Marks69BB

I currently have 3.08s with the keisler tremec TKO-II which has the 3.27 1st gear and the .89 OD 5th gear. This was fine with the mild hyd cammed 509 I had before.

My solid roller, AL head 555 motor is going to have tons more tq/hp so I'm planning to go with offset TAs with 30 spline axles and 3 1/2" half shafts with larger U-joints. However, I'm worried about the rearend holding up. Plus it probably needs rebuilding anyway.

According to VS, if I go to a 12-bolt, 3.70s are the minimum size gear I can go to. I'm worried about 1st gear being useless with the 3.70s out back.

Comments or experience with this combo would be appreciated.

ML67

I'm running a Tom's BOE 3.08 rear w/ 30 spline inner and outer axles w/ 1350 u-joints and offset control arms in my 548 and its been perfect.

What are your engine details? Sounds interesting!

Mark

Marks69BB

Hi Mark

You had helped me earlier with pics of your setup using the L88 airbox and milling the Victor Jr. to fit.

I've used your motor as my model/inspiration.

I'll post details on the custom Comp cams solid roller when I get the motor summary from my engine builder but it is over 700 lift 260-265 duration.

Gen IV GM Bowtie Block bored and stroked to 555ci
ProTopline AL heads 357cc CNC ported
Manley valves & springs
Comp roller rockers 1.7
Comp cam’s high lube roller lifters
Eagle 4340 steel crank & H-Beam rods
Forged JE pistons for 10+:1 Compression on premium pump gas
Port-matched Victor Jr intake with Race Demon 1060 cfm carb
Accel dual point tach drive dist with digital 300+ electronic ignition
McLeod Street-Twin clutch/flywheel
Lakewood scattershield

What's Tom's BOE? Is this a 12 bolt rear?

I looked on Toms' website and couldn't find it.

TheSkunkWorks

I've got a 3.55:1 gear set on an Eaton posi in my 12-bolt IRS.

ML67

BOE = Best of Everything. Look on page 20 in his web site catalog and scroll down to the 30 spline C-clip axles. Stage 7 w/ large cross shafts should do the trick (and this is what I run).

Are you going to dyno your engine? Sounds like it should scoot! When do you expect to have it completed?

Marks69BB

Where did you get it, how much, and what 1st gear ratio are you running?

Marks69BB

So about a grand should do it. Do you agree I should keep my 3.08s and not go any lower?

Yep, we'll run RW #s after she's broken in.

It's complete and going back in the car as we speak. Running into all of the little things and trying to get everything correctly hooked up again is driving me nuts. Main thing I'm worried about is fitting my Hooker sides to the angled taller heads; may have to cut and reweld them to fit.

TheSkunkWorks

Henry's Machine Works did mine back in the day. They were the subject of the original Hot Rod Shop Series article "Taxing the IRS" done over 20 years ago. Cost was $1,789.00, but keep in mind that we're talking '80's money.

http://henrysmachine.com/

Sold a Super T10-U with 3.44 first after breaking it (way too deep and heavy, anyway) and I'm now building up a Muncie with 2.52 first to put behind a moderate 496.

ML67

I think w/ a 3.27 1st you wouldn't want to go much shorter than a 3.08 rear. How did you like that combination w/ the 509? If you had traction problems w/ that setup, you're *really* going to have traction issues w/ the new 555! And the .89 OD is not too tall that you'll have problems at the other end either.

ZL1powr

Check out the following link. Just had to modify the Hooker side pipes to make them fit my new heads with raised exhaust ports. It was a simple mod and they fit nice. Didn't have to ding any of the pipes.

http://forums.corvetteforum.com/show....php?t=1772253

427Hotrod

A lot depends on what you're going to use for tires. Mine currently uses a 3.07 rear gear and a 3.497 first gear. That's a 10.74 first gear. You're going to be at 12.09 with a 3.70 rear. That's going to be a lot of gear. Serious drag folks use first gears like that but they use taller tires. I use a 28" tire and I *could* use some more overall first gear, so I'm not too worried about that part of it.

The biggest issue is going to be the large gear drops in the trans. With 4th being 1 to 1 and with only 3.70's...it's going to like more gear. Mine did pretty well with a 4.13 and a 4.08 final overall drive ratio. It's at a 4.40 now and loves it. My trans..as well as Mark's uses an underdrive 4th gear so we don't have very big drops going through the gears. Do the math and see how it looks in 2nd and 3rd gears with 3.08's.

For example....with a 4.08 final drive I was getting into 3rd gear just before the 1/8th mile mark and 4th just before the 1/4 mile ended. Basically had a 3 speed going though the 1/4 mile. Yours will be even worse with only 3.08's.

What RPM range do you plan?

The idea of an O/D is sweet. Even with my 3.07's, I could easily use an O/D on the highway to knock a few hundred RPM off. You'll be fine at that end.


JIM

ML67

Of course Jim is right….it depends on your intended usage, and how much you’re willing to compromise between street and strip; between 60’ times at the strip and traction on the street. Your 555 *will* be traction limited on the street; and the shorter the gearing, the worse your traction problems. It may sound like fun, breaking tires away at will, but from personal experience, it can also cause you to get religion……


Of course that is *precisely* the reason we build such engines.

427Hotrod

Aww c'mon...Mark....you told me it was FUN going through the 1/8th mile traps sideways and looking at the wall..then the other wall....then the first wall!!

You've already got the Tremec and the 555"...so it's just down to gearing in the rear to get best compromise. Nick..Vettemaniac ran 3.08's with his Tremec and his relatively mild 540 as a daily driver. He ran high 11's with it on pure/plain street radials and had to pedal it all the way down the track. Literally had black stripes the whole way. His best time were with granny shifting so he didn't blow the tires away.

If you're going to run drag type tires on it...then the deeper 3.70's will really help. If you're not..then the 3.08's will allow you to maybe bog it a little and get it to hook. Killing off some low end multiplication might help you get it moving and being *long geared* might help overall getting it down the track. In that case a Tom's BOE deal will hold up well. Mark has a buddy with a RO/D 6 speed in a killer '64 Coupe. He has a nasty 502 in it with N20 and regularly flogs it...pulling wheelies etc on slicks. After years of abuse he finally just broke a couple of teeth on the ring gear in his regular BOE 3.36 Tom's rear end. That's just normal stuff at that level. I think it would hold up pretty well for you.


JIM

Marks69BB

Thanks for all the great info and insight on my combo!

I'm now thinking the 3.36s or 3.55s since this will be a toy more than a cruiser. Any final thoughts?

ML67

The differential tongue frame bracket broke on a wheels up launch which allowed the entire pumpkin to rotate, and that in turn broke several teeth on the ring gear. He's since welded and reinforced the frame bracket and installed a center bar to help secure the differential.

Stu does NOT baby his car!

He runs a 3.27 1st gear w/ a 3.36 rear end. I forget his 6th gear OD ratio; its probably in the .78 - .84 range.