Weight and Bonneville:

[Rex Schimmer]

Awhile back we all discussed the idea of how much weight you need in a Bonneville car to make it fast. Alot of opinion was that you want to stay as light as possible becasue you have to accelerate the weight, my opinion is that you need enough weight to make sure that you have traction to be able to go as fast as your available horse power is able to push you, and that the as you get closer to your cars max speed, I am talking about a car that has qualified to run the long course, the horse power required to over come aero drag is much higher than that required to accelerate the car.

Well I think the Hooley in his No 974 Studie proved my point. I hung out with the 974 car some and one of the changes that they made from last year was adding 600 lbs of ballast, they ran around 227 and spun the car, back tires were spinning! They added 400 more pounds and set a new record with the car going out the 5 mile at over 240!! So they added 1000 pounds to the car over last year and set the record! So in my book it is not acceleration that is important it is having enough weight for traction vs your aero drag.

Rex

[Sumner]

Awhile back we all discussed the idea of how much weight you need in a Bonneville car to make it fast. Alot of opinion was that you want to stay as light as possible becasue you have to accelerate the weight, my opinion is that you need enough weight to make sure that you have traction to be able to go as fast as your available horse power is able to push you, and that the as you get closer to your cars max speed, I am talking about a car that has qualified to run the long course, the horse power required to over come aero drag is much higher than that required to accelerate the car.

Well I think the Hooley in his No 974 Studie proved my point. I hung out with the 974 car some and one of the changes that they made from last year was adding 600 lbs of ballast, they ran around 227 and spun the car, back tires were spinning! They added 400 more pounds and set a new record with the car going out the 5 mile at over 240!! So they added 1000 pounds to the car over last year and set the record! So in my book it is not acceleration that is important it is having enough weight for traction vs your aero drag.

Rex

Well yes and no .  We (Hooley and the Hooligans) started the week about 250 lbs. heavier than last year and the year before.  First year he had an exit speed of about 219 at the end of the 3 with no spin and no oil pressure   (that ended the week).  Also he didn't have a full belly pan that year (the car is a Stude) and the salt was pretty hard and dry that year.

Last year with the full belly pan and larger spill plates at the sides of the spoiler 212 was the max. speed achieved at 25-30% throttle.  As we all know the course was hard and bumpy.  Anything over 25-30% throttle caused wheel spin and the car would start to spin.  After the first run we found out that the suspension was bound up (none) front or rear.  We then got the front working and about had the back to the point where we would have some suspension when we blew a blower seal and we were done.  Hooley worked on the suspension over the winter and now we have shocks we can really dial in from soft to hard and better springs and more travel.  I think if we would have been set up like this last year we could have run faster on the bad track.

Over the winter using the formula -- Thrust = HP X 375 /Speed and taking that times an average .4 Friction Coefficient -- I figured that the car at it's then present weight of a little over 3000 lbs. was probably not going to run past 230 before wheel spin would limit the top speed (there was some guessing and speculations as to the numbers I plugged into the formula).

We decided to have the option for more weight so over the winter John found a 3/4 inch steel plate that he cut up into bars and Hooley worked on a mounting method.  He started with two plates that weigh a little over 200 lbs. combined that go right under the front driveshaft u-joint and above the belly pan there.  Those were in the car when we got to the salt.  He also made pockets on each side of the car about where the front of the rear radius rods attach for the rest of the weight (800 lbs) in any amount we chose.

Our first two runs were easy runs to dial in the air/fuel on Sat..  The Sunday run he was asked to try and run more WOT to see the air/fuel at longer periods of WOT.  Well he got 107% throttle in most of 2nd, 3rd, and into 4th when he spun the tires at 223 and spun the car.  He might have been able to peddle it a little, but I think we were close to our top speed with out more weight.  The course was certainly better than last year, but I don't think it was as good as 2 years ago.  A lot of moisture was coming up and it was slippery.  At this point we decided to add another 600 lbs. to the car.  The shocks had been set about mid range and we left them there, which with the added weight seemed to soften them up a bit.  

The rest of the runs the car went straight and Hooley said it was easy to drive.  Now our only problem was that the car was not accelerating as quickly as before.  On our qualifying run he tried to accelerate as fast as possible and short shifted 1st a little and ran higher rpm's in 2nd, and 3rd.  I was hoping to qualify in both the 4 and the 5 mile as that would give us a little cushion on our return run just in case something happened in the 5th mile.  That didn't happen, but we did qualify in the 5th mile .

The next morning we leaned the motor a little and we were in cooler air (still ran way rich) and the motor cleaned out faster off the line.  He ran his fastest time ever with a 233+ in the 4 and a 239.740 in the 5 with a 241.179 exit speed.  Looking at the rpm data and Hooley's feel that 241 is about all there is in the car as it is.  So in a way we were still limited by acceleration.  If we could have been at the 241+ at the end of the 4 and ran it all the way through the 5 we would have had a higher speed.

Hooley wants a AA lic. now (does it ever stop), so the plan for next year is go from 10% underdriven on the 8-71 to 10% overdriven.  We also could put 40 more cubes in the motor as we are a 400 in the 440 class now and the heads haven't been ported.  I imagine we will work with the blower and possible water injection first.  Now that he wants to go 10-15 mph faster I feel we might still need to add another 300-400 lbs of weight to the car.

Where the weight is being put in the car it is doing two things for us since any weight we add goes almost equally to the front and rear of the car. One it is adding traction to the rear, but the part going to the front is helping to keep the center of gravity forward, which I think is very important to the stability of the car.

Maybe Mike will elaborate on where and how much weight they added to the 1149 car to get them over 200 .

c ya, Sum

[Dynoroom]

At Bonneville weight is your friend.... as long as the class your running does not allow aero modifacations (GC, GT, etc.). The car #265 was well over 5000 lbs. when it went 300.
As a side note the #77 modified roadster added a rear wing this year. The platform became much more stable and eaiser to drive. On the negative side it cost about 80 hp or 15 mph.

[ddahlgren]

Why not fix the aero and leave the hood closed?? You can't fix bad aero with power they are two different problems with two different solutions. The aerro problem is simple in concept and complicated at times in solving.. From my seat here seems like the Cd has to be as low as possible the center of pressure as far back as possible with prefereably no lift and some downforce. If as much money was spent in a wind tunnel as is spent to add power the solutions might be better organized and in the end simpler. Maybe picking a better body design is cheapr and quicker in the end as well. Let's remember it is Cd X Area..which is to say the smaller the vehicle the less the part the Cd might play into the top speed. Starting by poking the smallest hole in the air is the best plan and only applying as much force as you need to run the speed a better plan as well.

[PorkPie]

Weight or aerodynamic?

For us at the salt we have to think different as a road course car designer.

If you create downforce by aerodynamic shape - it helps by low speed - so as formula 1 - but creates a big problem by high speed - it slows you down.

If you create downforce by weight - you get (if correct positioned) a stabilizing effect, a higher final speed - but in the other way a lower acceleration.

Sum and Dave comments shows the direction a speed racer has to go.

The complete answer is:

The shape of the car need a very low cd and small cross section with a base downforce which increase only a little bit going up to high speed - Costella & Yaccouci Theorem II as a example.

Also it need enough length to smooth the airflow and a clean rear end that the shape can go properly out of the air - the #77 is excatly the opposite example

Weight on the right place to produce the necessary downforce for high speed - the way as the Golden Rod from the Summers brothers done or Tom Burkland.

The result had to be a combination of downforce - at low speed, during the acceleration, the aerodynamic of the car produce the downforce - going faster the producing of the downforce will switch over to the weight produced downforce.

To get a low increase of aerodynamic downforce going up to higher speed it is necessary that the shape is extremely clean.

Any kind of corners, bumps, airboxes, wings....which disturb the airflow, will increase the downforce going faster - but in a bad way - the airflow will be disturb by turbulences - and turbulences means less aerodynamic stabilize and less speed - and at last the airflow can't rip off clean enough from the rear end of the car.

Depends now on what kind of class you run, the solution will be different....

A roadster will be always a brick in the air , a doorslammer can be a much smoother (aerodynamicly) racer , a streamliner can BE designed in the perfect shape...

So, if there is the question, weight or aerodynamic  downforce - at first see what type of racer you design - depends on the class you can start to think about how you can reach the goal........

Any questions, you can ask me here at the website or directly, so as some landracing.com user done it in the earlier time.

Both ways you are welcome to do it

[robin dripps]

Pork Pie,
I wanted to take up your offer of advice on things aero.  The problem we are dealing with has been discussed here, but the opinions were so varied that a conclusion was difficult.  We race a 32 roadster, a low moment in aero efficiency, and are trying to get some positive pressure to the intake.  We measured pressure in our current scoop and found that at least it was not producing a vacuum, but beyond that it's positive outcome was dubious and obviously its influence on CD would be bad.  We are now thinking about a NACA duct but again there seems to be no agreement on this either.  I would welcome your thouights.
Robin

[Sumner]

Pork Pie,
I wanted to take up your offer of advice on things aero.  The problem we are dealing with has been discussed here, but the opinions were so varied that a conclusion was difficult.  We race a 32 roadster, a low moment in aero efficiency, and are trying to get some positive pressure to the intake.  We measured pressure in our current scoop and found that at least it was not producing a vacuum, but beyond that it's positive outcome was dubious and obviously its influence on CD would be bad.  We are now thinking about a NACA duct but again there seems to be no agreement on this either.  I would welcome your thouights.
Robin

Do you have a picture of the car and the scoop from a couple different angles.  Also is the motor blown/unblown and what is the displacement??

c ya, Sum

[Sumner]

Starting by poking the smallest hole in the air is the best plan and only applying as much force as you need to run the speed a better plan as well.

That is the whole thing in a nutshell.  I'm trying to do that with my lakester, although for the present 750 motor the car is too heavy (more force than needed), but hopefully with a 500-600 'Busa motor later it will be about right.

In Hooley's case his first car was a Stude and he stills drives a Stude all over the country, so his goal was not a record or the fastest possible time, but to build a Stude and be "Just Glad To Be There"* with it.  To set a record and get a red hat with it was a dream he wouldn't even consider 3 years ago.  Now he just wants a AA license and we realize our record will probably be history as soon as next year, but for us it will be something we will have for the rest of our lives.

He has been "bitten" though and is looking at small "narrow" cars in the fields along his mail route and who knows what might come of that .

For me the building/designing is my main interest.  I'm trying to do everything I can to make my lakester fast, but there again I see how hard it is to actually get a record even with the best laid plans.

Like you mentioned Dave it is a delicate balancing act to get everything working together.

c ya, Sum

[robin dripps]

Sumner and anyone who wants to help,
Here are some views of the current scoop.  The engine is a 258 cid GM V6 with Hilborn EFI, naturally aspirated.  We run in E/STR and after two years of hard work finally set a new record of 168 plus.  And since this thread started with an inquiry about weignt, we added 500 lbs of lead between the frame rails and in the middle of the car.  The result was the ability to use full power on the short course.
Robin

[robin dripps]

I will try again with the attachment

[PorkPie]

Robin,

I know your problem - I saw them when I done some picture from you at the short course - I was the strange looking guy with a big hat and a more strange looking green vest..........with a lot of stickers on....

I give you a answer in the next day - currently I'm too busy to get the picture for the magazines ready.

By the way - the car is a real beauty, nice finish, good job

[PorkPie]

That is the whole thing in a nutshell. I'm trying to do that with my lakester, although for the present 750 motor the car is too heavy (more force than needed), but hopefully with a 500-600 'Busa motor later it will be about right.

Small displacement and power can only fixed with proper aerodynamic and cross section

[robin dripps]

Pork Pie,
I was thining that the person in the vest must have been you but was not sure of the proper protocall.   Thanks for your comments about the car.
Robin

[Sumner]

Small displacement and power can only fixed with proper aerodynamic and cross section

The cross section is fixed to allow room for growth on the drivers part  and the aero is yet to be determined .

If the car was designed to only run a small motor I would of made the drivetrain smaller and simplier and the cage would of taken advantage of the smaller tubing that would be allowed.

c ya maybe in Oct.,

Sum

[Sumner]

Sumner and anyone who wants to help,
Here are some views of the current scoop.  The engine is a 258 cid GM V6 with Hilborn EFI, naturally aspirated.  We run in E/STR and after two years of hard work finally set a new record of 168 plus.  And since this thread started with an inquiry about weignt, we added 500 lbs of lead between the frame rails and in the middle of the car.  The result was the ability to use full power on the short course.
Robin

Robin how many square inches is the scoop??

Is the volume increasing from the inlet backwards??

Do you think you are getting turbulance from the top of the grill shell at the inlet point??

I think the rules allow it and if so I would try and move it down into the top front of the grill shell and sticking out into clean air.

I've heard 2 lbs. of possible boost at 200 from a properly designed scoop, so at 170 you might only be gaining 1 to 1 1/2, but still worth going after.

On our last run we data logged a hair over 8 lbs. of boost, so I'm thinking we were only making 6-7 with the blower.

c ya, Sum