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Locost frame rigidity help
shevalev - 5/7/16 at 03:26 AM

Hello all,
I am new to this forum, but currently i am in a dilemma on whether or not I need to reinforce the chassis anymore. So the purpose of this build is to place the largest engine possible with a 6 foot 5 tall person into the smallest car. I have just finished building the engine and it's a 468ci big block chevy with 11:1 compression pulling 642 hp and 607 foot pounds of torque. I do have the F.A.S.T. XFI 2.0 installed and all is ready to run. I am planning to mate a T56 transmission to this block. So what had to be done to the chassis to fit the block was adding the McSorely 442 seating area width, Chris Gibss' rear independent suspension widened by 50.4mm and also elongating the passenger area and the engine bay by around 200mm. Thankfully, for simplicity, I will be incorporating Chris Gibbs' book front and rear suspension mounting points. So far I have been running torsion tests and kept on adding in beams to reinforce it. With the current design, I have managed to achieve 4688.3 lb*ft/deg without the R- tube. There simply is no space for it. You can find my designs of the chassis on https://grabcad.com/library/locost-1 and I was wanting to get some input on some unnecessary beams or some that i could add in. The suspension mounting points and engine dimensions are marked with the long construction lines. Here are the attachments. Thank you all for your help in advance.

Here is the link again.
https://grabcad.com/library/locost-1

benchmark51 - 5/7/16 at 06:02 AM

Sorry, but I think I may be missing the point of what you are trying to achieve. Is it a frame to house a gargantuan engine to use as a dragster or a lightweight, well handling car. I love the sound of a V8 but I reckon an up to date 4 potter is all you need in a 7. Also rigidity in a chassis isn't the only consideration. A degree of flexibility is good too.

shevalev - 5/7/16 at 06:08 AM

The idea is to place a huge engine inside. I do know that a 4cyl is sufficient enough, however, I have this engine already, it has been in my Lamborghini Diablo kit car and since the block has just been rebuild, it would be a shame for me not to use those extra horsepower. I have scaled the block and shredded off as much weight as i could and now i managed to get it down to 500 pounds with all of the accessories. The help that i need is to see if there is any other possibility to efficiently make this chassis handle this weight and torque.

sebastiaan - 5/7/16 at 06:20 AM

Can you do y-braces instead of the R tubes? Like so (not my car):


Mr Whippy - 5/7/16 at 06:40 AM

Welcome to the forum

Well you can build whatever you want off course but this car does sound totally overpowered and very over weight to be any practical use on the road assuming it doesn't just fly off it and I suspect it would in reality be a much more fun car to drive with less. Are you just planning on using this as a drag strip car as that seems to be its best use? and how large is the fuel tank going to have to be to make it to the next filling station? 7 fuel tanks are usually very small it won't be very good if it only does 20miles and then need filled up again. I'd also be concerned about how you would cool such an engine, there not much radiator space in the nose of a 7.

I've seen plenty of cars with enormously large engines fitted just think of Jay Leno's tank engine car , mostly for a laugh but I doubt they really get any use due to the shear impracticality of using them and trying to keep so much power on the road. Not saying it’s a terrible idea and I'm sure its a lovely engine but does seem a very problematic engine choice and really misses completely the whole concept of the 7 style car.

benchmark51 - 5/7/16 at 07:47 AM

There is a seven with a V8 owned by a member of Bristol Kit Car Club, it is used on the road but not sure it has any advantage over the duratecs ect. Heat can be a problem in any seven even a 1300 xflow can get hot and my 2L needs extra air flow too. I have a fancy for a Thruxton GT (Healey shape) and a V8 would fit in there nicely. Lots of V8's in cobra's some with jag suspension/axles, which would seem to me to be more suited?

Sam_68 - 5/7/16 at 10:24 AM

The short answer to your question is that, if you are already achieving almost 4,700 lb.ft/degree, then your torsional stiffness is adequate if you're are running road tyres (albeit I assume your figures are calculated, as it's impossible to test to an accuracy if 0.1 lb.ft/deg).

Ultimately, the tyres act as a 'fusible link', and it's impossible to impose more torsional load on the chassis, from the engine, than the rubber is able to react into the tarmac.

The chassis still won't 'efficiently handle the weight and torque', however, as the single, concentrated mass of the engine, and the fact that in a car with such low overall weight you'll have enough torque to break traction involuntarily with very little provocation, will mean that it will swap very unpredictably between understeer and oversteer, if you try to press on. And as benchmark said, there's more to chassis design than torsional stiffness.

The sensible approach would be to either put the engine in something more appropriate, or sell the engine and use it to fund an entire build with a more suitable power unit.

shevalev - 5/7/16 at 10:58 AM

Thank you guys for your promt replies. I have been fiddling around with the chassis and have managed to bring its torsional stiffness up to 6400 Lb*Ft/deg. So just to clarify, the purpose of this build is for high speed racetracks without many sharp corners. I am from Canada, and we have plenty of land and long straightaways to lay all of the power down. I did most of the planning of the drivetrain components and i managed to get the car to be at 1816 pounds with me inside it wet. The weight distribution is still being worked on since i am waiting to rip off some suspension parts off on my kit car. I believe it has fiero spindles, but ill have to make sure. If you guys have any ideas for anymore improvements regarding the chassis design, please let me know.


[Edited on 7/5/16 by shevalev]

Sam_68 - 5/7/16 at 11:03 AM

quote:
Originally posted by shevalevIf you guys have any ideas for anymore improvements regarding the chassis design, please let me know.


Put the engine at the back, where its mass will help with traction.

slingshot2000 - 5/7/16 at 11:46 AM

quote:
Originally posted by Sam_68
quote:
Originally posted by shevalevIf you guys have any ideas for anymore improvements regarding the chassis design, please let me know.


Put the engine at the back, where its mass will help with traction.


Brilliant !

[Edited on 5/7/16 by slingshot2000]

Schrodinger - 6/7/16 at 10:17 AM

Maybe you have missed the point of a 7, it was designed in the 50/60's for twisty tight circuits where power was by today's standards quite low. The point here being that aerodynamics were not important. A 7 has the aerodynamics of a brick so even with a modern engine is unlikely to exceed 140 mph and on long straights as you are talking about would be passed by most modern sports saloons. If you then don't use a 7 style body but something more slippery why constrain yourself with the 7 chassis?

MikeR - 6/7/16 at 11:12 AM

If you're still trying to raise the stiffness then someone on here did a v6 4x4 (not sure it was ever finished - i think it was someone called liam). They couldn't fit in the engine triangulation so they made a bolt on structure that went over the engine to triangulate.

As a design exercise / I want to do it bragging rights - this sounds great, but as others have said this may not be the best use of the engine / chassis and you may end up disappointed.

Also, i recall someone fitted a dodge viper engine into a modified seven. If you go onto google and search for "viper site:www.locostbuilders.co.uk" (without the quotes) you may find some interesting stuff as that chassis was strengthened.

Also, look at clubman racers - they do a more aero bodywork for our type of cars. It may help get it faster / keep it pointing where you want it.

Sam_68 - 6/7/16 at 11:14 AM

quote:
Originally posted by Schrodinger A 7 has the aerodynamics of a brick...


That's actually very unfair on bricks - the Seven's aerodynamics are much worse!

Very valid point, though: even in the 50's, the Seven only came into existence because the curvy, aerodynamic bodywork of the Eleven was too expensive for cheap clubmen when formed in alloy. The Eleven actually came first, and the Seven was a later, budget version of it with simpler bodywork on essentially the same chassis. We've got fibreglass these days, so the limitation no longer applies.

And if you go for aerodynamic bodywork you'll almost certainly have big, boxed-in sills that can be used to enclose 'pontoon' torsion box structures down either side of the chassis, which can massively increase your torsional stiffness.

Ivan - 6/7/16 at 12:04 PM

Your proposal will end up with a car very similar in all masses to a Cobra replica and they work just fine in the handling department when properly set up, even with much lower torsional rigidity than you are talking about.

The difference is the Cobra is a brick aerodynamically and I think the Locost is even more of a brick so will in all likelihood have a lower top speed.

At the power level you are talking about traction is a problem in any car but the right choices in diff ratios, diff locking type and tyre sizes and type can help make it easy to live with.

One thing to think about - you are putting a lot of effort into a car that might have poor to zero resale value.

Slimy38 - 6/7/16 at 12:55 PM

quote:
Originally posted by shevalev
So the purpose of this build is to place the largest engine possible with a 6 foot 5 tall person into the smallest car.


Just picking up on this particular statement, I'd agree with sam_68 and start considering a rear engined car. You then have a few more options for aerodynamics, and you could probably keep most of your existing development work.

If it's good enough for most sports car manufacturers, then who's to argue?!

ettore bugatti - 6/7/16 at 09:18 PM

Put a roll cage in and you will roughly double your stiffness.
Steel welded floors do help, but I dont know if it contributes a lot.
Oh, and shorten the wheelbase. (but that might not be a good idea for other reasons :cool

britishtrident - 7/7/16 at 07:31 AM

I muttered an expletive I read "big block Chevy" ----
However aginst my better judgement a link for Cymtricks chassis mods.

http://locost7.info/mirror/aussiemods.php

[Edited on 7/7/16 by britishtrident]

shevalev - 7/7/16 at 07:57 AM

Okay, so the roll cage is not a bad idea. I do have to say that. So I have made a model with all of the aussie mods in it, and at this point of time, the chassis that I currently have is more reinforced. I do like some of the beams that were added and i shall incorporate them in my model. Secondly, I have found that there was a viper engine put into the locost. Does anyone know what chassis that was and if any widening of the front end was done to fit the motor in? Here is the link. http://www.locostbuilders.co.uk/viewthread.php?tid=143342
Any explanations on what that viento rolling chassis really is? Thanks all

motorcycle_mayhem - 7/7/16 at 10:05 AM

quote:
Originally posted by shevalev
. I am from Canada,


I kinda guessed that, either Canada or Trumpton, all this talk of large Chevy engines.

I understand you're looking at the engine bay, but just one comment about the rest of the car. When I had a Westfield, a few years ago, the factory gave me some pretty interesting torsion figures for the car with (and without) the T45 Caged cage. I can't remember the figures, sorry, old age (and probably too much alcohol) have destroyed a few billion brain cells, but it was a significant difference.

Mr Whippy - 7/7/16 at 12:12 PM

quote:
Originally posted by shevalev
Okay, so the roll cage is not a bad idea. I do have to say that. So I have made a model with all of the aussie mods in it, and at this point of time, the chassis that I currently have is more reinforced. I do like some of the beams that were added and i shall incorporate them in my model. Secondly, I have found that there was a viper engine put into the locost. Does anyone know what chassis that was and if any widening of the front end was done to fit the motor in? Here is the link. http://www.locostbuilders.co.uk/viewthread.php?tid=143342
Any explanations on what that viento rolling chassis really is? Thanks all


that thread is a quite a good example of what can go wrong with a project like this.