Component RPM limits

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Map63Vette

Map63Vette

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So I'm finally getting around to installing a new cam in my 5.7 swap and had some questions regarding rpm limits. I've read a few things through the years of following the 3G Hemi design, but a Google search becomes problematic because most people are limited by the factory engine controller. I don't have that issue since I'm running an MS3 for fuel and the MSD box for the spark. I don't intend to wind this thing to the moon, but I'm curious how far I can push it if the need arises.

As is stands, I have a pretty much bone stock engine with an Indy Mod Man intake and TTI headers that seems to lay over around 5500-6000 from what the butt dyno tells me (maybe gets soft even a tad earlier than that). I've not had the chance to get it on a dyno to see what it makes and if my tuning is anywhere close to right, but I do have some WOT runs logged to keep an eye on AFRs and things look okay from what I can tell.

Most people tend to think the shorter runner Mod Man would be happier at high rpm and my new cam may also help to bump upper end power a little more; however, if it's still building power up top I'm not sure where to draw the line to conserve parts. I've heard the lifters are good for pretty much anything I'd throw at them (8k in the Drag Pak as I understand), so shouldn't have any problems there. I'm putting in 6.1 exhaust valve springs which I'm guessing will be the main rpm limiter, but I thought I'd also heard in the past that the stock 5.7 rods go out of round at 6500 or more. I have no idea when oiling will give up either as I know that's a frequent concern with higher rpm setups as well.

Long story short, does anyone have a chart of rpm limits for stock parts? I don't intend to wring the engine to it's limits if it's not making power, but if it keeps building I'd like to know where to stop to prevent issues.
 
I'll speak to what I know:

Most motors are limited in RPM by their valvetrain. I would agree this is the case on the hemi. The 'limit' for a hemi is based on a combination of: cam lobe profile, springs, valve weight, etc. I don't know the seat pressure on a 6.1 spring (or which of the 6.1 springs you have), but at this point, that's going to be your limiting factor. What cam are you putting in? How aggressive are the lobes? I believe a 6.1 cam with 6.1 springs is safe for above 6500, but not so with a more aggressive cam lobe.

I broke a PAC beehive over 7200 (ferrea valves), though we don't know why it failed (PAC looked at it, said they weren't sure what happened, but advised a different install height). Those were 1518's. I'll be putting in 1219x's this time.
More reading here: http://modernmoparforum.com/topic/11129-03-08-57-heads-with-single-beehive-valvetrain-max-rpm/

Oiling:
One member on FABO ran his 6 quart pan dry at the 1280' mark at the dragstrip over 7000 rpm. Be aware it is possible. More reading here: http://modernmoparforum.com/topic/12792-oiling-mods-and-other-things-at-7000rpm/

As far as the 'limit' to the rods, etc, I don't think you'll find it NA with a safe tune. More reading here:
http://www.hotrod.com/techarticles/general/hrdp_1105_what_breaks_on_2008_to_2011_dodges/


Hope that helps a bit.

I'd say shift at 6300 and never see above 6500 with 6.1 springs and a 'not overly aggressive' cam lobe. More with a better spring.
 
I say if you're gonna swap springs at least go with PSI 1511ML's, the above PAC's or Nextek 431's. They have ALL broke at one time or the other but IIRC Andy at PWR said he has'nt had a broke Manley yet. But I never see him advertising them for sale.
 
Cool, thanks for the info and reading. I'll have to look over those links and see what I can learn. The cam is probably fairly mild by some standards. It's an SRT Max Plus on a 110 LSA to give it more of the muscle car sound it needs. I believe the seat pressure on the springs I'm using is around 110 or something like that. I know it varied through the years with the different revisions of the springs, but I'm pretty sure that's what mine are. I don't think the cam is too aggressive as it's still technically usable on a stock PCM, though not so much with the LSA I'm using. To my understanding it should be more of a low-mid end grunt with the tight LSA, so I don't think I'll need the rpm, but if I ever get it on the rollers and see the power climbing I wanted to know when to stop being greedy.

On a separate note, do cam swaps typically need the timing changed significantly to take advantage of them or are they usually just more fuel based? I'm hesitant to mess with my timing much knowing the fragility of the stock top ring lands and my lack of tuning experience, but I'm all for learning (in the least expensive way possible hopefully). What I really need is a good friend with a dyno around me who'd let me borrow it after hours, lol.
 
If stu says it's okay with 6.1 springs, then you're probably fine. Most guys shim them for a bit more seat pressure. Did he recommend shimming them?

The lobe ramp rate is what I meant by aggressive lobe, not duration. Look for the numbers engraved on the end of the cam for the lobe numbers, and then you can see what lobe family they are from and know how aggressive the ramp rate is.

What are the exact specs on that cam?

Not entirely sure about the tuning question. Your peak torque will change, and keep in mind peak torque usually doesn't need quite as much timing. Also, the 'dip' in the factory timing curves will remain, at that rpm or a bit above.

When tuning mine, there was a 'safe' tune I started with, and then the tune I got to on the dyno. I added timing till it didn't want anymore. Night and day difference in how the car drove. If you get your fuel mostly right before you go to the dyno, you can have your timing spot on within an hour. Run a pull, add two degrees across the board, run a pull, compare the two graphs laid on top of each other. When power isn't added (stays the same or drops) at one of your rpm points in your table, pull that column back down 2*.

Can you screenshot your current table?
 
He didn't mention anything about shimming at the time, though he was a little frazzled from some customer work. I had read about people shimming them and wondered about that as an option. At the moment I don't really have any grand NA aspirations since the car has become more of a fun cruiser, so I wasn't too concerned about going all out. Honestly, as silly as it sounds I was mainly after the cam for the sound. The day I heard the "rumbler" version of that cam I knew I needed one in my car. Two years later and I finally pulled the trigger and bought one, lol.

I had a feeling you meant the lobe ramp for aggressiveness. My gut feeling is that it's not too extreme since it's still intended for a "stock" engine. I think Inertia is typically somewhat conservative in that regard and their off-the-shelf cams are designed to be streetable without having to replace springs all the time, but I could be wrong.

I don't have the card on me at the moment, but the specs are something like 218/223 and I think around .556/.566 lift on a 110 LSA. I'll double check when I get home and see how close that is. I believe RatPatrol has the same exact cam, but his engine is a 6.1.

I'll see about getting a table when I get home as well. I originally started with the base MSD table, but have since switched to my best approximation of a factory one that was posted here in the past. The main problem is the MSD setup is two graphs (one rpm and one vacuum), so I can't exactly mimic a table. With the graph setup, to change any one value in an equivalent table I have to change either a whole row or column. However with a table you can change an individual point without affecting the ones around it. Not typically a problem for WOT pulls as the vacuum curve essentially goes away, but for trying to optimize cruise tuning it's a little harder.
 
Agree with UHCoog - Common opinion is dont take it above 7k without exta oil capacity.

I have my limiter set at 6800... I change around 6700 - Modman, MSD 6013, cam id 218/227 556/566 110 lsa.

FWIW its actually still pulling at 7000! ..but to use the rpm range I need decent springs and the higher oil capacity.

I asked Andy at PWR why it revved so high - he seemed to think the Modman was the main cause....not so much the fact that the SRT MAX cams install 4 deg retarded from straight up to provide Piston to Valve clearance.

General opinion on the PAC is they arent as reliable as the PSI......but the PAC 1535 seems like a good option...nitrided and with the correct Inner Diameter so 6.1 cages can be used.
 
Okay, cam card says 218/226 at .050" with a lift of .549/.536 using a 1.6 rocker. LSA is 110 and it says 4 degrees advance ground in. Can't find any specific lobe info. The timing curves I have are below. I'd admit they look a little extreme in a certain sense (+26 degrees of vacuum advance for instance), but that's what I got when I converted the factory table into graph form and picked the best trendlines I could. The first picture is the graphs in the MSD, the second is the factory rpm based timing (each line represents a set vacuum value), and the third is the factory vacuum based timing (each line represents a fixed rpm). I threw out the pretty wild outlying lines on the factory table to try to pick the average.
 

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Re timing / MAP curves...Im very happy with what I ended up with - If you want I can post the graphs. 27deg all in was the absolute limit...it made no more HP at 30 deg, but made 15rwhp more than 23 deg.....so somewhere between 25 and 27 seems to be about ideal as a peak timing figure at WOT.

Ive also been told that factory cruise timing isnt much more than 27 as well.
 
You do know that when you select a MAP timing figure for a given PSIa - the ECU ADDS that timing on top of the rpm timing advance at a given rpm, yes?

So on your graphs - if your MAP is 3PSIA at 3000 rpm cruise ( which is very likely) - you are at 46 deg advance! (26 map + 20 deg mechanical)
 
Yep, I'm aware of the really high numbers. The high timing is to support lean cruise, so it's not as big a deal as it might seem. I hooked an OBD2 scanner up to my parents 5.7 Ram and went cruising and I saw it cruising at 40 degrees several times. The tables I used are in post #4 here http://www.forabodiesonly.com/mopar/showthread.php?t=127947&highlight=mbt+timing. I used the 5.7 table to make the two excel charts above and then based my MSD graphs on them.

At WOT, the vacuum curve essentially adds nothing anymore and the "max timing" is just the mechanical curve, in this case I've limited it to 19 because I run 87 octane. Also, I don't think I typically see cruise vacuum much below 3 or 4 psia, so max cruise timing is more like 38. Still pretty high it would seem, but I also try to run around 15:1 AFR for those conditions and it's really low load.

I've had this map in the car for several months now and it runs just fine and not really any noticeable difference from the stock MSD curves. It mainly came about because I wasn't seeing the gas mileage that I think I should. Have pretty much never topped 16 mpg since I've swapped the engine, carb or injected, and when I put in the 6 speed with .5 overdrive and still didn't see any improvement I decided it was time to rethink my tuning. I know the factory gets good mileage, so I decided to base my tuning on whatever factory numbers I could find and this is what came from it. Unfortunately I don't have a working speedometer yet after the trans swap, so I haven't been able to check mileage very well. Have traced my route on Google Maps to try to guess mileage, but not sure how accurate I've been.
 
Yes I realise that you're only bringing in a lot of advance at cruise - but when I asked on the LX forums what an acceptable advance figure for low load cruising was - I was told no more than 30 degrees!

I myself run about 36 at 3000 - 4000 at 3 PSIa, and there's no pinging at light load and the plugs are fine.

Its contradictory advice like I received on LX that makes me wonder if most people actually KNOW anything about the motors they are "tuning"........

Your efforts at replicating the factory tune advance seems far more sensible..;)
 
I'm a bit in the dark as well to be honest. I can't hear anything bad happening so far, though it might be hard to hear over the exhaust. It seems like the engine is fairly robust though, at least during cruise. I've had a wide range of timing values programmed over its life with multiple AFR values between the carb and fuel injection and it's never noticeable pinged that I can tell. I've had some surging issues in the past, but it was a fueling issue. I really need a dyno for tuning timing so I can sit still and watch things and listen closer.
 
Granted a lot of the effort in trying to simulate the stock timing map is maybe less important now with the cam change, but I was hoping it would at least be a good place to start. I tried my initial map with the new cam to see if I could just tweak it to work, but was having a tough time working out some AFR oscillations, so I tried to just start over with the table generator and estimated horsepower and torque numbers pulled from other people with a similar cam. Seems like it has appreciated the change. Didn't think it pulled too hard with the old modified map, feels like it keeps pulling better now with the new map, though I'm still probably soft on timing. Still just running 87 octane, so I'm not trying to break any records, but I feel like the car should have quite a bit more punch. I think the Viper is probably just dulling my senses. Need some 1/4 times or dyno slips to validate the power it is or isnt' making.
 
To be honest - I suspect theres a window where you wont cause any damage, but wont see any appreciable improvement either.

As far as WOT tuning...we went from a safe 23deg to 27 and made 11 rwhp more....then to 30 all in....made 1rwhp more but it didnt ping.

To be safe we set it back to 27.

Same rules at cruise may apply in your case.
 
I've found with the new cam my cruise and idle vacuum are way down (55 MPa idle and pretty close to that for highway cruise at least), which I believe is around 7 psi absolute since it's essentially half of atmospheric (in whatever units you like to use). With my overdrive that puts my cruise timing probably closer to 25-30 degrees, so I think I'm probably fairly safe there for now. Still working on smoothing out the fuel curve to work out some AFR oscillation. I need an abandoned airport so I have a huge stretch of straight road to hold steady state conditions for tuning, lol.
 
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