Narrow Body to ST for High Horsepower Engine

[CSRomney]

I'd love some advice from the forum.

I'll be putting a high horse power engine (over 300), in a narrow body 911T, I've been considering updating to ST flares, adding larger wheels/tires and upgrading the suspension handle the extra horsepower.

Is going widebody essential to handle the extra horsepower? The idea of stock wheels, or close to stock with all that power seems a bit sketchy to me.

I'd love to hear any plus/minus for the update as well as any other advice for the additional power.

Thanks!

[OldSpool87]

What’s your plan for the gear box?

[-Levi-]

im running a 3.6 in my 911 sc, 245 rear tires. it seems to do ok with a lsd transmission.
how do you plan to use the car?

[CSRomney]

Still working through the details on the drivetrain. I'm going to be using the car a mostly on the road, occasional track days.

[Bill Verburg]

Originally Posted by CSRomney

I'd love some advice from the forum.

I'll be putting a high horse power engine (over 300), in a narrow body 911T, I've been considering updating to ST flares, adding larger wheels/tires and upgrading the suspension handle the extra horsepower.

Is going widebody essential to handle the extra horsepower? The idea of stock wheels, or close to stock with all that power seems a bit sketchy to me.

I'd love to hear any plus/minus for the update as well as any other advice for the additional power.

Thanks!

all the 15s will be on the short side and will cause the engine to run at higher revs that most will be comfortable w/. W a stock '76 915/44 trans and ~250hp 964 engine I found even 245/45 x16 to be too short, 275/40 x17 will be too tall except for track use. So something between a 24.7" and 25.7" tire is what you'll probably want. A 255/40 x17 @25" is very good w/ just under 300 hp 993 and stock 915/67 from a '85 euro Carrera. W/ this combo I still reach for a taller 6th occasionally but that may be because I switch form my 993 w/ 6 speed g50/30 RSR trans w/ 300+hp

In 15
911t can accommodate up to 7" wheel all around w/ ~205/55 maybe/60 w/ little compromise to ride height. @23.4 to 24.7" these will be very short. You will probably find that to be smaller than you'd like. W/ custom wheels 8 allround can be fitted w/ up to 225/45 these would be ok for street use, probably want a bit more for track use, these are even shorter @~23" making street use very revvy

going to 16s helps w/ od but doesn't appreciable change widths thou I have seen 951 8 ET23.3 w/ 225/50 x16 used in the back w/ th n/b fenders

adding Carrera flares allows 8 & 9.5 w/ the right ETs, Here you will probably want 225/45 & 245/40 x16, these are available in 15 to but again very short, where as the 16 are only a little less short.

To be the sweet spot after experimenting for a few decades is 17, 8 ET25 225/45 & 9.5ET19 255/40 @ 25" od these are only the tiniest bit short

W/ the 10" ST flares you could go 9 & 10 in 15-18, but as you go w/ wider tires the torque cost can get very high, w/ a big motor this isn't a major concern. W/ 9 & 10 again 15s are likely to be too short w/ a stockish gearbox, in 15 you could fit specialty tires like Michelin TB 5 something like 225/50 & 265/40 @23.3" is a good width if a bit short. There just aren't any 16 that would do soin 17 9 & 10 245/445 & 255/40 or if you were open to a DoT-R Maxxis Vectra 245/45 or 255/40 front an 275/35 rear

Here's the decision tree I'd recommend be followed


Just for information purposes here are some pairs that work well, they work well because the alignment in height makes car set up easier, additionally You can compare torque costs


these pairings are more confusing because of the height variations, but there are more options too.


here are some SC/Carrera fitment boxes for various tires and wheels if you are in the box it fits.

[clutch-monkey]

I have about 300hp in my 911 sc and it is fine (with 245 rears and for track 275 rears), do not need a widebody.
My other narrowbody is 330hp, coil over suspension and is a right handful. I did not develop this car so the difference is eye opening.
My advice would be to spend time on the suspension tuning as a result of this experience- the thre width between the two cars is neglible but they react so differently.

[Bill Verburg]

Here's a comparison of some different tires effect on speed and rpm

[CSRomney]

Thank for all the great feedback. Helps me put it all in context.

[Flojo]

Originally Posted by CSRomney

.. in a narrow body 911T, I've been considering updating to ST flares,

allways makes me cringe to see a longhood being converted... especially because I'll probably never own one due to crazy prices.

I'd suggest to take an SC that already has the brake Booster, wider flares that can be massaged to easily fit 10s/11s at rear.
Tub is more solid as well.

[Jonny042]

Sticky modern tires, even in a modest size, will provide far more more grip than any ST ever had.

I'm with Flo. Except for the brake booster, I removed one from an SC to backdate it

[constaf]

Hi, this sounds like a fun project. I race a 911 SC in PCA Club Racing. All of the front runners run the following tire set up:

Front 225/50/15 on 8 inch wide wheels
Rears 275/35/15 on 9 inch with wheels

Pic attached.

[Bill Verburg]

Originally Posted by constaf

Hi, this sounds like a fun project. I race a 911 SC in PCA Club Racing. All of the front runners run the following tire set up:

Front 225/50/15 on 8 inch wide wheels
Rears 275/35/15 on 9 inch with wheels

Pic attached.

Yes, that would be the hot setup for track use w/ a lower power engine, the reduced torque requirements to turn the wheels and increased revs are great in that environment

but

you won't want to run Hoosiers on the street, the alternatives which would approximate those sizes are all specialty tires like TB5, TB15 or one of the Pirelli corsa variants. The other issue is the increase revs in a street environment aren't so desirable

w/ a torquey 3.6 in a l/w chassis there is much less need for higher revs, when you want to play these motors can certainly be rev'd but most of the time on the street you are short shifting and appreciate a little calm

[cnielsen]

Depends on several factors...

If aesthetics are important to you, then I feel you need to stick with a 15” Fuchs wheel, or in some cases a 16” wheel can look good too.

15” wheels are more than capable of handling the power and there are now some great tire options available too! 16” has very limited options.

You will certainly want to improve the suspension, brakes and strengthen the transmission with LSD.

Wide flares are not necessary, but you will fit more rubber. Many people including me are running 6’s and 7’s x 15 with 185/215 Avon’s which would provide plenty of grip! Michelin TB’s are amazing tires with more grip than you will ever need. I am running some TB’s on a car with 350hp and I can’t break them loose.

Fun journey! If you have any questions, let me know.

Where are you located?

[jac1976]

“15” wheels are more than capable of handling the power and there are now some great tire options available too! 16” has very limited options.“

Think you may have these numbers reversed.

[dwelle]

Originally Posted by cnielsen

Wide flares are not necessary, but you will fit more rubber. Many people including me are running 6’s and 7’s x 15 with 185/215 Avon’s which would provide plenty of grip! Michelin TB’s are amazing tires with more grip than you will ever need. I am running some TB’s on a car with 350hp and I can’t break them loose.

hey chris, how much work to fit the 215 avon's on the back of a narrow body car with 7"s? that would be a hot set up. i'd like to run taller tires on my green car next go around as it does a lot of highway miles and the 55 series tires put me at 4K @ 80 MPH.

have you ever set up a car on 7 & 8's with the TB's? might do that on my '74 but it seems the sizes may not line up for that application...

[QueWhy]

Originally Posted by constaf

Hi, this sounds like a fun project. I race a 911 SC in PCA Club Racing. All of the front runners run the following tire set up:

Front 225/50/15 on 8 inch wide wheels
Rears 275/35/15 on 9 inch with wheels

Pic attached.

Off topic but the flag on your door is backwards

[CSRomney]

Always impressed with the ammount of knowledge here, thanks everyone.

It seems that keeping it a narrow body is a good option if the drivetrain, suspension and tire/wheel set up are properly sorted. With that being said, I’d love more info about potential narrow body set ups.

Back to wheels/tires, seems the general concensus is that 7” is widest most people are using for a narrow body (if I wrong here please let me know).

I’m not married to any specific size 15, 16, or even 17...if that’s possible). Flexibility and future proofing are important considerations, options for good rubber (present and future) seem very important with the tires responsible for so much power.

Also, I’m not set on Fuchs, I’m open to other options like RS Watanabe’s or Campagnolo 40802 style wheels as well. I’m sure I’ll be running the car at eurospec or lower... I’m obviously not looking for a car that looks like it’s fresh off a 70’s car lot, In general I’m looking for the best classic/modern options.

[Bill Verburg]

Originally Posted by CSRomney

Always impressed with the ammount of knowledge here, thanks everyone.

It seems that keeping it a narrow body is a good option if the drivetrain, suspension and tire/wheel set up are properly sorted. With that being said, I’d love more info about potential narrow body set ups.

Back to wheels/tires, seems the general concensus is that 7” is widest most people are using for a narrow body (if I wrong here please let me know).

I’m not married to any specific size 15, 16, or even 17...if that’s possible). Flexibility and future proofing are important considerations, options for good rubber (present and future) seem very important with the tires responsible for so much power.

Also, I’m not set on Fuchs, I’m open to other options like RS Watanabe’s or Campagnolo 40802 style wheels as well. I’m sure I’ll be running the car at eurospec or lower... I’m obviously not looking for a car that looks like it’s fresh off a 70’s car lot, In general I’m looking for the best classic/modern options.

Ischmits uses 951 8x16 on his n/b, the ET23.8 of this wheel pushes it inboard relative to a 911 8

He also runs much larger 23/29 t-bars, probably a bit extra neg camber and it looks like a little higher ride height


Here's the data
I used 7Et23.3 on my '72 back in the day, it's ok as long as the tire is short, ~25" or less, but it also depends on suspension spec

as to 8 in back of a n/b the max backspace is <6" so an 8 w/ ET23.3 to ET40 fits w/ a 225/50 tire, here the higher the ET the more lip room

[jac1976]

Bill,

With respect to your ‘72 NB, did you have rolled fenders and/or extra negative camber. I have a ‘77 NB with rolled fenders and am considering some 16x7 951 for the rear with 225/50. The tires I’m looking at measure around 25.3” and, understanding there is no universal fit, I am wondering if your ~25” number will spoil my plan. Thanks. Your continued contribution to this site is rivaled by few.

[Bill Verburg]

Originally Posted by jac1976

Bill,

With respect to your ‘72 NB, did you have rolled fenders and/or extra negative camber. I have a ‘77 NB with rolled fenders and am considering some 16x7 951 for the rear with 225/50. The tires I’m looking at measure around 25.3” and, understanding there is no universal fit, I am wondering if your ~25” number will spoil my plan. Thanks. Your continued contribution to this site is rivaled by few.

Stock height, stock suspension, stock alignment
wheels 7x15ET23.3 Fuchs
tires 215/60x15 Pirelli P6 25.3" OD, 8.9" s/w

The tires rubbed a couple of inches up into the fender from the lip, on full compression.

A 25" tire on the same wheel would have been fine