Geared way too low.
Thread Starter
Instructor
Joined: Mar 2003
Posts: 195
Likes: 0
From: Eagle Wi
Geared way too low.
I just swapped in a 200-4R into a 77 with I think a 3.08 rear end.
I hear lots of people talk about how great the car is with these overdrive trannys but at 55 with the torque converter locked I am only reving around 1200. It's really low in my opinion. Heck at 75 I think I was at 1800 RPM.
I get on it just a little and she knocks in forth. I swaped in a 383 also and I am still playing some with the timing so I am not sure if I have it too advanced yet but It seems to me it's mostly being caused by the load at low rpm.
FYI: I have it timed with 36 deg advance with the mechanical all in and no vacuum advance. If I remember I get around 22 at idle. At idle I get another 16 deg when I hook up vacuum advance. I'm going from memory here so I might be off. Anyway I think I might back it off a couple degrees and see what happens.
Back to the main point. If I was going to swap out the rear gears what would people recommend for a higher ratio.
I hear lots of people talk about how great the car is with these overdrive trannys but at 55 with the torque converter locked I am only reving around 1200. It's really low in my opinion. Heck at 75 I think I was at 1800 RPM.
I get on it just a little and she knocks in forth. I swaped in a 383 also and I am still playing some with the timing so I am not sure if I have it too advanced yet but It seems to me it's mostly being caused by the load at low rpm.
FYI: I have it timed with 36 deg advance with the mechanical all in and no vacuum advance. If I remember I get around 22 at idle. At idle I get another 16 deg when I hook up vacuum advance. I'm going from memory here so I might be off. Anyway I think I might back it off a couple degrees and see what happens.
Back to the main point. If I was going to swap out the rear gears what would people recommend for a higher ratio.
Instructor
Joined: Jul 2005
Posts: 220
Likes: 0
From: Oakdale Ca
Tuned correctly, you should be fine with 3.08's...my F-body has a 700R4 and 2.77's, no ping (albeit TPI) but no knock retard either. You may want to go with an adjustable vacuum advance and think about running stiffer springs in the dizzy to slow the curve somewhat. Without OD, you should be perfroming (with the 200) pretty much the same as a TH350. Anything else change on the tranny swap?
Race Director
Joined: Jan 2003
Posts: 15,176
Likes: 88
From: State of Confusion
Originally Posted by big_G
No less than 3:55, no more than 3:70...3:70 equates to a final drive ratio of less that 3:00...
With 3.73s, a 700R4, and 255/R60-15 tires, I turn 2000 RPM at 60 MPH in 4th/OD with lock-up.
Race Director
Joined: Jan 2003
Posts: 15,176
Likes: 88
From: State of Confusion
Originally Posted by big_G
That sounds about perfect, Glen! 
great for mileage and top-end, but no mid-range 'punch' when 60 MPH was just 1500 RPM with the ol' Cross-Fire.....
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Intermediate
Joined: May 2005
Posts: 26
Likes: 0
2004r or 700r4? Need advice.
Hi all,
first post on the forum, although I've been reading your posts for awhile now and am extremely thankful for and impressed with all your insight and wisdom. You've been an invaluable source of information for me through my modification of my '77, which has been going on for about 2 years now. (This vette's been an oldie but a goodie - I've owned her for 22 years - but she's just plain tired out.) I'm pretty much done with the engine (still a few minor things left) and I've been thinking about swapping out my TH400 tranny for either a 700r4 or a 2004r (can't stand those high revs on the highway with 3.73 rear gears). I've read several posts about both overdrives, and it seems some say the 2004r is stronger than the 700r4. I realize that the later model 700's are stronger the older 700's, but are the 200's still stronger than the newer model 700's? Or is there any truth to the 200 being stronger? With my 383 pushing about 475 horsies and about 515 in tq, I really want a strong tranny to handle the low end. Any info would be greatly appreciated (once again). Thanks in advance to you guys - you're the greatest!
Marc.
first post on the forum, although I've been reading your posts for awhile now and am extremely thankful for and impressed with all your insight and wisdom. You've been an invaluable source of information for me through my modification of my '77, which has been going on for about 2 years now. (This vette's been an oldie but a goodie - I've owned her for 22 years - but she's just plain tired out.) I'm pretty much done with the engine (still a few minor things left) and I've been thinking about swapping out my TH400 tranny for either a 700r4 or a 2004r (can't stand those high revs on the highway with 3.73 rear gears). I've read several posts about both overdrives, and it seems some say the 2004r is stronger than the 700r4. I realize that the later model 700's are stronger the older 700's, but are the 200's still stronger than the newer model 700's? Or is there any truth to the 200 being stronger? With my 383 pushing about 475 horsies and about 515 in tq, I really want a strong tranny to handle the low end. Any info would be greatly appreciated (once again). Thanks in advance to you guys - you're the greatest!
Marc.
Melting Slicks
Joined: May 2003
Posts: 2,387
Likes: 2
From: Meriden CT
welcome to the wonderful CorvetteForum world Docmac, but i think you should start a new thread. You are kinda hijacking this thread with your new questions.
As for your tranny question, I'm not really sure. Start a new thread in the tech forum and everyone here would be more than happy to help you out. You have just embarked upon a long and lustrous relationship with this forum!!!
Joe
As for your tranny question, I'm not really sure. Start a new thread in the tech forum and everyone here would be more than happy to help you out. You have just embarked upon a long and lustrous relationship with this forum!!!
Joe
