Turbo ?

[Wills79Vette]

What about a nitrous system? Can someone tell me the plus and minuses to it? I would like to get more HP out of my 350, my neighbor suggest a set of 375 heads and a new cam. Im new to the car world, and this 79 Vette I bought is my first car project.

 

[sscam69]

:nono I would build up a solid bottom end before I would go nitrous on a stock bottom end. Jack told me the L-82's had forged pistons but you still have to put in better rods and bearings. Then you could go with a nitrous system.

These things were not built for stuff like that. Actually for any kind of power adder to be honest. They still aren't.

Are you shooting for a hot rod or just a cruiser with a bit of umf?

 

[Twin_Turbo]

and let's not forget that if you want a serious shot of N2O you will have to gap your rings wider than you do normally. (almost twice as wide)

Marck

 

[GWHITE75]

Twinne

You're right. You did see Terry's picture on the other forum. He abandoned the turbo when someone made him an offer he could not refuse for the whole motor. They really got a great deal. He then put in a 572" motor. He added a 125 shot of nitrous to get the motor up over 1000 HP. Runs pretty good now.

Wills79Vette

My opinion of adding nitrous is that it's easy, fairly cheap compared to other significant power adders, but it's harder on the motor than other types of add ons, like turbos and superchargers/blowers. I suggest you talk with people who have run nitrous for several years to see how their motors are holding up and how much work have they had to do to them, before you make that decision.

As others have said, you really need to make sure you have a strong short block before you add any device capable of adding a lot of horsepower to the rear wheels.

 

[MaineShark]

Hmmm.... I think this is the first I have ever heard anyone suggest that turbos are good for low-end torque. Generally, most turbos don't build any significant boost at lower RPM's. It isn't until the engine starts pumping out large quantities of exhaust (which is directly related to RPM), that the turbo starts to spool up.

Now, in the upper RPM ranges, the turbo produces essentially "free" power; the engine needs a certain amount of exhaust backpressure, and it really doesn't care whether that backpressure comes from an exhaust system, or a turbo, so you are getting boost, without costing power.

There is, of course, the issue of turbo lag - the turbo takes time to spin up, and to slow back down. Splitting the turbo system in two (twin turbo) helps, since two turbos with half the output of the one larger turbo have significantly less than half the rotational inertia of the larger turbo. But there will always be lag.

That's where centrifugal superchargers come in: similar boost characteristics to a turbo, but no lag, since there is a direct mechanical link between the compressor and the engine. Of course they add drag to the engine, so they don't produce quite as much power as a turbo would, but they have much better top end than a roots-type supercharger.

And, like turbos, they are compressors. Comrpessors can be intercooled, to lower the charge air temperature. With a positive-displacement blower like a roots, the pressure does not actually build until the air gets into the manifold; since the heat occurs where the pressure does, this is where the heat is, and it is already too late to intercool it.

And that brings us to positive-displacement blowers. Roots systems produce a lot of low-end torque, thanks to the massive amount of air they move. But they produce much more parasitic drag on the enigine, and cannot be intercooled (see above), which results in poor top-end performance, compared to a compressor.

Lastly, we have something rather unique, and my personal favorite for most street cars: the Autorotor twin-screw. These units are re-packaged and sold by a number of vendors - Whipple is the only one I can think of off the top of my head. I think these offer the best of both worlds: they are blowers, and compressors. So, you end up with a more well-rounded system. And, they can be intercooled, which is a big plus.

For a vehicle which was only going to be used for racing from streetlight-to-streetlight, I would favor a positive-displacement blower, for its low-end torque. For a cruiser to blast down the autobahn with the engine screaming, nothing beats a turbo (or, preferrably, two). For a well-rounded street car, well, the second phase of my '73 383 project (when it gets to that point) will be a Autorotor blower.

Joe

 

[sscam69]

We could go on and on about the finer points of each system but I will give you my .02 on turbos and why I prefer them.

1. They are a challenge. You just can't bolt one on. Takes a lot of work, time, money and patience. Why is that good? Because you learn a lot more and you become that much more knowledgeable.

2. There a LOTS of possiblities and choices to make. VERY similar to building and engine. IMO you really can't say that about an SC. SC's eliminate a lot of variables.

You CAN eliminate turbo lag completely but you are going to suffer at the upper RPM ranges. Just like and engine they have compromises within themselves. In other words strictly comparing just turbos a "smaller" turbo will give you the response when you need it BUT the adiabatic effic. (AE) will suffer at the top. OR you can go with a "bigger" turbo and get the infamous lag but your going to build awesome torque/power where it counts (ala Supra) in a race.

3. They are more adiabatic efficient, mechanically efficient and isentropically efficient than both Screw Roots. Centr. SC's on the other hand.....well their turbos run by belts not exhaust gases butare still less isent. eff..

4.They are less parasitic than SC's (all kinds) and you can see that in the torque and power they produce OVER SC's. A lot of people, actually most, like to only talk peak power and torque. And that is important but I think average torque and power over the intendid RPM range is even more important. It gives a better indication of over all performance-.


Drawbacks

1. Plumbing. Not exactly a bolt on deal. Takes thought and planning

2. Tuning a turbo system is a bit more tedious

3. Lag


I personally think it comes down to prefrence and what your willing to live with.

sorry for the long post

Frank

 

[sscam69]

This is a pic of dyno results from Rob Raymers Turbo setup on a Camaro with a built 375c.i. engine with a T-74 turbo. Just look at where the torque peeks, 730ftlbs@~4.2k Rpms:eek. Dont tell me you won't use that on a stop light to stop light race!

He has gone 9.94@136mph with that setup

The kit he sells to customers produces 534rwhp / 687rwtq and a customer has gone 11.44@125mph. The trap alone says there is still more in it! I am pretty sure with some really sticky tires and once the guy knows, if not already, how to drive it better thats a high 10 second car. The car weighed in at ~3800lbs. Not exactly light.


Turbos

 

[Monty]

It's amazing the misinformation regarding turbos that gets passed around the internet like fact...

 

[Twin_Turbo]

Yo Monty,

Nice to see you here

About the tubo lag, that was the case 20 years ago, new technology has made the turbos come a long way in getting rid of the lag, it's still there but not so apparent as it was. I can go and get very technical here and talk about impellers, inducers, diffusers etc. but take it from me, modern turbos are very efficient in a large rpm range if selected right.

On to centrifugal SC's not having lag, that's completely wrong. Centrifugal SC's are not positive displacement devices like roots blowers are and that means they buld pressure inside the supercharger itself and thus have to spool up. Postitive displacement devices like the roots blower (notice where it says blower) are in fact just air pumps, they deliver the same amount of air for each revolution independant of RPM, they don't make boost themself, the boost is because the intake manifold and the closed valves etc. are restrictions leading to a particular amount of boost

Marck

 

[MaineShark]

Frank: you can't eliminate lag. You can reduce it, but you cannot eliminate it. Even in the best systems, it is noticeable to a skilled driver.

And, regarding peak power vs. wide powerband, generally turbochargers are known for high peak power, but a narrower powerband, while superchargers are known for less peak, but a wider powerband.

Also, notice that 4200 RPM number on that torque peak in your example? Not exactly "low end"...

Twinnie: superchargers have not lag. A supercharger can no more have lag, than your distributor could - both are mechanically linked to the engine. Various types have different boost curves, but the boost curve is similar to the power curve of an engine - some engines make more top end, some more low, some more middle.

Also, while a positive-displacement blower delivers the same amount of air per revolution, that revolution rate is directly dependant on RPM, since there is a direct linkage. Actually, that ends up being the problem: you quickly produce more air than your engine can use, and it ends up blowing back through, which results in hotter air, more parasitic drag, and reduced top-end power.

Joe

 

[Twin_Turbo]

A centrifugal SC does not make boost at low rpm, only the wipple (screw) SC and the roots blower are efficient there. So, the centrifugal SC needs rpm's to create boost, simple as that. It too has a range of efficiency.

The roots blower makes less boost at higher rpm, not more. Often the max boost of a roots charger is aroud 2000rpm. Indeed high discharge termperatures are a big brawback.

Indeed since the blower displaces an equal amount of air per revolution the total amount increases w/ RPM. However, the engine also uses more air w/ higher rpms.This means the roots blower will give all it has on full throttle, no matter what the rpm. IT's the same throughout the rpm range.


Marck

 

[MaineShark]

Again, the centrifugal unit does make low-RPM boost. Granted, it's not much, but it's there. Anyway, a lack of low-end performance is simply a matter of the shape of the torque and horsepower curves; it's not the same as turbo lag. Turbo lag results from the time factor required to physically spin the turbo up to speed. Any turbo takes time to develop those tens of thousands of RPMs necessary to produce noticeable boost.

Regarding air usage, the amout of air used per revolution by the engine is a fixed amount. Every revolution takes in half the displacement of the engine (175ci, in our case). Of course, the flow into the engine is limited by the heads, which is why the roots blower ends up producing more air than the engine can use - the blower pumps air in relation to the RPM, but the engine uses less air per revolution as the speed of the air within the head approaches sonic. The amount of air that can flow at sonic is, of course, the upper limit of flow.

So, the blower ends up sending more air into the engine than the engine can use, at the upper RPM ranges. This increases pressure, resulting in leakback into the blower. Now, the blower is blowing pressurized air back into the already-pressurized manifold. This ends up adding heat, and reduces overall efficiency of the engine.

Joe

 

[Wills79Vette]

I would build up a solid bottom end before I would go nitrous on a stock bottom end. Jack told me the L-82's had forged pistons but you still have to put in better rods and bearings. Then you could go with a nitrous system.

I was wanting to add some ponys to my car with out too much mods. Some people have been telling me that adding 375 heads and a new cam would really help HP. But what are the down sides to this, what else would you have to do to make it work?

 

[sscam69]

Well it really depends on a lot of things. I mean how heavy is your foot.

If you just looking for a little bit more the best way to do it is a cam and some heads.

How much are you looking to spend?

Heads

If you go iron the "Vortech" heads seem to be on the top. That is for a bolt on situation. There is better but then you start getting into a more complex situation. Run a search for "Vortech heads.. not what there cracked up to be" or something like that. Everybody claims they are cheap heads but it has been found contrary. In that post I give a price break down on what is needed. Included are the HIDDEN costs.

If you want to go aluminum AFR puts out the best heads and probably the last, that is if the bug doesn't bite you!:L, heads you are going to buy. fc3 just bought a pair. Granted he ran into a few snags I don't think he is going to be disappointed once he mashes that pedal. Akray4play has a 400c.i. with thier 195's I believe and is very pleased with them.

Your going to spend about over $1000 on hardware as far as heads are concerned. Thats if you looking for a lot more power.

Cams

And cams well comp cams has Dual-Energy cams that provide really good low end-mid range torque for everyday drivability. Then theres the extreme energy. Those cams have more top end.

IF your looking to stay with the stock heads etc. Ron (rpounds) has tried several cams that would work great with a stock setup. Hopefully he'll chime in. Search for "installing a cam and words of advice" and he gave a few suggestions.

What are your goals? This might help us help you narrow down some choices.

Frank

 

[Wills79Vette]

Im looking for HP that will be there when I want it. I know one of the big keys to HP is air coming in and going out. I have thought about the nitrous some more and decided not to go that route. But I am leaning more towards Heads, Cam, Exsaust, and Carberator route of doing it. I would like to keep a relative good gas mileage, but be able to crank out the HP. Im looking for around 350 to 400 HP out of the crate 350. Im looking in to some of the heads you mentioned, thanks for the help.