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I understand where you are coming from completely, in fact I think we are much on the same page.

For me the big quibble is time vs effort vs desired result vs getting the b!tch on the road. This car will see many more miles driving the roads here in the hills. Roads maintenance is not a priority for the local townships and some of the more interesting roads can be fairly rough. This is the main reason why I'm looking at IRS vs a solid axle. Not for racing. I really want this car to be at least competent as a auto-x type tool, even with the V8, but that is not a reason to go IRS, IMO. It helps though. Also, adding the extra weight of IRS will help move some of the weight bias more rearward. So much for adding lightness. It's Ok, I don't pray at that temple anyway.

So with that as a backdrop, if I was to settle on a solid axle car, I'd likely look at the Watt's and Mumford setups and just pick one.

As was stated above, given the amount of deflection that the axle will see (what? +/- an inch or two in bump/jounce?) the Panhard is perfectly capable of keeping the axle centered "enough" in the car, particularly with the use of spherical rod ends versus delrin/rubber bushes. If you do the maths to see the arc that is travelled and given a sufficiently long bar the result in transverse movement is likely in the eigths of inches range. Not a big deal, really.

Sorry, all the above is just a long winded way to suggest you build what you are comfortable with. If that be Watt's then sounds like a plan.

I have and am still considering IRS for the rear, but which one?

Lots of options for this, but the biggest thought in my head is "which one will handle the power?" the late model Explorer unit looks like it will work quite well for what I have in mind, and I can always find a way to simplify and lighten the assembly over the factory build. The diff itself is the only place that none of us can find a way to save weight.

I agree about hte weight bias towards the rear. With any amount of substantial power the arse end breaking loose is going to be an issue. A little more weight can make the difference between controllable wheel spin and complete loss of traction/control.

I am really liking hte idea of the 215 V8 though. I know I can garner enough power out of it to get what I want, and I can get a core motor for 400 plus shipping. I have enough 350 Chevy motors that I could go that route, but it would be a waste of the motor and the car......too damn heavy, bulky, large.

Doc

_________________
Spectacles,testicles, wallet and watch.....yep I am ready to go.

Burt Munro

I'm interested in the 8.8" style stuff. Plenty strong, good TAD options.

Another option is the IRS parts out of a 2nd gen RX7 (FC). They'll stand up to V8 power according to "Granny's Speed Shop" (google).



Particularly when considering a transient/dynamic handling situation. Not sure if this is what you meant; I'm not so much concerned about launch as I am about the polar moment being too tightly coupled to the nose of the vehicle.

Another IRS option could be C5 Corvette with its rear moounted transaxle but then the weight starts going up yet again (torque tube, etc.). Sprint/Midget car stuff has similar parts meant for SBCs as well - or so I'm told.



I hear you.

I keep rethinking the V8 thing every day (better now than after the tubes start getting welded).

My issue with the SBC is mostly the weight. I can deal with size given a 442 style chassis. The problem with the SBC is that it makes too much power and as a result pushes you into needing a large enough transmission to deal with the power. Sure, a T-5 will live with a mild 5.0 in front of it... but you have to keep it mild. The other option is to go with a TKO or a T56. TKO is fairly pricey and the T56 is stupid expensive because they are in vogue. Add more weight as well. A T56 is roughly 2x the weight of a T5.

In my case I have a fresh all iron SBC. To knock 100+ lbs off it I'd have to spend cubic dollars to change the heads, intake, water pump, accessories and drive, etc., etc. Still be over 500 lbs. Doing that means that I've added probably 200+ lb-ft of torque at the same time. Say bye-bye to the T5.

Kinda painted into a corner with the SBC. An aluminum LSx SBC is just too expensive for me. And crazy power. Absolutely requires a T56.

I like the Rover in principle. My issue comes from passing familiarity with them in Land Rovers (i.e. reputation as junk due to head gaskets and other problems). Also, is there a decent looking intake for them? Something like a mini-ram or similar? Whatever I do requires EFI (non-negotiable) so one of those Offy/Holley combos aint gonna cut it.

Sometimes I think I'd be better off to go back to doing a Swift GT based build. ~160hp+ would stll be enough to light my fire in a ~1200lb car.

Ramble, ramble. Sorry.

Remove vehicle weight, diff/trans reliability increases. Increase traction or power, diff/trans reliability decreases. The most basic parts from a 3800lb vehicle(1989-1997 Tbird) installed in a 1400lb vehicle will be overkill. IRS is traction challenged anyway since the torque reaction cannot be used to aid traction 1/3 as much as a solid rear.

Monster Miatas use the 7.5” tbird diff and weigh 2500 lbs with a 225 hp 5.0l. The only reason they have a kit for the 8.8 is due to requests by customers. Nobody has broken a diff. There have been issues with axles bottoming in the cups and broken Monster Miata proprietary mounts.

The heavier duty the parts are, the greater the parasitic loss, which means less power to the wheels.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

The feel in the corners negates the use of a solid axle for me.

I am not big on the engineering terms/scientific explanations. My vocabulary of car stuff is written in two books "Been There, Done That" and "Seat of the Pants....the trails of broken parts" both by me. I tend to figure stuff out on my own without a large library of expensive books. I overbuild everything, and then figure out why it broke later.

The 8.8 LSD is a virtually bulletproof diff with power on the average of 500 to 600hp....even with a stick tranny. The 7.5" ring gear in the 10-bolt chevies is junk from the factory, and not worth wasting time on. The parts to make it better just offset the detonation event of the unit by mere minutes (Been There, Done That....page 137....in my noggin...not available from Amazon).

IRS does have some limitations for traction in most factory forms. You have to keep in mind that the factory didn't intend it to be pushed to the absolute INSANE limits we intend to push it to in its factory form either. They built it for "Joe Driver" who gets a bit spirited now and then......not constantly pushing the envelope of "How can I break it this week".

Besides, I like the mechanics of a well prepared and designed (my design) IRS setup. The beauty is in the machine, not the driving. It is the fluid motion of a mechanical thing that is exposed to the world to see that captures attention.....not the enclosed shell of contents.

Now, back to 8.8 based IRS. If I am thinking right (and I am not a Ford guy), the supercoupe T-birds diff is an 8.8 and the new explorers are certainly based on the 8.8 design. Large piles of useable spares available, and a wide range of gear ratios....and FACTORY LSD.

Now, to take a factory assembly as a whole, and rework it into a masterful work of art and function is the next goal. Lighter axles? Who knows? It can be worked out to be a solid performer, and I am sure there are others here who have already done it. I look to be one of them in time (maybe the second 7).

Short of casting my own diff housing (yes I have a small foundry), I can't think of a single "cost effective" way to lighten that housing though (the Explorer 8..

Now in regards to the solid axle rear, the 8.8 early explorer rear offers an LSD (look closely at the tag), and is only 3 inches longer overall than the S10 unit. It is much more durable, and the extra 3 inches will widen the wheel base by what may seem like an insignificant amount, but in the end may be the difference in a spin out and a power overdriv3en situation in a corner.

I don't recall reading where any 7 owners complained abouthte front end sliding out entering a corner, so I can only assume this behavior woudl be limited to those of us who would be running super heavy powerplants (SBC).

I seem to be rambling here.....hmmm

On a final note, I love the T5. It leaves the prettiest trail of parts behind a vehicle I have ever seen of a transmission. No large chunks.....just medium to small sized bits.....lol.

Doc

_________________
Spectacles,testicles, wallet and watch.....yep I am ready to go.

Burt Munro

I don't wish to hurt anybodys feelings, but if you don't want to learn anything, why pose the question?

FYI, the 7.5 also came with traction loc.

So far it sounds like you want to basically build a T-bucket with a 3.5L-v8, a powerglide, wrinkle slicks, and a 31 spline 8.8, not that there is anything wrong with that.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

And the 7.5 is a proven detonator.

I have done the T-bucket thing.....no joy. Much bigger engine, but same principle.

No, I am not interested in the drag racing principle. I have had my share fo fun in a straight line, and found without megabucks to spend it is really difficult to be competitive. It is not about the car anymore....it is about who has the most money to spend in a given class.

Not sure where you are coming from with the "why pose the question" comment.

Indeed, I am interested in learning something. On another note, I tend to overbuild everything in an effort to make it bulletproof or as close as I can and learn from the failure wherever it may be.

Which IRS diff is a proven performer with a nice range of gear ratios available?
This would be the determining factor in going IRS for me.

Doc

_________________
Spectacles,testicles, wallet and watch.....yep I am ready to go.

Burt Munro

I guess I could have typed that better. You are not going to break a ford 7.5 IRS in a 1400 lb car on street tires. You cannot get enough traction to do it. With a solid axle 7.5 setup, maybe. I have had a 7.5 solid axle in a 2900lb, 1983 5.0L ranger since 1990 and never had a failure. It’s an open diff so traction is hopeless. The ratio is 3.08 so the teeth are thick.

How heavy the car is determines how much power the diff can handle, not just a torque/hp number. That weight plants the tires and puts a greater load on the trans and diff (i.e. towing packages). An extreme example is take your biggest, baddest motor and trans with the most pathetic diff you can find. Put the rear wheels on a sheet of ice. You won’t be able to break it.

The 7.5 diff comes in ratios from 3.08 to around 4.10 in stock form. They came in just about everything ford made in the 80s and 90s. Solid axle carriers work in IRS diff cases except for the side gears.

As the ratio goes up numerically, the teeth must get thinner because the available room for teeth has not changed (i.e. 7.5”). That makes a 3.08 stronger than a 4.10 for the same diff size.

The 8.8 can be found in the 2.73-4.10 range. 8.8 IRS have either 28 spline or 31 spline axles with different size joints.

You probably could break it if you back up real fast, red line it in neutral, then slam the shifter into gear but that’s not really what we are talking about here.

Having said all that, the 1995 4.6L sohc donor I just bought has a 8.8 IRS. It came with the car but I doubt I will use it because it is open and 3.08. It depends on what I find. 3.27 traction loc 7.5 is pretty easy to find.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

I got a complete t-bird IRS given to me, 8.8 W/ LSD
can't argue with free.

from what I understand, this diff is nearly bullet proof.

Steve, can you give me a little history on your `67 with the 351 Windsor / T5 combo? In particular, how built is the engine and for how long have you been running it that way?

Can't argue with free!

I built the 351w/T5 setup in the 90's. It was in a ranger for a while. I bought a 1967 six cyl mustang that I put it in. I have been restoring the stang for a while so it has not been driven for a long time. Currently have some windshield glass sealing issues to resolve.

The 351 is .040” over, I don’t remember the cam specs but it is too short on duration to suit me and lift is not enough to make clearance checking necessary. Ported 1970 heads, Proform aluminum 1.6:1 roller rockers, screw in studs and guide plates. Performer intake, 750 vac secondary, late 70’s ford electronic ignition. Hedman shorty headers to fit the mustang chassis. It is very mild with lots of torque. The T5 is a world class I bought for $25 as a core and rebuilt with new synchros and bearings. King cobra clutch and home made hydraulic clutch release system with all the parts from Speedway. I use the clutch pedal and don’t “speed shift”. As a mechanic, I try to take it easy on the equipment since I will have to fix it.

I would use different heads, more cam, and a rev kit in the valley.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Sorry, I was referring to the GM 10-bolt 7.5" unit. Bad design from the word go. The Ford 8.8 (7.5" design) on the other hand is head and shoulders above the GM unit by far.

If you decide you want to sell off the IRS from your 4.6 donor car hit me up. I am interested.....

Doc

_________________
Spectacles,testicles, wallet and watch.....yep I am ready to go.

Burt Munro

Okay, I'll keep that in mind. Thats why I mentioned it. I didn't know if you'd want an open diff 3.08 to start with. I think it has the big cvs and axles but I have not measured. It has drums too. I'm going to drive it for a while. It's my first 4.6 "cammer". My build will be like Old Yeller. Not sure which one though. There were 9 different Old Yellers I believe.

http://oldyeller2.com/

http://www.tamsoldracecarsite.net/OldYe ... day05.html

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Kinda hate to admit but I remember when "Old yellar" was a fairly new car running at the LA county fair grounds.

I have bone a bit of research and picked up most needed parts and can comment a bit on the 8.8 IRS diff. This diff is used in everything from BEC, Deman, to 4000 lb 900 hp drag cars. The only one I have weight on is the 2000 Cobra R diff which as an assembly packaged for shipment weighed 68 lbs. The 8.8 is widely enough available that I wouldn't bother with a 7.5, unless I already had one. The internals, as best as I can tell, are the same reguardless of the application, save the 00R which is a gearator and the Torsen T2(OEM) (which is not machined for IRS which means it is the one that I am using). I believe that with the aluminum housing the 8.8 based IRS will be slightly lighter overall than a solid axle and have much less unsprung weight. What I have settleled on is an 8.8 out of a MK 7 for a solid axle in Put-put and a mix of parts for an IRS in Shagnasty. The mix for the IRS is housing from a MK VIII using the rear cover from an Explorer, this allows a 4 point solid mounting which I feel will be strongest, one of the bigest breakage points with the 03 Cobras is the rear cover. The carrier is a Torsen T2(OEM) which will require either remachining the T2 or (probably) remachining the C clips on the stub. I have OEM gear sets from 3.08 to 4.10 and will probably use 3.25. The half shafts are 03 Cobra and knuckles are MK VIII or Tbird with Cobra hubs and Mustang front 11" rotors which will either need to be turned down to 10.5 or something done with the caliper mounts. All done I will have well less than 500 in all these pieces.

The primary problem with the T5 is Stangers that do the "Drive it like you stole it". My 93 Cobra has 110k miles on the original T5 and clutch but is on the 6th set orf tires. The T5 is only about 85 lbs and if nore strength is needed G-Force has different gearsets up to the Dog face set which is supposed to be good to 600 hp. Abusing the T5 with a light car and high hp will result in a lot of sideways motion and in a LC with the weight even with 315s shouldn't result in excessive breakage.

http://team321.com/321HotRodIRS/DifferentialPage.html

Is this the sort of rear your talking about?