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Rear axle ratio (and now camshaft) recommendations for L05/T5 build

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Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Old 01-28-2019, 09:00 AM
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Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Need rear axle ratio recommendations from you guys on my '88 IROC.

I'm swapping a stock L31 cam and an Edelbrock performer intake onto an otherwise stock remanufactured L05, putting it in front of my T5 and putting it in the car with shorty headers and a 3" cat back. 14psi regulator spring and L05 injectors round out the package. I'm literally building this out of spare parts I have laying around, hence the somewhat unconventional build.

I have a 3.42 gearset available here, but I'm concerned that may not be the optimal gear for this low revving lump of spare parts. Should I spend the money and get a 3.08 gear set for it? 3.23? I'll be using a torsen limited slip, I have a 2 series and a 3 series unit at my disposal so no worries there. 5th gear is .63:1 in this trans. This car is my daily beater in the summer months and I commute a total of 70 miles per day, so fuel mileage is a bit of a concern as well.

Figured some of you guys here might have some experience with a stockish TBI engine and a 3.42 gear to tell me if you like it or not.

Last edited by 1MeanZ; 01-30-2019 at 12:21 PM.
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Old 01-28-2019, 11:25 AM
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Re: Rear axle ratio recommendations for L05/T5 build

I run 3.73s on stock L03. It does not put my engine in any bind actually I like the gear under 80mph. 3.42s or 3.23s would be better but I really didn't lose much mpg going from 2.73s At 60mph I'm only running 2100 + or- rpm. I have a set of 3.23s in great shape PM me if you need em I doubt I ever swap to them. My car isnt a stick like yours is though I'm sure there is a lil difference there yours would probably turn even less rpm

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Old 01-28-2019, 05:41 PM
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Re: Rear axle ratio recommendations for L05/T5 build

T5??? Better install it with wing-nuts so you don't need tools to take it back out when it shatters.

The deepest gears you can buy gasoline for would lessen the load on the trans: 3.73, 3.90, 4.11, etc.

The aftermarket has uprated internal parts, but of course they're expensive. Drive it gently.
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Old 01-28-2019, 05:52 PM
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Re: Rear axle ratio recommendations for L05/T5 build

Originally Posted by Schurkey View Post
T5??? Better install it with wing-nuts so you don't need tools to take it back out when it shatters.

The deepest gears you can buy gasoline for would lessen the load on the trans: 3.73, 3.90, 4.11, etc.

The aftermarket has uprated internal parts, but of course they're expensive. Drive it gently.
I've built more T5s than I can count. I'm aware of their shortcomings. The trans is the least of my worries. I'm looking for a gear to keep the engine in it's happy spot and get decent mileage. Do you have any experience with those gear ratios behind TBI engines with stock cam and heads?
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Old 01-28-2019, 06:03 PM
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Re: Rear axle ratio recommendations for L05/T5 build

2.73 posi from a 4th gen auto car would be my choice. I had a LT1 F-car cammed TBI head engine pulling around a G20 van with a 700r4 and 3.08 gears with a ~28" tall tire. 70 mph @ 1,700 rpm and plenty of torque to pull hills without downshifting much if ever.

That cam is JUNK! I HATE that cam in stock Vortecs with good flowing heads. It will be DONE by 4,000-4,500 rpm.

Last edited by Fast355; 01-28-2019 at 06:16 PM.
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Old 01-28-2019, 06:41 PM
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Re: Rear axle ratio recommendations for L05/T5 build

Originally Posted by Fast355 View Post
2.73 posi from a 4th gen auto car would be my choice. I had a LT1 F-car cammed TBI head engine pulling around a G20 van with a 700r4 and 3.08 gears with a ~28" tall tire. 70 mph @ 1,700 rpm and plenty of torque to pull hills without downshifting much if ever.

That cam is JUNK! I HATE that cam in stock Vortecs with good flowing heads. It will be DONE by 4,000-4,500 rpm.
I too had an LT1 F-car cammed swirl port headed 305 with a TPI setup on it. Backed it with a V6 T5 that had a .76 OD and I LOVED that combo in my '91 Trans Am. That car was doing the exact duty I expect this car to do and it was a fantastic little combo. Torque for days and no down shifting even with the cruise set in the smoky mountains. It got with it too, i'm sure it would have been at least a high 14sec car.

If my math is correct, a 3.23 gear with the .63 OD I have now would put me within 40rpm of the 2.73 gear .76 OD that I had back then and liked so well. dmccain you have a PM LOL.

Fast, I'm running stock swirl ports on this L05. I have a B-body LT1 cam but its in a running used engine that I don't want to start robbing parts off of. I figured the L31 cam would be an OK fit with the stock swirl ports, but have no personal experience. As stated earlier I did run an F-car LT1 cam in a swirl port headed 305 and loved it. Do you feel strongly enough about this to recommend I spend the $$ for a new cam? (I've had no luck finding any LT1 cam so far). I covet your opinion here, you probably have more experience here than anyone else on this site.
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Old 01-28-2019, 07:12 PM
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Re: Rear axle ratio recommendations for L05/T5 build

Originally Posted by 1MeanZ View Post
I too had an LT1 F-car cammed swirl port headed 305 with a TPI setup on it. Backed it with a V6 T5 that had a .76 OD and I LOVED that combo in my '91 Trans Am. That car was doing the exact duty I expect this car to do and it was a fantastic little combo. Torque for days and no down shifting even with the cruise set in the smoky mountains. It got with it too, i'm sure it would have been at least a high 14sec car.

If my math is correct, a 3.23 gear with the .63 OD I have now would put me within 40rpm of the 2.73 gear .76 OD that I had back then and liked so well. dmccain you have a PM LOL.

Fast, I'm running stock swirl ports on this L05. I have a B-body LT1 cam but its in a running used engine that I don't want to start robbing parts off of. I figured the L31 cam would be an OK fit with the stock swirl ports, but have no personal experience. As stated earlier I did run an F-car LT1 cam in a swirl port headed 305 and loved it. Do you feel strongly enough about this to recommend I spend the $$ for a new cam? (I've had no luck finding any LT1 cam so far). I covet your opinion here, you probably have more experience here than anyone else on this site.
From what I remember you tune. What if I told you that you can get a Crane 2032 hydraulic roller cam new from GM for under $100. It was used in some of the GM marine TBI and MPI engines. Its 214/220 duration, .452/.465 lift on a 112 LSA with a 108 ICL and would still make great off-idle and low end torque torque. The GM 395 marine cam is also an excellent choice but about 2x as much money.
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Old 01-28-2019, 09:25 PM
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Re: Rear axle ratio recommendations for L05/T5 build

I would love to hear more about that. Is there a GM part number I should dig for? Iíll go dig on Scoggin Dickeyís site and see what I can find.

Yes I tune. Planning to start with the 9C1 tune and go from there.
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Old 01-28-2019, 10:28 PM
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Re: Rear axle ratio recommendations for L05/T5 build

Where can I get this cheap roller cam is what I want to know? Man that would be nice for that L05 .Actually probably a better choice than the #049 GM camshaft i plan to use in my TBI L98 build.
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Old 01-28-2019, 10:51 PM
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Re: Rear axle ratio recommendations for L05/T5 build

Keep us updated on this swap chief, very interested. I also plan to swap my L03 for a L98 i have sitting on the engine stand hopefully this summer. I'm still buying parts n such.
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Old 01-28-2019, 10:55 PM
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Re: Rear axle ratio recommendations for L05/T5 build

This will be an interesting swap!
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Old 01-28-2019, 11:02 PM
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Re: Rear axle ratio recommendations for L05/T5 build

GM 94666492
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Old 01-29-2019, 12:17 PM
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Re: Rear axle ratio recommendations for L05/T5 build

Gotta be one of the best kept secrets on the 'net right there. There is almost no info on this cam. I wanted to verify that it was in-fact a roller cam, and it appears it is, amazingly. Mercury PN 431-866022T.

If I can verify all the info I'll be ordering this thing right up.

EDIT: I just purchased this cam. Lift is lower, but from a duration standpoint, this cam should be to a 350 what my XFI268 is to my 383. This might turn out to be a nice little combo after all!

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Old 01-29-2019, 03:10 PM
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Re: Rear axle ratio recommendations for L05/T5 build

...So GM cancelled my order. Apparently this cam is no longer available. So now my choices are...
  1. run the stock L31 cam I have
  2. steal the B-body LT1 cam out a running engine
  3. steal the L98 cam out of the running '92 L98 that I have
  4. buy a new cam
I want to keep this project moving, and have not had much luck finding an F-body LT1 cam yet.
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Old 01-29-2019, 03:34 PM
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Re: Rear axle ratio recommendations for L05/T5 build

I hate that. I recently traded off an extra 049 GM cam 207 213 dur 415 431 lift. Guy put it in a stock L31 powered S10 and it went 12.9s. I'm probably going to use my other one on my engine.
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Old 01-29-2019, 04:59 PM
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Re: Rear axle ratio recommendations for L05/T5 build

Originally Posted by 1MeanZ View Post
...So GM cancelled my order. Apparently this cam is no longer available. So now my choices are...
  1. run the stock L31 cam I have
  2. steal the B-body LT1 cam out a running engine
  3. steal the L98 cam out of the running '92 L98 that I have
  4. buy a new cam
I want to keep this project moving, and have not had much luck finding an F-body LT1 cam yet.
There was one on Ebay for $175.00. I guess the reason that cam was so inexpensive when I picked one up a couple of weeks ago was because GM was doing away with them.
'
The B-car LT1 grind is essentially what you have with the Vortec cam except the Vortec cam drops in 5* advance while the LT1 cam drops in straight up. An adjustable timing set or a degree bushing set would retard the Vortec cam and make it basically the same thing as a B-car LT1. L98 cam would basically give you a 9C1 caprice engine. I think they were rated at 205-210 HP net from GM.
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Old 01-30-2019, 09:34 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Fallowing this. i am wanting a diff gear as well. 2.73's i think is what i have now. even at 75mph i am just at 2k or a hair above rpm but i have the 700r4 auto. was thinking 3.42 or 3.73 gears.
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Old 02-01-2019, 01:35 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Sorry to hijack.

Fast, I'm building a a 350 for my 86 chev truck. tbi heads with some bowl work, flat tops, 030 over, qjet, etc i have a tpi cam that i was going to use because it has a fuel pump lobe, and im running a mechanical pump. was going to run 1.7 scorpion rockers to bring up the effective duration. would this gm 94666492 be a better cam choice? I really want to have a LSA of 112 or more. My heads have already been setup with compcams 981-16 springs. machinist said heads are good for about 550 lift. will eventually run 3.73s or 4.11s. with 29.5" tall tire

Last edited by morgsie; 02-01-2019 at 01:44 PM.
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Old 02-01-2019, 01:46 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Certainly a better cam...IF you can tune it.... The stock TPI cam would probably run fine on a stock 350 tune.
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Old 02-01-2019, 02:19 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Originally Posted by morgsie View Post
Sorry to hijack.

Fast, I'm building a a 350 for my 86 chev truck. tbi heads with some bowl work, flat tops, 030 over, qjet, etc i have a tpi cam that i was going to use because it has a fuel pump lobe, and im running a mechanical pump. was going to run 1.7 scorpion rockers to bring up the effective duration. would this gm 94666492 be a better cam choice? I really want to have a LSA of 112 or more. My heads have already been setup with compcams 981-16 springs. machinist said heads are good for about 550 lift. will eventually run 3.73s or 4.11s. with 29.5" tall tire
So you're hijacking my thread to ask about a cam that I specifically said is no longer available just a few posts above? And its in a truck and not thirdgen related? How bout you keep this thread on topic and PM Fast355 if you have questions directed at him....

Fast, you commented that the vortec cam was ground 5 degrees advanced from the B-car LT1 cam? Given the cylinder heads in play here, why would I not want to leave the cam advanced a few degrees?

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Old 02-01-2019, 02:34 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

It's on gmpartsdirect as well as on ebay. I'm. running a Qjet tuning should be no problem. fast's PM have been full for a number of years now.
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Old 02-01-2019, 03:04 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Again, did you not read my post? I said GM cancelled my order when I tried to buy one. I ordered it from GMpartsdirect.com.
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Old 02-01-2019, 07:50 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Your posts don't mention gmpartsdirect. AFAIK, GM does not own gmpartsdirect, it's a third party that acquires and sells GM parts. So when someone says "I ordered it from GM" most of us would think you went to the dealer. I apologized for hijacking your thread, but I am not sure why you have to get this cam from "GM" when it is still obtainable elsewhere.
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Old 02-01-2019, 09:44 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Originally Posted by 1MeanZ View Post
Fast, you commented that the vortec cam was ground 5 degrees advanced from the B-car LT1 cam? Given the cylinder heads in play here, why would I not want to leave the cam advanced a few degrees?
The cam is tiny anyway in both duration and lift. My Vortec 5.7 in my Express van in factory form felt like it lost power when it downshifted to pass. At 60 mph it would unlock the converter, drop to 3rd then downshift to 2nd. It was dead to the world at 4,600 rpm much less the 5,000 rpm factory shift points. Factory LT4 cam in the same van with 1.6 rockers would pull nicely to 5,500 rpm shift points. I had a LT1 F-car cam in a TBI G20 van at one point as well. I shifted it at about 5,200 rpm as well. Best budget cam I have ever run with TBI heads was a Crane 100052. It is a flat tappet cam but it keeps a person from having to spend a ton of money beefing up the valve train for a roller cam and its spring requirements. 272/272 @ .004, 218/218 @ 0.050", .454/.454" lift, 110 LSA, 106 ICL. In a 350 it idles very solid with about 17-18 in/hg vacuum @ 750 rpm. Single pattern cams work much better wth TBI heads .
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Old 02-20-2019, 07:43 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

1MeanZ, did you decide on a cam? Doing an 083 headed TBI in an S truck. Curious about the direction you chose.
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Old 02-21-2019, 09:25 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Yah I just stuffed the stock L31 cam in and called it a day. I installed it straight up, and measured the valve springs already on the engine and they were identical to the L98 ones I had so I just left them on as they were. I cleaned and rebuilt the lifters and bolted all the roller cam stuff on the L05 block. Primed it last weekend and it makes 60psi on the drill. Going between the fenders this weekend hopefully.
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Old 03-11-2019, 08:42 AM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Well how is this thing running? You get this project finished?
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Old 03-11-2019, 04:20 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Got derailed by an engine bay clean-up project that was miserable. But here we are as of today.





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Old 03-11-2019, 05:00 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

To you or anyone interested, I found the cam recommended by Fast355 and placed an order this morning. So far no cancellation, Iíll update the status either way it goes. $105 shipped to my door.
https://parts.chevroletbuickgmcofmur...shaft-94666492
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Old 04-10-2019, 07:20 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Originally Posted by Ty92Z View Post
To you or anyone interested, I found the cam recommended by Fast355 and placed an order this morning. So far no cancellation, Iíll update the status either way it goes. $105 shipped to my door.
https://parts.chevroletbuickgmcofmur...shaft-94666492
Did your cam ever show up?
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Old 04-10-2019, 07:47 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Yes, forgot to come back and update. Ordered on Monday, was at my door on Friday. $105.50!
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Old 04-10-2019, 07:53 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

So project update here. Engine and trans are in and running very well so far. Second chip I burned has been a winner so far. Still going to datalog it and get some fine tuning in, but its more than good enough to drive around reliably and gather data.

The 2.73s rear axle is still in it, I'll begin work on building a 3.23 posi disc rear this weekend. I'm running my old C4 Grand Sport wheels on it now, yes it has 17x11 rims and 315s on the back like it needs those LOL. The front tires are excellent, the rear tires are nearly bald (blame my other IROC). I also rebuilt the entire suspension last week with global west del-a-lum bushings, camber plates, PST steering kit, new ball joints, 36mm sway bar and KYB struts in the front, and a 24mm sway bar and KYB shocks out back. I may go back and cut the springs half a coil, can't decide if it sits up too high or not. Looks higher in pix than it does in person.

How's the power? Surprisingly good for as lame as the build is. It will spin the 315s from a roll in 1st gear on pretty much any surface and makes that cool quadrajetesque (is that a word?) intake howl at WOT. Its done by 4500 rpm which I expected, but it does a good job below that. It certainly buries the old L03 that was in it. I'd say its on par with a stock L98, I expect improvement in acceleration when the 3.23 gear finally goes in. So far I have no regrets except maybe that I should have cut the springs when they were out. It's just a mild daily driver that makes the right noises and is quick enough to be fun with a manual trans. Once the rear axle is finished I'll probably try and get the AC fixed, then some better speakers, carpet and I've got my eye on a set of grey Corbeau GTS II seats. I bought this car for $2400, it was sitting in a guys back yard for something like 5 years, hopefully it appreciates it's new lease on life. If I keep this up the car is going to need a paint job...







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Old 04-10-2019, 08:09 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Nice job, as usual, Jeremy!
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Old 04-10-2019, 08:39 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Man that's a nice daily driver it's got to be fun to drive!
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Old 04-11-2019, 10:39 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Excellent! When you get the rear axle ratio changed, that IROC should scoot pretty well.
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Old 04-26-2019, 03:26 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

Jeremy what injectors are you running on this combo and what PSI? I figure 350 injectors at 14psi should be plenty for my build which isn't far off from yours. May run sum 68lbers at 11-12psi though to keep from pulling that pump outa there, don't know if my old stocker will make 14lb..
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Old 04-26-2019, 08:51 PM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

I went with the 61lb injectors. The 65lb cop car injectors were a ton more money on eBay for some reason. I did buy a 14psi regulator spring for the throttle body. The previous owner replaced the fuel pump in this car and I have no idea what it is and I haven't checked actual fuel pressure yet nor do I have pulsewidth in my datastream when I datalog. So I don't know my fuel pressure nor do I know my injector duty cycle. All I do know is that I have enough fuel to drown the engine at WOT at 4500rpm( just under 10:1), I discovered that during tuning with my wideband. When I did the calculations to figure out what BPW to put in the tune, I did the math for 61lb injectors at 14psi. I was globally too lean, so I re-did the calculations at 12psi and that put me spot on for the most part. So I don't know if that means my pump can only do 12psi or what, but the car runs good and I've got access to plenty of fuel so I haven't cracked a line open to measure. I haven't done much TBI tuning up to this point so I just found a datastream definition that will give me knock counts, so now I'm going to start pushing the timing a bit. I started out only giving it 26* total advance at WOT, then I bumped it up to 29* and it leaned out a bit, so I added fuel and it ended up being too much. I'm at 30* now and I'm at a comfortable 12.5:1 AFR at WOT. I'll try going to 32 now that I can monitor knock counts.

The 3.23 gear is working out really well. It's a great gear for this T5 and a low rpm engine. 1st gear is just long enough, I wouldn't go any more than a 3.42 gear in this application. It's got great power for what it is. It's every bit as strong as a stock L98 car, I'd say. I'll have to go play with Pontiac_Pete's GTA or 92RS(real slow)'s 89 IROC and see what happens. For an assembly of spare parts, i'm happy with the combo. I know I left power on the table with the cam, I know the heads suck, but it is WORLDS stronger than the 305/2.73 gear combo was so I'm happy. The car got a host of suspension upgrades along with the posi disc 3.23 rear axle. Now I need to decide if I should fix the AC, get better speakers, new carpet/seats or all of the above! LOL







Last edited by 1MeanZ; 04-26-2019 at 08:56 PM.
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Old 04-27-2019, 07:17 AM
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Re: Rear axle ratio (and now camshaft) recommendations for L05/T5 build

You've done an excellent job with it man id throw that a/c in there. Very cool car!
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