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wheel choice big power seven
Dan. - 16/2/15 at 09:16 AM

Hi all, as some of you know I'm building a sequencual turbo saab powered indy. With all this power and torque I know getting the power down is going to be an issue. ...

unfortunately my brakes mean I can't go for the usual recommended 13s and wide tyre choices in this rim size are somewhat limited. So I'm looking at 15s... can get some 15 X 8.25J et0 at a very resonance price, obviously won't be the best wheels in the world in terms of quality but I can change them later.
How will these affect my handling running et0? And will 8.25j all round cause problems? Obviously I will require some bodywork modification but I'd rather do this than spend out 1.2k+ on a set of custom split rims atm.

Suspension wise the car is fully rose jointed front and rear. The rear suspension has been modified to raise the roll center slightly to decrease roll and improve camber in roll, the front suspension is standard but the front chassis has been significantly strengthened.

INDY BIRD - 16/2/15 at 09:28 AM

with that size of tyre on the front it will cause tram lining for sure so you probably dont need that big on the fronts etc, but rears i ran a 9" on mine with 0 offset on 235 tyre and a 7.5 on the fronts with 215 tyre no issues.

hope that helps

sean

Dan. - 16/2/15 at 09:33 AM

Thanks that's good to know, ideally I would have smaller fronts but staggered 15s Iin 4x108 don't seem that common ill keep looking but least these are an option.

steve m - 16/2/15 at 01:08 PM

Just for info, I used to have 13 x 7 with 205 tyres on my 7, handling and tram lining was awful
there now 13x6, 185/55 and its like driving a different car,

JMHO

steve

Dick - 16/2/15 at 04:50 PM

Ash that had the saab with a hb turbo used to run 195 70 15 on his and never had a problem think he was on 7 or 7 1/2 rims he all ways seemed to be able to put the power down

Dan. - 16/2/15 at 04:54 PM

quote:
Originally posted by Dick
Ash that had the saab with a hb turbo used to run 195 70 15 on his and never had a problem think he was on 7 or 7 1/2 rims he all ways seemed to be able to put the power down

guessing he didn't have over 400hp with very little lag? Even with big tyres I'm not expecting it to put the power down well but want to give it a fighting chance.

Dick - 16/2/15 at 04:57 PM

Oh im sure he will be along soon to tell you different , wide tyres give low ground pressure so you can end up going backwards in grip if they are to wide

steve m - 16/2/15 at 06:20 PM

ive been in ash car, bloody quick !

steve m - 16/2/15 at 06:23 PM

If still doubting ask Hicost, as he had 400bhp + and then nitrous, 650 at the wheels I believe

another car ive been in, and warp speed quick !

Dan. - 17/2/15 at 12:33 PM

Have spoken to hicost

He uses 265 x 40 x 15 on the rear and 235 on the front or 225 on the fronts and 245 on the rear.

Pat_T - 17/2/15 at 01:04 PM

No!

Whatever you do don't put that much tyre on the front you'll ruin it.

Even the Caterham 620R runs 185 fronts!!

I had 200+ bhp at the wheels and I changed from 195 front to 185 front and it improved the car no end.

Anything above 205 on the front is going to make it tramline like crazy and you will lose a lot of steering feel. If you do trackdays you will also really struggle to get heat into the fronts with a tyre that wide.

I ran 205 rears, I imagine 225 rears will be plenty for upto 350bhp...

Dan. - 17/2/15 at 02:00 PM

quote:
Originally posted by Pat_T
No!

Whatever you do don't put that much tyre on the front you'll ruin it.

Even the Caterham 620R runs 185 fronts!!

I had 200+ bhp at the wheels and I changed from 195 front to 185 front and it improved the car no end.

Anything above 205 on the front is going to make it tramline like crazy and you will lose a lot of steering feel. If you do trackdays you will also really struggle to get heat into the fronts with a tyre that wide.

I ran 205 rears, I imagine 225 rears will be plenty for upto 350bhp...

The 620R is a pussy cat compared to hicosts / my seven, I am expecting between 400 and 450bhp and oodles of torque.

I will have to suck it and see, I just dont want to invest big money into rims if they are not going to compliment the car, I have some 7.5J ET35 wheels I can put on the front and a friend has a set of 8.25J wheels I can put on the rear for testing and see how I get on.

As always many conflicting opinions...

JAG - 17/2/15 at 02:26 PM

When you're doing something different there's always an element of suck-it-and-see I'm afraid

You may well go through a few wheel and tyre options until you get one you like.

jeffw - 17/2/15 at 02:41 PM

I drive a 'pussy' cat car with 400BHP/300 ft lb and run 185/60 13 front and 215/50 13 rear...7J front and 8J rear wheels. With all your extra power I'm surprised your 'mans' car doesn't need 22" rims and spinners or something lol...

[Edited on 17/2/15 by jeffw]

Dan. - 17/2/15 at 03:00 PM

quote:
Originally posted by jeffw
I drive a 'pussy' cat car with 400BHP/300 ft lb and run 185/60 13 front and 215/50 13 rear...7J front and 8J rear wheels. With all your extra power I'm surprised your 'mans' car doesn't need 22" rims and spinners or something lol...

[Edited on 17/2/15 by jeffw]

Wasnt trying to insult anyones car... My point is the 620R 310 BHP // 219 LBS is a substantially different beast to 450 BHP // 350 LBS.
The only reason i dont want 13s is because they will not fit over my brakes... the question was around width and offset specifically.

rodgling - 17/2/15 at 04:37 PM

I'm running 205 15" at the front and 225 15" at the rear. IIRC rears are 7J, fronts are 6.5J. This seems to work well with 320 bhp/260 ft-lbs, no problems putting the power down. Although possibly the fronts would benefit from being a bit narrower for better feel.

8.25J sounds too wide to me.

beaver34 - 18/2/15 at 07:45 AM

in on 205 rear 185 front 13" @ 340bhp on a r888, its fine in regards to straight line grip

not sure what your building the car to do but i use mine on the road and its fairly pointless and was better with less power

just my experience

Dick - 18/2/15 at 09:20 AM

Im going to ask as im sure others are all waiting to find out like me ,
What engine are you using and what have you done to it to give 450 with very low lag ? The reason behind the question is I have a very good Saab engine sitting in my workshop and was thinking about what to do with it and what to fit it in . I have had lots of people tell me its easy to get power out of these engines but opinions all seem to differ

Dan. - 18/2/15 at 11:25 AM

quote:
Originally posted by Dick
Im going to ask as im sure others are all waiting to find out like me ,
What engine are you using and what have you done to it to give 450 with very low lag ? The reason behind the question is I have a very good Saab engine sitting in my workshop and was thinking about what to do with it and what to fit it in . I have had lots of people tell me its easy to get power out of these engines but opinions all seem to differ


Engine is a Saab B204 lump, when installed in my daily drive I fitted a holset, some 630 injectors and 3 Bar MAP resulting in ~450HP unfortunatly it didnt come on song till 4500RPM when all hell broke loose, not ideal for the kit car but very simple and resulted in lots of power for minimal cost. Spool could have ben improved with a better manifold, Cams and a shot of nitrus.

I decided I'd take a different approach... (I will do a thread at some point)

I have 2 designs I am going to test, the first and lightest design will use 2 x stock saab turbos, all exhaust gass will flow through one turbo untill it has spooled up to X PSI, at this point the 2nd turbo will be introduced and work in parallel. This is purely a mechanical solution and relied on a reed valve, butterfly valve, external wastegaste and a couple of actuators for the internal gates. I have built it but am yet to test, im confident it will spool nice and early but am concerned it may choke up at the top end.

The second solution will use the big Holset attached to the manifold and a small turbo down stream the exhaust gas will flow through the holset and when unspooled will be bypassed into the standard Saab turbo, however once the big turbo begins to spool the small turbo will be completly bypassed. I am more confident this design will work though it wont spool as early as the above setup but it will not choke up at higher flow like the other design might. Again purely a mechanical solution I am not confident enough to experiment with electronic control at this point... in the future who knows!

It is a case of suck it and see, it is the most experimental bit of my car hopefully it works out, if not there are plenty of other options I can try such as a VGT or just big turbo and nitrus etc.

[Edited on 18/2/15 by Dan.]

Dan. - 18/2/15 at 11:30 AM

quote:
Originally posted by beaver34
in on 205 rear 185 front 13" @ 340bhp on a r888, its fine in regards to straight line grip

not sure what your building the car to do but i use mine on the road and its fairly pointless and was better with less power

just my experience

I'm building it because I can... not the best of reason but good enough for me

Ive read many times its too much power etc etc, at the end of the day it isn't a race car trying to be competitive its a track day toy to have fun in and I'm sure it will be fun.... even if a little terrifying

[Edited on 18/2/15 by Dan.]

beaver34 - 19/2/15 at 09:09 AM

quote:
Originally posted by Dan.
quote:
Originally posted by beaver34
in on 205 rear 185 front 13" @ 340bhp on a r888, its fine in regards to straight line grip

not sure what your building the car to do but i use mine on the road and its fairly pointless and was better with less power

just my experience

I'm building it because I can... not the best of reason but good enough for me

Ive read many times its too much power etc etc, at the end of the day it isn't a race car trying to be competitive its a track day toy to have fun in and I'm sure it will be fun.... even if a little terrifying

[Edited on 18/2/15 by Dan.]


the same reason i built mine

sure will be fun

theduck - 19/2/15 at 01:36 PM

Is there any better reason to build a car?

jwhatley - 19/2/15 at 04:45 PM

Having had all the big pub numbers in my last MK, i have to ask what brakes you are using to suggest you can't use 13's? How heavy do you expect the car to be?

If the car is going to be above, say 750kg wet with driver then I'd say it would start to encroach on having bigger brakes, however if it is not, you will not get the heat in the brakes. Especially if you are keeping it road legal, which I suspect you are.

Do not go above a 7.5 on the front or a 205 tyre, again if you do, then the car will actually handle badly and you will get barely any heat in the tyres unless you run considerable toe in.

On the rear, I had a 9in on et20 with MK wide arches (this was an R chassis) and a 245 rear, and equivalent slick. Any more and you would probably start to loose effective grip (or not gain any more) due to the loading over the area, without having to look at adjusting pressures, which changes handling characteristics.

It's all very well having this power and torque, but let's face it's going to be un-usable. I speak from experience when I say it's best to loose say 40bhp when mapping for a chance to have a smooth, usable and linear power curve, this is what I did and it made a world of difference.

At 586kg wet with driver and 414bhp/262ftlb at the rear wheels. I will happily say I'll never get in something that could accelerate as quickly again. Sometimes I wish I didn't sell it, but I realised that if I kept it road legal I'd either die or loose my license. Hence why the new car is track only.

There's nothing better than experience, after all that's what building it will give you. You can only make it better by learning from experience.

Good luck I say, don't listen to the haters and enjoy your build!

Dan. - 19/2/15 at 05:24 PM

quote:
Originally posted by jwhatley
Having had all the big pub numbers in my last MK, i have to ask what brakes you are using to suggest you can't use 13's? How heavy do you expect the car to be?

If the car is going to be above, say 750kg wet with driver then I'd say it would start to encroach on having bigger brakes, however if it is not, you will not get the heat in the brakes. Especially if you are keeping it road legal, which I suspect you are.

Do not go above a 7.5 on the front or a 205 tyre, again if you do, then the car will actually handle badly and you will get barely any heat in the tyres unless you run considerable toe in.

On the rear, I had a 9in on et20 with MK wide arches (this was an R chassis) and a 245 rear, and equivalent slick. Any more and you would probably start to loose effective grip (or not gain any more) due to the loading over the area, without having to look at adjusting pressures, which changes handling characteristics.

It's all very well having this power and torque, but let's face it's going to be un-usable. I speak from experience when I say it's best to loose say 40bhp when mapping for a chance to have a smooth, usable and linear power curve, this is what I did and it made a world of difference.

At 586kg wet with driver and 414bhp/262ftlb at the rear wheels. I will happily say I'll never get in something that could accelerate as quickly again. Sometimes I wish I didn't sell it, but I realised that if I kept it road legal I'd either die or loose my license. Hence why the new car is track only.

There's nothing better than experience, after all that's what building it will give you. You can only make it better by learning from experience.

Good luck I say, don't listen to the haters and enjoy your build!


Thanks for the feedback it is much appreciated from someone who has had a similar car, though yours was busa powered wasnt it?

In answer to your questions:
Im hoping the car will be under 600KG's but this remains to be seen once built up, it isn't having any niceties however does have a cage and other chassis reenforcement and is a CEC all of which will push the weight up, so may well be over this target figure.

Current Brakes are cosworth items the car 'started' off as more of a budget build and wilwoods were out of the question, that however may change as the cosworth brakes would serve well as boat anchors, if so this will open up the option for 13s, I want to try the current setup before outlaying too much more cash as I may well be happy with it... but obviously 13s would be preffered.

Car will be a mixtrure of road and track, as with you I may well invest in some slicks too.

Mapping is something I will be able to adjust at the touch of a button, I will have access to numerous maps and be able to tweek the maps on the fly which is something I look forward to playing with, like you say the biggest power may not (probably wont) be the best option for performance in the real world.

Regarding tyres what brands are available who provide such wide 15/13s?

jwhatley - 19/2/15 at 06:35 PM

Yes it was busa powered.

Try Avon - look at the CR500 in perticular. Great all round track day/road tyre.

Under 600kg for you wet with driver I doubt will be achievable to be honest, especially if you are charge cooling and dry sumping.

I had adjustable boost with waste gate and spool up correction against RPm. It was the closest I could get to launch control as my Ecu didn't support it. I had just the one map which used boost/rpm/temperature compensation against MAP/TPS. That way I could control the boost through my controller and have the engine map correct for each boost setting.

Personally, I'd ditch the cosworth ones and sell them. You'll be surprised how much they will fetch compared to say a willwood setup. Plus you are talking a huge amount less unsprung weight.

TBH - It's all very well having the power and the go, but when you can't corner or stop then you really are wasting your time building the car to be 'quick'.

[Edited on 19/2/15 by jwhatley]

[Edited on 19/2/15 by jwhatley]

Dan. - 19/2/15 at 06:48 PM

quote:
Originally posted by jwhatley
Yes it was busa powered.

Try Avon - look at the CR500 in perticular. Great all round track day/road tyre.

Under 600kg for you wet with driver I doubt will be achievable to be honest, especially if you are charge cooling and dry sumping.

I had adjustable boost with waste gate and spool up correction against RPm. It was the closest I could get to launch control as my Ecu didn't support it. I had just the one map which used boost/rpm/temperature compensation against MAP. That way I could control the boost through my controller and have the engine map correct for each boost setting.

Personally, I'd ditch the cosworth ones and sell them. You'll be surprised how much they will fetch compared to say a willwood setup. Plus you are talking a huge amount less unsprung weight.

TBH - It's all very well having the power and the go, but when you can't corner or stop then you really are wasting your time building the car to be 'quick'.

[Edited on 19/2/15 by jwhatley]

Thanks will have a look ..

Luckily I only weigh 55KG... But I think you are correct Im unlilkely to meet the target weight... No harm in trying though

Boost control in mine is TPS vs RPM also tied into knock detection etc, I also have Launch control and Traction control.

Its a shame light weight uprights are not available to compliment light weight calipers / wheels, I'll keep an eye out for a set of wilwoods at a sensible price. Did you run 13s on your car?

jwhatley - 19/2/15 at 08:18 PM

Yes I had 13's, no problems at all with the powerlite setup on it including the handbrake.

Which Ecu are you using in this? If you run this sequential turbo setup, how will you regulate each waste gate for RPM vs TPS? Or are you bypassing boost in recirc?

How will you achieve launch and traction control, Are you going to use indivual wheel speed pick ups?

I'm intrigued in to this setup, it sounds quite complicated!

Dan. - 19/2/15 at 08:50 PM

[Quote]Originally posted by jwhatley
Yes I had 13's, no problems at all with the powerlite setup on it including the handbrake.

Which Ecu are you using in this? If you run this sequential turbo setup, how will you regulate each waste gate for RPM vs TPS? Or are you bypassing boost in recirc?

How will you achieve launch and traction control, Are you going to use indivual wheel speed pick ups?

I'm intrigued in to this setup, it sounds quite complicated!



good to hear your brakes were sufficient certainly inspires confidence in going for smaller ones....

Im using standard engine management which can be programmed using freeware! One of tbe msin reasons i chose this engine along with tbe fact they sre built like tanks can take abuse without being forged and also very easy to dry sump. I'm adding race logic traction control for TC and LC.

The wastegates will not be individually regulated by the ECU they will be purely mechanically controlled, however a master wastegate controlled by the ECU will controll overall boost pressure bypassing both turbos as necessary. With no boost the primary turbo wastegate will be closed to spool ASAP and the secondary turbos will be open to reduce back pressure.
At a set boost pressure (when the first turbo has met it's target) the 2nd turbo wastegate will close bringing it online allowing boost pressure to be maintained up the rev range.
The master wastegate will start to bypass both turbos to prevent over boost.

Would probably make more sense if I draw it out...

Yes I have individual wheel speed sensors cos worth hubs have ABS pickups on them and at the rear ill pick the signal up from each side of the diff.

It's not the most simplistic of systems but I like a challenge and I have an option b, c, and d. Won't cost me much to experiment other than my time some pipe and welding rods