Rev Limit / VVT

[Largekid]

Alrighty, after my race last night, I was thinking about looking into increasing my rev limit. Now I have it set to 7100. I was told when i purchased the car that the RB's experience valve float much over this...(7400 iirc). Can I just do a upgrade to the valvetrain and be ok? would i experience any rod streching or anything? how about oil that high in the RPM range? Also, how can I tell if I have VVT enabled? I dont really feel anything, but in the datalogit options, it says it starts at 4k. Can I disable the VVT, do I "really" need it? I'd really like to up my powerband more than 2k (5-7000RPM) thanks guys!

[240z4u]

You can't feel VVT, its not like V-tec so much..

My rev limit is set to 7800, but realistically you have to get on the dyno with supporting mods maybe even cams to breath enough air at that stage of the game. My car has not been on the rollers to 7800, but I suspect I will find power falling off. I just got sick of wacking the rev limiter so quickly.

So what did you run?

Whats your setup and how much power did you make?

Evan

[Darius]

Do you have an upgraded turbo? If so, which turbo?

The stock valve train has been said to handle about 7400 rpm like you said. I don't know how much of that is internet "knowledge" or real experience from people being passed along. The same can be said that with upgraded valvesprings, the hydraulic lifters are limited to about 8500 rpm. The stock bottom end should be fine up to 7500 rpm and even higher. The limit on the 25 bottom end are the rings and ring lands. Their life depends entirely on the quality of the tune.

Higher revs put more strain on the oil pump drive on the crank and it is prone to failure unless the crank collar has been fixed or you were lucky and got one with a long snout.

VCT is set to engage at 4700 rpm stock (at least that is what the PFC comes standardized at). It is typically left in operation. Most people lose power when it is disengaged. Try taking the plug off of the solenoid and see how well it drives...power sucks. It's not like v-tec because the cam lobe does not change and there are obviously no secondary runners. The 25 has variable cam timing on the intake cam only so it is not something you can hear engage or disengage.

[Largekid]

its a S1 RB25 bored +.80 w/ weisco forged pistons. P&P Head, Greddy intake mani, MSD IGN, T70@22lbs, PFC, 680 inj, FMIC, etx

So I shouldn't be reving much past 7500 then? Say the motor wont flow the air, but the turbo is pushing it into the motor, where is the stress put then? Pistons? The tune is trash now, we are working on it...but its hit or miss on when we can get to tune it. I 'should' have 550wh on 22lbs I would think.

I ran a S-Trim Cobra last night. Supposibly 440wh or so...I put a car on him thru 4th. I weigh 3100 w/ driver, he weighs 3600 w/ driver. Me w/ +500 on the weight, and +100whp...i should walk him pretty good...but my power band is only really hitting 5k+.

[StricNyne]

that big of a turbo u should be making power to redline, and with stock valve springs, yes dont go over 7400, you should do a set of tomei poncams, and tomei valve springs

[Cjmartz2k]

I'm a Mustang guy, just wanted to get that out there ;-)

I've got money it's your tune. You should have walked him. Revving higher it with a P&P head and a T70 will help. What cams? If stock, I'd shift around 7.5-7.8k.

That's a pretty big overbore on those pistons mang

[Largekid]

I'm a Mustang guy, just wanted to get that out there ;-)

I've got money it's your tune. You should have walked him. Revving higher it with a P&P head and a T70 will help. What cams? If stock, I'd shift around 7.5-7.8k.

That's a pretty big overbore on those pistons mang

stock cams for now...the original owners motor blew a ringland and this one was rebuilt. I guess it did some damage so he overbored it a bit. lol I'm assuming i'm about 2.7L or so...I dont know how much i'd pick up from the bore I'll bump my revlimiter to 7400 and go from there...that will help a little i guess haha

[BoostFab]

i wouldn't recommend you guys going rev happy over 7500rpm; the crank oil pump snout may result in oil pump failure fast.

[lilskyline240]

how do you go about disconnecting the VVT? is there a wire for it?

[BoostFab]

how do you go about disconnecting the VVT? is there a wire for it?

VVT are referenced on Toyota engines.

rb25det's known as VCT

i would not suggest disabling the VCT, as it help with emmisions and fuel economy, and low-end torque under 4500rpm. and when it activate at above 4500rpm, power is maximized.

VCT have nothing to do with rev limit, it's the behavior with your ECU cutting off at a set point. .

and again, your rod don't stretch. not sure where you get that idea. they either bent or snap due to dentation.

[lilskyline240]

i dont want to disconnect it. I just want to know is there a wire for a solenoid that goes to it? or what

[240z4u]

The solenoid is on the head near the temp sensors. About 1" diameter and a few inches long. Connector is square. It was one of the ones in the photos you sent me asking where the ecu coolant temp sensor was.

Evan

[lilskyline240]

o ok i gotcha. Just was interested to know where it was

[Largekid]

and again, your rod don't stretch. not sure where you get that idea. they either bent or snap due to dentation.

i know on other motors when you start reving super high, they can strech rods pretty easily. I didnt know if there was a problem on the bottom end of reving high, or if it was just the valvetrain. And I guess the crank snout.

[WhatsADSM]

Hate to say it but honestly considering the rest of the setup that turbo is too big. Have you ever considered getting a smaller turbo and moving the start of the power band down instead of trying to rev it more.

IMO honestly your car would be faster with a smaller turbo as is. A 35r would be a MUCH better fit.

**Edit** Also a .080 overbore on a rb25 is a ~2.62L

[BoostFab]

i know on other motors when you start reving super high, they can strech rods pretty easily. I didnt know if there was a problem on the bottom end of reving high, or if it was just the valvetrain. And I guess the crank snout.

no! your rod don't stretch. it's the rod caps bolt that become the weak point when reving too high, that's why i suggest upgrading to ARP rod cap studs if still running on stock rods after certain power level. When the weak cap-bolt fail (stretches), causing the bearing to lose clearance at the narrow point, leading to bearing seizure and the rod grenade out your block.

When you are aiming anything 500+ and upward might as well drop in new rods and pistons for long term reliability.

[Largekid]

Hate to say it but honestly considering the rest of the setup that turbo is too big. Have you ever considered getting a smaller turbo and moving the start of the power band down instead of trying to rev it more.

IMO honestly your car would be faster with a smaller turbo as is. A 35r would be a MUCH better fit.

**Edit** Also a .080 overbore on a rb25 is a ~2.62L

thats good to know w/ the overbore...thanks!

The 35R and the T70 arn't much different in sizing at all really. Agreed, it is bigger than I was told/expected, but I think the turbo will get the job done...we will see after I get it tuned and play w/ it out on the roads more for sure though. If I end up changing turbos, i will deff go 35R, but only time/money will tell. I got a great deal on this T70 unit also, thats why I decided to go this route. Leaves me room to grow

[StricNyne]

t70 = dynoqueen or single turbo 5.0 mustang lol, nah its a good turbo, but u need some bump sticks to adj that powerband, maybe even a little nitrous to get that sucker spoolin, also since i am running a rb26 pfc, i gont have vct control, so i made one, its a msd rpm activated switch with digital display, thing is freaking awesome