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using a 13b as a stressed chassis member

Old 06-09-03, 12:00 AM
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using a 13b as a stressed chassis member

Hi all,
was I've been checking out a hill climb / super sprint car - it is an ex- f3000 Ralt (open wheeler) using a transaxle for the trans and it features the engine as a stressed chassis member.

Are there any other cars people are aware of that are using the engine in this way? Obviously the 787 Lemans car, but that was with the 4 rotor that was built for it. Is anyone using the 13b in this manner.

To make it all fit he has replaced the front cover with a piece he machined out of billet alloy and incorporates the water hoses and front seal around the main shaft. THe engine is based on a 3rd gen 13bT and uses the stock (for the chassis) transaxle which *might* be a hewland, but I'm far from certain.

It's positively weapon like in performance.

Mark
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Old 06-09-03, 09:43 AM
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check with Tony at AWR he has a conversion kit for Ralt and Swift Formula Atlantic cars(DB-5 and RT-4/41 I believe). he has all the brackets/ headers and parts needed to convert to rotary power. he also is reproducing some of the carbon fiber and fiberglass parts for these cars.
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Old 06-09-03, 10:07 AM
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Re: using a 13b as a stressed chassis member

Originally posted by buzz
Hi all,
...features the engine as a stressed chassis member.

....Obviously the 787 Lemans car, but that was with the 4 rotor that was built for it. Is anyone using the 13b in this manner.


Mark
the 787's Did NOT use the engine as a stressed menber - They used a hybrid tub w/ a spaceframe extension to pick up the rear suspension loads
Given the "sandwich" nature of the rotary engine design I dont think it is well suited to being a stressed member. at the very least it would need to be dowel pined and assembled w/ uprated tension bolts.
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Old 06-09-03, 10:25 AM
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I find it hard to believe anyone uses a 13B as a fully stressed member. Seems the 13B with its "sandwich" construction and through bolts would have absolutely terrible torsion characteristics if you try too feed suspension loads through it?

I have a close friend who runs a Ralt with a 13B and the motor is most definately NOT fully stressed. Are there other setups?
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Old 06-09-03, 11:49 AM
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I think the car he is talking about has a "semi" streessed engine like a formula atlantic. suspension is mounted to transaxle and engine has several brackets holding it to the main bulkhead. the 13b or 12a should work fine for this type of application.

Last edited by tims; 06-09-03 at 11:51 AM.
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Old 06-09-03, 05:49 PM
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THanks for the AWR link - I hadn't come across formula Atlantic details before, but I think I'd heard about it. This car is an ex f3000 that then became an Australian domestic series "formula holden" which is based around the f3000 chassis and the Holden v6 engine, a local derivative of the buick v6 from about 15 years back.

I'm pretty sure its fully stressed (ie no more baracing from the bulkhead to the trans) but I'll try and check my pics - I'm bugging a friend to post up on his site some pics of it.

Like I said, it is silly silly fast and power is held down to relatively low boost levels as it smokes the wiiide rubber at will.

Altantic looks cool... can I guess that with a 12a bp and open headers they sound great?
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Old 06-09-03, 08:43 PM
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Tony is a fantastic fabricator and a former mechanic of the year in IMSA with the Nissan prototypes. crew chief for Geoff Brabham I believe. He would know what could and couldn't be done with your car. shoot him an email. he loves rotaries and open wheeled race cars.
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Old 06-10-03, 07:26 AM
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Originally posted by buzz
I'm pretty sure its fully stressed (ie no more baracing from the bulkhead to the trans)
A fully stressed v-6 I bet it does have. A fully stressed 13B I don't think will work.
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Old 06-10-03, 09:09 PM
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I've been checking my photos - it looks to be sitting between the bulkhead and the transmission with nothing else supporting, bracing or even cheering on the transmissing, suspension or rear wing.
The rear suspension is braced and triangulates to the transmission and the rear wing hangs off the back of the trans. He has machined up a nifty adaptor plate to mate the trans to the back of the 13b.

I'm hoping to visit their workshop late this week to discuss gearbox options for my 1st gen, and have a look at a Renesis they are apparently sectioning for Mazda Australia, so if he is there I'll get the definative word.

I am still bugging my other friend to host up some pics, pity mine aren't digital.

So, back to the question - no one can think of anybody using a 13b engine as a fully stressed chassis member. He did say that everyone told him it wouldn't work either...
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Old 06-10-03, 11:55 PM
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Any motor can be used as a stressed chassis member. It is just not a good idea. Look at how the 13b is held together. It has bolts running though it's entire length holding it together. It is not 1 beefy cast piece as most piston engines are. Formula type cars are very light so it might not see much loading but I stile don't think it is a good idea. Even if you could run stress calculations, you won't know until you try it. An awful lot of time in design to end up splitting your motor and having to starat from scratch.
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Old 06-11-03, 12:43 AM
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I was going to do this with my 20b in my 2nd gen. Basically the plan was solid mounts and incorporating it into the stut towers and firewall essentailly making it a stressed chassis member. The engine has a 3/4" billet sump plate with tapped out threads to accomodate larger bolts. Thought that would negate any twist. Was heavily advised against solid mounting etc. by the engine builder and then thought about how much I spent on the build. Didn't take long to convince me. It is more of a problem or potential problem for 3-4 rotors even though they apparently run smoother. Can run solids on dowelled 13bs with no worries he told me. There are quite a few rotary powered transaxle racecars out there obvoiusly.
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Old 06-12-03, 08:20 PM
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I don't think the odd number of rotor engines are as inherently well balanced as the 2-rotor (or 4-rotor) engines. That may be the reason for the advice not to rigid mount it to the chassis.

Back to the real issue... making a rotary a fully stressed member seems like a bad idea to me. Just because it works doesn't mean it is a good idea. It seems like it would make the car impossible to setup as it moved around, and it seems like it would kill the engine quickly, too.

-Max
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Old 06-12-03, 09:43 PM
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RX_Heven - I know a heap of people with solidly mounted engines in normal street chassied cars, just mounting the gearbox on a normal rubber mount seems to make it all work fine. Usually they have either replaced the rubber mounts with solid machined urethane or alloy chunks, although one nutter (timbo - aka 4sfed) has had an engine plate made to bolt to the front of his engine and then had the front cover machined to fit over this (the car is a ta22 celica, www.fastfours.com.au should have pics ).

The idea of it being a stressed member in this application is that the whole back of the car (transaxle, wings, etc) bolts onto the back of the engine and the engine is what solely ties the front to the back.... no other bracing or chassis components.

AFAIK, he has yet to kill an engine and he has put some hard work through this chassis on a number of racetracks.
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Old 06-13-03, 07:59 AM
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Originally posted by buzz
The idea of it being a stressed member in this application is that the whole back of the car
That's not truly a stressed member, that's a solidly mounted motor. In racecar terms a stressed motor is having chassis loads actually fed through the block. You could make the argument that your friends arrangement does this, but it is not really contributing to chassis stiffness.
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Old 06-13-03, 08:24 AM
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precisely: stressing the engine block in a sports car is a pretty dumb idea when you already have a full chassis there (and all of its incumbent weight) to deal with that load. reinforce the chassis, don't comprimize performance when you don't have to.

Originally posted by 80-CU.IN.T
Formula type cars are very light so it might not see much loading but I stile don't think it is a good idea.
um... *cough* not quite. it can be done: with the right big-*** super strong dowels and bolts (or get creative with studs??), as RX-Heaven was saying a really beefy sump pan (etc.), you can MAKE it strong enough to use. you'd be adding mass to the engine, but it would still end up smaller and lighter than a piston variant, with as much power (at least).
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Old 06-13-03, 04:30 PM
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Originally posted by DamonB
That's not truly a stressed member, that's a solidly mounted motor. In racecar terms a stressed motor is having chassis loads actually fed through the block. You could make the argument that your friends arrangement does this, but it is not really contributing to chassis stiffness.
Correct

Also, not that I know from personal experience, but since the 20b is seperated by 120' and a four rotor by 90'(?), wouldn't that make it run smoother than a 13b seperated by 180'? People I have talkked to that have/do run three rotors also say they are smoother, not to mention my engine builder agrees.

Last edited by RX-Heven; 06-13-03 at 04:35 PM.
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Old 06-13-03, 04:40 PM
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Originally posted by buzz
RX_Heven - I know a heap of people with solidly mounted engines in normal street chassied cars, just mounting the gearbox on a normal rubber mount seems to make it all work fine.
Are these all drag cars and how many are rotary powered.
We used to run a 700 hp big block in a 66 Chevelle with solid mounts. Chased cracks all over the car.
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Old 06-14-03, 12:33 AM
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Originally posted by wakeech
precisely: stressing the engine block in a sports car is a pretty dumb idea when you already have a full chassis there (and all of its incumbent weight) to deal with that load. reinforce the chassis, don't comprimize performance when you don't have to.

--------------------------------------------------------------------------------
Originally posted by 80-CU.IN.T
Formula type cars are very light so it might not see much loading but I stile don't think it is a good idea.
--------------------------------------------------------------------------------


um... *cough* not quite. it can be done: with the right big-*** super strong dowels and bolts (or get creative with studs??), as RX-Heaven was saying a really beefy sump pan (etc.), you can MAKE it strong enough to use. you'd be adding mass to the engine, but it would still end up smaller and lighter than a piston variant, with as much power (at least).
Typo- should read (as much loading.) I never said it could not be done. I said it wasn't a good idea because of the design of the 13B. ( To make it short ) If you want to machine a Billet sump, Dowel pin, find expensive studs, ECT, ECT, ECT - go for it. Just about anything can be done with enough cash, time and dedication. It would be an awesome combo. I am a rotary nut now, Unfortunately. Do what you want. I stile don't think it is a good idea to use the 13B as a fully stressed chassis member. It just isn't / wasn't designed to take all that torsional loading.
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Old 06-14-03, 01:03 AM
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When Mazdatrix was putting a 13b turbo into a Miata they realized the Miata 4 banger was a stressed member of the chassis and took a lot of work to reinforce the chassis when the beer keg motor went in there.

There's better ways to reinforce the chassis than tie it to the motor . . . . like 1" square tubing!
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Old 06-14-03, 03:45 AM
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Originally posted by RX-Heven
Also, not that I know from personal experience, but since the 20b is seperated by 120' and a four rotor by 90'(?), wouldn't that make it run smoother than a 13b seperated by 180'? People I have talkked to that have/do run three rotors also say they are smoother, not to mention my engine builder agrees.
Smoother power delivery, yes, but that is different from engine vibration. I searched around on the internet for information on the topic, but didn't find anything about three rotors. My intuition tells me that they aren't as well balanced as engines with even numbers of rotors since the eccentric + counterweights can't be symmetrical. It seems that you would automatically get more vibration that way. The power delivery will be smoother since it fires more often, but the engine will vibrate more as it runs if my intuition is correct.

The picture that was posted does look like the engine is a fully stressed member. If the suspension is attached to the tranny, that is attached to the engine, and those loads go exclusively through the engine to mount the assembly to the front of the car, that seems fully stressed to me. Maybe it does work with appropriate dowel pins and heavy duty tension bolts. It just seems like that is a lot of load to put on the tension bolts. With a piston engine block, you have one big hunk of metal to carry the load. With the sandwich design of the rotary, that would seem to put huge stresses on the tension bolts.

-Max
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Old 06-15-03, 06:27 PM
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buzz said
... in this application (is that) the whole back of the car (transaxle, wings, etc) bolts onto the back of the engine and the engine is what solely ties the front to the back.... no other bracing or chassis components.

and from MaxCooper
If the suspension is attached to the tranny, that is attached to the engine, and those loads go exclusively through the engine to mount the assembly to the front of the car, that seems fully stressed to me.

but from DamonB
That's not truly a stressed member, that's a solidly mounted motor. In racecar terms a stressed motor is having chassis loads actually fed through the block.
We might be disagreeing about the same thing. You have front half of car all the way to the bulkhead behind the driver. Engine bolts to bulkhead. Trans bolts to engine. There is nothing structural linking any component (eg trans, rear suspension, rear wing) to anything forward of the adaptor plate on the back of the engine. So...., yes, it is a solidly mounted motor - and the trans is solidy mounted onto the back of it and collectively it all forms a chassis.


And re solid mounting....
Are these all drag cars and how many are rotary powered.
Some drag cars (10SecRX7 / Dale, for example), with the usual 13bT combo's, although 3 people I know with Rally cars (rx5/cosmo, and 1st gens) have them solid as well. The Rx5 guy had broken "normal" mounts and finished a race with the engine wobbling around in the engine bay. hmmm.... would mounting solidy to a chassis x-member would likely be less straining on the front end than mounting a torque monster directly to chassis rails?
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Old 06-16-03, 10:06 AM
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this is the same setup used in formula atlantics(bulkhead-engine-transaxle with suspension). debating whether this will work without any experience with this type of racecar is ridiculous. contact some of the race shops who have done these conversions. there or 10-12 of these cars racing regularly in national SCCA racing. it seems to work for these cars without any crazy dowel pins or billet sumps. all are dry sumped for clearance but nothing to terribly special.
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Old 06-16-03, 06:08 PM
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OK, thanks all. Now I can pass on to the owner of the car some details of who else is doing similar work.

Here is a crummy pic (well, in terms of detail)


On the left you can see the inlet, turbo and exhaust, over the right is the IC. I'll try and get someone to scan some other pics I have showing proper rear end detail and the layout.

Mark

Last edited by buzz; 06-16-03 at 06:15 PM.
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Old 06-16-03, 10:56 PM
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that Ralt looks very similair to the Swift DB/4
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Old 06-16-03, 10:59 PM
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that Ralt looks very similair to the Swift DB/4 obviously they are not the same but very similair
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