over here.
Jim K
Verde
Verde
Posts: 1751
Joined: Tue Nov 30, 2004 12:10 am
Location: Athens,Greece

Post by Jim K »

Fedesyl, obviously the 24v flows a lot better. I have measured a very mild 24v modded head I did for my engine and its good for 146cfm at 11mm lift (to obtain more lift is difficult with the 24v, given the small 33mm followers, valve spring coil bind and valve guide height). When I finish (...) with the 12v, I will also measure the stock 24v. I estimate it to be ~140cfm intake. The problem with the 24v seems to be the exhaust, it has very little flow compared to the intake and needs some serious porting to go from ~96 ~to ~115cfm to keep 'proper' proportions between in/ex flow. We'll see when we get to it.
Jim K.
User avatar
Zamani
Site Admin
Site Admin
Posts: 1757
Joined: Sun Nov 28, 2004 8:20 pm
Location: Cameroon

Post by Zamani »

Jim,

Do you think there is a way to implement a relatively "simple" two stage valve lift or valve timing for the DOHC 24V head? I say "simple" because it sounds damn difficult to do. But since I am saddled with emissions testing, I can't help to think about this.
Jim K
Verde
Verde
Posts: 1751
Joined: Tue Nov 30, 2004 12:10 am
Location: Athens,Greece

Post by Jim K »

Given the egine architecture, I wouldn't have a clue! The simplest approach I can think off the bat would require 4 special cam pulleys, with an internal centrifugal mechanism (weights and springs) like the aftermarket ones available for some older VW OHC engines. At idle you'd have timing A and you could tailor the curve for high rpm. This however would only shift valve events without changing duration (like TS). Other mechanisms (Vtec, Vanos, Valvetronic) are great but of academic value here.
There's a good friend here in Athens an old guy, Alfa legend of sorts, had a dyno and Norton cam grinder in 1968 and worked on GTAm's and stuff, great mind (never went to college either!)He developed and patented a gearless LSD (no friction plates or strange cams and pawls to wear) AND...a variable timing AND lift cam, which lived in his 4-door Alfetta 2.0 for more than 12 years! I was amazed when he explained and showed me how it worked, you should see the lobes grow in and out of the cam !!! Of course the cam is hollow, containing among other things a thin rod with wedges to drive out the separate cantilevered lobes. The mechanism is operated by oil pressure (like TS) controlled by a simple ECU (prm/vacuum-throttle sense) This is something that I suppose could be adapted for any Alfa since it only needs special cams, no mods anywhere else. Simply amazing, I have great respect for this guy, he did all this over 20 years ago, no Vtec no shit, original thinking at its best!
Jim K.
User avatar
Maurizio
Verde
Verde
Posts: 680
Joined: Wed Dec 01, 2004 4:49 am
Location: the Netherlands, 153.1km from the N'ring :-)

Post by Maurizio »

Sounds nice, the wedge drivin cams, had a similar idea ones, other idea would be split lobes which could be rotated towards each other to in- and decrease duration also pressure drivin like the TS.

At the moment playing around with piezo actuators at work, very fast ,accurate stuff. Thinking fuhrter, you could directly actuate the valve, so with the valve timing everything is possible, probally F1 technology. All nice ideas almost impossible to work out, serious budget/time needed for playing with.

ps the TS turbo is that Ron's?
Banned.. ? ;-) Daily donky.. ==> BMW 325d Image
E36M3 (3.0) Ringtool :twisted: ==> definitely BANNED!

AR 75 TS Ringtool '90, AR Spider 2000 veloce '79
Post Reply