4.56 Gears - Input Please

[Scootsmcgreggor]

Ok so I've been making and staring at gear ratio charts till I'm blue in the face and want a sanity/gut check please.

Crunching the numbers, 4.56 + MT82 D4 is as close as I'm going to get to 15-17 ratios. I know I can swap in a 15-17 trans but there's a lot more details involved there than I care to address right now. My trans also has only 15k miles on it so planning on putting a trans cooler on it and see if I can get some life out of it.

My question is am I crazy? Seems almost nobody does this. 4.09's are more popular but still super long compared to a closer ratio box or a 15-17 setup. Check out the numbers below. Ideally I would do 4.3's but nobody makes them and neither Yukon or Richmond have any interest to do so.

Car has stock power so with some bolt ons one day for my home tracks I may eventually need 5th but for now 121-125mph in 4th should do it at most tracks. Home tracks are Laguna, Sonoma, Thunderhill, and Buttonwillow.

If I did 4.09's I would definitely not need to get into 5th, but my concern is leaving in-gear acceleration on the table compared to 4.56's. Seems the in-gear acceleration of 4.56's would more than make up for needing 5th occasionally.

Gearing Analyzer with Shift Tracer

Enter gear ratios, tire and diff ratio to analyze RPM vs velocity at shift points with tracer

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2018+ with 4.56 (compared to 3.73):


2018+ with 4.09's (compared to 3.73):


2015-17 with 3.55's:


Thanks in advance guys.

 

[blacksheep-1]

I would mostly agree, with the possible caveat that it does take time to make those extra shifts.

 

[JDee]

I like the look of that 15-17 3.55 graph. With 3.73s I am getting to 7250rpm (that's the redline with the FP Power Pack 2 tune), and 147 mph on the back straight at Mosport. I like the idea of getting the revs down closer to the 6750 stock redline. I might lose some grunt out of the only slow corner at that track, but overall it would be a lot easier on the engine. I'm not chasing every tenth, I'm trying to have fun and keep the maintenance costs in line. Keeping the revs down would help with that.

 

[TMSBOSS]

One consideration when running 4.56 gears is the gap available for the c clip retainer in the Torsen. You will need a two piece retainer block. The ring gear is thicker the higher the number, making the where the block is inserter smaller. Blow Fish Racing made a two piece unit to accommodate the higher ratio.

 

[blacksheep-1]

One consideration when running 4.56 gears is the gap available for the c clip retainer in the Torsen. You will need a two piece retainer block. The ring gear is thicker the higher the number, making the where the block is inserter smaller. Blow Fish Racing made a two piece unit to accommodate the higher ratio.

blowfish made such cool stuff, I wish they were still around

 

[Scootsmcgreggor]

One consideration when running 4.56 gears is the gap available for the c clip retainer in the Torsen. You will need a two piece retainer block. The ring gear is thicker the higher the number, making the where the block is inserter smaller. Blow Fish Racing made a two piece unit to accommodate the higher ratio.

Interesting. Anywhere I can find further info or pics of this to visualize it?

 

[TMSBOSS]

I looked for their website, gone. What they did was take the metal block which is inserted into the carrier locking the c-clips in place and ground it down to half thickness. Then they would insert both and bolt it in. A full size piece would not into fit through the space available because of the thickness of the ring gear. If you ran into this issue you could take two of the standard blocks to a machinist and have then ground down to 50%. I found this on Ebay

8.8 FORD TORSEN SPACER BLOCK SET | eBay

WE DISCOVERED THAT THICK RING GEARS, SUCH AS 4.56:1, BLOCK THE HOLE TO GET THE SPACER BLOCK IN AND OUT OF ANY TORSEN DIFFERENTIAL FOR THE FORD 8.8 REARS. WE DEVELOPED THIS SPLIT PAIR THAT ARE THIN ENOUGH TO INDIVIDUALLY PASS BY THE RING GEAR AND THEN STACK TO FILL THE GAP BETWEEN AXLES.

www.ebay.com

 

[Scootsmcgreggor]

I looked for their website, gone. What they did was take the metal block which is inserted into the carrier locking the c-clips in place and ground it down to half thickness. Then they would insert both and bolt it in. A full size piece would not into fit through the space available because of the thickness of the ring gear. If you ran into this issue you could take two of the standard blocks to a machinist and have then ground down to 50%. I found this on Ebay

8.8 FORD TORSEN SPACER BLOCK SET | eBay

WE DISCOVERED THAT THICK RING GEARS, SUCH AS 4.56:1, BLOCK THE HOLE TO GET THE SPACER BLOCK IN AND OUT OF ANY TORSEN DIFFERENTIAL FOR THE FORD 8.8 REARS. WE DEVELOPED THIS SPLIT PAIR THAT ARE THIN ENOUGH TO INDIVIDUALLY PASS BY THE RING GEAR AND THEN STACK TO FILL THE GAP BETWEEN AXLES.

www.ebay.com

Thank you.

Is there a chance that these are not needed for the super 8.8? There’s a guy on M6G that did a thorough write up on 4.56’s in his gt350 and no mention of the spacer block issue. I’ve not changed a gear set prior in these diffs. Do the spacer blocks have to come out to get the ring gear off the diff?

 

[TMSBOSS]

Not sure.

 

[67GTA]

Thank you.

Is there a chance that these are not needed for the super 8.8? There’s a guy on M6G that did a thorough write up on 4.56’s in his gt350 and no mention of the spacer block issue. I’ve not changed a gear set prior in these diffs. Do the spacer blocks have to come out to get the ring gear off the diff?

That’s a great question - the spacer block is used to keep the c-clips located on the live axles, but are probably not used in the IRS cars.

 

[Bill Pemberton]

Blacksheep1 has the one caveat I would put a lot of consideration into --- how many more shifts are you going to incur at the tracks you frequent the most. The old rule of thumb is that every shift takes a 1/2 second , you might find yourself stirring the shift lever enough you would give up the time you felt you gained with a gear swap.

 

[Dave_W]

Torsen offers the 2-piece block kit. Not sure if it's needed / works with the IRS LSDs - you could call their tech line to check.

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