Hey All,

I just finished building and installing my new fuel injected 383 engine, and I'm having pretty noticeable shuddering while cruising when the torque converter locks up around town. I would like to reduce this if possible. That said, I do still like to drive the car to work occasionally, which requires me to cruise on the highway, generally around 80 MPH. Right now I think I have narrowed my best options to be either the less common, but definitely existing 3.55, or the more common 3.73. I am currently running my factory 3.23. I also autocross the car, so I'm sure a higher ratio to some extent would benefit that.

Current Vehicle Specs:
- Holley Stealth Ram Intake with dual 58mm throttle body
- D.U.I. Distributor
- High Flow Water Pump
- SLP 3/4" Shortie Headers
- Billet aluminum adjustable fuel pressure regulator set to 45 PSI with vacuum disconnected.
- 2600 RPM stall 9.5" converter in my reworked 700R4 trans. Have to see how long the trans lasts...
- AFR #1040 195 intake runner, street CNC aluminum heads with 65cc chambers.
- Smeding Short Block including full rotating assembly, oil pump, oil pan, timing set, timing cover, hydraulic roller lifters, dog bones, spider, and camshaft "450 HP" .544"/555" Lift W/1.6 rockers, 231°/236° Duration @ .050”, 111 LSA, 9cc 'D' shaped dished pistons to achieve a 10.46 CR with a 0.032 head gasket and resulting in a 0.042" quench.(They call it their 450hp Extreme cam, but in their dyno test sheets they use a carburetor and 1.5 ratio rockers. With my 1.6 ratio rockers and fuel injection it may make a bit more...I'm expecting this build to be in the ballpark of 460-480 HP at the flex plate)
- Comp Cams Ultra Pro Magnum 1.6 ratio 3/8" non-self aligning rockers
- South Bay 36 lb/hr injectors
- 255 LPM fuel pump
- 30-0300 AEM 52mm Wideband UEGO Air Fuel Ratio Sensor Controller Gauge in Passenger exhaust bank. (Wired to ECM for logging)
- Tuning with Moates Burn 2 chip programmer and ALDU1 datalogger
- 3.23 ratio 10 bolt posi rear end, with reinforced cast aluminum cover.
- 3.5" Catback with Magnaflow straight through muffler and single turn down outlet (No cats though)

Engine Build Thread:
Fuel Injected 383 SBC Build for Street and Autocross - Third Generation F-Body Message Boards
Engine Tuning Thread:
Tuning New 383 Stealth Ram Engine Build For AutoX & Street - Third Generation F-Body Message Boards

 

I've done some calculations to see what my engine speed would be at different vehicle speeds with the various gears. I'll share that below. I guess the question is, is cruising at 80 on the highway with the engine spinning along over 2700 rpm ok? Ok for the life of the engine? Ok for me as a driver, I would think that would be pretty loud and annoying for any extended period of time... Then again my cam seems to like some RPM and runs smoother at some higher RPMs, Its really pretty clearly not happy between 1000 and 1500 maybe even higher...

 

I wouldn't go anything numerically less than 3.42.

3.42 + TH700R4 is a perfect combination IMO. Anything steeper and the 1st gear starts to get unuseable... especially with a 383.

It's very comfortable cruising along at 80 mph.

 

I'm just worried 3.42 may not be enough of a difference to smooth out my engine on cruise... that's why I liked the idea of the 3.55, or I just use the far more common 3.73 but have to put up with a few more rpms on the highway...

Any other experiences or opinions floating around out there?

 

I have a ford nine inch w 4.11s. My old setup was a 450hp/tq 350. For a short period of time I had a t5 w that engine/rear. It was terrible. It was way too. Like way too low first and I was in 5th at 50. Then I swapped in a t56 and then double OD made it perfect. Ive driven some 3.55 and 3.73 cars and w an engine that likes to rev, 3.73s are perfect. You will be happy w 3.55s or 3.73s. A 383 will pull either really well. Just make sure your torque converter will have the proper stall. From a performance point of view, I'd probably do the 3.73. Don't go lower than that. It will be miserable. I had a 350hp/400tq 350 w 3.55s and I felt it needed a little more gear. What size rear tires do you have? If they're taller they'll be better w 3.73s. Also, is your car heavier? If you have a fully loaded car that's 3700-3800 that's more to consider. Some of these cars are 3200. A light car w smaller tires and a 383 may feel better w 3.55s.

I really like the lower gears in my car, I liked them w the N/A 350 and now w a blower. I have 305/35/18s in the rear. It drives really aggressively and blows through the gears quick. If you want that feel, 3.73 will be better for you. The lower gears will also be better for your trans.

 

Manual trans and Auto trans are apples and oranges when it comes to rear axle gear selection. The OP has an auto trans.

 

Yeah, I aware of both. More my point is how aggressive he wants it to drive/feel. Also not to go too low. The final drive ratio w a t5 and a th700 is similar. If he goes below 3.73 (like 3.90/4.10) it will likely be too low w that engine. The auto 3.55 cars I've driven also seemed a little less snappy. In the past I've struggled picking ring and pinions in multiple vehicles. I'm more just putting out experience/feel in these cars. I've had and driven a whole bunch w numerous trans and rears. Didn't mean to come off confusing.

 

I think I follow what you are saying. Reality is, for auto x I would like to be able to say in second, and not ever have to shift to third. The 3.55 gears would allow me to get to about 80 MPH before running out of RPM, and the 3.73, would allow me to get to about 75 MPH with the same engine speed... I know both those speeds are pretty high, but a quick google search does bring up a couple events where 75 to 80 mph has been seen, so maybe this pushes me a bit in the direction of the 3.55? I just wish I knew if that gear was going to be enough to smooth out my shuttering at light throttle cruising speeds when the converter locks...

 

I have no doubt that your 383 will pull w the 3.55s well. The 3.55 will give you longer gears and like you said, more likely to keep you out of third. Yeah, the shudder may be decreased by lower gears slightly but your trans will do more shifting also.

 

Also, it was on my spreadsheet above, but i lever typed it out in the post. My tire dia is pretty small, factory size. So that may reduce the necessity of going all the way to the 3.73 gears.

275/40-17... 25.7 inches tall dia.

 

Yeah, that size w a 3.55 would be even better. I had that size for years. It is a smaller tire and a little tougher to hook up with I bet you'd be happier w 3.55s all around.

 

Does it shudder without lockup? I'd expect to keep a cam with duration like that above 1500rpm almost all the time. I just don't see any of those gear options making enough of a difference to fix the symptom.

 

No, it seems relatively smooth with the converter unlocked. Only have the issue when locked and very light throttle around 2-4% (cruising).

Could it also be effected by other tuning parameters? AFR? Spark advance?

 

IMO you're trying to do small cam things with a medium cam. Change your lockup to only activate in 4th gear above 45mph, it'll probably be fine as-is until you do the t56 swap.

 

Remind me what you have for engine management system and how you tuned the engine?

This engine has a lot more cam overlap than stock with more exhaust reversion in the intake manifold and poor cylinder fill at low rpms. It's going to be a lot more finicky about cruising at low rpm's than your stock engine, especially at a low % load. It might get better with some detailed tuning, but your shift points and lockup points are going to be different than stock. Don't make the engine run unhappy at low rpm's, this is where detonation is high risk.

 

I'm tuning in Tuner Pro, burning chips with my Moates burner, and logging with the Moates logging adapter. I could share a log if that might help.

I have tuned my shift governer for higher shifts. Right now 1-2 seems to be about 5500 when I can get traction, 2-3 is around 6. Converter is a 9" 2600rpm stall.

My knock sensor is hooked up and seems to be working, I always start my logs before startup, so I can track the 2-3 knock counts associated with the system test done by the ecm at startup.

I fully understand it's not going to run like stock, but this seems like a problem I need to resolve, with gearing or otherwise...

 

New concern... I am starting to come to the conclusion that 3.55 gears would be the ideal ratio for my application and needs, BUT it looks like the only offerings are from Motive or Excel by Richmond. Are either of these manufacturers going to give me the quality and reliability I need for hopefully years of road and autocross driving??? Which would be my best choice? Sounds like Motive owns Richmond now, so they may literally be the same gearset...

 

Are we talking about the the torque converter clutch shuddering? Or the motor bucking because of the camshaft? This problem of bucking is more pronounced in stick shifts or the lockup clutch coming on too low of an rpm in the 700R4, especially when under a load.

 

You make a good point. Then again, if you're considering 18s (super common these days) and have a plan to end up with taller tires on those, maybe 3.73 or 3.90 is exactly what you'll need then.

Pick out your new autox and street tire sizes for fun and let it guide you.
I don't plan on running 15s or 16s or 17s. Maybe you do.

 

305 35 18s fit really well in the rear and hook up so well! Just got my second set today!

 

Very nice, I bought the wheels I have now, specifically for my start at autox'ing. I don't plan on buying any other wheels. I have found the strange reality, that while there are less options in the 17" size, which is annoying, for some reason, they're significantly cheaper than the same tire in 18" size. That was part of my consideration...

I did some more paying attention to how the car runs and feels at various rpms. Like cruising at higher speeds in 3rd gear instead of 4th, and I think the 3.73 won't be as bad as I though, plus for the most problematic slow to mid speed driving I do, it will get the rpms into a better range for my engine, so that is now the route I'm planning to go. Only thing now is while I can get a good quality gear set and installation kit for around $1k, I think I can get a full new rear end for between $2500 and $3500, given the power I'm making, there is no way to know if my 7.625" 10 bolt will hold up, so I'm strongly considering just replacing the whole rear end to get into the ratio I need and not have to worry about running too much torque through it... Now I need to go down the rabbit hole of 12 Bolt vs S60 vs Ford 9"... Pretty sure they will all handle anything I can throw at it, so I just need to find the one that is cheapest at the end of the project, I've heard some end up having fitment issues, or need lots of extra little bits that make them more expensive options that they start out at first...

 

I have a moser 9in and I'm really happy w it. But it was a pain to get set up well. In the end, happy I did it. I had wilwood brakes w internal drum parking brakes. I'd say take the price of the rear and add 2500 in additional stuff tor installing it. Between a driveshaft/brakes/parking brake cables and all the other stuff it really added up quick. I needed adjustable trailing arms to move it back 3/4 of an inch.

 

That's what I'm realizing the more I research... I am trying to finalize if I can reuse my rear calipers if I use LT1 adapters and discs... i think i can for the 12 bolts or S60, i think... need to make some phone calls.

Now though, I'm starting to reconsider giving my original 10 bolt one more chance... I had written that option off when it looked like $1k for a decent gearset and installation kit, BUT THEN I found that advance auto seems to sell the Motive performance G8 series gearsets for $180 right now with the current 20% off! Similarly they had the Motive "super" installation kit (granted with the Koyo bearings not the Timkens, though I read they are plenty good too) with everything for only $112! So while I can return it all if I decide to, I ordered them to see if what shows up is really what I expect. This would have been 3x or more from summit!

All those deals aside, I'm now becoming concerned about all the specialty tools I'm going to need if I want to do the gear and bearing swap myself...
Maybe someone can speak to which are truly critical or which have reasonable workarounds for a single gear swap... Or which are readily available ad rental tools? (I have advance, O'Reilly, and autozone near me)
- Case spreader
- shim setters
- dial indicator with mag base
- Hydraulic press
- special threaded carrier bearing removal tools
- probubly more...

Or what could I reasonably expect to pay a shop to do the work for me?

 

I think you're at the max for a stock rear. It will work but your not gonna get a ton of use out of it w a 383 auto x ing. The parts are usually 1-1.5k depending on what you get. It's another 1k(ish) for labor. I'd plan on 2.7-3k for the stocker to get a full rebuild w high quality stuff. Last time I had my truck re-geared it was hard to find someone to do the work who was knowledgeable. It's kind of a dying art. It used to be pretty easy to find someone who will set up a R&P.

the 9in is nice w the removable third member. It's also nice to dump my clutch w sticky tires and not have to worry (much!!). But the swap over is a deal.

I always have tried to use Timken bearings but I've had koyos and had no issues w them. They should be fine.

 

That's exactly why I'm reconsidering building up my 10 bolt. Instead of parts costing 1.5k, it seems I've got most everything for less than $300. Maybe cheap enough to give it a try, or buy some time... My '91 rear end has the larger axles, clutch type posi that still seems to work relatively well, I already have the reinforced Aluminum over with cap preloading bolts and my auto trans, makes me think maybe it will hold on for a while. I also am able to weld, so if I come to the conclusion, that I can actually do the gearset myself, I can hopefully weld up the tubes at the same time. I'll put some fresh C clips in it, as those may have worn a bit, and I also ordered a solid pinion spacer kit, which is supposed to help improve reliability a bit, not sure what other parts would be wise to replace if I am going to try sticking with the 10 bolt for a bit longer... I'm still just a bit concerned about all the specialized tools...

 

Honestly can't believe it, but all the 10 bolt parts came today, and they're exactly as advertised! These less than $300 of parts would have been $760 at summit racing! Now I just need to decide it I try them out or return them and get a 'real' rear end for more 10 times the money... I will say the 7.625" gearing really is quite small...

I will say though, the Motive Performance gearing looks really nice , well made and machined. And, that is coming from the engineering manager of a company that manufactures industrial gearboxes!

I also got fresh C clips and a crush sleeve eliminator shim kit for setting pinion preload from Yukon! Sounds like i still need a shim driver and a bar style 0-80 in-lb torque wrench for checking pinion drag, and I would be about ready to do the job!

 

So I need a sanity check here... I know I need to go 3.73 for ratio and my two options are a whole new rear axle assembly, 12 bolt, S60, or Ford 9", which at the very least looks like it would cost $3500 plus a new drive shaft, and whatever it costs to get rear brakes sorted out...

Or, I rebuild and beef up my 10 bolt. I was leaning toward the new whole axle, till I started finding some really good deals on components and now think I could fully rebuild and beef up my current 1991 10 bolt for about $877. Even if this doesn't last forever, it still may be the right choice for the next few years... I could return every item at this point and go full axle assembly, but I'm leaning more and more toward giving my 10 bolt a chance... I alredy have a cast AL cover with bearing cap supports, I plan to weld my axle tubes during the rebuild, and for this money, I'll be replacing all bearings and seals, get a new yukon limited slip, new axles from the stronger new material with a beefier profile, new gearset, and I'm running an auto with 2600 stall converter, so there should be no super intense "hits" on the rear end. My engine should make around 475 hp once I finish tuning. I estimate it to be around 410 hp currently...

What are your thoughts? Could a 10 bolt built this way last, or is it a waste of money? Some of these deals I found are really good too!

 

I haven't gotten many responses here, and we're not deciding on ratio anymore anyway. That's been decided on, 3.73.

So I started a new thread to discuss the rebuild here.