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arturo64 Avatar
arturo64 Arthur T
Billings, Montana, USA   USA
so i'm new to this exact forum, i usually just use the Spit/gt6 forum. anyways, i have a 68 spit i've decided to dedicate to racing fun. i want it to stay functional as a car as well as it will be used for the handful of SCCA solo races held here in my hometown. after my first race i realized my suspension was in need of change so i went with lowered and uprated springs in front and new shocks(nothing fancy) i also scored a camber compensator for the rear(also new shocks in back but nothing fancy) that really helped a ton but i was still tucking just a little bit(as told by fellow racers) and i was pulling a rear tire off the ground and thus loosing drive. so now i'm thinking i should lower it an inch or so in the back with a lowering block. i'm hoping to make one.

big question, would it be crazy to use a 3.89 diff??? i found that i could have dang near stayed in 2nd the whole time, never "feeling" the need to shift up, BUT i was spinning the crap out of my engine. going over 4500(which was happening alot) seems excessive for a weekend racer that i don't want to rebuild at the end of each year. i'm not to concerned with over all speed/acceleration, but rather cornering as fast as possible. thoughts?



Arthur
68 spit
70 gt6+

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Triumph Racer Avatar
Triumph Racer Patrick N
south bend, IN., USA   USA
1962 Triumph TR4 "My First Triumph"
1962 Triumph TR4 "Big Red"
1964 Triumph TR4 "Ugly Duckling"
1971 Triumph Spitfire MkIV    & more
You did not say what diff you are running now? I assume from your statements and year of car it is a 4.11?



Sometimes you succeed,other times you learn.

arturo64 Avatar
arturo64 Arthur T
Billings, Montana, USA   USA
yup, standard 4.11.



Arthur
68 spit
70 gt6+

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OFRacer Avatar
OFRacer Mike H
Poughkeepsie, NY, USA   USA
I race a (dedicated to the track) 63 Spitfire with a 1296 engine in it. I use the 4.11 for short tracks like Limerock, Thompson and Milville (NJMSP). When I go to Watkins Glen, Summit or Pocono, the 3.89 goes in. because of the long straights there. I've used the 4.11 at the Glen, it really helps climbing out of the boot, but then I die on the main straight, hitting the rev limiter just past the infield tunnel (at least a 1/4 mile before I should).

mike h

arturo64 Avatar
arturo64 Arthur T
Billings, Montana, USA   USA
so my dilema is this; would it be better to have the acceleration of the 4.11 and then be having to shift all the time(which is fun but takes work) or sacrifice some acceleration with the 3.89 to be able to stay in 2nd gear for the whole course?? the miata crew all say that they stay in 2nd the whole time....



Arthur
68 spit
70 gt6+

Spitfirejoe Avatar
Spitfirejoe Joe Guinan
Fremont, Nebraska, USA   USA
1980 Triumph Spitfire 1500 "The Phoenix"
For some reason, I've not been to this forum section before. Odd.

I don't see any reason to worry about that RPM range on your engine. Those things will SPIN. Over 7 grand I'd start worrying a bit. Putting a 3.80 in the car would make it a little easier to drive on the long, flat, straight highways we have out here in Nebraska. If you are going to autocross the car - leave the 4.11 in it, get it into 2nd gear and drive. Every shift costs several precious 10ths of a second, and if you shift UP, you then have to shift back down. Tick, tick, tick goes the stopwatch. Plus, shifting often upsets the balance of the car right when you don't want that to happen.

I lowered my 1980 at both front and rear - shorter springs up front with "nothing fancy" shocks like you are using. I made up a bunch of 3/4 inch lowering blocks, installed one of those along with a set of Corvette air shocks - Monroe MA785. Little modification was needed for the air shocks - swap out the bushings in both ends, and use a couple large washers on the bottom end to keep the air bladder on the shock body from rubbing on the vertical link. These allow me to "tune" the rear end height by several inches. If you want to get fancy, run two air lines to the trunk - one for each side. Then you can tune each side independently. I run the rear end moderately high for regular driving, and let a lot of air out to drop the rear for autocross runs. If I get the rear too low, the front end won't stick. A Spitfire that won't steer is no fun. If I forget to let some air out, I'll know right away because an axle will tuck and I'll be facing backwards quite soon. If I get it just right, I can dance the rear end around to rotate the car nicely and the fronts still stick. I readily admit this is a cheap, "band aid" approach but it does help the car handle better.

Tires are the big thing for this purpose. I can't find any 13 inch high performance street tires. Fortunately, I have a friend that vintage races a Sprite. New tires can make a few seconds a lap difference for him, so when his get a little worn he puts on new. I get his old ones for a song. Yeah, I have to have another set of wheels and those tires aren't legal street tires. I trailer the Spit lots of times. Thought about getting a light trailer to pull behind the Spit so I could bring tires, tools, etc. but it's just easier to throw the car on my little trailer and put everything in the truck.

One word of warning... Autocross is like a "gateway drug". It's a lot of fun, but you soon need something stronger to get your fix. I'm trying to finish an early Spit with an 1147 for vintage racing, and took my competition driving school this Spring. I will still autocross the 1980, but probably not the early Spit.



Joe Guinan
Fremont, Nebraska

arturo64 Avatar
arturo64 Arthur T
Billings, Montana, USA   USA
I very much agree that autocross is a gateway drug. It is absolutely awesome and I love pushing my lil car. Hopefully I can stave off the temptations....as the tracks are pretty far away and the money it takes needs to go to other restorations.
Now I have to figure out a seemingly decreasing camber issue up front. Would lowering springs and thicker anti sway bar contribute to this?

As for the diff...I think I might keep my eyes out for a 3.89 just to try it. But I'll stick w the 4.11 for now.



Arthur
68 spit
70 gt6+

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Spitfirejoe Avatar
Spitfirejoe Joe Guinan
Fremont, Nebraska, USA   USA
1980 Triumph Spitfire 1500 "The Phoenix"
?Now I have to figure out a seemingly decreasing camber issue up front. Would lowering springs and thicker anti sway bar contribute to this?"

I'm not sure what you are asking here. For simplicity - with the tires pointing straight ahead, are the tops of your tires leaning in toward the center line of the car (negative camber) or out away from the center (positive camber). Saying "decreasing camber" makes me think you are seeing the former.

The anti-sway bar won't do much to affect camber. Shorter springs certainly would. Camber into the negative range is a good thing for autocross. Within reason, the more negative you go, the better. As the car "leans" over on the tire, the tread flattens out on the road surface. I see lots of Spits with neutral or positive camber. Steering effort is a little easier when set up this way. You won't see a good handling car with positive camber, in my opinion. I'm sure there are exceptions.



Joe Guinan
Fremont, Nebraska

arturo64 Avatar
arturo64 Arthur T
Billings, Montana, USA   USA
My camber seems to be becoming more negative. I'll try to post a pic....I suppose I could bust a ruler out and measure too. I'm just worried if my bearings are failing and racing/driving fast is a very bad idea. I have a race tomorrow. Once I exchange my crusty gt6 calipers for new ones, I'll be putting on gt6 front axles and all.



Arthur
68 spit
70 gt6+

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clshore Carter Shore
Beverly Hills, Florida, USA   USA
If you are lifting a rear wheel, likely need a bigger anti-roll bar up front.
ISTR a '68 has 5/8" stock, you would want 3/4" or even 7/8".
A bit of front negative camber is a good thing.
Be sure to set the toe after any suspension changes, including springs.
In the end set the car to be comfortable for your driving style.

arturo64 Avatar
arturo64 Arthur T
Billings, Montana, USA   USA
My anti sway bar is not stock, got a thicker one from a newer spit. Can't remember how thick but it was close to an inch(measured to be 7/8ths). I'll measure it when I check my camber. (initial measurments as follows. Across the 14.5 inches of the rim it angled 3/8ths away on one side and 1/2 inches away on the other. NOT supper exact)



Arthur
68 spit
70 gt6+



Edited 1 time(s). Last edit at 2015-06-26 10:43 AM by arturo64.

1964Spitfire Avatar
1964Spitfire Tim P
Santa Clara, CA, USA   USA
Keep in mind there is a bit of a interchange problem with Spitfire diffs. Square versus Round input flange, small versus large output flanges. I'm not saying it can't be done but you may have to change more than just the diff. Don't ask me how I know.

Here is a bit more diff info:
http://www.canleyclassics.com/technical-archive/different-differentials/

But as others have said, stick with the 4.11 for autocross and use a bit more RPMs. If you are concerned about over-revving, Pertronix makes an affordable rev limiter that works pretty well. You'll spend less time looking at the Tach and more time looking at the Track!

Tim

arturo64 Avatar
arturo64 Arthur T
Billings, Montana, USA   USA
Anyone able to do the quick math for my camber? My math skills are lacking and Google ain't helpin.
I forgot about the flange issues. I was able to swap out a 4:11 for a proper 3:89 in my gt6. And I was able to swap in a 4:11 from a 69/70 spit into my current spit. Remebered wrestling w some flanges but for em to work. I'll do some more research.



Arthur
68 spit
70 gt6+

clshore Carter Shore
Beverly Hills, Florida, USA   USA
In reply to # 1299392 by 1964Spitfire Keep in mind there is a bit of a interchange problem with Spitfire diffs. Square versus Round input flange, small versus large output flanges. I'm not saying it can't be done but you may have to change more than just the diff. Don't ask me how I know.

Here is a bit more diff info:
http://www.canleyclassics.com/technical-archive/different-differentials/

But as others have said, stick with the 4.11 for autocross and use a bit more RPMs. If you are concerned about over-revving, Pertronix makes an affordable rev limiter that works pretty well. You'll spend less time looking at the Tach and more time looking at the Track!

Tim

Square vs round make no difference as the centering hub is same diameter, but bolt hole patterns differ between small/big flanges.
The UJ are same for both, and so it's possible to use the correct UJ yoke to adapt a given diff flange (front or side) to a given axle/driveshaft.



Edited 1 time(s). Last edit at 2015-06-26 03:37 PM by clshore.

OFRacer Avatar
OFRacer Mike H
Poughkeepsie, NY, USA   USA
My 4.11 and 3,89 have slightly different flanges in the front. Both of them have the large diameter side flanges for the 1/2 shafts. I had my engine builder elongate the holes into slots on the main drive shaft flange so I can easily switch the diffs with out swapping drive shafts as well. I gave him a spare, small bolt pattern flange without the u joint in it and both diffs so he could get the measurements right, I didn't want to drill it by eye and end up with something out of balance at speed.
It's worked well for the past 8 years or so.

mike h

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