Landracing Forum
Tech Information => Technical Discussion => Topic started by: mitchell968 on February 21, 2009, 10:19:41 PM
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hi guys. looks like im gonna build a grmr (gas rear engine mod roadster). who can i talk to that runs in this class to help me get started in the right direction ? thanks mitch :-D
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We run in front engine modified roadster. What kind of info are you looking for?
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well...basiclly, everything. probablly should start with frame bench ideas that will accomodate this type of car , one off you know. other then that, i guess ill start looking for info on frame rails(tube or rectangle),and coming up with the base line ride height numbers. what other info should i look for in these beginning stages ? thanks mitch :-D
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That's a good idea. I know a guy who had welded a few I-Beams together to build a frame bench to help him get started. I don't know if that's up your alley or not, but it seemed to work for him. We used square for the frame, but that was just because it was easier to work with. IMO the round tubing looks better. I would also get a rule book so that you can make sure you are building the standards of SCTA.
IMO I would make the car as long and low as I could. One thing on our car that I would've done differently would've been to make the frame fit to the roadster body. What I mean by that is that a roadster body doesn't just come straight back. The body kind of bows out a bit. If you make the frame to fit this bow in the body, it will give you more room to put things.
Let me know if this helps, or if you would like some different info. :cheers:
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I am returning a big favor by helping a friend build a RMR. In the next few weeks I will start a build diary on his car. I am drawing the frame and will utilize both tube and rectangle structure. We settled on the car having a mid-30% aero balance (front divided by total). There are about 10 of us working on this project and all of us have day jobs, so it will be a slow build.
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Go to one of the venues and look at them. Get an inspection form from the venue your going to run. Reread the rule book 100 times.. Good Luck
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Jimmy six is right about not only reading the rule book but getting a copy of the tech inspection form (it's on the SCTA web site). That form helps with a lot of little things you don't think about during the build.
This is the frame of our car on the jig & on the trailer. It's not a rear engine car but ou can see some of the chassis build detail.
(http://i127.photobucket.com/albums/p126/Dynoroom/Modified%20Roadster/Fromshop810Small.jpg)
(http://i127.photobucket.com/albums/p126/Dynoroom/Modified%20Roadster/Fromshop868Small.jpg)
Here's a rear engine car underconstruction.
(http://i127.photobucket.com/albums/p126/Dynoroom/Modified%20Roadster/Fromshop905Small.jpg)
(http://i127.photobucket.com/albums/p126/Dynoroom/Modified%20Roadster/Fromshop907Small.jpg)
Here's our car at the salt in '08 during it's rookie outing.
(http://i127.photobucket.com/albums/p126/Dynoroom/Modified%20Roadster/Roadster1stBonneville2008Kristins08.jpg)
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I am returning a big favor by helping a friend build a REMR. In the next few weeks I will start a build diary on his car. I am drawing the frame and will utilize both tube and rectangle structure. We settled on the car having a mid-30% aero balance (front divided by total). Their are about 10 of us working on this project and all of us have day jobs, so it will be a slow build.
I saw pictures some-where showing suspension on a rear engine car [not independent]. The engine- trans and rear were all solidly hooked together and moved like a swingarm, pivoting from front area of engine. One frame work inside another [something like that].
JL222
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Like this John.....
(http://i127.photobucket.com/albums/p126/Dynoroom/Modified%20Roadster/Fromshop906Small.jpg)
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thanks guys ! got the 08 rulebook ! waiting on 09 . mitch :-D
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I've really liked building my car on a wood build..............
(http://purplesagetradingpost.com/sumner/bvillecar/Jig%20Surface%20Plate-2.jpg)
table. It is easy to place parts ................
(http://purplesagetradingpost.com/sumner/bvillecar/rear-surface%20plate-2.jpg)
...........almost anywhere.....
(http://purplesagetradingpost.com/sumner/bvillecar/roll%20cage-34.jpg)
.....on it and then replace them....
(http://purplesagetradingpost.com/sumner/bvillecar-2/12-30-07-t12.jpg)
.......with the real thing. It was extremely versatile. Now if I was doing more than one frame/car and they were going to be identical then a steel build plate would be the ticket.
c ya,
Sum
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That's a good idea Sum. :cheers:
Pop, thanks for posting those pics. I couldn't find mine on the CPU. :cheers:
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nice benches ! anybody got a ballpark weight of these cars to build a bench that wont squat over 3-5 years ? ill build steel if i have too, but i think im going build a wood one. thanks :-D
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nice benches ! anybody got a ballpark weight of these cars to build a bench that wont squat over 3-5 years ? ill build steel if i have too, but i think im going build a wood one. thanks :-D
Here is the link to mine..............
http://purplesagetradingpost.com/sumner/bvillecar/construction%20page-11.html
.......... and it hasn't sagged over my extended build time :cry:. I doubt your car would weigh much more than mine.
I wish I could take the credit for this idea, but while visiting with a friend in Phoenix about 10 years ago he took me to a guys house where the guy was building a really nice street rod on one. He made all is own suspension, frame, etc. and the easy of locating components using the wood stuck in my mind,
Sum
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Best part of using a wood fixture table and mock up parts is that you have fuel for the fireplace after the conversion to steel.
DW
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Like this John.....
(http://i127.photobucket.com/albums/p126/Dynoroom/Modified%20Roadster/Fromshop906Small.jpg)
Yea thats it what a great idea. Whose is it and what's it for?
JL222 :cheers:
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I think that was Roy Fijasted's rear engine modified roadster. (Sorry Roy, I think I spelt his last name wrong)
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wow ! great stuff. definitely a wood bench, and sums web site is loaded with good stuff. thanks .looks like the record for grmr is around 208 vs 202 the previous year, how far out do you think record might go in this class in 5 years or so? thanks for all bits and pics.. mitch :-D
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Like this John.....
(http://i127.photobucket.com/albums/p126/Dynoroom/Modified%20Roadster/Fromshop906Small.jpg)
Yea thats it what a great idea. Whose is it and what's it for?
JL222 :cheers:
Just curious with all that unsprung weight going up and down how did it effect the traction? From looking at the shocks it looks like their is 2" of travel (1"up and 1" down). Does anybody know? It sure is an interesting set up. :cheers:
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This may sound sarcastic, but if you get a good time slip you needent worry about "too much unsprung weight".
We're all guilty of maybe because of the imperfections in Landspeed Racing of a lot of little things that may be more correct from an engineering standpoint that are violated and yet people run amazingly fast.
Good example - the frontal area violations caused by the huge scoop and zoomie headers hanging out of the 66 RDSTR! Shame, shame!
Only 249 on dirt!
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I wasn't knocking it just trying to understand the logic behind it. The parts on the BMR car are mostly determined by fuel and the engine Doug is running. When they were on gas they had a different exhaust and scoop.
The reason I ask is I am helping a friend build his rear engine car and in the phase of drawing the frame out. Its an interesting set up, just trying to figure out the logic.
"but if you get a good time slip you needent worry about "too much unsprung weight". This is like horse shoes and hand grenades, close is good enough. But if you have a clean sheet of paper why not optimize it. :-)
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Once I figured out how far the car would travel in 1/10 of a second at 270 I went back to solid suspension & Torsen.
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With all due respect to "The Racing Tea Salesman" and your informative posts, indeed unsprung weight is VERY important since TRACTION is as impostant as Cd IMHOP.
Too many examples of maximum speed on 40% throttle etc. etc.
Keeping the rubber to the road.
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"The Racing Tea Salesman" Now that's funny. :-D
I am still trying to figure out why he went with that set up. If it worked, great then it might be an option to look at. But does anyone know why it was used? The Lee Chapel stream liner used a similar set up and I am sure some others have done it also.
Tony
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I'm thinking packaging was the criteria for loading the suspension with the whole drive line.
In the '50s it wasn't too uncommen for shortening up the Ford driveline to the U-joint -had to be six spline -at the trans thus having the engine and trans hooked to the early Ford or quickchange center section input. The FRONT axle wishbone was used and attched to a pivot on the frame with the engine trans and the attached rear end now encapsulated in that package. It used a stock-type Ford rear cross spring for suspension, if you follow, on the r engine modified roadsters of the day.
An alternative today might be to turn the engine and transmission around and take a drive off the trans that would be now the FRONT over to the left or right alongside the rear-facing motor to an offset pinion on the rear housing.
You would avoid the complexity of U-jointed half shafts.The shaft off the trans past the engine has U joints of course, and you could devise most any kind of live axle linkage as required.
Been done a few times.
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interested bystander, Thanks, that was very informative. :cheers:
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Yrs truly rewoked his post above - I re-read it and realized it was hard for ME to follow!
Maguromic- "Aw, shucks."
Thanks for the kudo!
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I B dont give up- :?--inquiring minds need to know.. :-D
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Once I figured out how far the car would travel in 1/10 of a second at 270 I went back to solid suspension & Torsen.
Everybody interested in suspension should read the ''bloodhound thread'' under thrust- powered land speed information [home page near bottom]IOOmm or 4'' total bump and droop 1000 mph design.
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Like this John.....
(http://i127.photobucket.com/albums/p126/Dynoroom/Modified%20Roadster/Fromshop906Small.jpg)
Yea thats it what a great idea. Whose is it and what's it for?
JL222 :cheers:
Just curious with all that unsprung weight going up and down how did it effect the traction? From looking at the shocks it looks like their is 2" of travel (1"up and 1" down). Does anybody know? It sure is an interesting set up. :cheers:
I would think that Roy went to suspension to keep from shocking the tires [not as in shock absorbers]. With solid suspension your wheel rate [as Carroll Smith explains in his books goes to infinity!!!] RESULTING IN WHEELSPIN. Well just add weight but hang on.
JL222 :-o
Company coming might not be back today
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Adding to my post above it looks like he has suspended the engine-trans and rear end between latter bars.This enables transfering weight from front area of car to rear and to change the instant center position if he has different mounting holes for the latter bar. Same principal as ordinary latter bars but more unsprung weight to deal with.
For some that don't know, with a rear engine car and straight axel rear end there is no room for a drive shaft. A driveshaft enables the rear end to move up and down with its ujoints and to have springs and shocks. If you have an independent rearend [as in Maguromic's build] no problem.
JL222 :cheers:
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(snip. . . )
For some that don't know, with a rear engine car and straight axel rear end there is no room for a drive shaft.
I'm not so sure of that. IIRC, the Bean Bandits had a short driveshaft in this car in '06.
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This car had the entire engine, trans, and rear end all mounted on a common plane with a pivot location at the front of the engine.
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This shows the location of the pivot point. It is basically a subframe mounted within the car frame. Since there is no differential motion between the trans and rearend a greek coupler can be used.
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Here is a shot looking from the back, forward to the engine. That is the greek coupler attached to the rear of transmission. The rear end has been removed in this pic. Everything is attached rigidly together and they all move together as the rear moves up and down. The frame they are mounted to is separate from the car frame and pivots toward the front of the engine. The rear end is bolted solidly to the pivot frame very near the shocks location.
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Here is a different car that ran in '03.
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Same car but a close up. Enlarge the pic and you will see the trans under the blanket and the quick change. I think this car is pivoted toward the middle of the mass. (or the CG of the mass). That saves a huge amount of unsprung weight.
Sorry about the multiple postings but the size limit wouldn't let me combine pics in one posting. :-(