A/F measurement with high overlap cams

For further comparison, here is a stock Kjet 328 with a tubi, I believe.

 

It was surprising to me and the dyno tech. The runs were sequential on the same day following only a jet change (140 to 145); for me that's about 40 minutes soup to nuts. On seat of the pants as said before, it seems to respond in real world driving better being leaner with the 140, or perhaps I need a smaller accell. jet
In any event will stick with this third jetting until after re-dyno with new cams.

 

yes, runs 1 & 2 getting richer.. We do let the engine run a while on the dyno before the pull. Of course, no cool ram air into the scoop.

Today's big debate is if to spring $400 for a true dual free flow exhaust. Although I don't think it would help much, the stock 3.2 dumping them in together after uneven tube lengths does not seem like it would be as good as a dual system to take advantage of the flat crank exhaust pulses. Probably would end up like $400 for 8 hp, so might really not be worth it.

 

Philip and the other acid techies

Personal opinion only as I don't have a graph, but would look at backing off those 70 idles keeping the 150 mains unless your transition is just that crappy. The idea of 70 idles and 145 mains boggles my pea brain.
If I were venturing a guess from this limited data, I'd say:

60 idles, 150 mains, 160 a/c.
And as always, I'm a fan of F24 ETs

I will bet you a pint that this will hold you in the high 12s - mid/high 13s the whole way. That will pretty much optimize your hp as a function of mixture delivery, as the engine tolerates a bit of variation in A/F.
Spring for $400 and open up the exhaust would be my next suggestion. Even with your lower CR, would bet you are pushing 100hp/liter, which is quite the feat at 8.8:1. Heck, you can run Albanian pump gas with that CR.

Let me know when you're ready to buy me that pint.
rt

 

Philip,

One thing I'd like to challange is your assumption that the jets are additive. Are you thinking that the main system adds to the mixture that the idle and progression systems are supplying once you go beyond the transition zone? I don't think this is the case. While there may be a point where all systems are supplying fuel together, ultimately, the idle and progression systems stop supplying fuel and you are on the main system only. The way I understand DCNF's is that the emulsion tube has a great influence on when the main system comes in. If the mains come in too soon, you wind up with too much fuel in the mid range. Float level also has an influence when the idle/progression circuit stops and when the main comes in. A higher float level should delay cutout of the idle progression circuit and speed up when the main system comes in. A lower float level should do just the opposite. The main jet, in my mind supplies a base load of fuel over the mid to upper range. The air corrector modifies the fuel supply by leaning out the mixture at the upper range. While the air corrector may have some influence on the mid range, it primarilly controls mixture at the upper range. I'm sure much head scratching has been done over the years to get the transition from idle/progression to main system correct. It seems to me that if the low and mid range are ok and only the upper range is rich, then the thing to do is put larger air correctors in to lean out the upper end.

 

Philip

Your Bass was here, but had to drink it myself to prevent wastage.

Talked to Pierce - the Weber carb body casting plant in Spain is in bankruptcy. They are looking for 44's as they have none - one option they mentioned was to try the 40s WITHOUT chokes to verify the air hunger. Doing the math however, 320 hp for a V-8 with 400 cc cylinders by the numbers requires right at a 34mm choke - so I am also considering the possibility that I have 'run out of cam'. Have decided to wait on the new cams before deciding - the current 40 DCNF set up theoretically flows over 2000 cfm without an aircleaner which you would think would be enough.

best
rt

 

Russ and Phill,

I just checked and you guys have over 400 reads on this thread - there are a log of guys who haven't done what you two have, but certainly enjoy reading and thinking about the technicalities of generating power. TV doesn't hold a candle to this stuff.

I'm a changed man and if i could, I'd buy you both a beer.

(nw if i could just replace all of those rotten fuel hoses and find a spare set of P-6's and maybe a bace of 44s...)

chris

 

Philip - I have the same manual.

What Pierce Manifolds was using was an Alfa Romeo racing engineering formula for determining Weber venturi requirement to match desired parameters; here's the best I remember from the phone call:

(individual cylinder capacity) (desired rpm peak) = M

(square root of M)/(50*) = choke requirement.

* - this was some constant related to the fact I wanted 320 hp at the targeted rpm of 7500 that went by faster than I could write. The number he got was 33.46mm.

Other interesting numbers we batered about was CFM ratings. While weber never published CFM apparantly, the numbers they use for a 40 mm carb with 34mm chokes is about 500 CFM per carb (2 barrels). For a 45mm carb with 36mm chokes it came to 560 CFM per carb.

Now I went and plugged all of these into my desktop dyno and they are very close based on my dyno numbers. When I simulated a stock 3.2 FI motor working from the stock lifts, durations, timing, bore x stroke, CR, etc, etc, - I found to achieve the stock rating of 260 SAE hp (pretty reliable average based on many dynos on this board) the stock Bosch K-jetronic should flow 900 CFM.
Simply substituting the number above of 500 CFM per 40 mm carb, as if all I did was replace the FI with the carbs, I got 290 hp from the sim which is within some error close to my dyno'd 288 (assuming 18% driveline loss). The mismatch occurs as I was using a 36 vs a 34 mm choke to achieve that number, but it is in the ballpark for comparison and development work.. Just for fun, I then kept everything constant and added Dema's new intake cam specs and retarded the exhaust cam 10 degrees: 320 SAE hp. How cool is that? It did lose a little bit of power down low but picked it back up above 4500 rpm. While I know this is NOT very accurate, it is pretty neat.

Kermit - you out there? How do these flows compare with your bench #s?

Time for my meds - where's the Hefeweizen?
best to all
rt

chris - most of those hits are just us trying to bump up our count.
rt

 

chris - most of those hits are just us trying to bump up our count.
rt[/QUOTE]

Let me make that a six pack of hefeweizen, on second thought, how 'bout a case of Mad river brewing IPA???
(nother bump)
chris

 

Hey guys, keep going, I'm loving this!
FWIW, a weber tuning guru told me some years ago that A/F and mains should be about 30 points apart. If not, something else is out of kilter (E/T's)Every time I have been on a dyno, this has proved to be correct.
Probably not the most technical bit of advice, but historically has worked for me.

Best
John

 

I know that. I just meant to say I was in the same data confliction as you.
Must be not enough beers yet this am.

Not a controversial subject, but if anyone out there knows cfm rating of paper filters and K&N filters for carb'd and injected cars, would certainly help to understand the various results.

OBTW - Also interestingly I was able to manipulate the event timing of the STOCK FI cams to give almost 300 hp on the sim by retarding both ignition and exhaust cams. While this would work well for those of you who already have EFI, if I can tweak these #s to avoid reversion, this should work with the Bosch stock Kjet. Will post the numbers when I'm home if anyone is interested. Imagine 20 - 30 or so hp increase for 3.0qv and 328 folks by re-indexing cams at your next belt change - wonder how close reality would be to the computer model?

best
rt

 

I think you have touched on a topic, but not really gotten into it in much depth as to how it affects the whole matter. Cam events on these motors, as in when they open and when they close are very much a part of the formula. With the 3x8 series motors, the rod/stroke ratio is an almost perfect 2:1. This causes them to be very "tuneable" when it comes to dialing them in at other than stock settings. The longer rod, compared to other makes, gives the following action in the cylinder: Piston acceleration rates, and the amount of time spent at TDC, and of course BDC. Compared to a more standard rod/stroke ratio motor, say 1.75:1, they tend to "hang" at top and bottom for a bit longer time. Then as the piston starts to move away from TDC, and BDC, for the first 20 degrees of crank travel they move comparitively less, then acelerate to full piston speed at 90 degrees. This is where they become very tuneable. On the intake, for example, the later that the valve closes, the more power it will give at higher RPM's due to the motors being able to continue to take advantage of any ram effect that it has, that being the inertia of the intake charge will be more than the pressure of the rising piston, thus stuffing more in. At lower RPMs however the later closeing will tend to encourage the reversion of the mixture back up the runner, due to the lack of inertia of the intake charge being less than the pressure starting to be exerted by the pistons riseing in the bore. On the exhaust side, the earlier the valve opens has the following effect: you trade off combustion pressure for starting the flow down the header. By opening the valve earlier, while there is still a significant amount of pressure being exerted on the piston by compression, that same pressure will push the spent gasses out the exhaust valve, thus starting a healthy flow (1700 to 1800 FPS). This greatly assists scavenging by virtue of the ovarlap portion. Envision the exhaust traveling at speed down the header, then as the piston starts to rapidly slow, as it aproaches TDC, the intake valve opens to a cylinder that is in effect in a vacuum created by the inertia of the exhaust pulse still moveing, but the piston comes to a stop rather abruptly.

The timing of the intake becomes important here, as if the intake starts to open at this time, there is vacuum in the cylinder, and it will start the intake charge moveing far before TDC, often called "the ram effect".
I hope this helps to clarify. Perhaps I should have had a bit more coffee before I started to type.
As To the Weber tuning, I'm learning from you guys in some areas, and really dont have anything that I feel I could add right now that hasn't been covered.
Enjoy The Drive,
Kermit

 

wow, great stuff guys. i just received my 34mm choke venturies from pierce. be careful, i had to take these to my machinist to machine the lip which was way off causing the air horn to not fit (the lip was too wide and needed to be 4mm. right now with my dual exhaust, hi comp pistons, krank vents and direct fire ignition and euro cams, i am running 140 mains with 175 AC, and this is at 6800 feet!! the car runs great and pulls strong to 7000 rpm, but i feel i can get more out of her. i ahve not been to the dyno with this configuration, but my plug insulators are barely tan. i am anxious to put in the 34mm chokes and go to the dyno, although i feel that the larger diameter venturies will have slower velocities at lower rpms, causing a higher pressure in the venturi region, where a lower pressure is needed to draw fuel. i think the dual exhaust setup is a must, and allows you to go richer in jetting as the exhaust scavenging is optimal - even if i have unequal header lengths.
john
78 308 GTS euro

 

John - what a great sounding engine (Good looking car as well)! What compression are you running? Agree you may want to bump up the richness a little with larger venturis, but at that altitude you may get by with what you have. Would surely do a quick A/F check, even if not on a dyno. Sounds like fun!
Somehow, my warning light went off when you said the venturis had to be machined. They are a VERY snug fit to put in and sometimes need reseating. The 34s I got from them required no work at all. I'm wondering if they sent you DCOE venturis or something. Would give Pierce a call in any event - I'm sure they would like to hear about this. Check the bags they came in for the part #.

Philip
Agree - have been taught that ETs are the most subtle and sophisticated part of the whole carb, and lend the jetting it's 'midrange personality'. Even when discussing them with Pierce, they are very slow and methodical in looking at the wall thicknesses and hole placements in comparison. The two ETs I am familiar with are the F24 and F36. F24s were used in Dinos (6 & 8s) and F36s in later V8s. It is very interesting to go through Spec sheets and see which types of cars used which ETs - you can see some patterns. Of course Weber did us no favors by not having a standard way of comparatively describing ET characteristics in the designation.
In retrospect over several threads, perhaps the reason I tend toward 'leaner ' jetting recomendation tendencies than Philip (especially A/C) is that I usually am thinking from primarily an F24 experience base (even richer than F36) and Philip is an 'F36 guy'. I had talked to Pierce about going to an F36 to subtley lean out my mid range and after much cipherin', they 'guessed' it would be a good choice. I am wildly interested in the effects of the F30s.

I am going into the shop next week for a custom (quieter) free flow exhaust, FINALLY put the cams in Dema says will be here Tuesday and put on the single distributor. would do this myself, but will need a pro to index the cams.

best
rt

OBTW - A good reference magazine for everyone that tweaks their car, 'Grassroots Motorsports', is available at Barnes and Noble and has some great basic articles. One article compared many free flow muffler systems and while differences were found, all 'free flow mufflers' differed VERY little in power (My definition of a free flow muffler is that a golf ball can pretty much go from one side to the other, Flowmaster excepted). This pretty much jives with all of the muffler discussions around here and the old board as well - once you go to a free flow muffler (Borla, Tubi, Stebro, customs, etc) you will pick up a bit of power but the main reason you get it is sound. Perhaps we should resurrect an exhaust thread.

 

hi Russ, I called pierce and they are pulling the venturis off the shelf and doing research. it was indeed the lip, not one of the 8 i received had consistant widths anyway. i have the borgo hi comp pistons fitted during a rebuild of my 2V euro motor, i believe they are like 9.8:1 compression ratio. the dyno guys will do an A/F reading during dyno testing. well, i just got over 2 feet of snow last nite and snowing strong, so i wont be out in the 308 for a while. my machinist did a terrific job of correcting the venturies.