Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
JohnnyB1275
Senior Member
Offline
I just put together a rear end with a 5.37 ratio and double bearing hubs(already leak oil). It used to havea 3.90 ratio rear end in it. How much with the higher ratio effect the acceleration of the car?
-
Hi Guest!
You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
There are some perks with a member upgrade!**Upgrade Now**
(PS: Subscribers don't see this gawd-aweful banner
Rear end ratios
- Thread starter JohnnyB1275
- Start date
Share this page
Hello John,
you are lowering your gearing to approximately 3\4 of what it was, so the car should feel very lively but run out of revs very quickly, top speed will also be reduced and the cruising speed will be a lot noisier.
Why do you want such low gearing?, do you have an ultra high revving engine installed?
Alec
you are lowering your gearing to approximately 3\4 of what it was, so the car should feel very lively but run out of revs very quickly, top speed will also be reduced and the cruising speed will be a lot noisier.
Why do you want such low gearing?, do you have an ultra high revving engine installed?
Alec
OP
JohnnyB1275
Senior Member
Offline
[ QUOTE ]
Hello John,
you are lowering your gearing to approximately 3\4 of what it was, so the car should feel very lively but run out of revs very quickly, top speed will also be reduced and the cruising speed will be a lot noisier.
Why do you want such low gearing?, do you have an ultra high revving engine installed?
Alec
[/ QUOTE ]
It's for autocross use only, so I'm not really worried about cruising noise and top speed. I don't have a high revving engine, but I'm putting a higher rpm cam in so that might help a bit. There is a pretty big power band above 5,000rpm with the engine that's in it now. Thanks for the responses. /ubbthreads/images/graemlins/cool.gif
Hello John,
you are lowering your gearing to approximately 3\4 of what it was, so the car should feel very lively but run out of revs very quickly, top speed will also be reduced and the cruising speed will be a lot noisier.
Why do you want such low gearing?, do you have an ultra high revving engine installed?
Alec
[/ QUOTE ]
It's for autocross use only, so I'm not really worried about cruising noise and top speed. I don't have a high revving engine, but I'm putting a higher rpm cam in so that might help a bit. There is a pretty big power band above 5,000rpm with the engine that's in it now. Thanks for the responses. /ubbthreads/images/graemlins/cool.gif
John, the 5.38 will give you an awesome launch from the corners. It's a perfect autocross gear. Where you were turning 5000 RPM, you will now see in the neighborhood of 6900.
I road race with a 4.88, and one of my bud's runs the 5.38. He has to feather the throttle to keep it below 8000.
Jeff
I road race with a 4.88, and one of my bud's runs the 5.38. He has to feather the throttle to keep it below 8000.
Jeff
OP
JohnnyB1275
Senior Member
Offline
[ QUOTE ]
John, the 5.38 will give you an awesome launch from the corners. It's a perfect autocross gear. Where you were turning 5000 RPM, you will now see in the neighborhood of 6900.
I road race with a 4.88, and one of my bud's runs the 5.38. He has to feather the throttle to keep it below 8000.
Jeff
[/ QUOTE ]
Feathering to keep it below 8000 /ubbthreads/images/graemlins/eek.gif I guess a high rpm cam will come in handy then /ubbthreads/images/graemlins/thumbsup.gif
John, the 5.38 will give you an awesome launch from the corners. It's a perfect autocross gear. Where you were turning 5000 RPM, you will now see in the neighborhood of 6900.
I road race with a 4.88, and one of my bud's runs the 5.38. He has to feather the throttle to keep it below 8000.
Jeff
[/ QUOTE ]
Feathering to keep it below 8000 /ubbthreads/images/graemlins/eek.gif I guess a high rpm cam will come in handy then /ubbthreads/images/graemlins/thumbsup.gif
GreenHornet
Jedi Trainee
Offline
Cripes! 8000 rpm..whats the life expectancy on something like that? Sounds like just a short time before "The big ones eat the little ones".
77_MG_Midget
Jedi Trainee
Offline
I assume your running a 1275 engine? I didn't think the 1500 engines would take that kind of rpm.
Tim Hollister
Jedi Trainee
Offline
[ QUOTE ]
Cripes! 8000 rpm..whats the life expectancy on something like that? Sounds like just a short time before "The big ones eat the little ones".
[/ QUOTE ]
I think I may be the guy Jeff was referring to above. Yes, the car has a 5.38 rear end gear in it and I also spin the engine up to 8,000 rpm. I'm on 20 inch diameter Hoosier slicks.
The track we run at is only 1.5 miles long and is a tight, narrow, technical, handling type of track with 13 turns. It has only two real straights and the longest is only 1,000 feet (with a 70 mph curve leading onto the straight).
With the above description, I'll tell you that I'm at 8,000 rpm and 89-90 mph just over halfway down the straight and well before my braking point for the 90 degree right coming up. But still, I love the 5.38 for the launches at the race start and for getting off the corners. Plus I'm only using third and fourth gears thus less actual shifting.
Options for running out of rpm on the straights? Put in a 4.88 and see what that does to the overall lap times or increase engine rpm even more, to 8200 or 8300 but now we are really starting to get into a questionable (will it hold together and for how long?) area.
The engine itself is a 1275 built to SCCA national racing specs. I hate to admit this but it has has survived one accidental instantaneous over-rev to 9,100 rpm as seen on the tattle-tale tach (lost 5 psi oil pressure immediately afterward). The over-rev was due to a botched shift from 3rd to 4th, err, 2nd in that 70 mph curve I mentioned above. (The rear end of the car stepped out right smartly too and with a BIG sound wall looming very close to the edge of the track!! Those that know Waterford Hills know exactly what I'm talking about!!)
How long will it last? Who knows but I'm hoping to complete the season without having to tear it down (plus or minus 25 hours). Over the winter, it'll be refreshed and ready for next year.
BTW, spinning up these A series engines is really only a matter of dollars spent in engine development and "reliability upgrades." There are folks out there racing at the national level that regularly run up to 9,000 rpm. Of course they are running $2000.00 billet cranks and Carillo rods at $1,000.00 a set plus a myriad of other upgraded components.
Want one of these high dollar race engines? Give Joe Huffacker a call and don't choke at the $12,000.00 plus quote!! (No, my engine is NOT that expensive -- was purchased "refreshed" for a third of that.)
Sorry to be so long-winded. Just a small look into what is possible and what it can cost (but certainly does NOT have to) in the racing world.
Tim /ubbthreads/images/graemlins/cheers.gif
Cripes! 8000 rpm..whats the life expectancy on something like that? Sounds like just a short time before "The big ones eat the little ones".
[/ QUOTE ]
I think I may be the guy Jeff was referring to above. Yes, the car has a 5.38 rear end gear in it and I also spin the engine up to 8,000 rpm. I'm on 20 inch diameter Hoosier slicks.
The track we run at is only 1.5 miles long and is a tight, narrow, technical, handling type of track with 13 turns. It has only two real straights and the longest is only 1,000 feet (with a 70 mph curve leading onto the straight).
With the above description, I'll tell you that I'm at 8,000 rpm and 89-90 mph just over halfway down the straight and well before my braking point for the 90 degree right coming up. But still, I love the 5.38 for the launches at the race start and for getting off the corners. Plus I'm only using third and fourth gears thus less actual shifting.
Options for running out of rpm on the straights? Put in a 4.88 and see what that does to the overall lap times or increase engine rpm even more, to 8200 or 8300 but now we are really starting to get into a questionable (will it hold together and for how long?) area.
The engine itself is a 1275 built to SCCA national racing specs. I hate to admit this but it has has survived one accidental instantaneous over-rev to 9,100 rpm as seen on the tattle-tale tach (lost 5 psi oil pressure immediately afterward). The over-rev was due to a botched shift from 3rd to 4th, err, 2nd in that 70 mph curve I mentioned above. (The rear end of the car stepped out right smartly too and with a BIG sound wall looming very close to the edge of the track!! Those that know Waterford Hills know exactly what I'm talking about!!)
How long will it last? Who knows but I'm hoping to complete the season without having to tear it down (plus or minus 25 hours). Over the winter, it'll be refreshed and ready for next year.
BTW, spinning up these A series engines is really only a matter of dollars spent in engine development and "reliability upgrades." There are folks out there racing at the national level that regularly run up to 9,000 rpm. Of course they are running $2000.00 billet cranks and Carillo rods at $1,000.00 a set plus a myriad of other upgraded components.
Want one of these high dollar race engines? Give Joe Huffacker a call and don't choke at the $12,000.00 plus quote!! (No, my engine is NOT that expensive -- was purchased "refreshed" for a third of that.)
Sorry to be so long-winded. Just a small look into what is possible and what it can cost (but certainly does NOT have to) in the racing world.
Tim /ubbthreads/images/graemlins/cheers.gif
aeronca65t
Great Pumpkin
Offline
In my unbalanced 1500 with stock 4-speed trans, I'm running a 3.9 ratio. Sometimes, I kinda wish I had a 3.7. My self-imposed redline is around 5800 (by my observation, rod bearings will last about 20 to 25 hours with this limit).
A 5.38 would be cool.....if I had a Zetec or Rover "K" motor!
A 5.38 would be cool.....if I had a Zetec or Rover "K" motor!
Yeah Tim, I was telling stories about ya!
My 948 should be good for 9000, but I've got an 8600 chip in the rev limiter.
It also has the aforementioned billet crank, Carillo rods, etc.
Nial, my 1500 lived a long and productive life with the 7650 redline, until the guy I sold it to overheated it and lunched a rod bearing at about 7100. Poof!
Jeff
My 948 should be good for 9000, but I've got an 8600 chip in the rev limiter.
It also has the aforementioned billet crank, Carillo rods, etc.
Nial, my 1500 lived a long and productive life with the 7650 redline, until the guy I sold it to overheated it and lunched a rod bearing at about 7100. Poof!
Jeff
Matthew E. Herd
Jedi Warrior
Offline
Jeff, I don't suppose you could remind me what the bottom end modifications were for your 1500 and how many hours the engine lasted at that rate? In my region's autocrosses, I hit about 6000 RPM on most courses in second gear with a 3.9 rear end, and I'm thankful to Nial for the estimate of 20-25 hours with 5800 RPM limit. My crank and rods are stock nitrided, with forged pistons and the rods are lightened. The whole assembly is dynamically balanced. I believe you said you had a "T" strap on your center main bearing? Was there anything else you did, and did you use Carillo rods/billet crank? Thanks for the input.
Matt
Matt
Matt, I was running the Carillo rods, and a cross drilled, nitrided and polished crank. All ARP studs down below, and the center main cap was reinforced with a strap made of 304 Stainless. Everything was balanced to the Nth degree.Up front I had an aluminum crank pulley, and at the rear an aluminum flywheel and lightened clutch assembly.
I opened up the oil passage to the center main to .312, and ran a GT6 oil pump modified to fit the Spit engine.
I made an extended oil pan with integral baffling and a windage tray. I also ran an Accusump to provide oil in hard cornering situations.
I ran it for 23.9 hours one season, but lightly spun a rod bearing on the cooldown lap of the last race of the year. That particular season, it had been buzzed to 8100 RPM twice, and 8400 once, all on missed shifts. I would expect to normally only run it for about 10 to 12 hours between teardowns. Oil changes after every weekend, which at 11 quarts of Redline 30 Wt, plus filter, gets expensive.
Jeff
I opened up the oil passage to the center main to .312, and ran a GT6 oil pump modified to fit the Spit engine.
I made an extended oil pan with integral baffling and a windage tray. I also ran an Accusump to provide oil in hard cornering situations.
I ran it for 23.9 hours one season, but lightly spun a rod bearing on the cooldown lap of the last race of the year. That particular season, it had been buzzed to 8100 RPM twice, and 8400 once, all on missed shifts. I would expect to normally only run it for about 10 to 12 hours between teardowns. Oil changes after every weekend, which at 11 quarts of Redline 30 Wt, plus filter, gets expensive.
Jeff
Matthew E. Herd
Jedi Warrior
Offline
No kidding ... 23 hours. Amazing. Thanks for the information, its a great help!