Supercharged Upper limit KPA

[39ClevoUte]

So if your running 5PSI with a S/Cer do you set upper limit KPA as 133??? in the general settings table??

Also if your running %baro does 0=100% in the ARF load and Fuel load tables = KPA 0 - 100 (zero boost) or KPA 0-133 (5 psi) @ 100%.

I ask this because when you calc the inj size and fuel pressure size this takes into consideration the boost or the "equivalent engine size" these details are entered into the required fuel settings area.

It seems to me that when you calculate the required injector size and fuel pressure for a S/C'ed setup, then you shouldn't see much greater than 100% in the fuel load tables? At the upper limits that those injectors and fuel pressures were calculated for.

Does this make any sense???

[jsmcortina]

Upper limit as in barometer upper limit? The maximum you'll see for that is maybe 105kPa in Death Valley.
I'd set your AFR, VE and ignition tables to go up to 140% on the Y-axis.

James

[39ClevoUte]

Thanks for that answer. I thought I'd replied previously but its not here?
I now understand this point. However I have another question of interest.

A 351 running 5psi (5/14.7=30%) basically becomes a 460. ie 30% bigger or (1/3 atmosphere x351)+351=aprox 460.

In the Engine and sequential setting area if you use the same size injector eg 46lb/hr for a 351 and a 460 the calculated required fuel ms amounts becomes 10ms for a 351 and 13ms for a 460. This is a 30% increase in injector time. This makes sense. These figure is for 100% MAP.

Both engine sizes generate the same AFR table.

The VE tables seem a little different, which makes sense, since I increase torque and HP by 30% for the 460. Bear with me here. Here are the differences at 3000RPM:

MAP 351 460
15% 38 40
40% 52 53
60% 61 63
100% 79 82

I think these are pretty close and not a problem.

Now for the bit I don't get:
The AFR for a 351 supercharged by 5psi is the same as above up to 100 an slightly richer at 117% and 135% which makes sense.

However the VE, which I thought would be similar to a 460 comes up as follows:

MAP 351 460 351S/C % Fuel more than a 351 What I'd expect
15% 38 40 49 25% 38
40% 52 53 75 50% 52
60% 61 63 86 30% 61
100% 79 82 102 25% 79
120% 123 50% 86
135% 127 55% 102

As previously shown the 460 injector pulse is 30% longer for the larger engine and so the numbers are similar in the VE table for the two NA engines.
The 351 S/C results are 30% larger than the std 351 up to 100%, but at those map reading there is no boost, so the fuel needed is the same as for a 351?
At 5psi or 135% MAP a 351 burns similar fuel load as a 460.
So a 351 utilises a VE of 79 at 100% Map, which is 79% of a 10ms pulse = 7.9ms.
This would need to increase by 33% to deliver the same fuel as the 460, ie 10ms * (79 *1.3=102) = 10.5ms. But this is at 135%MAP not 100%
The 460 @ 100%MAP is 13ms*82%=10.66ms, pretty close.
So the increase to 127 with the 351S/C at 135% is 10ms * 127% = 12.7ms. But a 460 at 100% only runs 10.5ms.

Does anyone agree.

Note that the 460 at 100% is 82 but the ms is 30% more so 82 * 1.3 = 106, so close to 102.

[jsmcortina]

Put in your real engine details.

The VE table generator is a starting point only, once the engine is running proceed with tuning.

James

[72bluetr6]

Typically, your SC does not "kick in" until kpa is above about 100. Your engine is a 351 below 100. Values from 100-133 or so on a VE table depend on how efficient the SC can pack in more air/fuel mix. Tune below 100 first. The VE table is an "efficiency of filling" table for a particular engine, not based on engine size.

[39ClevoUte]

Put in your real engine details.

The VE table generator is a starting point only, once the engine is running proceed with tuning.

James

Thanks James, but I think the S/C VE tables are too far out. I reread what I wrote last night and Its pretty obtuse so Ill have another go at what I think is not quiet right. I want a starting point that makes sense, or at least I need to understand why I'm wrong about it.
Rob

[39ClevoUte]

Typically, your SC does not "kick in" until kpa is above about 100. Your engine is a 351 below 100. Values from 100-133 or so on a VE table depend on how efficient the SC can pack in more air/fuel mix. Tune below 100 first. The VE table is an "efficiency of filling" table for a particular engine, not based on engine size.

Thanks 72blue tr6, I agree, but I cant make sense of the S/C table. I going to have another crack at describing what I think is a problem.
I think I can demonstrate that it is putting in an extra 30% between MAP 15 and 100 while its still in the "351" zone. Then it adds another 30% between MAP 100 and 135.
In my humble view the 351 S/C between 15 and 135 MAP should look fairly close to a 460 15 to 100 MAP, with corrections for injector MS timing.

I'll post some screen shots.
Rob

[jsmcortina]

The VE table generator is a best guess. Who cares if it isn't 'right' ? Get the engine running and tune it.

James

[39ClevoUte]

I'll be doing that thanks James.

[nismoautoxr]

Another thing Id add to this is that even though the engine may not be in positive boost ...the blower still is improving airflow and reducing pumping losses even under 100 KPA so try as you will to try and apply the cubic inch math ...it will not be close. Best bet is as James said ...get it close and tune the engine with the real engine parameter numbers plugged into the tune.

[Blown88GT]

...even though the engine may not be in positive boost ...the blower still is improving airflow and reducing pumping losses even under 100 KPA ....

Well stated & very noticeable when driving. This is where, I believe, a MAF is superior to a MAP.

[dontz125]

...even though the engine may not be in positive boost ...the blower still is improving airflow and reducing pumping losses even under 100 KPA ....

Well stated & very noticeable when driving. This is where, I believe, a MAF is superior to a MAP.

Why? SD at 95kPa MAP uses the same math and injector PW calcs as SD at 140kPa MAP. Unless someone wants to tell me I'm out to lunch ... (It happens! )