L'échange d'antologie avec Jim

On 10/6/05, < Arnaud > wrote:
Hi Jim,
This is extremely interesting. I will try and get this software somewhere.
The way I understand it is the 30PICT stangles the engine. At intake the engine must suck air hard through the carb which takes energy.

The horse power figure : 49.2 / 42.6 : that is 19.5% improvement !!
Torque figure : oh you missed it for the 30PICT. no big deal let me know if you still have it
BFSC at 3.5K (highway speed) : 0.552 / 0.572 that is 3.5% less fuel
BFSC at 4K (faster highway speed) : 0.590 / 0.615 that is 4.06% less fuel

This is awesome. Thanks a lot for doing this for me.

Now for fun : at 3$ per gallon, how many miles do I need to drive to pay for the new carb (150$) given that current mileage is 18.5 mpg.

18.5 mpg : fuel cost per mile : 0.1621$
when fuel economy is increased by 4% : 19.24 mpg, fuel cost per mile 0.1559
Difference for each mile : 0.6 cents
Miles to drive to be even with the new carb: 150$ / 0.6 cents : 24292 miles.

That is a lot of miles, but I'll change the carb anyways because more hp for less $ is a total deal.
The other thing is : the engine is so weak now that I am using the higher rpm often. It is precisely at the higher rpm that it is the least efficient. Hence with the bigger carb i can use it at lower rpm, where torque and power are already available, but BFSC is low. Overall the gain may be more than 4%.

I'll keep you posted !

Thanks again Jim.

- Arnaud

On 10/6/05, Jim Hayden wrote:
Arnaud:

OK - here is the executive summary re use of the 30 PICT for the DP 1600, instead of the proper 34 PICT, straight off the Engine Analyzer program:

IT'S CHOKING THE MOTOR TO DEATH, NO WONDER YOUR GAS MILEAGE S*CKS lol

The longer summarized version of the table - 34 PICT first. Peak horsepower is occurring from 3.5K to 4K (49.2 to 50.2 - essentially flat at those points), and BSFC is rising from .552 to .590. The lowest BSFC is .551 at 3K, so figure from 3K to 3.5K your BSFC plot is flat, which is good. Peak torque is happening at 3.5K (73.8), but also keep in mind that at 3K it's showing as 72.6, so the torque plot is essentially flat at those points too.

Using the .778 value for the conversion to 30 PICT CFM figures, I got an 89.5 CFM rating. The program balked at it and flashed me with an error message - "It's restrictive!!! Danger Will Robinson! Danger! Do you want to continue?" God, I LOVE that program! We proceeded at full steam anyway :-)

The peak hp for the 30 PICT is happening from 3.5K to 4K (42.6 to 43.1 - YIKES!!), but the BSFC for those same rpm ranges is .572 rising to .615 and rapidly climbing. The lowest BSFC is .568 DROPPING to .567 - however this is happening from 2.5K to 3K rpms. Peak torque is happening at 3K, but it works out to only 37.1 horsies...

I think it would be safe to say that the program has given us some VERY good insight as to why running the 30 PICT instead of the proper 34 PICT on the dual port motors causes poorer mileage, especially considering the rpms you're turning for freeway driving. The rpms could be dropped by using an 091 transmission, but then you'd be chasing your tail with not turning the motor fast enough to maintain cooling airflow. Nor is a big dollar 091 cheap, especially compared to what a new replacement 34 PICT would set you back...

Engine Analyzer solves another thorny, real world problem :-) You'll be receiving the bill in the mail - just kidding... You know - and come to think of it, the other person I know who I think is also only getting around 18 mpg highway, is ALSO running the 30 carb (and an 009)!?! Do you think there is any connection?
----- Original Message -----

From: Arnaud

Hi Jim,
I digged a bit into CFM of my small carb but found nothing relevant.

Assuming you have the CFM rating of the 34 pict, we could assume that the CFM of the 30PICT scales with the throad surface. The ratio of the surfaces is 30^2 / 34 ^2 = 0.778

With these assumptions, the CFM of a 30PICT is 0.778 * (CFM of a 34 pict)

Could you plug these two carbs on a 1600dp and run some stuff ?

I use my engine the most between 55 and 60 mph. That corresponds to 3400-3700 rpm. I have the exact measured number somewhere. Will pass it on to you.

I'd be glad to see whatever output you get out of it. Does the program take jet sizes into account also ?

In my job i do computer sims all the time. For wireless networks though, not engines.

- Arnaud




On 10/4/05, Jim Hayden wrote:
Arnaud:

If you can find the CFM (cubic feet per minute) rating for the 30 PICT somewhere I can plug it into the modeling program - so far I've only been able to turn up the rating for the 34 PICT... I'd bet that off the top of my head, if I was to model a SP 1600 running the 30 PICT vs a 1600 DP w/ 34 PICT, you'd probably very likely see improved BSFC at somewhat higher rpms; I mean, why did the factory get away from the single port/small carb in the first place? A friend of mine had a miserable pig combination of a motor - was sort of an old school, low compression (sub-7) 1915 running a very mild cam, stock heads with a 34 PICT, header and an 009. In reality it was not much fun to drive because the torque came on like a rocket from idle speeds, but peaked at about 3K rpms, got poor gas mileage, and would really not pull much beyond 4K rpms because the carb just strangled the motor. I plugged all the values into the program and the "model" mimic'd EXACTLY the motor in real life; and about that time I started becoming a real believer of using the program to check into misbegotten ideas that people would pitch about, like how a 1776/1835/1915 running a stock carb is a great idea 'cause it helps you keep the low end grunt ;-)

What I find it most useful for is figuring how (on virtual paper, anyway) specific combinations of things might work, and whether or not such things might be cost effective additions - as opposed to blindly accepting advertised claims. The modeled version of the Ghia motor didn't show that much change running 1.25 rockers; but a 2110 did (which is kind of what you would expect) - and at $200 a set, it wasn't a good investment for the Ghia. Also good for figuring out how one camshaft might behave versus another grind, or the effects of changing lobe centers, advancing/retarding the cam. I used it to suss out that given a relatively low compression ratio (8 to 8.5:1), the Web-Cam 218 grind is just great for smaller motors (such as the wife's 1776) or on larger motors (like a 2110 for bus use) that don't need to turn some amazing rpms. All very interesting stuff that you can goof off with on paper, research what others have to say about the proposed changes, and then ask your own intelligent questions.

Let me know if you can find the CFM on the 30, I'll see if I can generate some numbers for you...

From: Jim
Sent: 10/4/05 11:57:34 AM
Subject: Re: T2.com Thread re '77 Westy Mileage


Counter intuitive is it PERFECTLY! I've done some messing around with one of the engine modeling programs, and although it can't be 100% accurate, one of the things I watch out of the "modeling runs" is where does the least BSFC (Brake Specific Fuel Consumption) number fall on the rpm range - i.e. the point where you are using the least amount of fuel per hour per horsepower. The single carb rigs tend to hit the low number very early (low/mid 2K range) and just keep rising, whereas the dual carb rigs tend to see the lowest BSFC number somewhere in the middle of the 3K rpm range... If my big 4s run in the 3 to 3.5K range in 4th at highway speeds - that's pretty much exactly where I see my best fuel consumption... It's like there is a very precise combination of events that need to happen, but if you find it and can maintain that speed - you're golden!

Very interesting. Have you compared the BSFC of say a 30PICT versus a 34 PICT on the same engine ? If I understand what you explain, the 34PICT may be most efficient at a slighlty higher rpm than the 30 PICT. And yes since we all do at least 50% of freeway driving, that is what matters really.


I've also learned to let the vacuum can take care of as much intial "throttle action" as I can in any given gear - or put another way, stay off the accelerator pump as much as possible (gee, where I have I heard that before in this exchange :-) )


Agreed



BTW - sometime back you posted up some GREAT data to the list on your findings on keeping your bus cooler, and one of the items you posted had to do with using the upright motor with the wider alternator belt, instead of the generator belt. I had accidentally bought some of the 11.3 x 912 alternator belts anyway, so I robbed some extra pulley shims off the '61 bug and used the set-up on the Ghia (which has always been a bit of a "warm runner")... And it worked! Yay! I even had my brother-in-law have some spacers made to be used instead of the extra shims - that way you could pack the extra width with the spacer and still have the stock amount of shims involved...

Glad it helped. John Conolly originally hinted this to me.

- Arnaud

So a big thank you for that little tip! I've been so un-involved with the upright motor for such a long time (Type3 cars before Type 4 motors in 914s/buses) it's really great to learn some little tricks that benefit the upright :-) Which is good, because the d*mn things keep proliferating in my yard - in addition to the wife's Ghia, we won a '61 rag-top bug at a show this spring...

Pray for the bonus ;-)
----- Original Message -----
From: Arnaud
Sent: 10/4/05 9:52:35 AM
Subject: Re: T2.com Thread re '77 Westy Mileage

Jim,
Here is my story:
I owned two busses. Both 71, both pretty much stock. The #1 had the stock carb and a meximotor. The #2 has brosol 30/31 and a american rebuilt engine. Both stock vacuum dizzy, and stock ignition system.

gas mileage averaged over 12'000 miles, bus #1 : 21.2 mpg
gas mileage averaged over 6095 miles, bus #2 : 18.6 mpg

That is 14% difference, it has to be coming from somewhere ! It's in the same city, pretty much the same driving patterns.

Oh, #1 was serviced in a shop. I fully take care of #2 and I am self taught.

Maybe the smaller carb in #2 makes the engine combo less fuel efficient. That is a bit counter intuititve, but may be a good enough reason to swap a stock 34PICT in there. It makes no sense anyways to have a 30/01 on a dual port. It's a bit of the same story as your Dual Dells.

I read the archives on the CDI box you mentioned. It seems to have good reviews. Let's see what kind of bonus they give me at work :)

22mpg would be great

Best regards
- Arnaud
On 10/4/05, Jim wrote:
Arnaud:

I hear you on not wanting to mess with the various points replacement items - they really don't do very much in terms of making a dramatic improvement to mileage... They WILL do a much better job keeping the car staying in tune, but that is about all. The money is much better spent on the CDI box, and even though only some of my cars still have stock distributors, the combination of points and the CDI box is not necessarily a poor choice. The points only pass 12v across the gap when running CDI, and they last as long as the rubbing block is still there, so you have a fall back position. I have run Compufire units (and do prefer them over the Pertronix) with the CDI, but that's only because the distributors were already upgraded with the Compufire.

I tried the Pertronix units one time (after running Compufire since the late '80s), and I was not very impressed with them - the first one failed after about 15 seconds of run time, and it's replacement failed in about 15 minutes... I took the second failed unit back to the vendor, asked for a Compufire and have never looked back. One other thing that I noticed recently - prices on points and condensors (Bosch, let's say) are not exactly cheap (in a relative way) any more. I picked up an SVDA for $5 at a swap meet for the wife's Ghia, and really didn't want to spend the $60 or so for the Compufire, since the CDI box was already installed. I was somewhat surprised when the bill for the two items was about $15, and I always have to get a laugh out of those who wonder if indeed, the $60 for the Compufire/Pertronix is worth it, especially since points/condensors are SO "cheap" ;-) I also have to get a laugh out of the amount of list traffic generated by those who are always having trouble with point/condensor sets going south - it seems as though the build quality of such things is slipping all the time, particularly as points/condensors have become antiquated automotive technologies, and manufacturing has moved to places unmentionable.

18 mpg seems to be about the limit for relatively stock 1600 powered buses when driven at 55-60, IMHO... and Lord knows, when I am travelling in a bus-a-van with 1600 buses I know the drill very well - because that's how the speed shakes out for the 1600s to get their best mileage numbers. I have come to believe that about the only way to improve on those figures is the motor has to become MUCH more efficient at making power at the rpms you're going to be winding them. If you can start getting closer to the old time "magic numbers" of 1 horsepower per cubic inch (or it's metric equivalent), you can start seeing better returns on the mileage. People look into the engine compartment of my '72 and '73; all they see are the twin 2-barrel Dellortos that just simply MUST suck gas like a mad-dog (and they do if you insist on tear-*ssing around all the time). What they don't see is are balanced packages of displacement and available power, tied to a transmission optimized for the size of the motor. When I'm obligated to be traveling at 55-60 with the stockers, I'm barely touching the throttle and still running on the idle jets... Trying to push around a big box with a motor really only designed to output just enough power to push around a small car is just asking for trouble.

At least that's MY story and I'm sticking to it :-)
----- Original Message -----
From:
ToSent: 10/3/05 9:15:40 PM
Subject: Re: T2.com Thread re '77 Westy Mileage

Hi Jum,
Thanks a lot for your email !
I have stock ignition system for now and cannot claim to fully understand how it works :)

I read some horror stories about compufire and pertronix (which aren't CDI though) and because of them decided to keep the points.

I'll look into the CDI box that you mention and figure how it works. For sure there must be things that can be done to get more than 18mpg out of a stock 1600dp with a 30/31 Brosol carb and vacuum advance distributor!

- Arnaud

On 10/3/05, Jim wrote:
Arnaud:

Been a while since we last spoke...

$125 Universal Corp. CDI box on all my aircooled rides ('72 bus w/2260 T4, '73 bus w/2055 T4, '73 914 w/1.7L, and the wife's '69 KG with 1776). Worth every penny - the buses in general went from using the better part of 3/4 tank per week on the M-F slog to only using around 1/2 tank, the 914 (w/ dual 36 Dells) used to score 35 mpg on L.A. to El Paso runs, and the KG gets better mileage with a hipo 1776 + 36 Dells than it did with a bone stock 1600 SP motor... You need to regap the plugs from stock to "about" .045", else you NEVER see the improvment and that's the critical step the luddites commonly miss, so you will hear stories about CDI not doing cr*p for some... Dig deeper and you'll find out why ;-)

John Connolly @ aircooled.net used to sell them, but you have to buy them directly from Universal now (can send you the link if interested). They are not as high-tech on the inside as the Mallory Hyfire boxes, but they are nowhere near as prone to issues with stray RFI and you can still use the stock Bosch coils. When I've been slowed down by stock 1600 DP powered buses, the '72's 2260 w/ 45 Dells has seen 25 mpg, and I regularly see that with the '73 - even as much as 30 mpg :-0... I didn't believe it myself either, but I double checked the math and did the refilling myself. Using a wide-band air/fuel meter for carb tuning has been a big help in getting the 25+ mpg figures out of the '73...

That's not the complete story to getting really-really good mileage out of the buses, but I read all about the CDI on Type2.com starting in '97 and '98. After about a year of hemming and hawing, I ponied up for one when the '72 still had it's first 2055 in it. After one weeks worth of driving around, the usefulness was proved and every one of my cars got one as money permitted...

HTH