Group C replica Mazda 787B
Discussion
ceebmoj said:
what would you do for a trans-axle on the rotary engine? I have seen one matted up with an adapter-plate to an Audi gear box and the starter was in a challenging location.
Porsche G50 has the starter on the 'box side, as opposed to engine side, I believe... Not the cheapest option, mind you!I am a rotary purist (almost) and have been for 20 years plus. There has never been a point in the last 20 years i havent owned at least 1 rotary powered car and all have been modified but i can completely understand why you would go with the V8. We have built a 20B (3 rotor) RX7, RX8 powered kit car, 13b turbo powered kit car, 13b powered Vauxhall VX220, 20b first generation rx7 and i have lost count of how many 13b turbo RX7's we have modified.
A Peripheral ported 13b (2 rotor) will just about make 300 bhp if you are lucky but the power band will be more like a sports motorbike power band, will be a very lumpy idle and take some serious silencing if you want to get on track. It will also throw more fuel out of the exhaust than the Audi would use. Although the noise and revving nature of the PP is very addictive. If you go turbo route, then you can easily make 500 + bhp but you will exceed the weight of the Audi lump when you add the turbo, manifold, intercooler, wastegate etc. To give you an idea, the stock FD rx7 set up is only 25 kg's lighter than a full LS3 6.3L engine conversion
The grief of getting a transaxle to fit a rotary engine would also be costly plus the audi box has the wrong gearing for a high revving rotary. You can probably change the gear sets but again more money required.
If expense is an issue, which it sounds like it will be, throwing a rotary engine in it will cost you a lot in comparison, an ecu will be in the region of £1500 plus mapping (you can get cheaper but you get what you pay for, (the stock ECU is not mappable, the audi IIRC), a decent turbo to make 400 bhp will cost you a minimum of £500, then you need to make a manifold and buy a wastegate, boost controller, fuel rail, new injectors, big fuel pump etc etc. I would never buy a used rotary engine and just use it, i would buy a dead for a few hundred quid and then rebuild it, they are too prone to mistreatment by people who dont understand them. I have no doubt you could rebuilt it if i can. You can buy all the parts you need from Atkins rotary including a DVD on how to do it. One thing to bare in mind though is that if you put a 13b in it, it will still sound nothing like the original car as it wasnt a 2 rotor. We have a 20b (3 rotor) RX7 and it sounds very different to any 2 rotor.
If you want to go 20b then the 13g race engine that someone above has put a link to then you need £19k plus. The below is a quote from a guy on the FD owners club has posted in response to that link, he had WGT, a reputable rotary tuner, build him a 20b engine for his track RX7 "£19k seems fair when you look at what a 20B PP costs to put together properly " A bare block needing a rebuild will set you back between £2 and £3k
As most projects always have teething problems, and you never really call them finished, as we all like to keep tinkering, you could start with the Audi, get the rest of car working and then start looking into rotary power, and saving up.
Just as a side note, the most powerful RX7 in the UK at the moment is V8 twin turbo
Also, i know of a complete 13b turbo set up for sale with ecu, its mounted to a 4 speed Porsche 911 gearbox. It has all been working in the 911 before removal. That set up is capable of running upto 300 bhp as it is, depending on boost level. Not sure if it is any good to you as it is rear engine as opposed to transaxle, but it has every thing you need to make the car start and run, would just need to sort the drive shafts.
A Peripheral ported 13b (2 rotor) will just about make 300 bhp if you are lucky but the power band will be more like a sports motorbike power band, will be a very lumpy idle and take some serious silencing if you want to get on track. It will also throw more fuel out of the exhaust than the Audi would use. Although the noise and revving nature of the PP is very addictive. If you go turbo route, then you can easily make 500 + bhp but you will exceed the weight of the Audi lump when you add the turbo, manifold, intercooler, wastegate etc. To give you an idea, the stock FD rx7 set up is only 25 kg's lighter than a full LS3 6.3L engine conversion
The grief of getting a transaxle to fit a rotary engine would also be costly plus the audi box has the wrong gearing for a high revving rotary. You can probably change the gear sets but again more money required.
If expense is an issue, which it sounds like it will be, throwing a rotary engine in it will cost you a lot in comparison, an ecu will be in the region of £1500 plus mapping (you can get cheaper but you get what you pay for, (the stock ECU is not mappable, the audi IIRC), a decent turbo to make 400 bhp will cost you a minimum of £500, then you need to make a manifold and buy a wastegate, boost controller, fuel rail, new injectors, big fuel pump etc etc. I would never buy a used rotary engine and just use it, i would buy a dead for a few hundred quid and then rebuild it, they are too prone to mistreatment by people who dont understand them. I have no doubt you could rebuilt it if i can. You can buy all the parts you need from Atkins rotary including a DVD on how to do it. One thing to bare in mind though is that if you put a 13b in it, it will still sound nothing like the original car as it wasnt a 2 rotor. We have a 20b (3 rotor) RX7 and it sounds very different to any 2 rotor.
If you want to go 20b then the 13g race engine that someone above has put a link to then you need £19k plus. The below is a quote from a guy on the FD owners club has posted in response to that link, he had WGT, a reputable rotary tuner, build him a 20b engine for his track RX7 "£19k seems fair when you look at what a 20B PP costs to put together properly " A bare block needing a rebuild will set you back between £2 and £3k
As most projects always have teething problems, and you never really call them finished, as we all like to keep tinkering, you could start with the Audi, get the rest of car working and then start looking into rotary power, and saving up.
Just as a side note, the most powerful RX7 in the UK at the moment is V8 twin turbo
Also, i know of a complete 13b turbo set up for sale with ecu, its mounted to a 4 speed Porsche 911 gearbox. It has all been working in the 911 before removal. That set up is capable of running upto 300 bhp as it is, depending on boost level. Not sure if it is any good to you as it is rear engine as opposed to transaxle, but it has every thing you need to make the car start and run, would just need to sort the drive shafts.
You can do an n/a sideport 20b three rotor and make an easy 300 hp quite cheaply and still maintain mild characteristics such as low idle and drivability. As mentioned above, a p-port 20b will net you an easy 450 hp but with some sacrifice. You can purchase a decent used core 20b for roughly $3700 US and easily rebuild it and then all you would need is an ecu and a basic header. Unlike the post above, a decent ecu such as a Microtech or Haltech can be had for far less than $2000 US. W
When budget allows, put on a turbo and the supporting hardware to achieve 800 hp with the sideports and still have a very "mild mannered" car.
Kennedy Engineering makes adapter plates for anything to anything and have extensive knowledge of working with rotaries, not to mention many adapter plates in stock for a plethora of transaxles.
You can put together a peripheral port 20b with a better dry sump system for far less than that 13g mentioned above and easily make the same power. The slide throttles are nice though but there is a rotary tuner in the US who will be making those available shortly.
Take a gander over to:
http://www.rx7club.com/forumdisplay.php?f=95
For s
ts and giggles, here is my current project:
When budget allows, put on a turbo and the supporting hardware to achieve 800 hp with the sideports and still have a very "mild mannered" car.
Kennedy Engineering makes adapter plates for anything to anything and have extensive knowledge of working with rotaries, not to mention many adapter plates in stock for a plethora of transaxles.
You can put together a peripheral port 20b with a better dry sump system for far less than that 13g mentioned above and easily make the same power. The slide throttles are nice though but there is a rotary tuner in the US who will be making those available shortly.
Take a gander over to:
http://www.rx7club.com/forumdisplay.php?f=95
For s
ts and giggles, here is my current project:RobBiggs said:
Bearing in mind I was estimating 600-700kg with the Audi
thats one hell of a target, how are you going to get that light?Im building something a little heavier but along the same lines and even if you go for lightweight items the brakes, wheels/tyres and uprights etc are going to be close to 150kgs, then the chassis 100kgs, engine 150kgs, gearbox/clutch 70kgs... that leaves you only 140-240kgs for the body, glass, seats, battery, loom cooling system etc etc.
as an example Im aiming for 1100kgs wet (what my lightweight noble now weighs) and my wheels/tyres/brakes and uprights weigh 200kgs, engine 180kgs, box/clutch 90kgs, chassis 120kgs.
As I thought from the beginning, going the rotary route from the outset is going to be expensive. The Audi engine and box are a cheap and powerful package and that is what will be powering it, for now..
I must emphasise I am a massive car enthusiast and absolutely love cars such as the 787B and have been wanting to do this for ages, but I simply do not have the money that some people have to pour into a project and as such I am trying to keep expenditure to sensible levels so I can have a working vehicle sooner rather than later. However, I am not making any compromises in some areas such as the suspension and uprights which will live with the design forever but things like the engine and box combo are far more easily changed at a later date..
As for the weight questions, initially the car will be track only and as such will be lacking some of the extras you would more likely find on a road car. A road going version would likely weigh a bit more than the numbers I stated..
Weight reduction has played a huge factor in my designs. The BBS rims I have are incredibly light and with my hub & upright set-up, corner unspung weights are going to be near 30kg each. The engine without all unecessary ancillaries is going to be somewhere around the 150kg mark (I still reckon it is less than this but need to get out the scales to check). The audi box weighs around 50-60kg. Chassis weighs 120kg. Lexan front screen for the track only version.
It will be tight but I think it is possible. I have noticed that a lot of road going cars and hence replicas using their parts have hugely heavy unsprung weight at all four corners. This is why I went for my own design and where I think the weight and performance advantages will be quite significant. No worries about the comments, it's good to hear everyone's thoughts..
I must emphasise I am a massive car enthusiast and absolutely love cars such as the 787B and have been wanting to do this for ages, but I simply do not have the money that some people have to pour into a project and as such I am trying to keep expenditure to sensible levels so I can have a working vehicle sooner rather than later. However, I am not making any compromises in some areas such as the suspension and uprights which will live with the design forever but things like the engine and box combo are far more easily changed at a later date..
As for the weight questions, initially the car will be track only and as such will be lacking some of the extras you would more likely find on a road car. A road going version would likely weigh a bit more than the numbers I stated..
Weight reduction has played a huge factor in my designs. The BBS rims I have are incredibly light and with my hub & upright set-up, corner unspung weights are going to be near 30kg each. The engine without all unecessary ancillaries is going to be somewhere around the 150kg mark (I still reckon it is less than this but need to get out the scales to check). The audi box weighs around 50-60kg. Chassis weighs 120kg. Lexan front screen for the track only version.
It will be tight but I think it is possible. I have noticed that a lot of road going cars and hence replicas using their parts have hugely heavy unsprung weight at all four corners. This is why I went for my own design and where I think the weight and performance advantages will be quite significant. No worries about the comments, it's good to hear everyone's thoughts..
Keep going Rob, Just keep going.
Your 30kgs unsprung weight per corner sounds realy good. i think we got the weight on the social climber down to 19kgs per corner using the uprights shown earlier, 13" rims, non vented rotors, sliding calipers and cross ply avon acb10s which are known to be quite light when compared to radials. We could probably take more weight out but not a lot. Getting down to 30kgs with an 18" ish wheel and big breaks is fantastic
so KEEP GOING
Ryan
Your 30kgs unsprung weight per corner sounds realy good. i think we got the weight on the social climber down to 19kgs per corner using the uprights shown earlier, 13" rims, non vented rotors, sliding calipers and cross ply avon acb10s which are known to be quite light when compared to radials. We could probably take more weight out but not a lot. Getting down to 30kgs with an 18" ish wheel and big breaks is fantastic
so KEEP GOING
Ryan
30kgs in unsprung is very impressive... thats 20kgs less than mine per corner, ok I have huge brakes and 19wheels etc but rest is light...
thats the problem when you start upping the power... everything ends up getting a lot heavier to cope, box, brakes, big wheels etc etc all add huge weight.... my porsche box is 85kgs dry, but its the only thing that can take the power within my price band.
Enjoying the progress and got to say IMO stick with the audi, packaging is often key to lightness and being able to bolt the engine to gearbox with no adapter and use std clutch etc can often save weight
thats the problem when you start upping the power... everything ends up getting a lot heavier to cope, box, brakes, big wheels etc etc all add huge weight.... my porsche box is 85kgs dry, but its the only thing that can take the power within my price band.
Enjoying the progress and got to say IMO stick with the audi, packaging is often key to lightness and being able to bolt the engine to gearbox with no adapter and use std clutch etc can often save weight
At long last I have an accurate 3D model of the 787B!! Many thanks to Jun who I found on the SMCars forums and kindly let me have a copy of his hard work. If you haven't seen some of the work these guys produce it is definitely worth a look. Some of the renderings look incredibly real!
I've attached a pic of it sat over my chassis and it all looks good...
I've attached a pic of it sat over my chassis and it all looks good...
Solidworks doesn't really do it justice. Proper renderings can be found here:
http://www.smcars.net/forums/work-progress-renderi...
http://www.smcars.net/forums/work-progress-renderi...
ezakimak said:
That is goodness indeed. Shame that bloke keeps talking! lolHi everyone,
As you may have suspected,there has been no progress on the group c replica. The costs are rapidly heading skywards - wide tyres, large brakes, one-off closed cockpit body shell etc. all require lots of money that I don't have right now! I haven't given up on it though. Meantime, I've been playing around with some lower cost forms of motorsport/car modification..My Merc 190 16v that I'm making into a track toy and a simple closed wheel, bike engine powered hillclimb car that I've nearly finished designing. Info on both will be updated on my blog.
Also, I'm now working at a motorsport chassis and suspension design company. Getting to work on the likes of this:
As you may have suspected,there has been no progress on the group c replica. The costs are rapidly heading skywards - wide tyres, large brakes, one-off closed cockpit body shell etc. all require lots of money that I don't have right now! I haven't given up on it though. Meantime, I've been playing around with some lower cost forms of motorsport/car modification..My Merc 190 16v that I'm making into a track toy and a simple closed wheel, bike engine powered hillclimb car that I've nearly finished designing. Info on both will be updated on my blog.
Also, I'm now working at a motorsport chassis and suspension design company. Getting to work on the likes of this:
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