Hi,

I am asking myself how driveable seven kit cars are with a turbo charged bike engine and with an output of around 300hp?

If I am driving a normal sport car (not a seven) at its limits I rather prefer to drive a NA powered car and not a turbocharged one.

Will a seven be difficult to drive at its limit with a turbo charged bike engine?

How smooth and linear is the power delivery? How noticable is the lag? How is the throttle response?

I already learned that increasing the power doesn't make a car always better and more enjoyable to drive.

Furthermore I am asking myself how well bike engines and their gearboxes cope with the additional stress due to the turbo?

I am looking forward to read first hand experiences from bec owners with a turbo.

Mine drives fine. 205bhp from a 1.6 mazda turbo. ECU boost controller, so the power is delivered very smooth. Small TD04 turbo so there is very little lag.

Generally speaking as i understand 200BHP is about the limit of the power you find usable with a seven type car. Bike engines are very light so the pwer to weight is crazy. I have been in bike engined cars and they are crazy but for me track day cars of occasional loon machines. I like a car i can use all day everyday so i am going down the zetec route. Lots of guys on here had more experience with them and i am sure they will add more.

Take a look at this thread

link

I think it covers most aspects of what you are considering, as usual there are views both ways, but I am very inclined to agree with Matt above, that if you have a light car, anything over 200BHP, particularly with good torque is going to be fairly mental!

I have just over 220bhp and a nice slug of Torque in a na car and find in great on and off track,
with a turbo setup the key would be power delivery esp with light cars.

I've just got my car on the road. 252bhp and 300 ish ft lbs. Starts boosting below 2000 rpm so very little lag. It's got the best of both worlds. If you want to crack on it's mental quick and gives you the grin factor everytime. Or if your taking a leisurely stroll stick in in 4th and drive it like an auto.

Not a bec but you get the idea although I can imagine a 300bhp bec being insane and with the added lightness an animal to control. I'd suggest unless you spend ££££ to build a top spec motor you'd have to treat the engine like a consumable item! The gearbox would also need to cope. Not impossible though as there are plenty of busas out there running chargers.

Personally I think sticking a turbo on a BEC these days for a road car is overkill and completely unnecessary. Unless on track I really don't think the extra power / torque will get used. With the latest modern superbike engines giving 170+ bhp then this should be plenty to handle for most drivers - they're flippin quick!! Stick something like a CBR1000RR or Zx10r in, or if you want more torque lower down then a busa or ZZR1400 and I recon it'll be more than enough.

Small turbos on a car engine make more sense to me where they can be set up to give the near instant boost from low revs - like the Ecoboost above.

I think you probably answered your own question when you say you prefer to drive at the car's limits with an n/a engine. A BEC is all about high revs and light weight for me - and already totally different to a normal sports car. Add a turbo and it will be insane to drive and I doubt you'd get anywhere near the limits on the road.

I'd say if building a BEC then keep life simple by picking an appropriate engine to what you're looking for from it - especially if this is your first se7en style car

Thanks for all the replies but can we please concentrate on turbo charged bike engines in this topic.

I noticed that some are basing their advise on turbo charged car engines.

I think the differences between these two engine concepts are to great to compare them.

I am aware that on mountain or normal backroads a 200hp bike engined NA Seven is more than enough.

My only concern is that I would also regularly like to use the Seven on large high speed tracks.

Hence I will probably not be able to keep up with traditional cars which have ~300hp (e.g. Megane RS) on high speed sections of a race track.

Obviously I would be much quicker in corners and can brake much later which can offset a lower speed in high speed sections to a degree.

My bec doesn't have an exhaust manifold yet and it needs to be custom made.

Hence I considered to turbo charge the engine straight away as a turbo exhaust manifold is easier to fabricate compared to a good NA exhaust manifold.

If I want to upgrade to a turbocharger at a later point of time I will probably have to sell the expensive N/A manifold for cheap as it is custom made for my seven.

Please also take the drivers weight into account if you calculate the power to weigth ratio.

Especially with a light BEC the drivers weight can mess up a good power to weight ratio pretty quick!

The lighter the car, the more the drivers weight will contribute to the power to weight ratio.

Anway, are there any other seven owners with a turbo charged bike engine which can contribute to this discussion?


Edit: Thanks for the link to the other thread russboost, interesting read!

[Edited on 19/5/17 by reb]

Problem with seven style cars is aerodynamics you need a decently high bhp output to get past 135mph what circuits are you driving it on ? Remember these are trackdays not a race I had more fun in my striker with 140 bhp keeping up and and passing cars with much more powerful engines there's a massive difference in driving a well set up seven on track compared to much heavier more powerful cars on track .

[Edited on 19/5/17 by ian locostzx9rc2]

To a degree? Driven properly, a 170-200bhp BEC should be fairly regularly lapping a typical road going 300bhp Megane etc. Whilst you might lose out slightly above 100mph once drag becomes a bigger issue, you should already be so far down the next straight that they wont be catching you. Which tracks are you looking at?

Dont forget that if you do decide to turbo the car (either now or later) that you'll be needing a longer final drive to get more top speed anyway. That could add quite a lot to the build cost also if you're looking for a 3.14 Sierra diff etc.

Do you already have an engine at the moment?

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Originally posted by reb

My only concern is that I would also regularly like to use the Seven on large high speed tracks.

Hence I will probably not be able to keep up with traditional cars which have ~300hp (e.g. Megane RS) on high speed sections of a race track.

Obviously I would be much quicker in corners and can brake much later which can offset a lower speed in high speed sections to a degree.

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I've never seen a Dyno graph to show how the torque rises on a turbo bike engine which would give you a good idea as to how driveable they might be on track especially in poor grip conditions . Mines a twin turbo v8 and the torque curve is very flat from 2000- 5500 and is pretty good on track as the power although too much is easily controlled .

Adding to the experiences of everyone else, owning a MK Indy with a zx10r lump was an amazing experience. The pure pedal factor of having 12k rpm at your disposal is more than enough to keep you happy when the roads are dry enough to exploit.

Relaying back to your original question.

Reliability... Very good providing the engine is baffled and sumped correctly.
Driveability.... Absolutely awesome if you have clear roads and the car setup is perfect..

Referring back to the link I gave earlier & your particular questions regarding high speed circuits etc. I think one major point you need to consider is what is the lowest diff ratio you can get & what size tyres you are going to be running.

One of the reasons BEC 7's struggle at much over 120/130 MPH is certainly aerodynamics, but also a lot of cars with lower diff ratios (great for acceleration IF you have the grip to get the power on the floor) simply run out of revs

With the Furore I don't seem to have the same aero problem, but I've still never pushed the car over 140mph simply because I'm quite keen on staying alive! I'm running a 3.28 diff with 255/45/17 rear tyres, so it's actually slightly higher geared than it was in the bike, at 140 it's still pushing you hard in the back & I really don't know how much quicker it would go, at 140 it's doing around 9500rpm in 6th which is where max power is, but the power doesn't drop off significantly until 11,500, the standard "max revs" which would give a theoretical top speed of 170 Gulp! - I very much doubt it would ever get there & have no particular wish to find out!

In the other link I point out that the more grunt you get out of an already fairly highly tuned engine the more reliability you will lose & the more expensive it gets when it finally goes "POP", how long will a turbo'ed bike lump last being held at max or nearly max revs down a high speed straight?

As people have already said,if it's top end speed you want a turbo won't alter that,as the gearing and engine max revs will still be the same as the standard bike engine.

I'm currently turbo charging my R1,why I don't know!As it was easily fast enough for what I use the car for.
The tracks I use it doesn't run out of top end revs/gearing.
But I wouldn't want to use it on say the ring/Spa etc,no fun holding a BEC flat out at high revs IMO.
They are all about acceleration,ideal tracks you won't see over 120mph top end for a few seconds

I'm currently on with supercharging a Westfield Hayabusa, I decided to go S/C rather than turbo for the linear power delivery, I'm looking at 350+bhp from the finished article and will be able to give you an idea on how controllable the car is once I get it around the track, hopefully 5th of July. I agree with what most people are saying on here though, with the standard busa engine in on a 3.1 sierra LSD I was overtaking pretty much everything on the track.. Why did I got for double the BHP then? because I can .. I do plan on using a traction control system and running slick on the track to assist with traction as much as possible. On the road I think I'm going to have to be pretty careful with the right foot.

Isn't one answer to use an aftermarket ECU with dual maps (or more)? I have motec electronics and can make changes to the map from the steering wheel. Motec has a information sheet which suggests that a 10 position switch can be set up for "allowing your mate to drive" and "valet parking". With an electronically controlled boost valve you could basically switch between naturally aspirated and turbo.

I am assisting a mate with a twin turbo 964. Its a dog and has blown up every time it has been used (at vast expense). Having blown up the turbo bottom end we are doing a temporary bodge fitting the turbos to a N/a engine. To get away with this the boost control will be coming in seriously early....in other words the turbos will be for decorative purposes only until the original engine (with low compression) is fixed.

Good point regarding the limitation of the gearing.

I recommend everyone who is concerned with top speed and wants to run small tyres ( 13" ) to convert to a BMW diesel diff.

As it was noted here the longest Sierra final drive ratio is only 3.14 and is very rare.

BMW longest, smallest (168) BMW diff has a final drive ratio of 2.47 (118d E87), and there is also the option of a 2.65 final drive ratio (116d, 118d, 120d - F20), as well as an 2.79 final drive ratio from the E36 318 tds.

BMW diesel diffs are not hard or expensive to come by, the smallest case (168, 168L, 168LW) is also not very heavy (~25kg).

However converting these open diffs to a limited slip diff isn't easy, at least the E36 318tds diff with which I am currently messing around.

I can report more about converting such a diff to a limited slip one, once I am done.

The car would be geared to a max speed of ~ 155mph with 205/60/R13 tyres and a 2.79 final drive. This should be well suited for a 200hp NA bike engine (2nd gen Hayabusa).

Furthermore some who commented regarding the poor aerodynamics of Seven kit cars are on point and this is another huge factor for the top speed.

Kit cars designed by Jeremy Philips with a full bodywork will have a great advantage on high speed race tracks.

The racetracks in question for me are the Nürburgring and Spa.

Here is an interesting comparsion between a Donkervoort D8 RS, Porsche 996 GT2 and the new BMW M2 coupe:



The Donkervoort weight is 1/2 of the Porsche but it needs 2/3 of its power to be quicker. However the Donkervoort has normal sport tyres and the Porsche has semi slicks. The BMW M2 has the same power as the Donkervoort, better aerodynamics but weights 1520kg.

Check out the front splitter, rear diffusor and spoiler of the Donkervoort to keep this thing planted:

Be worth your while calculating your speeds in gear with your chosen engine as 1st could well give you almost 100mph!! 🤔🤔

3.38:1 for me with a CBR1000rr. It's what the RGB racers use in my car so no doubt the overall fastest overall ration for U.K. circuits in my car (more aerodynamic than a se7en)

quote:

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Originally posted by Paul_Arion
Be worth your while calculating your speeds in gear with your chosen engine as 1st could well give you almost 100mph!! 🤔🤔

3.38:1 for me with a CBR1000rr. It's what the RGB racers use in my car so no doubt the overall fastest overall ration for U.K. circuits in my car (more aerodynamic than a se7en)

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quote:

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Originally posted by froggy
I've never seen a Dyno graph to show how the torque rises on a turbo bike engine which would give you a good idea as to how driveable they might be on track especially in poor grip conditions . Mines a twin turbo v8 and the torque curve is very flat from 2000- 5500 and is pretty good on track as the power although too much is easily controlled .

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