Hello, I have an '86 Olds Cutlass street car with a 455+.030 s that I race. I need some real advice from G-body guys who have FAST street cars, so I came here.
Car runs high 12's, TH400 w/ stock conv., 3.73's, Holley mech. fuel system is not cutting it -running out of pressure so I want to go electric.
I did my homework - I know the GN's have different fuel tanks, pickup ass'y, wiring, etc. I am leaning towards 2 chioces:
1) Aeromotive electric pump and bypass regulator, Comp Engr weld in dump, etc etc.
-OR-
2) GN style (quiet) in tank electric pump, sender, and tank. I am planning on fuel injecting the motor later, so I may want to use the high pressure SFI pump and let the regulator dump the excess back into the tank rather than a '87 4.3L Monte Carlo tank with a H/V TBI pump (454SS?).
It seems like you guys can go high 11's with stock tanks and pumps, right? I see that you go to the Walbro pump, so I could too, but do you have probs with the sump uncovering? With my 1.87 60ft's the G-force is 1.06 average, fuel should slosh to 47 degrees at least... Do you guys modify your tanks at all? Do you have to keep more than 1/2 tank of gas or what? Does the GN tank have some special baffling in it or something that keeps the fuel from uncovering the pickup? Anyone got a stock setup they are selling? I can get a new tank but not pickup. I could fab the pickup though.
Let me know what you think! And please don't hammer on me cuz' I'm an Olds guy - at least I know when I'm outclassed - you guys know your stuff! I don't want to hack my car - want it like GM would have done it!!
Thanks in advance!
Bob Powers
Akron, OH
rpowers3@neo.rr.com
That should be "weld in SUMP", sorry
Is there an "edit" capability on this thread??
The GN tank has a baffled sump in it (different from the N/A cars). As long as we have a 1/4 tank of gas or more, I can do 1.5 short times all day without problem.
The stock pump is weak (and was marginal when new!), but a simple upgrade to a Walbro or XP solves that problem. We also "hot wire" the pump with heavier gauge wire to make sure that it gets all the voltage it can. Some folks also run voltage boosters to the pump.
As far as edit capability, click on the little "notepad" in the message header (next to the date). You should be able to edit your post within about 30 minutes of posting it.
Thanks Ken, love this site for tranny and axle tech too. So from what you say, I think I want an upgraded GN fuel system, BUT I read on this site about how some Canadian aftermarket GN fuel tanks have a different metal instead of plastic baffle in it that does not control the fuel as well and those guys have had probs. True? Any one tank that is good? Local store has American Design (Advance Auto). Don't want to spend $166 to have fuel starvation!
I've read the same thing ... some of the "repros" seem to have a problem with the baffle.
As far as a good tank I haven't had any direct experience with it...
I read some tech articles here on the GM factory & aftermarket fuel pump ouputs and regulator return volumes...
Someone replied to my e-mail and said I couldn't use the GN system with a carb'd car because fuel pressure varies with boost... correct me if I'm wrong but I thought the fuel pump is always putting out it's max volume, and the fuel is supposed to be at max pressure between the pump and regulator. Then the regulator keeps the fuel rail at whatever varying pressure it needs to be at by bypassing extra fuel back to the tank.
If this is true, I could do the same, except instead of my regulator holding 40psi to the rail at idle, it will be holding 7psi to the carb inlet at idle. Lets just say (my numbers are off I'm sure) a 50GPH pump will feed 400HP in a GN. Then 50GPH will feed my carbed motor up to 400HP also, right?
Don't think you can get the pressure of a fuel injection pump to 7 psi or deliver the volume you need there? Why not just use a low pressure aftermarket pump like most carb'ed race cars?
Bob, you are right ... the rail pressure is regulated to keep the same DIFFERENTIAL pressure across the injectors.
When pressure in the manifold goes up, the pressure in the rail goes up to match to keep the the pressure across the injectors the same. Basically, as pressure goes up (i.e. less vacuum, in your case) the fuel pressure will rise proportionally.
I wonder (as Nick pointed out) if at the low pressure you'd need for the car if you'd get enough volume? Most of the pumps put out about 1 gpm with no regulation (i.e. just open with no pressure regulation) which is about 55-60 gph. Voltage can make a substantial difference in pump output, BTW. Is that enough for your application?
http://www.gnttype.org/techarea/fuelsystem/pumpflows/Walbro242Graphsmall.jpg
Oohh boy - I am learning here but also thinking of new questions at the rate of the sqaure of a GN's fuel pressure!!
1st - as far as Nick's ques., I don't want to use an external pump because they are noisy from what I have seen, and much less reliable than in-tank ones. If it can break, it does for me twice. Also I think putting the aftermarket pump ahead of the tank using the stock sump will be hard on it, and may ucover it (no special baffling in stock tank), so the ideal way is to weld in a sump and have the pump behind the tank. This looks RACEY - I want mine to look stock - and I think it would be BAD in a rear end collision. My car looks like GM could have built it. I am really serious about putting DFI on the 461 in a year or 2; it's the only way to have any real control over the fuel distribution. If I am gonna put an in-tank pump in it, I figure I might as well put in the high pressure pump now, instead of having to re-do this again. Just figured it would be only a little more effort to get the high pressure system in.
Ken; I am confused as crud about fuel volume now. My Holley is rated at 80GPH. Holley regulator is set at 6.5psi. In the beginning it was fine - 6-1/2 psi all day long. I am on my 4th Holley. 2 went bad, stranding me. Rubber diaphragm flow check valves turned rock hard. 3rd one I just started loosing pressure- down to 2psi one day at the track. Checked it -it seemed fine. Changed it - same prob with a new pump. It drops more when it's hot, but I can pull the car out of the garage and go 1 block at 1/2 throttle and watch it drop from 6-1/2 to 5. It's not the carb or filter (clogged filter would make press. go UP), checked the hoses; didn't pull the tank down to check sock, but I checked that last year 1000 miles ago!
My point with the pressure was that I figured if a GN can go lets say 11.50 with a stock system + Walbro pump, so could I. Volume is volume, right? GN's and my car weigh similar & similar aero, so they whould require same HP to go a given speed. Any given HP requires the same ammount of fuel, ignoring efficiency. Holley tech said the mechanical pump is marginal for my power level. I AM CONFUSED because how can a 80gph pump be marginal for 12.9's, while I have seen GN's with stock 50GPH pumps go high 11's?
AAAAGHH! I believe my car is 3650-3750# w/out me (68 motor, iron heads, 2.07"/1.68 valves, I ported them, 1-3/4" headers, TH400, stock 1800 stall, 8.5" 3.73's, A/C, steel hood...), I weigh 175, BFG Drag Radials, 1200RPM launch, best is 12.92 @103.5. Best MPH is 105.5. Haven't raced in under 90 degrees yet. I'll let you guess at my HP.
P.S. converter is stock 'cuz I'm building a 2004R, thanks to a lot of your guys' info!
I can get a GN original tank and pickup/sender ass'y w/ pump for $200 + shipping.
Bob, I used to be an Olds guy myself, (1970 Cutlass 442 w/455. I did not know a thing about them until I met Dr. Oldsmobile himeself, Joe Mondello. www.mondellotwister.com Check it out, he has a tech line and will give you tips on how to make your Olds a screamer.
Chris
Thank you for the tip Chris... Joe knows more about fast Oldses than just about anyone, but very little about helping the little guy get a lot for his money. I got BURNED by Lynn at his place and got a lawyer to get my $460 back... don't want to get into that though. I am on realoldspower.com a lot, and can get LOADS of info on huge aftermarket pumps, cutting up cars, making them loud and undrivable on the street... making a race car is easy. There are plenty of GM and GN parts that can make my car quieter, nicer, sleeker, and FASTER than the other street guys' cars, I know it.
Sorry for the negativity, but I have found Mondello's to be VERY VERY hard sellers on many occaisons. They do know their stuff though.
Volume is related to pressure ... it's like when you squeeze off the end of your garden hose. Pressure goes up (and it sprays further), but volume goes down, since only so much can get thru the opening.
I would think that, as long as 60 GPH is OK for your car at 6-7 psi, a high pressure fuel pump should work. It's just not what they are usually running at, so I was questioning whether the pump could keep up.
You might want to look at the return line (and feed line, for that matter) to make sure they are sized appropriately ... the GN return line is sized assuming that most of the fuel goes into the motor most of the time. If the return line is too small you might end up with run away fuel pressure.
I understand... from the graphs, with reduced pressure against the pump, flow goes up, right? If a 11.50 GN holds 40psi (or whatever it actually is) pressure on a pass, it consumes a given ammt of fuel. If that system is in my car, assuming return lines and regulator is adequate, my car requires less pressure head, so the pump should actually be able to supply more fuel at 7 psi than 40.
If a pump holds pressure for a GN, it should be no prob for me, because an 11.50 GN and an 11.50 Cutlass 461 would require the same volume of fuel because they make the same HP, and I need less pressure, same volume. RIGHT? Know what I mean?
P.S. - under say 14.7psi boost, full throttle pass, what is the fuel pressure in a GN's fuel rail versus ambient air? It seems injectors run at about 40-45, so it would be 45+15=60psi, right?
Here is my thoughts, not being a fluids expert.
Using a GN pump and system to supply 7 psi [that normally supplies 45-65psi] for a carb'ed motor is covering new ground. First problem is getting it to operate properly at that low pressure.
If it does, fine. If not, the carb runs out of fuel. So, probably no damage done like would be on a turbo motor going lean. But maybe there is a chance it would lean out enough during the "learning process" to take out a head gasket or???
My point is, there are inexpensive good, quiet pumps that will satisify your carb'ed needs which seems like the best approach.
A reply is not necessary as this is just my personal opinion!
Lots of traffic on this subject!
I'm confused about your last statement which compares two 11.50 cars. I always thought you compare 1/4 mile terminal MPHs, not ETs, to arrive at comparable HPs. On the other hand, our cars are torque monsters just like BB 455s are, so there may not be that much difference in fuel consumption after all.
I wish one of the more knowledgable experts would step forward and settle this conversation so we could move on to other subjects.
Donald, yes you're right, should use 1/4 mile terminal MPH's, I was just assuming they would be close - don't know what MPH that is off the top of my head.
BSFC (brake specific fuel consumption) and BSAC (brake specific air consumption) are lowest at peak torque, and is higher at peak HP. Fuel consumed is a primarily a product of HP. Vehicle weight, areo., etc change the ammt of HP needed to push the car, so if cars are similar in this regard, ad similar in ET & MPH, they make similar HP. Efficiency really does not change all that much. Better engines are mostly able to pump more air, not really extract more BTU's from the fuel. Yes it varies, but not enough in this case to change the fuel pump capacity.
I didn't mean to upset anyone here with a large post - I figured if there is a lot of talk on it we are all learning something. I know I have. I understand the concepts more than I have used them - I lack experience. At least it looks like I stumbled on a gray area here.
I will probably end up installing a GN system - I got a lead on a complete tank with the OEM sump and pump. I'll see how it performs and re-post in a few months. If the stock pump is not enough like a lot tell me, I will pull the tank down and replace it. The sump/puckup assy I am getting comes with the pump, so it's essentially free. Might as well try before spending more cash.
Please feel free to keep commenting guys!
P.S. - It is almost weird how alike the GN and my car are... a 231 CID at 14.7psi (I know you all run more) is theoretically the same as a 462 CID N/A motor. My motor is 461 CID. My buddies mostly stock GN runs low 13's, it feels a lot like my 461 when the boost is in. His torque curve is flatter I think though. We both shift at similar RPM's... my car is black too!
Bob, I'm not upset but I am looking for the list expert, in this area, to step in and explain to us what the answer, to all the speculation, really is.
It sounds to me like you've got your engineering fundamentals down pat. Maybe you could shed some light on a question I've wondered about.
What is cruising speed? My argument is; It's the point at which the engine is most efficient. Which, to me, is when the pumping (gas loads) are balanced by the rotating and reciprocating forces at which point the frictional forces are the lowest. On a NA car, tribal knowledge says, it's point at which your vacuum gauge reads the highest.
Do you have any insight on this subject?
We are all trying to learn and share!
That I do have SOME input on - it is LONG though -2 parts. I have seen "cruise RPM" advertised in a lot of cam manufacturer's ads and used to wonder the same thing.
For ANY constantly held RPM, the "gas loads" must be balanced by the rotating forces, or the engine would accelerate or decelerate. Engine friction is lowest at lowest RPM.
Like I said above, the engine consumes the least amount of fuel PER HP at it's PEAK TORQUE. This measurement of fuel used vs HP made is Brake Specific Fuel Consumption, or BSFC. Same goes for air (BSAC). Remember this for later...
Now we have all seen HP/Torque dyno graphs...lets say a motor makes peak torque at 3500RPM and peak HP at 5000. When you are driving in the city and hold a constant 1/2 throttle, notice how the motor noses over at like 2000 RPM? If we were to dyno the motor at 1/2 throttle, we would see that it obviously has a different lower HP/Torque graph, with both peaks occurring at lower RPM's. So at full throttle, BSFC is lowest at 3500 RPM. At half throttle, BSFC is lowest at probably about 2000 RPM (again, peak Torque).
To cruise down the highway, the motor must overcome a given load - air resistance is the largest factor, also includes tire rolling resistance, axle, tranny, and engine drag/friction, etc. Part of the load is constant for any 1 car at 60MPH (air drag, rolling resistance). Tranny friction varies with what gear & throttle you are in, and engine friction varies a lot with RPM and throttle. So the best cruise RPM is the one where the engine uses the least fuel to produce the amount of HP necessary to overcome the car's constant drag/friction force, PLUS the friction of the motor. Tricky because lets say we set up the car and it cruises at 2800 RPM. Lets say we change it to cruise at 2000 RPM. Which is better? For my 461, 2000 probably. For a 231 turbo, 2800 maybe. Why? because my big engine draws more air at 2000 than the 231, and makes lots of HP at 2000 with little throttle. Lets say it takes 50HP to push the car down the highway, the motor will need to make 50HP plus overcome it's internal friction at 2000 or 2800 RPM. On my motor the crank weighs 78 pounds & the rings are big - plus 24 of them vs GN's 18 - the majority of the fuel consumed at 2800 RPM at low throttle goes towards spinning the motor, not pushing the car. So lowering RPM to 2000 will lower the frictional losses a lot, and get the motor closer to it's peak torque for that throttle too. A 231 low compression turbo motor has very little friction at 2000 RPM relatively speaking, and makes very little HP there too at 1/8 or 1/4 (off boost) throttle. So you wind up not making enough HP to push the car along with the 231 at 2000 RPM, and wind up opening the throttle until you do make enough HP - now you are in boost and getting bad gas mileage. Increasing the 231's RPM to 2800 is a smaller friction penalty, plus the motor is closer to peak torque and lowest BSCF.
PART 2:
If engine friction increases directly with RPM, it's best to always rev as low as possible down the road - but we all know that doesn't work. The other half of this is that like I said in the beginning, for any given throttle opening, the motor will have a HP/Torque curve. If we were to try and go 60MPH at 1000RPM, any motor would probably be at ¾ throttle and be WAY down below it's peak torque for that throttle opening, and therefore far away from best efficiency. The best vacuum reading probably occurs when everything is just right, and for whatever throttle position you are at, the motor is running at it's peak torque at 60MPH. Again, lets say my 461 is revving 2000 at 60 and loving it. Lets say I am at 25% throttle exactly. Lets say this is the combo that nets best MPG. Lets say I give it less gear and rev 1800. The motor cannot make the same HP/torque at 1800 as 2000 without giving it more throttle. I will be at about 35% throttle now, and my peak torque just moved into a higher RPM, and I am revving at a lower RPM. Now not at the lowest BSFC. See?
Now lets say I throw more gear at it and am revving 2200RPM. The engine's friction just went up, and we are now above the peak torque, so we need to make more power to overcome the added friction, plus we are making less power per unit of gas. I have to give it more throttle, and again, the engine is not running at it's optimum RPM.
I think that cruise RPM is based off of the fact that most muscle cars have kinda similar drag forces, and we will gear the car for best ET. They are posting that with their cam X in car Y with optimum gear ratio Z, this cam will have some greater efficiency at this RPM. I look at as a one-number answer, instead of an article like this for the average cam buyer. That cruise RPM tends to be right at the bottom of the power band I think. Some cam companies make it sound like if you cruise at less RPM than this, the car will spontaneously combust. Not true - big blocks can get good MPG if you get them into a low enough RPM at highway speeds without lugging them - point and case, A guy I know with a '70 442 with a 461, 4.11:1's and ZF 6-speed (2 overdrives, the top one is 0.5:1 I believe). I think he can get 21MPG highway with a Q-jet 4bbl. Change that to a TH350, you're talkin' 12MPG. Larger motors draw more air at a given RPM than a smaller one, so the larger motor needs to be at a lower RPM than the smaller one for best MPG. Unfortunately, affordable tranny technology has not kept up with engine tech. It's a struggle to get a good 2004R 4 speed for my Cutlass, let alone a SECOND overdrive gear!!
I hope this makes sense - no short way to explain this that I know of.
Fasinating! I had to read your answer twice and will read it twice more. Questions beget questions!
I'm not sure about what you meant when you said, "the engine noses over at 2000 RPM".
Please correct me where I'm wrong about cruising speed.
Both cars (G bodies) traveling side by side at 60 MPH are developing about the same HP even though the throttle positions may be different. Neither, one, or both, could be in their "sweet spot". (Vacuum reading at highest point.)Or, maybe I could say, "The most efficient use of fuel for the speed required."
I had a 32' Chris Craft with twin 'vette engines. The cruising speed was at about 3200 RPM and was using about 4 GPH. Any faster or slower, and your GPH (Gal/Hr) would climb drastically. In this senario, I was trying to make most efficient use of the engines regardless of the desired speed. I've often wondered if it works the same for a car, only not as dramatic an effect.
You seem to be saying that, there is a point at the base of the power curve where fuel is utilized most effectively. Is this the point where if you went any slower, you would have to downshift because the engine will start lugging?
Is it also the point at which if you went any faster, your efficientcy would start to drop because of wind resistance and engine friction?
I guess it's obvious to others on this list, but I guess I'm a little slow sometimes. Could I conclude by saying that if my 3.42:1 rear end is ideal for the 1/4 mile because it doesn't shift into overdrive until just after the finish line, and, because of the overdrive, it gets great gas milage because at normal throttle openings, it shifts into OD at 42MPH. It seems I have the best of both worlds.
Sorry, I'm not very good at articulating my thoughts.
Too large again for 1 post...PART 1
1) By "noses over" I meant you feel the power drop off.
2) Both cars at 60 - remember highest vacuum is not the only criteria - my Cutlass pulls 20-22" vac on the highway, but that's because it has 3.73's and no overdrive, and is revving 3000 RPM. Mileage is poor (ok, BAD) even though vac is high. It's a balance between 2 changing variables - RPM and vacuum. But for any one given RPM, if you increase the vac reading, you will get better fuel economy because the cylinders are less full of fuel.
3) I know enough about boats to know that’s a boat… there’s another variable at play here – the water drag. I don’t know all of this for sure, but this is what my logic/engineering principles say:
First, air is a fluid – it has mass, volume, and inertia when it moves. It is very compressible though. Water too is a fluid, but basically incompressible. The main difference is water’s MUCH greater drag force on objects moving through it (ever try to run with your legs in water?). With the car moving through air, the drag force slowing the car down is Cd (coefficient of drag) times frontal area. Drag increases with the square of speed – this means that say it takes 3HP to overcome the air resistance ONLY for the car at 30 MPH, at 60 it takes 9HP, at 120 MPH it takes 81HP, and so on. In water, we have an additional factor…
PART 2:
When the boat is still, it is at equilibrium (if it’s not leaking). The weight of the boat is counteracted by the buoyancy of the boat, which is due to the boat weighs less than an equal volume of water. Even a bajillion ton ship weighs less than the volume of water it displaces. Now lets say the boat is moving at 10 MPH or knots or whatever… let’s pretend we are in another boat along side it at the same speed, so we can assume the boat is sitting still and the water is moving at 10 MPH. The moving water has inertia, and the boat in effect pushes it out of its own way. The net result of this is an upwards force on the boat. At 10 MPH that force is small, so the amount of the boat in the water is about the same as when still. At some speed, they “come up on the plane” – or some terminology like that, right? That’s when the boat rises out of the water, and has less boat in the water, so drag reduces. My guess is that 3200 RPM correlated in the boat to some balance between the motor’s torque curves (that would be near peak torque if you were between ½ to full throttle, right??), the water resistance dropping, and air resistance going up. I would guess that if you go slower, the boat sinks into the water, and if you go faster, the boat doesn’t rise up much more, but the engines are working too hard, and also air resistance may be beginning to be a factor. I think it starts to become a larger force at 30-50 MPH, buy my SWAG (Scientific Wild A** Guess). Also – with a boat you can vary your prop(s) diameter and pitch – this is the boat’s “gear ratio”. A larger diameter or higher pitch prop is equivalent to a numerically lower gear ratio on a car, right? (Propeller pitch is the distance the prop would cover in one revolution if there were no slippage). You could probably change the props and vary the speed at which your best fuel efficiency occurs. Just like a car – this would also change its acceleration. Would be interesting to see if peak mileage occurs at a different RPM with the new prop!
4) From what you say, I think you get what I am saying. But remember – “base of the power curve” – the RPM for peak efficiency is the PEAK TORQUE RPM, because at peak torque, all engines use the least amount of fuel to produce each HP. But… what I was trying to say is that if your full throttle peak torque occurs at 3500 RPM, ½ throttle peak torque is NOT at 3500 RPM – its at like 2000. ¼ throttle peak torque is at like 1700 RPM, etc (just guessing these RPM’s).
PART 3
5) What you say about ¼ mile gearing and 42mph are true – they are the resultant of the car being a good combination. My Cutlass would also like 3.42 gears and O/D (runs kinda high RPM thru the trapps now – 5500 to 5600 RPM) but the 3.42 with O/D would still not be enough for optimum highway fuel efficiency. I wouldn’t complain about it, but with a gear vendor’s added, it would probably be better. Your car works better in that regard because it is happier revving higher down the highway, where a 455 or 461 V8 could comfortably rev at 1800RPM instead of 2300 or 2500.
One more thing to think about... even in a GN intake, there could be say a trailing wake vortex off of say a bolt boss casting in the manifold. This vortex could be changing the air distribution to 1 or more cylinders. It gets worse - It would be different at different RPM's and throttles. For example, it could be feeding extra air to cyl #1 at low RPM, then at higher RPM or throttle position, diverting air away from cyl #1. I don't want to go into this stuff too much... an 8 hour airflow seminar I went to just barely covered all this stuffl let alone text here. Anyone REALLY serious about learning more go to:
http://home.attbi.com/~technical_insights/ti_new_releases.htm
and buy the 9 hours of tapes of this seminar for $250. Taught buy a VP at GM and one of Dodge Motorsports' NASCAR guys. Amazing airflow test footage... well worth it.
And you didn't think I could be any longer winded!
BTW - I found out that a '92 Roadmaster low pressure TBI pump outflows a '89 454SS truck TBI pump. I may try the Roadmaster one.
Bob,
Excellent, excellent stuff! A big thanks and I hope that others who are following this thread appreciate all the time you've taken to explain a murkey subject. Your explanation and analysis of item #3 was especially well done. I can relate completely. Because of your equating the prop to the rear end ratio, I can state the obvious now. The ideal would be to keep the 3:42 for the drags, and to gear your OD for whatever your chosen highway driving speed will be.
Last question, I promise!
I'm 45 miles away from my $4/gal-100 octane-76 gas station and about 60 miles from the drag strip. (Jackson near Augusta, GA)It's all 60 MPH 2 lane black top. Should I get some dyno time, and do a print out for 60 MPH? Could I then use that information to see how close I am to the peak torque for that speed? That should tell me how good my OD gear is for that RPM. You see, it's all about $4/gal gas.
I know somebody out there is thinking, "Why doesn't he just get a trailer and be done with it?" Well, money's tight right now.
Thank you for your time.
Don
HEY GUYS, K I HAVE A TE44 ?? TYPE TURBO,STOCK INJECTORS,THRASHER STREET CHIP,HOUSTON DOWN PIPE,2 1/2 EXH. I HAVE THE CAR RUNNING AT 38 PSI FUEL PRESSURE VAC. ON, IF I INCREASE THE FP I GET BACKFIRING, IF I INCREASE THE BOOST I GET 2 MUCH KR. A CLEAN PASS IS ONLY GIVING ME 101 MPH AT THESE LEVELS! IS IT TIME FOR DIFFERENT INJ'S OR A NEW CHIP??
you need some larger injectors id recommend 42.5's
. i assume you already have a larger fuel pump? if not youll need one. after these mods you also need a new chip to get the most out of it.