holy spool time batman, but great numbers! Congrats SGP

 

What size injectors are you running?

 

that's unreal man.. any dyno videos or just videos of the car at all?

 

Don't you lose a couple pounds of boost with a high duration cam. I would just use the stock cams. Save the 1000+ for cams, new headgaskets, and 8 hours fo work $1000+ for tuning and other things. You can save 2000 right there and you might see a 30-40 whp gain if your making 500+ whp. Tune it good and all you have to do is turn a know and increase boost to gain that power back.

 

Those are nice numbers... Mabrook Kudos lol. I guess the car spooled at 4K RPM at this dyno because there wasnt much load on the wheels to help the turbo build boost fast. I guess the dynojet drums were heavier than the load u guys did on the dynapack. If u guys try to load the wheels u are going to get boost much faster and maybe even faster than a dyno jet. Good luck.

 

You're right, i do live in Qatar and i'm extremely anxious to get the car.

Good luck with your build up, the reason mine took so long was because many of the parts were not available at the time. I'm sure the same setup would take less than half as long these days.

Abdulla,

 

Insane power. Your looking at 130 mph trap easy....what size injectors??

 

RC 750 cc's

http://store.yahoo.com/sgpracing-store/ab03ni35.html

 

I know the feeling

Mabrouk (Congrats in Arabic)

Abdulla, Could you please (if you may) PM me the cost of the engine without the turbos. I'm thinking of building an engine and having it shipped to Riyadh.

Abdullah
AKA: Az

 

If you are going for big turbo power, you definitely DON'T want a high overlap cam like big N/A power cams usually are. Keep the duration down a bit, the overlap to a minimum and go with some extra lift.

 

I've always heard this as well. Makes since because you can't build boost in the cylinders if it just leaks straight through the engine. However, the overlap would probably help cool the engine and improve combustion. Especially on low compression pistons where exhaust gases will linger.

The Z has variable valve timing in the form of cam phase (intake only). It would be cool to use the VVT system as a boost controller. Simply increase overlap to hold boost in check. If the turbos run out of steam at higher rpms, then just dial the overlap back out.

I wonder how hard it is to intercept and control the VVT system?

Taking into account the maximum that cam phase can be adjusted would dictate how much overlap you could get away with. Also, at high enough boost, you will have to worry about exhuast backflow (which will probably put a damper on the idea). This is probably more useful for superchargers rather than turbos....

--
Jeff

 

Well usually overlap just dirties the mixture up and runs things afoul. Turbo cars do not like any overlap expect perhaps for spool. The VVT system would be very handy for keeping overlap at low revs and to spool and then taking it out for power. Cooling the combustion chamber is done with A/F ratio. Cams are not going to have enough of an effect to alter boost level much at all. The exhaust backpressure (turbine inlet pressure) is something that is checked and tuned to match the turbo to the motor.

 

Currently , SGP and others recommend the JWT S1 grind. Minimal overlap increase an a nice lift increase. Not a perfect street turbo CAM profile , but close enough to add noticeable mid band grunt. The more radical Tomeis (ie 268 duration are counter productive for a Streetable turbo setup IMO.

 

I had to step in after reading that. There is something that people need to know about building engines for forced induction, that most people do not take the time to learn. They just run around chanting this crap about using mild cams because turbos and superchargers don't like radical cams...

Keeping overlap down is a BANDAID, not a rule. If you have a well designed turbo setup that flows exhaust gases well, then your backpressure at the exhaust valves will be lower, and you don't have to worry about reversion. If you want to make awesome top end power, you NEED the overlap, whether boosted or not.

Think about it like this. A naturally aspirated car might have something like 10 psi of backpressure at the exhaust valves. (It may be even more, I don't know) This pressure is overcome by the velocity of the gases flowing out of the combustion chamber, and overlap works well in this case.

A well designed turbo setup could have 20 psi on the intake side, and 30 psi on the exhaust side. Pressure differential across the motor is the same as the naturally aspirated engine. Overlap would work just as well here as it did in the naturally aspirated setup.

A poorly designed turbo setup may have 20 psi on the intake side, and 50 psi on the exhaust side. Here, a bunch of overlap wouldn't work quite as well.

Now, I've never actually measured the backpressure numbers at the exhaust valves, all I know is the theory and practice of minimizing it to make power. These numbers are used for reference only, they may be higher, they may be lower, but in real life, you WILL see a difference of backpressure at the exhaust valves with a very well designed turbo setup. This has been proven. It has also been proven that the age old rule of reducing overlap for a boosted application is NOT necessary unless there is something wrong with the way the engine expells exhaust gases.

 

Depends on your target application. For a "well mannered,streetable" Turbo setup , you generally don't want a large sacrifice in idle quality and low end grunt for improvement at the top end. Currently the only current way on the VQ35 to "improve" idle quality when increaseing overlap is to bump up the idle. The VVT can not compensate. What made all the old NA hot rods less than civil on the road was the need for huge overlap and the comensurate "crappy" idle and "tear gas" exhaust.

 

OK, since you are going to "teach" me something; what did I say was wrong? I've tried an enormous amount of cams on turbo cars back to back. With the redline where it is on a stockish VQ35, you don't need a bunch of duration. Sure, duration and lift give more power on turbo just like N/A but you don't want a lot of overlap. You don't want to go too low on exhaust valve pressure because you don't just have an open exhaust after that, you have a turbo that WANTS turbine inlet pressure. Otherwise you get too low and the the turbo doesn't work optimally for the car and the powerband you are after. Cams must be matched with the turbo as well. It isn't just the motor and the cams; there is a third entity that comes into play.

 

This is very true, but you would be surprised how much overlap you can have in an engine and still get a good idle. It's definitely enough overlap to cause all the brainwashed internet racers to cry,"That's too much overlap for a turbo application!"

 

Ever heard the term "crossover"? That is the theoretical point where turbine inlet pressure and boost pressure equalize. Turbo designers everywhere in the world are trying to achieve crossover in turbo systems now. Why would they be doing that if the turbo needed pressure? It doesn't. All it needs is flow.

 

Yep but it isn't going to happen with any of the parts shelf turbo kits out there with older technology. Like you said, turbo designers. Meanwhile we have 18G's and other tuner selected turbo setups.

 

That's true, but those tuner selected setups are already far superior to the stuff that came stock on the turbo cars that caused people to steer away from overlap in the first place.

On a 2G DSM for example, you can hit 60 psi of exhaust manifold pressure with 20 psi on the intake side, simply because the turbo is too small, and the exhaust manifold sucks. With an 8cm 18G, like the ones that come in the Greddy 350Z kit, I bet that number is dropped considerably.

With a Greddy kit on a 350Z, you have 1.75 liters pushing each turbo. Those turbos are big enough that you shouldn't have ridiculous backpressure at the turbine inlet. I think that application could use more overlap if the owner wanted to push his powerband up higher, and sacrifice a little low end grunt.

Basically, all I'm trying to convey, is that your cam choice should be done based on what kind of power band you are trying to achieve, whether or not the engine is boosted. If you want to rev your engine to 9000rpm and make good power up there, you need the overlap, even on a turbo application.