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:in before the lock:

 

Just wondering if you value your opinion more than others? Because I could tell you that one is better than the other OR you could find out which one works best to your power goals. If you want the cheapest then the stroked l3.1 is not for you. There are a few threads that show the cost comparison from going that route. If you are looking for 250-300whp then either will d fine.

 

Not sure if you have looked at the 3.1L post and just been in the "wishing"/ drool mode but do some searching then come back with some goals and we can help you get there.

 

Happy hunting!

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You will always spend more money on an NA engine to make numbers comparable to a forced induction motor of the same type. Please enlighten me on the advantages besides less parts and points of failure in an NA.

 

NA engines don't have to worry about turbo lag, they weigh less, and you don't have the ricer, PUH-CHEW from the blow off valve.

 

Also, there is no replacement for displacement. A larger engine with running the same amount of boost as a smaller engine will almost always be able to make more power. Sure it's an extremely simplified reality that doesn't take into account harmonic balance, air flow, or a numerous amount of other things, but in the end, a larger engine will always be able to make more power than a smaller engine.

 

But I believe the answer to this OP lies in what he wants to do with the car. Usually if you have to ask how much one costs, it's usually better to go with the cheaper one. There's always plenty more things to fix and make better on the Z, the engine is really the last thing you should worry about, so I'd keep it stock with some basic mods for as long as possible.

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na engines do have to worry about cam lag though, the added weight is barely noticeable in most applications (worried about weight drive a striped car and maintain a lean body mass index). a turbo car does not need to make an excessive blow off sound if plumbed correctly.... both options have there ups and downs i find the question is not about turbo or NA, V8 or straight 6 ect... its how do you want to make your power (eg low down torque or reving till 11k or somewhere in between) also do you want to go with an engine for and aesthetic reason eg pop culture reference, restoring.

 

then when its all said and done is it better to spend $30k+ and make a L31ET or $2k and use an RB20det (or RB30ET) and with an other $2k or so get a real close result ~

 

have fun with your dilemma i decided to build an L31 and one RB20DET one for aesthetics and one for speed and cost

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NA engines don't have to worry about turbo lag, they weigh less, and you don't have the ricer, PUH-CHEW from the blow off valve.

 

Modern turbos have very little turbo lag, it's essentially unnoticeable. You may be thinking of boost threshold, and what ovenfood brings up is a good point; what about cam threshold? It take time for an NA engine to "get on the cam."

 

As far as the blow-off valve sound, I'm not sure if you fully understand how turbocharged engines work. A "blow-off" valve should not be vented to atmosphere, but instead should be used as a recirculation valve on throttle drop in order to prevent surge and keep the compressor wheel spinning, in a nutshell.

 

Also, there is no replacement for displacement. A larger engine with running the same amount of boost as a smaller engine will almost always be able to make more power. Sure it's an extremely simplified reality that doesn't take into account harmonic balance, air flow, or a numerous amount of other things, but in the end, a larger engine will always be able to make more power than a smaller engine.

 

Incorrect, and a terrible generalization: "a larger engine will always be able to make more power than a smaller engine."

 

Like I said in my first post, forced induction is the replacement for displacement.

 

Use the ideal gas law as a model for the air entering the engine during one engine cycle; PV = nRT.

P is pressure, V is volume, n is # of moles, R is the universal gas constant, and T is temperature.

 

(1) Solve for V (volume); V = nRT/P.

 

Note that density is mass per unit volume; rho = m/V.

 

(2) Therefore, V = m/rho.

 

(3) Substituting for V in the ideal gas law; m/rho = nRT/P.

 

(4) Solve for density (rho) with m/n=M; rho = MP/RT.

 

Therefore, with M and R being constant and holding temperature constant, doubling intake pressure doubles intake density.

 

(5) Look back at the density equation (2) and double the density, so V = m/2rho.

 

(6) Put the right side of the equation back into the form of (2) and you get 2V = m/rho.

 

This means that when you turbocharge an engine, you are effectively increasing displaced volume. Double the intake pressure and you effectively double displacement, e.g. take a 2L engine and put in 14psi of boost and you now have an effective engine displacement of 4L.

 

I do enjoy letting the nerd out once in a while... ;)

 

When we talk about two turbocharged engines, the comparison remains the same, increasing intake pressure increases effective displacement. So you can say that theoretically, "a larger engine with running the same amount of boost as a smaller engine will almost always be able to make more power" but where does that really get you? Can't you just slightly increase the boost on the smaller engine and get to where the slightly larger one is?

 

Using the 3.1L vs. 2.8L comparison, and let's say that the 3.1L runs 10psi of boost. In order for the 2.8L turbo to match the 3.1L at 10psi, it would have to run 11psi. The performance difference is essentially negligible as there are other factors in ultimately making power and going faster besides the amount of "boost." For example, the 2.8L can spin faster than the 3.1L, holding everything else constant (lower mean piston speed at equal engine speeds). Will that alone make up for the discrepancy, I don't know and I don't feel like doing the calculations to possibly find that out. The price difference, however, is not negligible.

 

I'll take the 2.8 turbo over the 3.1 turbo, thankyouverymuch!

 

My 2 cents.

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if both are getting a turbo (like said before) im not seeing much reasoning, then again most people complain of cost....essentially its just a different crank, because in a well built or just plain "built" motor the pistons are going to be forged-same price as custom/forged anyway.

 

To be completely honest, i dont see that much cost difference between a well built turbo setup and a stroker turbo....except for a few small things.

 

1. Strokers love to rev, that being said either way everything should be well balanced.

2. Most people that build turbo motors thing PSI/#of boost is what matters...WRONG, but on a higher compression motor (and everything else stock) will not be able to run as much boost/psi vs a lower compression non stroker.

3. Fuel plays a big part either way in both for tunes and detonation.

 

 

Honestly why not get the extra bump for the cost of the crank? You HAVE to port the motor/head to flow better/run more efficiently for BOTH...you HAVE to get forged/custom pistons for BOTH, you HAVE to have the motor well balanced for BOTH, etc etc....

 

Really when you think about it the BIG arguement is...if im looking for 250-300 hp which is cheaper...turbo, but remember that when youre going higher in the HP range why not get as much as you can out of it, and making it not work as hard at doing it?

Yes it costs more to go stroker vs turbo IF you only want 300hp (but both will hit that mark pretty easily if done correctly) but when you want more you might as well take a small hit in price on the crank and punch it out to 3.1

 

Then again if you are worried about cost, a simple 383 sbc with a nitrous plate will run all day and forever (if tuned correctly) and make well over 400 (maybe that on just the motor depending on how much $$$ you throw at it, dollar for dollar i dont think it can be beat, and the fab work is VERY minimal with all the "kits" now and dirt cheap.

 

/rant...my .02

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I'm glad my ranting on camshaft lag are now starting to bear fruit. Well done!

 

I can show you Turbocharged L-Engines with a power delivery curve almost identical to a 454 BB Chevy.

 

To paraphrase the old lady from the BK Adverts: "Where's the Lag?"

 

Parroting stuff from books written 30+ years ago is really kind of sad.

 

When driven properly either an N/A or a Turbo gives instantaneous response---just the Turbocharged car gives you FAR more.

 

And below their optimum thresholds, the torque given by a turbocharged engine will usually far outpace a significantly larger N/A engine. That is to say, and turbocharged engine driven below boost threshold while not being able to give, say 'full' boost, will likely give 2-5psi at almost any throttle opening when given WOT versus an incrementally larger N/A engine given WOT well below camshaft sweet spot...

 

This miniscule amount of boost gives a large boost in Volumetric Efficiency over a comparable N/A engine. A 2.8@3psi with identical porting as a 3.1 at 2000rpms versus a 3.1 at 2000rpms.

 

My bet is the 2.8 pulls harder, all things being equal.

Edited by Tony D
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  • 2 weeks later...

Im using a stroked 3.1 with a Holset hx-35.

 

A went from a 2.8 using the exact same turbo {not that i like the hx35 but for now its what im running}.

The stroker from day one pulls harder over hte 2.8.

At 14PSI on the 2.8 i would be at 2800RPM.

At 14PSI on the 3.1 Im at 2500RPM.

 

The stroker feels stronger down low, and more responsive over the 2.8.

 

Im not here to one up the 2.8L when all is said and done im sure the 2.8 can produce the same amount of power as the 3.1 {when talking turbo applications} the

only real question to me is how long will it hold up to 20PSI or more?

 

I have run 18PSI at mine on the dyno and will be pushing 20-24PSI this upcoming fall, goal is 500whp or more.{using a Borg Warner}

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