geerookie

I have a '99 C5 Coupe w/LS1. The engine has 103k miles and has been extremely reliable and runs great. The car is a 6 speed with a 3.73 rearend, aluminum flywheel and pressure plate. I really enjoy the setup, it's very responsive and has enough power for now. The motor is completely stock. I run about 14 - 20 track days a year and have been doing it for 2 years now. I have coilovers, larger front and rear adjustable sway bars and run DOT tires at the track.
My problem is that as my driving has improved, I find myself at the rev limiter (6200) all the time and having to shift early or hang at the limiter for a few hundred yards. Sometimes, mainly at Watkins Glen this means 5th gear.

What I would like to do is bump my rev limit up to 6800 but I'm concerned about the valve train. I don't want to redo the entire top end. My plan right now is to change push rods, valve springs, seals and maybe retainers.
I'm looking for recommendations on springs.
Comp Cams 915's or 918's
PAC 1518 or 1511?
Others?

I'm going to be leaving the motor stock except for these changes.

Any other advice of things to consider would be GREATLY appreciated.

Thank you in advance.

NemesisC5

You can get you some fresh C5Z springs and supporting components that will work fine and save a few $$. I've run my factory LS1 up to 6600 rpm's without issue on oem springs but that was on low mileage car. FWIW, the LS1 did not fall flat like I expected but seemed rather strong and the extended rpm range was beneficial as opposed to upshifting

geerookie

Thanks NemesisC5. I'm considering going that route but the redline on the ls6 is 6500. I need 6800. I did all the calculations considering tire diameter, gear ratio's etc. and If I can get to 6800 in 4th that will be 140 mph and in 3rd it will be 108 mph. This should work for most of the tracks I've been running at.
I'm shooting for safe at 7000 rpm. I'm not sure an ls6 valve train can do that. Also the ls1 has heavier valves than the ls6 so it will require a little more spring at the higher rpm's to keep from floating the valves.
And unlike drag racing, sometimes this will be sustained rpm's.

tcmc5

Besides valvetrain issues you should be concerned about rod bolts in your early LS1. They were failing in ASA engines and GM upgraded them in '01 when the LS6 was introduced. 6800 is likely asking for trouble with stock bolts in a '98 motor.

Bill Dearborn

How about getting a C5Z 5th gear ratio installed in the tranny? It will bring 5th gear into a nice speed range with the 3:73 gears.

The other thing you could do is go back to the stock 3:42 rear gear which will give you about 110 in third and 137 in 4th. The LS1 falls off in power once you are over 5800 although the drop isn't too bad. When I was running my 97 I had the rev limiter bumped to 6500 for a few track sessions but found I was just bumping the limiter at the new setting anyways so put it back to stock and started shifting at 5800. The car actually felt better that way.

Bill

PA Z06

[QUOTE=Bill Dearborn;1568336893]
The other thing you could do is go back to the stock 3:42 rear gear which will give you about 110 in third and 137 in 4th.

I was thinking the same thing, 3:42 would prolly cure ur problems

Timz06

I would think opening up the engine with that many miles would be asking for trouble. I would not mess with it.

rbl

Maybe I have overlooked the obvious but it seems to me it is a LOT easier to make the couple extra shifts!

Like Tim said ... you're asking for trouble.

geerookie

I looked into doing this. It will be expensive. You have to change 5th and 6th gear and the countershaft. I had the tranny rebuilt last winter and looked into that at that time. It added about $500 in parts. At the time I wasn't planning on doing anything because when this motor dies I'm going to a blueprinted LS6. Hence the reason I'm looking for an inexpensive was to up the redline.

geerookie

I don't have a problem with making the extra shifts but at Watkins Glen that shift is required about 1/2 way thru the esses. Not the best place to try and shift. So I end up holding it at redline for about 600 - 800 yards until I'm on the backstrech.

geerookie

I'm concerned about this which is one of the reasons I'm asking the question. This motor has been very dependable and I would like it to survive this season and then next winter I'm going to an LS6 or a different car. (C6)
I was thinking a few hundred dollars in valve springs, pushrods and misc., parts would keep me safe at higher rpm's. I don't think this would have an impact on the rest of the motor but you never know.

geerookie

I haven't heard much about this. I would think if it was a big issue you would hear a lot more about it here on the forum.
Maybe some of the engine builders will chime in.
Of couse it could be because I'm working with a lowly LS1 and most everyone on here is dealing with an LS6 already.

varkwso

It is a big issue on the early LS1s. I would not run a 99 LS1 bottom end at those rpms - the bottom end is the problem not the valve train (it just keeps you from overrevving the bottom end) - I shredded one at Hog Pen at VIR.

geerookie

Looks like I might have to either get back in the tranny and change 5th and 6th ratios or go back to the 3.42 rearend. Neither fits in my budget or plan.
I'm leaning towards changing 5th and 6th ratios since I like the way 3rd and 4th pull but since WG is my favorite track and I can't complete the esses without a shift to 5th maybe the 3.42 rearend is the smart thing to do. Decisions, decisions

Anymore advice or insight?

AU N EGL

Tim and Vark made Two very good points.

The LEAST expensive way, would be to buy a new LS6 create motor and install that. Or an LS2 create $5500 http://www.sdpc2000.com/product/1916...eAssembly.aspx with the LS6 adapter parts.

2004 LS1 creates can be had for well under $4900 now. http://www.sdpc2000.com/product/1780...reHarness.aspx

2005 LS6 Create $5300 http://www.sdpc2000.com/product/1780...EngineKit.aspx

If not a create just run what you have until it blows up.

The 3.42 rear end seems to be the best gear. Would be nice if 5th was .85 and 6th was .75 or close to those.

Oyishdog

My car still has the original ls1 (1998) rev limit is set to 6500. Last winter I did some minor mods to it to get the power up to ls6 levels in order to compete in ST2. I went with the LS1 hot cam with ls6 springs (new seals etc)...put a new oil pump on, timing chain, underdrive pulley and ls6 intake on it. Essentially, all of those items are "stock" GM parts. Yes, it would be been "easier" (not cheaper) to put in a new ls6 crate motor, but where is the fun in that? This is a hobby and part of it is working on the car and learning about it - the learning experience was invaluable. The motor is strong and tuned extremely conservative currently making 377/380 to the wheels - the tuner had alot more at one point and I told him to back it down. Granted, the motor could blow up, and while that would suck, it is something I have already assumed will happen one day. Once that happens, I will go with a ls6 crate motor.

gkmccready

Have you tried short shifting and checking your lap times? With your 3.73 rear and the torque you've got it'd be interesting to see...

mikahb

No matter what gear/tranny/rev limiter you have there's always going to be some turn(s) at some track(s) that needs a shift - up or down - at just the wrong place. My setup is LS6/MN12, but I always have to short-shift from 3rd to 4th just after I crest under the bridge at Road Atlanta because the natural shift-point is right as I turn in for 12 - not a great spot to shift either!

Short-shifting won't cost you nearly as much as you might think - and it might even make you focus on carrying more momentum up into the esses at WG. If you've got an LS6 planned for the near future anyway, why spend time and money on your LS1? Best option would be to sell this motor in good working (as-is) condition and put that money towards a crate motor.

varkwso

I run both a LS1/MN6 and LS6/MN12 depending on the car we are in. I can really tell the difference in gearing. VIR and Road Atlanta like the MN12 and SCCA Sebring course and Barber like the MN6.

We short shift a lot in both cars since I am a chicken.

geerookie

Eventually I might try running ST2 so I will go with a crate LS6, maybe next winter.
I think the best route to go now would be change 5th and 6th gear to the M12 ratio's of .84 and .56 instead of the MM6 with .74 and .5. This way I can leave the 3.73 and use 5th gear. Plus with the LS6 I can get 6800 without any issue.

I might just change to the LS6 springs and put in new seals and bump my rev limiter to 6500. The time and effort to do this doesn't bother me. I like working on my car and this is something I can do easily.
Otherwise I could change 5th and 6th now and try short shifting. I'm just not sure I have enough torque to pull the esses in 5th. Plus this would be something I have to pay someone else to do. I'm not brave enough to tear down the tranny and attemp this.