Any way I'm planin on having loads of torque because the engine I plan on building will be a 4.25 bore and 4.25 stroke to 482CID, or a 4.31 bore and 4.5 stroke to come out to 525CID. I dont really need a high revving engine at all, I just need a max at like 5 or 5.5K rpm and thats enough for me. So I think that any power adder I use will give me even more torque and hp figures.

I thought that Turbocharged Engines that use a lot of boost have a lag time because it takes time to get the big Turbos to a high enough rpm to make that high boost number to provide all that power. I see it as they are coming out with turbo packages or custom projects that have little or none lag time because they are running higher boost that 8.5 and are running less than 10psi. So as an affect you are not lossing the power that you lose when you go down in compression, and you get the instant response of the turbos b/c they take less time to spool up. SO I said that maybe use 4 turbos, two for the low range that max out at low rpms, then the other two start getting exhaust pressure from opening of vavles that will allow the other 2 to run and create even more power in the upper range rpms. Do you have any thoughts or feedback about that setup? Or suggestions that could help me out on this topic. ;)

 

The turbo size and design vs. engine displacement is what dictates whether or not the tq peak exceeds the hp peak or not. You'll notice on the Cerra Racing turbo setups you were referring to they use a single 62-1 turbo, which is pretty mild for a 346ci V8. The turbo is small enough to spool up almost instantaneously and provide excellent torque and power in the rpm range that falls within normal public road driving. Unfortunately, once the engine rpms increases, in this case around the 5000 rpm level, the turbo can't maintain the airflow and power/torque decreases. It just depends on what you want...

I think the main reason you're not seeing too many monster motors being turbocharged is that in the racing series' that allow turbos, they are weight penalized based on engine displacement. Additionally, when you already turbocharged smallblocks or destroked big blocks making 2000+ hp, they are at the point that NHRA Top Fule and Funny car are at - too much power to apply to the tires. If I remember correctly most of the fastest guys are running something around a 390 ci displacment, 35+ psi of boost and relatively high static compression around 10 to 1 or more. It becomes more of a traction and clutch managment race, rather than a horsepower race.

The sequential turbo concept, where a smaller turbo feeds into a larger turbo, providing both low end torque and high end power is a popular one. Several of the OEM's have gone with that arrangement, but in reality a properly sized single or twin turbo setup will provide very similar results with much greater simplicity.

On pump gas, you'll generally make more power with a lower compressionr atio and more boost. The sweet spot seems to be around the 8.0-8.5 static compression ratio. Going below that range, the engine tends to get lazy, throttle response sufffers, and as mentioned, the turbos are a little slower to spool up since the exhaust energy is so diminished by the low CR. The 8.0-8.5 CR range gives good detonation protection on pump gas without sacrificing non-boost engine performance and response. If we're talking 114+ octane racing engines, then it's a different story. Some of those guys are running 10.0-10.5 CR with 35+ psi of boost and making 2200+hp out of a 390 ci destroked BBC


[Modified by Monty, 11:38 AM 11/27/2002]

 

Thanks for the info Monty, have you run your vette with more than 5,6psi yet? Fear of breaking the rear end?

 

I cracked open the boost controller a little but barely got up to 8-9psi before I had to slow down. You run out of space real quick with the acceleration this car has when driving around suburbia. I need to make an effort to find some open space or deserted roads to play around on. Breaking the rear end is certainly a consideration. Right now I just have forged yokes and spindles from Tom's Differentials. I'm getting stronger halfshafts made and I'm fabricating halfshaft loops this winter. I'm hoping that with street tires the Dana 44 will stay together, if not I'm probably going to do a custom IRS based off of a 9" or Dana 60.

Good luck with whichever route you decide to take.

 

Could you give me some advice on this turbo/Supercharger choice, Monty? The question is that I'm building a 496CID Engine, 4.25 stroke and 4.31 bore, and what poweradder would give me more low end Torque and HP more TQ though, I dont what a engine that will only make good power on a very high rpm in which the engine may never really see, or if it did only for a split sec. So with your amazing knowledge in building performanc cars, which way would be best? I mean a turbo setup would be cheaper for me because I could Fab up all the parts for it, exhaust and everything I already have the plans for that, the roots charger would cause me to cut the hood which would make put on a scoop.

Anyway are you for real that you run out of road, maybe you should try the airports runway :lol: :lol: :lol: Or you could go out on the freeway at 3:30am on a not so trafficy Highway and rip it up, test the beast out.

 

Obviously I'm partial to turbocharging, but it'w not for everybody. A supercharger can obviously provide excellent results, it's available as a "bolt-on"(yeah, right!), and it's relatively affordable. Any turbo setup will end up costing you more and taking more time, but performance wise it will exceed that of the supercharger and generally prove more reliable and flexible. It's very easy to design a turbo system which will make awesome power and torque, yet drive as easily as your daily driver. It all depends on what you power goals are, and what rpm range you want it to most most effectvie at. Turbos provide a much broader torque curve than a supercharger since turbos aren't rpm dependent and don't necessarily need as many rpm's to make maximum boost.

For your 496, something like a T76 would provide huge off the line increases in torque with a fat mid rpm torque and power curve. You could expect to make almost 900hp with that turbo, making your car potentially capable of running 9's. You could go a little smaller to a T70 or T72 and still make almost 800 hp.

My only advice is that regardless of which way you decide to go, do it right the first time. There are plenty of horror stories out there reblated to blown engines and poor attempts at forced induction.

 

Thanks for the info on the turbo, but I think I'm going to go with a roots because of its simplcity and I dont really have too much time to build a turbo setup. Maybe sometime when I get older I could make a crazy azz turbocharged monster.