Question about boost.

[TheRedWedge94]

So I am wondering how power made with a cam, is different than power made by a turbo. More so with how it stresses the internals of an engine I suppose. To me, 400 horsepower is 400 horsepower, but I could make it with a turbo or with a cam and you need X amount of air and fuel to make that but a turbo... with boost... is a little more complicated than flowling more air with a cam.

I appreciate the advice !

[Tom68]

400 hp with a turbo, are we talking a 2 litre engine ?

If so the 400hp will come with high cylinder pressures at moderate revs. Detonation control and good parts will be necessary, valve train speeds low.

400hp from a 2 litre NA means you'd have to rev it high to get it. Poor low rev performance. Still need good parts and a more expensive high speed valve train.

If you're talking 15 psi on an NA 200 hp 305, you've got a very cheap standard converter streetable 400 hp that'll go forever with a good tune and an intercooler.

Put it against a 400 hp NA 350 or 383 and it's all about the same but the 350/383 will need to rev higher but still reliably low, just a lot less crap in the engine bay. Valvetrain will be worth a few extra dollars.


So really it comes down to the revs required, Big cam high speed valve trains are expensive and the big cam kills off idle performance.

[BLSTIC]

Assuming you start with a 300hp mildly tuned n/a engine like an early LS and you aren't road racing it...

400hp with a turbo kit is going to involve no internal component changes and won't add any stress while not using the power. While using the power you'll have higher average cylinder pressure and your engine will be absorbing/making dramatically more heat. Everything is under proportionally more pressure, but that really only affects combustion and airflow at this kind of power increase, you're not introducing enough stress to fatigue parts or anything. You'll need to be careful about octane and spark plugs.

400hp n/a involves a wilder camshaft and a decent intake and exhaust at a minimum. You probably also have stiffer valve springs. To get the horsepower you may be going past the factory redline. The conrods will be under more stress due to high rpm than they would be under the turbo scenario, and the valve springs are probably now a service item. The engine will absorb/generate less heat than with the turbo because half of the volumetric efficiency gains come from getting air out faster and that reduces internal temperature slightly (particularly in the exhaust port and combustion chamber on overlap).

There's a lot more to it than that. Note that boost makes for a nicer street car for any given power output, but making power through extra torque can be hard on the gearbox.

[Orr89rocz]

Theoretically a turbo should be easier on the rod and rod bolts due to higher backpressure in exhaust port on the exhaust stroke when piston goes to tdc. Suppose to act like a cushion, denser air is harder to move thru so piston trying to separate from the rod should encounter more resistance and put less stress on low end parts

[David Redszus]

Let's build a paper engine to compare the effects of turbocharging.

B = 89.15mm
S = 80.0mm
R = 135mm
Disp = 2.0L

NA engine
SCR = 12.0
DCR = 9.39
BMEP = 11.03bar
Power = 223hp @ 9000rpm (mSp = 24.0 m/s)

Turbo engine
SCR = 9.39
Boost = 14.3 psi
BMEP = 21.75bar
Power = 223hp @ 4550rpm (mSp = 12.1 m/s)
Power = 440hp @ 9000rpm (mSp = 24.0 m/s)

A NA engine, SCR 12.0, DCR 9.39, would need to turn 9000rpm
(mean piston speed 24.0 m/s), to make about 223 hp.

That same engine, with reduced compression, SCR 9.4, with 14.3psi boost would
make the same power at just 4550rpm (mean piston speed 12.1 m/s).

But if we turned it to 9000rpm, it would produce 440hp.

Clearly, we could make similar power with a turbo, at much reduced speeds,
resulting in much less strain on the engine. And we could easily raise rpm to
higher power levels without possible engine destruction.

[BLSTIC]

It's probably also worth noting that the Mercedes M139 engine is a 2.0 with 400hp that meets emissions and has a warranty. 400hp isn't technically difficult these days, there's some obvious tech that the Mercedes doesn't have (like variable valve lift, or even full variable valve timing), but there's also a lot of "why would they do that?" that they found necessary because of the huge torque loads (like the rear cam drive, the inlet port design, spark plug boss...). But the engine doesn't breathe that well, it just runs a fat stack of boost, resists detonation very well, and is strong enough to not bend while taking 30psi.

It doesn't even rely entirely on direct injection for fuel and detonation resistance, apparently it runs port injection at high loads because DI couldn't supply the minimum fuel requirements for some conditions/combustion features while also supplying 100hp/injector

[gunt]

if i had time id like to trow up 2 dyno graphs , butyour here so you should be able to visualise it

don't consider any new engines as with vvt and di they are more comparable to a large v8 than a traditional fixed cam engine , as in , if you take a hp figure 400hp , that could just have easily less than 250lb tq probally ot 280lb tq , this is why they can be warrentied ,
so fixed cam engine

400hp , thats 400hp at atmospheric if n/a , no idea whay you were intending , but considering you said building one to it be it n/a or boost , so i assume it starts with less , say 280hp , take a look at the graph , and consider the tq not the bhp , now you will have an idea what it will take to climb tot he 400 , compression cams / head / valves , bla bla , as you climb to the right you know you will be loosing to the left , and at some point far left you will be worse off , you will be extending the rpm range to the right , and now a diff maybe nessary

so boost

take your original 280bhp graph , and it will make the 400 8-10psi depending on a few things , this will all hape in the same rpm range , [ usaully ] far left tq will be very similar , and once boost hits tq will rise signifantlly be it @ 2000rpm or 4000rpm , you could have gained 100lb tq , it will hold maintain the std tq curve , and you will end up with the 400bhp on the right , but you will have gained a serious amount of tq the n/a could only dream of with out scaraficing a thing , so this will require a huge differance in fuel and ignition , not even related , makeing the tq will change cylinder pressure , in so much of the rpm range

[gunt]

we do a little 1.3cc , all turos will make 300bhp , some we struggle to make this on the lowest setting [ gate ] , and 320lb tq , wet dreams won't get 300bhp out of this even sacraficing 150lb tq

[TheRedWedge94]

To everyone so far, thanks for the words and extra explanation !

I really would prefer to go with a turbo but id like to understand more how it would effects the engines internals over just running a cam. With a turbo you keep gas mileage, and the snappiness of the low end torque the engine makes naturally so its still enjoyable to drive. I know depending on the converte, it can make the car feel like it lays over or feel like driving in mud. There also isnt a need to open up the engine either if I would keep it around 10 psi.

I wonder if it is the added low end torque that concerns others when boosting an engine that was NA from the factory. BUt if an engine should handle an extra 100 horsepower with a cam, then it should with a turbo...right ?

[TheRedWedge94]

Assuming you start with a 300hp mildly tuned n/a engine like an early LS and you aren't road racing it...

400hp with a turbo kit is going to involve no internal component changes and won't add any stress while not using the power. While using the power you'll have higher average cylinder pressure and your engine will be absorbing/making dramatically more heat. Everything is under proportionally more pressure, but that really only affects combustion and airflow at this kind of power increase, you're not introducing enough stress to fatigue parts or anything. You'll need to be careful about octane and spark plugs.

400hp n/a involves a wilder camshaft and a decent intake and exhaust at a minimum. You probably also have stiffer valve springs. To get the horsepower you may be going past the factory redline. The conrods will be under more stress due to high rpm than they would be under the turbo scenario, and the valve springs are probably now a service item. The engine will absorb/generate less heat than with the turbo because half of the volumetric efficiency gains come from getting air out faster and that reduces internal temperature slightly (particularly in the exhaust port and combustion chamber on overlap).

There's a lot more to it than that. Note that boost makes for a nicer street car for any given power output, but making power through extra torque can be hard on the gearbox.

Yes ! It is very appealing that I may not need to open up the engine at all. So right there saves some worry.

[TheRedWedge94]

if i had time id like to trow up 2 dyno graphs , butyour here so you should be able to visualise it

don't consider any new engines as with vvt and di they are more comparable to a large v8 than a traditional fixed cam engine , as in , if you take a hp figure 400hp , that could just have easily less than 250lb tq probally ot 280lb tq , this is why they can be warrentied ,
so fixed cam engine

400hp , thats 400hp at atmospheric if n/a , no idea whay you were intending , but considering you said building one to it be it n/a or boost , so i assume it starts with less , say 280hp , take a look at the graph , and consider the tq not the bhp , now you will have an idea what it will take to climb tot he 400 , compression cams / head / valves , bla bla , as you climb to the right you know you will be loosing to the left , and at some point far left you will be worse off , you will be extending the rpm range to the right , and now a diff maybe nessary

so boost

take your original 280bhp graph , and it will make the 400 8-10psi depending on a few things , this will all hape in the same rpm range , [ usaully ] far left tq will be very similar , and once boost hits tq will rise signifantlly be it @ 2000rpm or 4000rpm , you could have gained 100lb tq , it will hold maintain the std tq curve , and you will end up with the 400bhp on the right , but you will have gained a serious amount of tq the n/a could only dream of with out scaraficing a thing , so this will require a huge differance in fuel and ignition , not even related , makeing the tq will change cylinder pressure , in so much of the rpm range

Oh absolutely ! A turbo would really make a huge difference in fixing the top end of a power band with potentially increasing the power everywhere else. I would so very much prefer to turbo charge rather then heads and cam, losing the low end power would be a little bit of a bummer; however I dont mind if a turbo wouldnt be.... as safe.

[TheRedWedge94]

400 hp with a turbo, are we talking a 2 litre engine ?

If so the 400hp will come with high cylinder pressures at moderate revs. Detonation control and good parts will be necessary, valve train speeds low.

400hp from a 2 litre NA means you'd have to rev it high to get it. Poor low rev performance. Still need good parts and a more expensive high speed valve train.

If you're talking 15 psi on an NA 200 hp 305, you've got a very cheap standard converter streetable 400 hp that'll go forever with a good tune and an intercooler.

Put it against a 400 hp NA 350 or 383 and it's all about the same but the 350/383 will need to rev higher but still reliably low, just a lot less crap in the engine bay. Valvetrain will be worth a few extra dollars.


So really it comes down to the revs required, Big cam high speed valve trains are expensive and the big cam kills off idle performance.

More so a 5.7 liter engine. I dont think I will ever rev higher than 6200. That is what I am looking for, reliable power. Or more so a solution to up the power at the end of a power band, around 4000 rpms and above.

[Tom68]

Yes ! It is very appealing that I may not need to open up the engine at all. So right there saves some worry.

You really should at least know what your ring gaps are, If the factory ring gaps are at the small end of their tolerance you'll have no safety margin.

More so a 5.7 liter engine. I dont think I will ever rev higher than 6200. That is what I am looking for, reliable power. Or more so a solution to up the power at the end of a power band, around 4000 rpms and above.

That could still need a cam and even a manifold depending on what you're starting with. i.e a TPI would be an inefficient turbo motor if you were trying to make power at 6.

Look at Richard Holdeners videos.

Centrifugal superchargers increase boost with engine speed.
Turbos just make more power over the same rev range (same power curve) unless you electronically control the boost over the rev range.

400 drivable economical HP out of a 5.7, I wouldn't turbo it, Vortec heads, compression, cam, intake and exhaust.

[TheRedWedge94]

Ah thank you, that is something I did not consider. What kind of range should I be in for forced induction ? Is it different for NA ?

I really enjoy all of Richard's videos. Eight psi in most of the power band would still be better than stock, even if it falls later, that number would still be higher.

Why wouldnt you turbo ?

[Tom68]

Ah thank you, that is something I did not consider. What kind of range should I be in for forced induction ? Is it different for NA ?

I really enjoy all of Richard's videos. Eight psi in most of the power band would still be better than stock, even if it falls later, that number would still be higher.

Why wouldnt you turbo ?

Because of the low power level you're after.

Turbo installs make a mess of your car and unless you have a good known kit that's known to fit well you're actually in for a lot of work.