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Need opinions. For a weekend/track car only focused on quickness, which combined 1st gear is preferable....9.73 vs 10.68 for the following car.
1967 Olds Cutlass weighing 3375, w435HP 468BBO, 9.5:1, Cs, Torker, headers, 800 QJet, Lunati Voodoo 227/233, .510/.522, built 200-4R, and either my 3.55 (9.73) or my 3.90 (10.68). I guess I always felt steeper must mean quicker, but some feel a big block can have too much gear. For 1/4 mile acceleration on this car, which do you like...9.73 or 10.68 combined 1st?
Last edited by Chris6542; September 16th, 2020 at 10:45 AM.
Nice car by the way. What size slick are you running? Where does your peak HP come in? What stall are you running? The 3.90 gear will be more fun horsing around on the street but hooking at the track will be more difficult. There is a 67 struggling to get below a 2.0 60 ft due to traction issues, I believe he has 3.90 gears as well. He has air bags and aftermarket suspension along with a 4 spd manual to add in another variable. I am sure some of the experts will chime in. You have fun cruiser with the 2004R. Depending on the cam and tire size, it might cruise better with the 3.90 gear down the highway as well.
To answer some questions.... 10" slicks, will probably step up to 11" as my wheelwells will accomodate. Cam is medium Lunati and peaks about 5100rpm. As for RPM thru traps: My desktop dyno predicts 12.65@ 108.35. So, at a projected 108.35, that crunches out to 4678rpm in 3rd at the lights with 3.55 and 5139rpm (perfect) with 3.90 installed. As for cruise RPM, 2169rpm at 75mph with 3.55 and 2383rpm with 3.90. I also have a plan to get the car to about 3075 (300 off current) with a number of changes.
Last edited by Chris6542; September 16th, 2020 at 03:00 PM.
Rear end gearing has more to do with trap rpm. A good starting point is to figure out your potential mph at the stripe. Remember to take into account converter slip. With the combo you listed the 3.90 is a good starting place. You can vary you trap rpm with tire hight. Pick a tire hight that allows you to move 1 inch up or down to start. 27 to 28 should work. This will allow for about +/- 200 rpm. Don't worry about width so much.
Need to see how long the power carries after peak to determine the best gear ratio...
Also, what converter brand and style are you running (size and expected stall range)? The design and manufacturer will make a big difference in how much slip you end up with, also, does it have an upgraded lock up clutch that you can engage at full throttle? That will help a bit on mph and E.T.
You have an overdrive, you can use more gear because you don't want the cruise RPM to be too low and have the engine below a good power band (lugging).
Last edited by Battenrunner; September 17th, 2020 at 10:36 PM.
Sorry Battenrunner, just saw your reply. My cam is pretty tame, the Lunati Voodoo 268/276 (227/233 @ .050 and .510/.522). Saw a similar 455 build and dyno online with this exact cam and it only lost 20HP on the dyno from 5000rpm to 5700rpm (carried it out pretty well). As for trans and converter. I built my 200-4R with upgrade parts from Chris @ CK and the converter is a Torco 2200-2500 full size with lockup. They are made here in LA and get great ratings for garden variety builds. I wanted to keep the lockup which is why I didnt go a bit higher like 3000. Ironically, i just found a converter house that builds full billet race converters for the 200 with a full race double clutch for lockup. Any stall I want up to 5000 WITH lockup. About $1100 bucks though. As for tires, with my 275/60 Mickey ST radials, I tach about 2400rpm at 75mph. Im looking to go to the Hoosier Quick Time 295/60s (29.6 diameter) which will tach about 2225rpm at 75mph. While my torque peak appears to be about 3700, Im sure its still making alot of torque at 2225 being 468 cubes....I would think. The 1995 LT1 Corvette I had with only a 350 tached about 2050 at 75 and it never lugged. Thoughts?
Last edited by Chris6542; October 1st, 2020 at 10:33 AM.
I am also planning 3.90 gears, building my 2004R up with parts from CK and have a similar PATC 2200 to 2500 stall lock up converter. It flashes around 2300-2350 with my current 350, hoping to push closer to 2500 with the 424. I would think you will be flashing at 2500+. You won't lug even with a tall tire, your cam isn't big for a 455, especially if you drive at 75 mph.
That converter you have is really for more of a daily driver or nice fun hot rod, not a street/strip race car... I think You need something to flash in the 3500rpm+ range to have a chance to get some good E.T. out of this combo.
If you go to a 29.6 tall tire, I would say the 3.90's are a minimum gear, and 4.11's would be even better.
Also, consider if you are always going to be running Naturally aspirated or if you will be spraying some Nitrous at some time. I would still say the 3.90's are the best choice if you move to the tall tire and spray it.
If you want the car to be fast, you have to start thinking about this in a performance perspective, not how low of RPM you can turn at 70mph..... It won't lug, but, you actually may not get as good of fuel mileage at the lower RPM as you would turning it a little faster.
This also has lots to do with the ignition timing, fuel curve tuning, and carburetor booster responsiveness. With a cam close to the size of yours, I got better mileage with a 400 trans and a 3.42 gear than I did with an overdrive and the same gears... just saying.
On a side note, I don't know if you will see as much power gain swapping to E85 as you hope, but, I would like to see a positive gain for you. The milder the combination of compression and cam, and the smaller the cfm that the intake port flows, the less power you will likely gain switching to E85.
Last edited by Battenrunner; October 1st, 2020 at 09:27 PM.
September 15th, 2020, 11:01 PM
