RPM in high gear

[EWalshak]

Can anyone tell me what rpm they are running at say 70mph. Im using a 1st gen 5. 9 with a 518 trans for a conversion project. Im thinking of looking for a newer trans with lockup converter because I think my rpm will be a little steep at highway speeds. Any help will be greatly appreciated. Gears are 3. 55, trans has overdrive

 

[BDaugherty]

Gear Ratio Calculator



Use the above calculator to see what different combinations would do for you.

You'll need to know your tire size.

 

[DBF]

Can anyone tell me what rpm they are running at say 70mph. Im using a 1st gen 5. 9 with a 518 trans for a conversion project. Im thinking of looking for a newer trans with lockup converter because I think my rpm will be a little steep at highway speeds. Any help will be greatly appreciated. Gears are 3. 55, trans has overdrive

Here are my calculations from back when:







Speed vs. RPM for tire and gear:



This is the theoretical speed for a gear and RPM.

Torque converter slip is not taken into account.



This calculation is for a Chrysler A518, 3. 56 rear end,

and 235-85/R16 Load Range E tires (31. 73" dia).



RPM 1 2 3 OD

1000 11 18 27 38

1500 16 27 40 58

2000 22 37 53 77

2500 27 46 66 96

3000 32 55 80 115

3500 38 64 93 135



AT Ratio: 2. 45 1. 45 1. 00 0. 69

 

[phillips5]

yea thats bout right im at 1550 at 55 on flat ground 355 gears in overdrive i think round 18 at 65

 

[EWalshak]

phillips5, thanks for the response. That sets me at ease a little if I use the 518 trans in the conversion, the rpm wont be that bad. That lower than I thought it would be.

 

[MMeier]

My tach shows an even 2000 at 70 MPH... 3. 54's, NV4500, BFG 235/85's.

 

[PToombs]

My tach shows an even 2000 at 70 MPH... 3. 54's, NV4500, BFG 235/85's.

Mines just about the same with the Getrag.

 

[EWalshak]

Thanks MMeier and PToombs, I haven't had success finding a 47rh so for now I am going to go thru the 518 with a master kit so I can get the burb project rolling. I can always upgrade later if it is neccesary. Thanks again

 

[EWalshak]

PToombs, what mods have you done to your 92?

 

[PToombs]

60mm kit for the H1C, PDR I/C, 370 injectors, fuel screw bottomed out, custom intake horn, ATS manifold, 4 inch exhaust turbo back, and whole bunch of other little stuff. It goes pretty good. :-laf

 

[EWalshak]

Can you tell me more about the 60mm kit. I dont want to sound like an ignoramous. Is that the size of inlet/wheel? (Dont laugh too hard) LOL

 

[PToombs]

Yes, you buy a kit, which is a compressor wheel and a housing. They're not hard to swap either. Things have changed since I bought mine. I got a stage IV, which was the 60mm 6 blade wheel, (stock is 56mm) housing, and backing plate. The plate was machined because the wheel was deeper. Stage 3 was a 8 blade wheel, housing, and no plate.

Since, I've heard that they changed things, and I think you need to have the stock plate machined. Best to call and ask. GDS (gillettes diesel service) is also a good place to buy. I bought a III kit from them because the IV wasn't available from HTT. After I got it, about a week later, HTT called and said they got parts, did I want a kit? I sold the III for what I had in it and bought the IV.

Hope this novella helped.

 

[EWalshak]

PToombs, Thanks for the info. Does changing the exhaust housing make a difference? Ive read in other posts about people changing something that was 12cm to 14cm or something like that. Whats that all about. Do these changes effect fuel mileage for the better or worse? What about injectors? As far as fuel mileage. Or can you do pretty good if your not too heavy with the right foot? I would like to have power available but dont want fuel mileage to suffer too much if possible. Or within reason.

 

[PToombs]

Putting a smaller ex housing on makes it spool faster. You're pushing the same amount of gases thru a smaller opening, so the compressor wheel spins faster giving you more air sooner to burn. It gives a faster response when you step on it quick. As for MPG, It should help, because you're burning the fuel faster.

Just having the old injectors cleaned and set will help mileage too. Bigger injectors will give you more MPG, if you can keep your foot out of it. I can't. When I went to SOP last fall, I got 23mpg at about 75 mph. I did have 10 gallons of motor oil in there too, so I'm sure that helped. Around town I get about 15-16, I just like to take off too quick to get good mpg.

 

[EWalshak]

Would a bigger turbo be an option? The motor is going into a big heavy vehicle(Suburban), its to haul the family around in but I want it to move out pretty good. Im just not sure exactly what mods I need to do to it toaccomplish this. I did however get a full 4'' turbo back exhaust from source automotive for it. It seems that 370 injectors are a popular choice amongst the tdr crowd.

 

[PToombs]

I'd be leary of 370's, unless you're going to a S300 or Super HX40 turbo. Your burb is heavier than my 92, and it gets hot! I can hit 1500* just blasting on it. And I have some good air flow mods, as mentioned in the previous post. I know the problem is the turbo, it's out of the map range. When I go above 3k rpm, the temps climb real fast. I even backed the fuel screw out 1-2 turns, and it only helped a little.

I'd say a not necessarily bigger, but a better turbo, 3 piece exhaust manifold, intercooler, maybe a set of Tim's CoolerTubz, that should help a lot.

 

[cerberusiam]

Would a bigger turbo be an option? The motor is going into a big heavy vehicle(Suburban), its to haul the family around in but I want it to move out pretty good. Im just not sure exactly what mods I need to do to it toaccomplish this. I did however get a full 4'' turbo back exhaust from source automotive for it. It seems that 370 injectors are a popular choice amongst the tdr crowd.

A turbo upgrade is going to do a lot more than other things for what you want. You can upgrade the existing one but you will still fall short of the capabilities with the newer turbo's. If you don't mind some fab work a HE351VE is about $150 of Ebay and will make a huge difference in driveability and spool up. It will take some work to mount but its worth it.



A straight HE351 off an 04. 5-07 5. 9 will fit nicely with few mods. It will also cost your more but much less than a custom aftermarket.



I have 370 injectors turned up pump and a HX35 on a 16 cm housing and its great unloaded. Loaded I have to watch long steep grades when I go over 16k GCVW but otherwise its good. More turbo would cure any problems I have with it.