"where did the 1.92 CFM/HP come from?"

"I would say that your max WHP/CFM is a little conservative "

a fair question. when we deal w relationships there are always outcomes that fall a bit outside the curve. OTOH, probably 85% of the results are pretty close.

there are lots of variables. for instance take compressor maps. the east side of the map just stops at some efficiency ratio... say 65%. most look at that spot as max delivery and it generally is... or is close. the real boundry, where a turbo reaches max delivery, is where the RPM plot goes exactly vertical. if you note the GT35, the rpm isn't quite vertical at the efficiency line. this indicates a touch more than 62 pounds delivery.

another excellent way to determine ROTARY rear wheel hp is to take max flow, multiply by 10 and divide by 1.3.

so you can do:

62 X 14.471 = 897 CFM/ 1.92 = 467

or

62 X 10 = 620/1.3 = 477

are either of these methods a replacement for a dyno? of course not but they give you a pretty good initial starting point.

"why do you have to run the same pig rich AFRs with water injection"

i don't have the answer as i have never run water. some like really rich AFRs at high hp levels and others don't. i may do some comparative dyno testing w water in March depending on what i decide to run fuelwise for the Texas Mile. others are very welcome to share their AFR-Water AFR data.

"what tranny, rear diff and what size wheels/tires"... for 200 in the Texas Mile

i will be running a Tremec T56 6 speed gearbox. i am currently examining options as to gearing but plan to run my FD diff so it will be either 4.1 or 3.9. tire size will depend on the RPM range of my engine which will be determined in march.

"whats the fastest you have gotten previously?"

i ran my Fd (racegas w the stock turbos) a number of years ago at Brainerd Int'l Raceway at 3 Ferrari Club of North America track events. Brainerd has a 6000 foot main straight (that you enter at 70+ mph) followed by a 90 degree banked wide radius turn (think Daytona). while my FD was still accelerating as it was close to entering turn 1 due to the fact i was on street tires, had no fuel cell or roll cage i backed out at about 6500/160. the car was very stable in turn one and shed about 20 in the turn.

hc

 

Running leaner AFRs is a compelling reason to add water. If I still have to run low 11s, I'm less interested. Dumping fuel is dumb (not to mention emissions go through the roof), and it contaminates the oil. Tuners should be all over this issue.

 

Great info Howard. I'm actually going to mess around with some numbers today to figure out what injectors I'll need for my GT4294 E85 project. I've also been referring back to your chassis thread for the suspension setup on my car as well. Thanks for all the inadvertent help. haha

 

Howard,

I plan on running 850cc for both primary & secondary, but I plan on using an Xcessive LIM (4 secondary injector bungs)

Do you think that would be sufficient for BNR SIII's @ 20psi?

I don't plan on boosting that high at all times, more just as "boost scramble"

Or, do you think I should go with 4x 1000cc injectors for my
secondaries?

I want to try to maintain a smooth transition between primary/ secondary injectors.

+ I'll be using a Marrin FPD, Bosch 040 fuel pump, surge tank, metal substrait fuel filter, inline collector (reduce pulsation from fuel pump) & if neccisary a Ken Belle boosta pump.

Any imput is appreciated!

Thanks for taking the time to read my post!

 

Prometheus,

i welcome all questions as to fuel requirements in this thread. after we have done a few it will become easier for all to run the numbers...

fuel calculations start with airflow. i don't really know what the air delivery of the BNR setup is. if we know what HP (max) BNRs make we can easily reverse into airflow. i believe they have made 400...

maybe someone can give us a good max (legitimate) SAE number for the BNRs and we can then answer your question.

howard

 

Hello Howard, some great treads you have written, all great reading.

Howard I would like to ask your opinion on the following:

We race an FD RX7 - Circuit/Road Racing.

SetUp : 13B REW Large Extend/Turbo Port, 3mm PTS Apex Seals, Dowelled & balanced.
Match ported REW intake manifolds & emisions & sec butterfly removed.
1680cc Secondaries & 880cc Primaries, 2 bosch 044 pumps feeding surge tank &
1000Hp SX main pump feeding engine.
Turbo is to be changed to either BW362 or BW366 with extended tip & possibly
race cover. Wastegate is 45mm Turbosmart, 20psi, plumbed back into 3" Exhaust.

We are changing over to E85, and are unsure as to what fuelling (ie injectors) we will need for a projected 550RwHp @ 20psi, (or if this is even possible with the turbos we are looking at & psi.)
We are looking to change to a 4" exhaust, if this would help.

Many thanks in advance

 

So we have a good idea how to match single turbos to injectors/fuel systems because the manufacturers publish max hp/max cfm numbers?
If we take that case to the stock turbos: then are we running the optimum injector size to maximize hp? Let's assume for the sake of arguement that stock turbos/ports plus intake/exhaust/pfc maxes out safely near 350rhp...with your calculation is there a better injector combo to be utilized? Maybe a combo that isnt working the injectors to the limits of there duty cycle.
Then let's assume the BNR's max out at 400rhp, whats the optimum injector combo for that level of cfm? (at 85-90% IDC to have a bit of headspace left).
A lil sumthin for the tt guys if you please.

 

"SetUp : 13B REW Large Extend/Turbo Port, 3mm PTS Apex Seals, Dowelled & balanced.
Match ported REW intake manifolds & emisions & sec butterfly removed.
1680cc Secondaries & 880cc Primaries, 2 bosch 044 pumps feeding surge tank &
1000Hp SX main pump feeding engine.
Turbo is to be changed to either BW362 or BW366 with extended tip & possibly
race cover. Wastegate is 45mm Turbosmart, 20psi, plumbed back into 3" Exhaust.

We are changing over to E85, and are unsure as to what fuelling (ie injectors) we will need for a projected 550RwHp @ 20psi, (or if this is even possible with the turbos we are looking at & psi.)
We are looking to change to a 4" exhaust, if this would help."

road racing presents significant challenges as nowhere is hp under the curve more important. the ideal turbo for road racing makes 400 rwhp at 5500 rpm. ports have a lot to do w making the number.

i have a compressor map for the BW 362.
the cold wheel is 62 X 86 or 6.291 average are in sq inches.
it makes 59 pounds at one pressure ratio (14.7) and 68 at 20 psi.

59 = 854 CFM or 445 rw rotary hp
68 = 984 CFM or 513

the Garrett GT3582r
61.4 X 82 or 6.386 av sq inches
56 pounds at 1 PR and 62 at 22 psi
56 = 422
62 = 467

as you can see neither of these turbos will get the desired top tick 550 done. i do think that finding 400+ at 5500 and 500 tops will win any road race given the FDs immense chassis advantage.

if you step up to a larger turbo, the 67 MM class (PT67, GT500 ASpec, TO4Z) the compressor wheel is 7.003 sq inches and you will be trading more top end for a bit less midrange...

here's a dynosheet from a motor i built & ported running another turbo that i really like... i believe it is actually a BW turbo and it has also been marketed as an R85 and TEC300.

compressor is 61.5 X 84.7 or 6.667 av sq inches. this turbo has a rotor friendly huge hot side turbine which is 6.93 av sq inches. compare to the S362 at 6.7 and the GT35r at 5.171. ASpec markets a similar turbo, the GT3574 that i llike because they use a large turbine wheel (5.89) on the Garrett GT35 compressor.

anyway here's the sheet. hp is in the more understated SAE correction:



IMO, this is what you want for road racing.

now let's do the math:

500 rw rotary hp using E85.

road racing generates huge cumulative heat and CCP. the alcohol will deal with it.

500 rwRhp requires 960 CFM (500 X 1.92)
960/14.471 = 66 pounds per minute

at a max rich AFR of 10 that's 6.6 pounds per minute of gasoline times a duty cycle max of 85%

1/.85 = 1.176 X 6.6 pounds = 7.764 pounds of gasoline

7.764/ 6.35 (pounds per gallon) = 1.222 gallons

1.222 gallons X 116,090 BTUs per gallon = 141,953 BTUs needed to do 500 rwRhp

BTUs per gallon:

gasoline 116,090
Ethanol 76,330

at 85/15: 82,293 BTUs per gallon from E85

141,953/82293 = 1.725 gallons per minute of E85 to make 500 rwRhp

1.725 GPM = 6529 CC/Min

you have 5120 and will need additional injector capacity.

i do like your battle plan and it is always great to see FDs on the type of track for which they were built.

howard

 

"If we take that case to the stock turbos: then are we running the optimum injector size to maximize hp? Let's assume for the sake of arguement that stock turbos/ports plus intake/exhaust/pfc maxes out safely near 350rhp..."

since there really aren't any compressor maps for our stock setup (yes i have one but it doesn't disclose the numbers) let's just reverse into it...

assume 350 rwRhp...

350 X 1.92 = 672 CFM / 14.471= 46 pounds per minute.

46 pound of air

4.6 pounds gasoline X 1.176 to correct for 85% max duty cycle = 5.41 pounds fuel/
6.35 = .8519 gallons per minute = 3224 CC/Min

the FD has 2800.

255 flywheel hp X .85 to correct for rwhp = 217

217/350 = 62%

.62 X 3224 = 1998... (needed for stock 255 flywheel output)

we have about 800 CC/Min additional injector capacity. (good for 300 rwRhp)

if 217 requires 1998 then 400 requires 1.8433X or 3683 CC/Min

howard

 

Awesome awesome info.
See now guys at all power/mod levels have a method to justify fuel system mods.
I may not need 2 fuel pumps yet but with the math displayed in this thread I can see that I should run bigger secondaries for my setup.
Thanks

 

here's the executive summary:


...................gross...................net
..................gasoline............gasoline.... .....Energy.........Cooling...Addit'l Cooling BTUs
rwRhp........CC/min...............CC/Min..........BTUs.............BTUs...........from water AI

217 (stock)....2018...............1559...........47,82 3............392..............640........ 300 CC/Min

300...............2790...............2156......... ...66,128............542.............854.......... 400 CC/Min

400...............3720..............2875.......... ...88,172.............723.............854......... .400 CC/Min

500...............4650..............3593.......... ..109,741...........900..............1068......... 500 CC/Min

600...............5580..............4311.......... ..132,258..........1084..............1495........7 00 CC/Min

fuel requirements assume we can deliver at a 10.0 AFR at 85% max duty cycle.

column 2 is required max nominal injector capacity the stated hp level using above assumptions.

column 3 is the fuel required to make stated hp (net of the 85% duty cycle and using an 11 to 1 AFR)

column 4 is the BTUs to make the stated hp

column 5 are BTUs of cooling in the gasoline

column 6 is the additional BTUs of cooling from the introduction of water.

column 7 is the amount of water.

note that the water adds approximately 100% additional cooling. this is not small potatoes. remember, we are easily running 10% more gasoline in an effort to cool our motors courtesy of Mazda.

at the 400 hp level 10% of the gasoline cooling BTUs is 88.

the introduction of 400 CC/Min of water adds 854 cooling BTUs!
win win win.

lose the gasoline and it's carbon

cool the CCP by an additional 9X

steam clean the carboned up motor.

hc

 

running high 12s to low 13s AFR would be win win win....and more win - 10.0 AFRs are absurdly rich

so why isn't anyone doing it? is everyone scared?

 

Very useful, thank you!

 

Yeah, people are probably scared to rely that heavily upon water injectiontime and again under racing conditions that you describe no_more_rice.
If the AI goes out on you (even with all the safety measures inherent in modern AI systems) while your runnin 13.5 to 1 Afr down the strip then its probably instant kaboom.
Most FD owners prefer to spread the responsiblity to not blow the engine up a bit more evenly and not have it come down to any single ancilliary system.

 

True, but if you're running high boost (i.e. 17 psi and up) and your water injection system fails, it seems like you're still going to be screwed (with pump gas at least).

The big problem I have with these mega rich AFRs is I get tired of smelling 5-10% gas in my oil and having to change it every 1500 miles. I don't think alot of people seem to care about this, but it drives me nuts. Excessive fuel dilution degrades the hell out of the oil, it's black after a few hundred miles.

if I was running a cat I'd also be concerned, fuel dumping trashes cats.

 

Fo sho no mo...
But if you're an FD guy who races his car and drives regularly on the street then you probably have settings for each environment.
In a race setting you may as well lean the afr and cross your fingers that nothing fails. Racing is always a high risk proposition no matter the car.
It seems that if you're on the street you can drop the boost a bit (12-14), lean the afr a bit(high 12's) and still experience good power/efficiency while lowering risk.

 

Tag.