Max RPM Question
Thread Starter
Instructor
Joined: Jun 2005
Posts: 236
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From: Cedar Rapids Iowa
Max RPM Question
I have a 355, stock crank, 6" Lunati rods, TFS Forged flat top, TFS 64cc CNC ported heads/195 runners, 270 Magnum Solid Lifter cam, 1.6 rockers, Air Gap intake, DT Headers, 750 Bigs Stage 5 carb. MSD Digital 6 ignition. Now my queston is, what is the max rpms that I can run for a short time? I was running an autocross today and gained 4 seconds by changing the rev limit to 6400 from 6000. I was still hitting it just before the corner and still pulling hard. I just dont know how much a stock crank can take for max rpms. The motor is around 10;5;1 comp also. The difference of the set-up also is I have a Keisler 5 speed and 2nd gear run the best for performance and the handleing. 3rd gear was alot harder to drive not pulling as many rpms staying in the power band. thank you for any help, its a learning experience!
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Nice strong 6 inch lunati rods how high would you like to go. do you have
a cast iron crank. if you have any form of a forged crank you are in real
good shape on RPMs. they used to turn the old pink chevy rods 7500-8000
in 350s I think they were just 1053 or 5140 steel the rods you have are probably
4340 steel and a lot better rod bolts. Unless you have a cast iron crank
you have no problems.
a cast iron crank. if you have any form of a forged crank you are in real
good shape on RPMs. they used to turn the old pink chevy rods 7500-8000
in 350s I think they were just 1053 or 5140 steel the rods you have are probably
4340 steel and a lot better rod bolts. Unless you have a cast iron crank
you have no problems.
Last edited by Little Mouse; Aug 26, 2006 at 09:48 PM.
Drifting
Joined: Dec 2004
Posts: 1,345
Likes: 3
The factory LT-1s redlined at 6500. My street engine, a 355 with a Comp Cams 294S, Brodix -8 heads with 2.055" intakes has it's redline set at 7000 rpm. I needed to add titanium spring retainers to avoid valve float - with steel retainers I suffered float qt 6400 RPM.
Valve float will set your effective rev limit - the parts you have should easily be good for 7500 RPM.
Valve float will set your effective rev limit - the parts you have should easily be good for 7500 RPM.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
I ran my stock LT1 short block with a 248 dur @ .050 with a 525 lift and AFR heads with dual springs to 7000 rpm many times with no problems at all. My rev limiter was set at 7100 rpm and I hit it a bunch of times. The short block now resides in another forum members car and is running great. 
Thread Starter
Instructor
Joined: Jun 2005
Posts: 236
Likes: 0
From: Cedar Rapids Iowa
Little Mouse, thanks for the reply. I do not know if it is cast or forged. It is the stock crank that came with the car. 1975 with the 4 speed. The VIN is 1Z37J5S401433, engine all I have is a L48 350 cid.
165hp 8;5;1 4bc man. May 27 Flint Plant (engine). The Engine shop noted that the block was square decked and that the engine nember was removed. Any other way of telling if it would be cast or forged?
Its not something I have to do, its more of a want situation. This car was a blast yestday at the autocross. Not in the same class as the C5 and C6s, but the times I had were right there. I feel now if I would turn the rev limit to 7000 I could improve on the times again.
thanks again. Any help from anybody else is also appreciated
165hp 8;5;1 4bc man. May 27 Flint Plant (engine). The Engine shop noted that the block was square decked and that the engine nember was removed. Any other way of telling if it would be cast or forged?
Its not something I have to do, its more of a want situation. This car was a blast yestday at the autocross. Not in the same class as the C5 and C6s, but the times I had were right there. I feel now if I would turn the rev limit to 7000 I could improve on the times again.
thanks again. Any help from anybody else is also appreciated
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
That would be a cast crank you have.
Turning a cast crank with stock rods much past 6000 rpm is pushing it. 7000 rpm you will be collecting your engine on the ground in a short time.
Turning a cast crank with stock rods much past 6000 rpm is pushing it. 7000 rpm you will be collecting your engine on the ground in a short time.
Last edited by Gordonm; Aug 27, 2006 at 08:31 AM.
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Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Originally Posted by 1atti2d
Little Mouse, thanks for the reply. I do not know if it is cast or forged. It is the stock crank that came with the car. 1975 with the 4 speed. The VIN is 1Z37J5S401433, engine all I have is a L48 350 cid.
165hp 8;5;1 4bc man. May 27 Flint Plant (engine). The Engine shop noted that the block was square decked and that the engine nember was removed. Any other way of telling if it would be cast or forged?
Its not something I have to do, its more of a want situation. This car was a blast yestday at the autocross. Not in the same class as the C5 and C6s, but the times I had were right there. I feel now if I would turn the rev limit to 7000 I could improve on the times again.
thanks again. Any help from anybody else is also appreciated
165hp 8;5;1 4bc man. May 27 Flint Plant (engine). The Engine shop noted that the block was square decked and that the engine nember was removed. Any other way of telling if it would be cast or forged?
Its not something I have to do, its more of a want situation. This car was a blast yestday at the autocross. Not in the same class as the C5 and C6s, but the times I had were right there. I feel now if I would turn the rev limit to 7000 I could improve on the times again.
thanks again. Any help from anybody else is also appreciated
someone has spent some money making sure the decks are strait
and maybe 0 decked it. It would be hard for me to believe that
someone would spend that kind of money for good rods and
machine work and use a cast iron crank does not make any sense.
Do you have a bolt in the end of the crank in the center of the
balancer?? Your original two bolt block may be long gone for a
4 bolt.
Last edited by Little Mouse; Aug 27, 2006 at 02:45 PM.
