Rev limit advice needed

[GM Ontairo]

I've been searching and reading threads tirelessly for the last 2 hours and am still undecided as to what is a safe limit to set. So please feel free to chime in here for me.

My current set-up is

2.8 block, bored/stroked to 3.2
heads are off a 2.8fi Camaro
3/4 cam lifter kit
Index ground 3.1 Crank
Line bored crank internals
Blue printed
bored/honed to 40 thou over
9.5 compression

I've got an MSD 6AL2 and I currently have the rev limiter set at 4500. At 4500 the blower puts out 4lbs of boost. For every 500rpm upwards boost builds by .5

Prior to installing the MSD I could sping the motor up to 6500+ no problem. If I wasn't paying attention it would be there very quickly. I can't help but feel that is to much for what it is.

What can I safely spin this combination up to? The bottom end is stock, stock cast pistons and it's an '84 block with a small journal crank. Motor was completely gone through and rebuilt professionally less then 2500 miles ago. I like to road race with and it could potentially see the highest rpm for a 5 seconds or so at a time. So the rev limit* definitely needs to be safe.

Please input is appreciated.

Andrew

[geoffinbc]

6500 is fine especially if it is balanced. Did you have the 3.1L crank journals machined down to the small journal? Never see this done. I would not worry about the small main journal crank as long as your oil supply is good. Are you using a 2.8L aluminum pump or the 3.1L cast iron pump?

[GM Ontairo]

yea the crank was sort of a last minute oh shit moment. We had all the machining done and everything was set up and ready for installation and we realized the 3.1 crank was different. So I had it custom ground. It's the stock 2.8 pump.
At 6500 I'll be pushing 6 lbs. My cooling system is above and beyond, griffin aluminum rad with dual electric fans. If I can spin it up to 6500 will I run into problems with the valve train potential float issues?

[dskopek]

If you had the 3.1 crank turned down on the mains do you know if the lead in oil grooves were cut back in? I ran both 2.8's and 3.1's hard before and that was the fix for spinning rod bearings. If they are there it should live just fine at 6500 like betterthanyou posted.

[geoffinbc]

Yea the 2.8L pump is fine brand new. But as it ages it wears out prematurely. The aluminum body just wears faster than if it were cast iron. So keep an eye on oil pressure and temps and get use to how they correlate. If you ever notice a difference from the norm then take note. For instance if oil pressure is 15PSI at idle with oil temp at 215*F then thats great so make a mental note. If it drops to say 6PSI with everything else the same then you know something is up.

The vale train will not float if you used the correct springs for the cam you have. If your using old factory springs then I would never rev it that high. Also remember that boost effects the intake valve as it begins to close on the seat. So extra spring pressure needs to be added as boost increases.

[Superdave]

You may run into valve float but that depends on your valve springs. Mechanically you should be fine up to 7K but i'd say 6500 is a safe limit.

[GM Ontairo]

The cam is pretty mild,

Valve springs are just stock replacements. The entire valve train was replaced with new.

If you had the 3.1 crank turned down on the mains do you know if the lead in oil grooves were cut back in? I ran both 2.8's and 3.1's hard before and that was the fix for spinning rod bearings. If they are there it should live just fine at 6500 like betterthanyou posted.

I spoke to the guy who did the machining to the crank today. To be honest 95% of what he said was just way above my head. So trying to repeat is going to make me look pretty foolish, something about enlarging the radia of the cheek and a bunch else haha. I would probably have to get him to draw me a picture to actually understand. He did however say oiling should not be a problem at all and that the crank is now stronger then it ever was stock.

Thanks for all the input guys it's much appreciated. This leads me to my last question, (that I can think of at the moment)

What are the rods rated to? Is it just 7000rpm? If so then running it to 6500 on a boosted application is going to be pushing it a lot is it not? So far no detonation problems as I'm running it slightly rich with not a lot of timing. I know getting into these rpms detonation can do some damage verrry quickly.

[pocket-rocket]

I've spun my engine just over 7k countless times (rev limiter set at 7150 RPM). We have the same rods since yours are stock, and my bottom end is bone stock and not balanced.

[GM Ontairo]

^ Sorry I'm not really familiar with your set up. Are you running a power adder or n/a?

[pocket-rocket]

N/A 3.4 DOHC. There's Fiero guy that had a 3.4 DOHC in his car with basically a shoebox for a plenum sitting on top of the LIM and spun his to over 8k on the dyno. I would say you don't have to worry about the rods.

[Mars]

I'd run that to 7 if it still makes power there.

[Schmieder]

If the springs are in good condition you should not have any problems at 6500. I had a limit of 6200 because my max shift occured at 5800 rpms. But it was built w/ cam advance for more grunt, so my power region was a tad lower.

I personally would set the limit 500 RPMS higher then the max shift rpm. And I would have the trans shift before the power starts to nose dive, letting it land back in the 'sweet' spot.

But I also beat the piss out of my transmission into near failure. I think I was subconsciously giving myself a reason to do a manual swap.

It was a stock 4t60e behind 8psi of boost.

[GM Ontairo]

N/A 3.4 DOHC. There's Fiero guy that had a 3.4 DOHC in his car with basically a shoebox for a plenum sitting on top of the LIM and spun his to over 8k on the dyno. I would say you don't have to worry about the rods.

I'm just trying to gain a better understanding of the physics involved here. So please don't take this as me questioning your statement.
From my understanding an engine under boost will see higher loads. So for a N/A to run 7k in comparison to a 5lbs running 7k there is a good bit of difference in the stresses happening to the components. If I'm mistaken someone please feel free to correct me.

If the springs are in good condition you should not have any problems at 6500. I had a limit of 6200 because my max shift occured at 5800 rpms. But it was built w/ cam advance for more grunt, so my power region was a tad lower.

I personally would set the limit 500 RPMS higher then the max shift rpm. And I would have the trans shift before the power starts to nose dive, letting it land back in the 'sweet' spot.

But I also beat the piss out of my transmission into near failure. I think I was subconsciously giving myself a reason to do a manual swap.

It was a stock 4t60e behind 8psi of boost.

The springs are brand new and just inspected prior to installing the blower. The trans is a non wc T5 in it right now. So shift points is a non issue. Could you care to elaborate a bit more on your set-up? 8lbs, sounds like you are in the neighborhood I would like to be in.

[Schmieder]

The springs are brand new and just inspected prior to installing the blower. The trans is a non wc T5 in it right now. So shift points is a non issue. Could you care to elaborate a bit more on your set-up? 8lbs, sounds like you are in the neighborhood I would like to be in.

My valvetrain is stock but rebuilt all around except for the camshaft. New heads w/ mild port myself (just simple floor smoothing, pocket clean up and exhaust polish) I did deshroud the valves though, my cylinder heads are truly unique now. They run great under the autotrans.

So the springs are new. I also replaced the timing chain just in case.

Here is the list of stuff I did so far.......it is a bit long, lol.

32lb injectors, new KB hypereutectic pistons, chromoly rings gapped myself for boost w/ the hypers, tri-metal rod bearings, ARP connecting rod bolts, crank scraper, walbro high flow fuel pump, MLS head gasket at oem thickness, modified UIM gasket (oem leaks easy), new solid motor/trans mounts, 180° T-Stat, Oil cooler pre-turbo oil feed, T04E Turbo at .50/.63 trims, external wastegate w/ 4-6 lb spring, simple boost controller, small intercooler, 3" BOV w/ modified spring, custom welded cross-over to turbo manifold, 2.5" mandrel bend exhaust, "fake" catalytic, dual flowmaster 40 mufflers, cherry bomb resonator, several flex joints, Heat wrapped exhaust from heads to DP, wideband afr gauge, oil press/temp gauges, boost/vac gauge, HP Tuner suite, swapped a 97 Lumina PCM (I had 96 GP, no HPT support), Getrag 282 w/ EP LSD, new hubs, axles, trunk mount battery....................

Not all of it is needed but some I would not boost to 8psi w/o. All stock (except for injectors, fuel pump) should handle 5psi safely.

[pocket-rocket]

I'm just trying to gain a better understanding of the physics involved here. So please don't take this as me questioning your statement.
From my understanding an engine under boost will see higher loads. So for a N/A to run 7k in comparison to a 5lbs running 7k there is a good bit of difference in the stresses happening to the components. If I'm mistaken someone please feel free to correct me.

Hey, this kind of thing is what these sort of boards are for

If you read Corky Bell's book Maximum boost, you will read that, yes, load levels do go up, but not extreme amounts. I will have to go back and reread that section to find out just how much they go up and get back with you, unless someone else who has read it recently remembers.