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Old 04-18-2006, 08:39 PM   #1
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How Many Revs = Too Many?

I just picked up my car from the transmission shop tonight. They did a rebuild on my 700R4, put in more aggressive shift points and a custom built planetary.

First, the performance is waaaaayyyyyyyyy better than before. Much more juice off the line (to the detriment of my tires) and snappy downshifts when you drop the hammer at speed.

My one concern was redlining. As you know, the '86 LG4 tach yellowlines at 4500 and reds at 5000. When I did a WOT take off from a light, the tach hit just over 6000 without shifting to 2nd gear. I left off at that point because I had never seen the car redline with the stock trans. My worry is: how much is too much? With such a low redline, am I in real danger going over 5000 rpm or is the serious problem when you actually hit 7000 and oil starts spraying on your windshield??
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LG4 305 w/4bbl Edelbrock 1406 (600cfm) carb, Edelbrock Performer 3701 intake, mild street cam,
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Last edited by DCJLove; 04-18-2006 at 08:42 PM.
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Old 04-18-2006, 08:42 PM   #2
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Re: How Many Revs = Too Many?

Dude.. dont hammer the gas yet..lol Let the tranny break in. Cant answer your question though.
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Old 04-18-2006, 08:49 PM   #3
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Re: How Many Revs = Too Many?

Quote:
Originally Posted by V8 Slayer
Dude.. dont hammer the gas yet..lol Let the tranny break in. Cant answer your question though.

C'mon man, 20,000 mile warranty!!! I gotta make the most of it.
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LG4 305 w/4bbl Edelbrock 1406 (600cfm) carb, Edelbrock Performer 3701 intake, mild street cam,
Nitto NT450 245/50R16 tires on '91 RS wheels, 700R4 trans with performance banding
& heavy-duty planetary, "Arrest-Me" Red, t-tops, Flowmaster exhaust
**FOR SALE** PM me for details.
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Old 04-18-2006, 09:15 PM   #4
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Re: How Many Revs = Too Many?

Na, id take it easy at first, for real. Becaues you might just severely shorten the life of your transmission and it will go out at 25,000 miles as opposed to the expected 80,000...then what?

But anyhow, sounds like you dont have to worry about the trans going at those RPMs, but bending a pushrod or snapping a valve spring..VERY likely...I've seen it happen.
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Old 04-18-2006, 09:17 PM   #5
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Re: How Many Revs = Too Many?

With the LG4 5000 rpm is probably a good shift point. So yes the governor is set way to high or there is a problem. I have a higly moded L98 and I have the shift points set up at 6000 for the 1-2 shift and 5600 for the 2-3 shift. The 6000 is because of the low first gear ratio of the 700R4. With my next round of mods I will up that a few hundred rpm.
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Old 04-18-2006, 09:24 PM   #6
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Re: How Many Revs = Too Many?

^If anything the LG4 will rev higher more safely than the L98; the L98 simply wasn't made for high rpm usage. The LG4 should be fine hitting a 6k shift-point.. but ONLY once in a while when racing. Do NOT make it the normal shift point
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Old 04-18-2006, 11:25 PM   #7
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Re: How Many Revs = Too Many?

Thirdgen Tacs have been known to be off, esp at higher rpms. If you can, hook your car up to a laptop and see what it's really shifting at.
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Old 04-19-2006, 07:06 AM   #8
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Re: How Many Revs = Too Many?

I definitely don't want to go bending up parts of the motor, that's my main worry. I noticed this morning that the car shifts crisply and at good points under "normal" driving. When you go about 3/4 throttle, it shifts nicely at 5000.

I'll have to check WOT again, but that 6000 worries me! I need to know because I am racing a buddy's '85 Z this Saturday.
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LG4 305 w/4bbl Edelbrock 1406 (600cfm) carb, Edelbrock Performer 3701 intake, mild street cam,
Nitto NT450 245/50R16 tires on '91 RS wheels, 700R4 trans with performance banding
& heavy-duty planetary, "Arrest-Me" Red, t-tops, Flowmaster exhaust
**FOR SALE** PM me for details.
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Old 04-19-2006, 05:44 PM   #9
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Re: How Many Revs = Too Many?

Quote:
Originally Posted by 85_305
^If anything the LG4 will rev higher more safely than the L98; the L98 simply wasn't made for high rpm usage. The LG4 should be fine hitting a 6k shift-point.. but ONLY once in a while when racing. Do NOT make it the normal shift point
What makes the engine safely "rev high" isn't the induction system. It's the balance and the quality of the rotating assembly. I wouldn't be reving a stock 3rdgen motor anywhere near 6k.

When I dyno'd my car I was suprised to find that my tach was reading 5k when the engine was at 5.5k. I'll be shifting shorter from now on.
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Old 04-19-2006, 09:17 PM   #10
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Re: How Many Revs = Too Many?

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Dude.. dont hammer the gas yet..lol Let the tranny break in. Cant answer your question though.
I hear this a lot and I'm a mechanic for the U.S. Air Force. There is a civilian that works in my shop and he's one of the best i've ever known. He really knows his ****. He's been doing it for 38+ years. I asked him about this and he says he does not what so ever believe in a break in period. He said drive it how you would normally drive it on a daily basis. So if you drive careful and every now and then really get on it, then thats how you should do it.

He use to build motors for cars and bikes and has rebuilt probably thousands of motors by now and he said he has never had a problem due to this factor. He's had them to obvious mess ups on his or operator error. So its all up to you, but I really lean towards him because I work with him every day and know exactly how good he is.
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Old 04-19-2006, 11:49 PM   #11
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Re: How Many Revs = Too Many?

Quote:
Originally Posted by iansane
What makes the engine safely "rev high" isn't the induction system.
Right. But since a TPI is made to only rev up to 4600 R's... whereas a carb'd motor is designed to rev up to 5-5.5 R's it's a bit different.
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Old 04-20-2006, 12:09 AM   #12
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Re: How Many Revs = Too Many?

safe rev limits are dterminied by the rotating assembly and your valve train... if you have a stock set of heads on there... and they have never been reworked i would worry about taking up that high.. could easily have something snap. same for the bottom end... I have reved a 305 once or twice up into the red.. and like the third time i immdeitaly started having valve problems.... about 3 months later a bearing spun.... I think the high reving probably had something to do with it ( ice pretty much bites as it equals no traction and you can not always see it). I would probably stick with the stock style shift points or maybe a little higher.. but stay at or below the yellow.... if you have built the valve train up to handle the rpm's and have a ballanced rotaing assembly than I would suspect higher would be very much in range
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Old 04-20-2006, 11:47 AM   #13
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Re: How Many Revs = Too Many?

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Originally Posted by 85_305
Right. But since a TPI is made to only rev up to 4600 R's... whereas a carb'd motor is designed to rev up to 5-5.5 R's it's a bit different.
If a tpi engine is only made to rev up to 4600rpms then why does both of mine have a 5500 redline and there's where they shift.
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Old 04-20-2006, 12:25 PM   #14
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Re: How Many Revs = Too Many?

Quote:
Originally Posted by 85_305
Right. But since a TPI is made to only rev up to 4600 R's... whereas a carb'd motor is designed to rev up to 5-5.5 R's it's a bit different.

With that logic you'd think the carb'd motor was the performance motor in turdgens and the tpi motor was the base engine.

Whereas we know they all suck.
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Old 04-20-2006, 01:14 PM   #15
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Re: How Many Revs = Too Many?

Actualy that number is 4800rpm's and that is where the peak HP rating is on the 305 TPI engine. It is not the top safe RPM for the engine,that would be 5500 rpm's I do believe. Sure it can be taken higher,but how many times is up to the internal parts. I have seen 6500 rpm hit on a stock engine more that a few times with NO problems,and I have seen them blow at 5600. If you want to abuse your engine wump on it all you want it will break eventually. If you take care of it and keep the RPM's down to a safe zone you will see many, many miles from it.
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Old 04-20-2006, 01:14 PM
 
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