How high can engine rev safely? [Merged 12-7]

[Eagle 5]

How high can the 420A engine rev safely on stock springs and retainers without worrying about valves floating or what not? Also, what is needed to get rid of the rev limiters ? (7200 and 7800 fuel/ignition cuts) would a msd ignition work? just wondering. Im rebuilding my engine and Im trying to decide what to do head wise. Originally i was going to get stainless valves, crower springs, retainers, pt cruiser lifters, rockers but someone said I should get cams and get port work done instead of getting the wprings, retainers and lifters since the stock ones are fine. anyone know?

 

[joeshoaf]

I have no idea... It says around 7 is where it starts to redline but i never get close to that. I pretty much baby my n/t engine and wont push over 5 unless im in life and death takeoff. I wouldnt never rev my engine over 5 sitting still because i think reving it high sittin still hurts it but aslong as you wheels are pulling it wont hurt to drive it a mile or 2 over 6k rpms.. IDk im not a perfect car expert......

 

[Eagle 5]

man you really do baby your NT. guranteed on a normal basis my car doe snot see much above 3500 in normal driving, still I have fun with it. highest my engine has seen since I have owned it was about 6800-6900 rpms. i rev it up high once in awhile too just for fun. wont hurt anything. im asking because some people have said the engine or valvetrain can handle reving to 8200-8500 rpms on the stock stuff... if that is true than crower retainers and springs can wait and i can get some cams and port work done instead. not that my engine will see that high of revs anytime soon but if it can handle it then I can wait on some things until I get mroe money.

 

[davo345]

i have hit around 7200 rpm...i was surprised.

 

[Kirby]

They will handle at least 8000 before you worry, but the point is you will never see that because of fuel cut. And even if you did get past fuel cut the ign redline is 7800. The howell ECU ups the ignition cut, but you still can't go past fuel cut. The only time you would need to do those upgrades is if you have a standalone ECU with fully adjustable cutoff points. Now I believe the PT crusier lifters or rockers (I can't remember which ones) do have better oiling charecteristics so you could go ahead and do those if you want. Trust me though spend the money where it will count, those parts don't need to be stronger and it won't gain a single bit of HP. Now if you want to do oversize SS valves that will help get air into the engine faster, so it will help performance a little bit.

 

[Eagle 5]

im mos likely going with cams, porting and oversized valves. anything i can do to spool the turbo sooner so i have more use out of it. (a 57 trim t3/t4 with .63 a/r exhaust housing and .60 a/r comp housing is pretty big)

i bleieve a guy in my area has no rev limiter (or so he says) i should ask him what he did to do that.

 

[Talon5786]

I've hit bout 7.5 then it cuts off even in gear
the govner or whateveri got first going 40 it was nice cause i tore the road up going into 2nd

 

[Kirby]

Well a 3 inch exhaust will spool it faster. There are other things you can do as well, but not many. That turbo is going to take longer than a 16g. But it makes up for it by giving more HP when it kicks in.

 

[BD1]

8,000 RPM is where my engine just lets go and you have to shift, I usually go to 7.5 in races, it's pretty safe. But 8k is definately my limit.

 

[truwarrior]

Obvisouly, torque kinda sucks for fwd. What's your guys opinions for a making a higher reving gst (8500-9000)?

Think a ported head, upgraded rods with stock 2g pistions, balance shaft removal,cams, and one hell of a fuel system will be enough?

What turbo would you recommend for under 20 psi boost (16-18 psi redline (8500-9000)).

Just planning my setup. I think I'm gonna buy a second beater car after I get my gst paid for to mod the hell out of it....damn I hate having a 7 bolt though...

Wait a minute...I can buy a 6bolt mod it, then drop it in....

 

[McGruffAWD]

just having a ported head isnt going to help rev the car better. For anything above 8,000 rpms i would recommend some upgraded springs and retainers, so you dont float a valve. Altho i have seen people rev there stock head up to 8...i for one wouldnt. Stock valves and some mild cams would help with the power. A good turbo for around that boost range would be anything from a 14b to t28 a big 16g maybe even a 20g. As for having a 7bolt, your right it does suck.

 

[pneumo]

With that kind of redline I wouldn't go with anything smaller than a 20G. Smaller turbos will run out of steam at high rpm. You might get one to maintain boost, but the exhaust wheel will be choking off the power.
Sheet metal intake manifolds will raise the power at high rpm. The stock IM tends to favor low end torque.

18 psi might not seem like much, but to get it to flow well at high rpm will take some thought, like a free flowing intercooler and 2.5" pipes. Injectors need to be bigger to flow enough up high. The ECU was tuned to match the stock 5800 rpm power peak, so you'll have to do some advanced tuning with the fuel and ignition timing. DSMLink is the best for tuning a 2G.

 

[truwarrior]

Just picked up dsmlink last week

 

[kpt4321]

If you want to rev high, you're going to have to do a few things people in the DSM community don't usually do:

1. Head work. Valve spring and retainers ar the big ones, if you want to go past 8000 rpm. Porting helps, but isn't necessary... these heads flow very very well.

2. Cams. Unquestionably, it's worthless to rev without a set of cams. Don't even bother.

3. Intake manifold. The stock manifolds are designed for peak power below 6000 rpm, and you can gain a LOT up top by going to a well designed one (30+ hp is not abnormal).

4. High flowing turbine wheel/housing. Don't screw around with TDO5H crap, just go TDO6H. If you're revving to 8500 or so, trust me. You'll thank me later.

5. Turbo. See above. With the TDO6H in mind, a 20g or a green will fit your needs VERY well. A friend of mine with a 2g trapped 123 mph on a TDO6H 20g this year, with "some problems." Very impressive.

6. Lots of injector. You'll need larger injector than normal, because avaliable flow drops off bigtime at higher rpm's, if your airflow stays up.

7. Tuning. This is obviously the biggie, no question. The stock maps will kill your power at higher rpm's, so you're going to have to deal with that.

Obviously you also want normal stuff, like a good flowing intercooler, etc.

 

[truwarrior]

How much does a good 6 bolt motor cost? How much cheaper will it be if I build it myself opposed to having a shop build it?

Do our trannies really perform poorly at high revs or do they just need stronger mounts and lighter clutches what will hold the proper amount of power?

 

[Suparata]

You might want to take a look at this http://www.dsmtuners.com/forums/showthread.php?s=&threadid=91141 . It may give you a few more answers to your question .

You might save a few hundred bucks by "doing it yourself" but do you know what you would get into? Do you think that is worth to try to save a few bucks and throw away the money you spend by doing the job wrong? There is so much work involved in installing the engine in the car and make everything work so don't get in to something more that you might not be able to do. Tell your machinist what you want and let your machinist do it's job and you take care of the other things like a good oil cooler, a good I/C and piping, fuel delivery and management and other things that you know how and will have to do.

A six bolt is probably the best thing you can do in addition to what the guys said before me. A "good" 6 Bolt may cost a lot but the BEST one you can get is the one you have custom built with your goals taken into consideration.

Think twice and you will do it once.

Mitch.

 

[mike9146]

Originally posted by truwarrior
Obvisouly, torque kinda sucks for fwd. What's your guys opinions for a making a higher reving gst (8500-9000)?

While I won't disagree that more RPM can make more power, the idea that building a higher revving engine will somehow keep you from spinning the tires simply isn't true. Your front tires are going to break loose when x amount of torque is applied to them, regardless of whether it's being applied by a slow spinning engine with a "tall" gear ratio, or a high revving engine with a "short" gear ratio.

 

[pneumo]

The theory behind this thread is that by making the engine rev higher it can produce good HP with less torque, thereby putting the power to the ground without wheelspin. Have I got that right?

I don't know if the theory is true or not, but it passes the "That seems right" test. Since you can make the same HP at higher rpm with less torque, regardless of what gear it's in. I just don't know if it's torque or horsepower that makes the wheels spin. I'm pretty sure the answer is "torque" from other examples I've seen, but a good arguement to the contrary should convince me.

Re: trannies at high rpm. DSM trannies don't like to shift at high rpm. The faster the engine is going when you shift the harder it is for the syncros to do their job. Usually a driver compensates for this by shifting harder, which can lead to shift fork breakage, or shift rail end breakage. Shift nicely and it will hold just fine.

 

[mike9146]

Let's try this again. His limiting factor is traction. Traction is overcome by torque at the wheels. Let's say that the limit of traction occurs at 300 LB/ft of torque. This will be limit of acceleration regardless of how fast he can make torque, also known as Horsepower. Wheel Torque is the product of engine torque and gear ratio at any given speed. The tires don't care if he spins the engine 1/2 as fast and uses 2/1 gear, or if he spins the engine 2/1 and uses 1/2 gear, so long as he can maintain that 300 LB/ft of torque at the wheels equally as well in both scenarios, (and he obviously can exceed that number already since he has a wheelspin problem) he will accelerate at the maximum possible rate that traction will allow. This isn't to say that he might be able to build a motor with a flatter Torque Curve that will make it easier to modulate that Torque at the wheels, but that's not what he was asking, and for what it's worth, the higher you rev an engine, the "less flat" the Torque Curve becomes. This is a grand oversimplification of reality, but the concept still holds true.

 

[pneumo]

OK so lets not get stuck on the gear ratio thing. How about we just look at what happens as a theoretical engine revs from it's torque peak at about 3500 rpm and up.
I get my theory from this equation; HP= torque X rpm divided by 5252. If the tires can hold 300 ft.-lbs, then
300 ft.-lbs at 3500 rpm = 200 HP.
300 ft.-lbs at 5000 rpm = 285 HP.
300 ft.-lbs at 6000 rpm = 343 HP,
at 7000 rpm that's 400 HP.
I'm not saying this engine will automatically make that power if it's reved higher, but that's the ammount of torque the tires can theoretically hold.

Right?

The thing is I'm not 100% covinced that the tires can only hold 200 HP simply because the engine is turning slower, and yet the same tires can hold 400 HP at higher engine speed. Weird...

 

[mike9146]

The key issue here is that cars *do* use gears, and it's torque to the wheels, not at the engine that's at issue. He stated that he wants to build a high-rev engine, not to make more power, but because he thinks it's going to somehow gain him traction because the engine is making less torque. Yes, the engine will typically be making less torque, but it will also be turning faster. This "turning faster" part means that he will not have to use as much "gear" to go the same speed. If he can make the same "average" horsepower from 6k-9k as he does from 3k-6k right now, he would theoretically be able to reduce his overall gear ratio by 1/3 and produce the same torque to the ground as he did before He can already spin the tires as is. All he would be doing is spinning the tires at the same speed before. If all he wants to do to reduce the torque to the wheels, all he has to do is shift.

Yes, he will potentially make more horsepower by revving higher, but thinking that that will make him accelerate faster in the gears where he is traction-limited is a false assumption. Any more torque to the wheels than what he currently has traction for, at equal wheel speeds, whether by a high-speed engine/short gearing or low-speed engine/tall gearing will result in wheelspin. The best way to maximize this situation would be to build an engine with a perfectly flat torque curve, (torque line?) whose resultant torque at the wheels was right at the maximum that his traction allowed. That would be an electric motor.

BTW: Tires don't "feel" horsepower. Horsepower is a measure of *work,* not of *force.* Assuming the same overall gear ratio doesn't change, the car you describe with 300 lb/ft of torque all the way up the rev range would accelerate at the same rate (and have equal "tire spinning ability") as the RPM's went up and the horsepower increased. It isn't working any "harder," but it is working "longer."

 

[truwarrior]

No matter what, I'm not going to get traction in 1st. What I'm looking to do is stretch out 2nd which I do for the most part get traction (if the weather is perfect, wind isn't blowing, and the street is flat and just been swept), before shifting into 3rd.

So since 2nd is a lower gear, I figured I'd get more useful power before having to shift into 3rd. Basically 2nd is like my 1st and 3 is my 2nd gear

 

[nine5raptor]

Another option to 'stretch' your gearing a little more is to install larger outer diameter wheels/tires. Granted you have more loss with the larger moment of inertia and more unsprung mass, but it is a lot cheaper than building a motor. Other options would be to call up TRE or another tranny shop and have them throw in a taller first and/or second.

 

[Tallen]

You won be able to shift after 9k without a built tranny.

 

[Awdboost]

I’m in the processes of building a 6-bolt motor for my 98. I want to rev to 9K.. I’ve heard from more than one person that the lifter at that RPM will see too much oil pressure. Any where from 100-130 psi at the head witch the lifter can not bleed out fast enough and end up with bent valves. This is something I do not want to experience. As delightful as bent valves sound I don’t think it something for me. I will have a race head with HKS 272/272 on a good old 2.0L. From what I heard that can help is instead of doing the Balance shaft removal is just mashing the counter weight off and leaving them in. This will remove most of the rotational mass and should allow you to rev higher with out all the extra oil pressure. Any other things that I could do? Or is anyone out their reving there motor to 9 with the Balance belts and not having any problems. All input is welcome. Thank you guys for your time.