Does a turbo restrict your engine's rev??

[NewyorkKopter]

lets say I have a 7.0L V10 that I want 800 hp from it, so I twin turbo it. Now is there a way to get the turbo hitting full boost or just under it at 2000-3000 rpm and continue the boost all the way upto the redline(about 8,500 rpm)???

[2.2 Straight six]

yes, it can be done. mainly because with such a big engine there's plenty of exhaust flowing out to get the turbos to spool up fast. you might need some proper boost control at high revs to keep it all in good order.

[NewyorkKopter]

wow thats awesome. If the 2 turbos spool at 2,000 rpm and give full boost until redline thats hardly any lag at all. some cars idle at like 800 rpm. Also would this make the powerband wider??

[2.2 Straight six]

yup, it should do with the right tuning. the lag comes from big turbos an smaller engine, but the bigger the turbo the bigger the lag (compare turbo size to exhaust flow to get that)

[NewyorkKopter]

so basically
bigger engine= less lag with bigger turbos
smaller engine= more lag with bigger turbos

also wats the diffrence between a flat and wide powerband??

[nissanfanatic]

WTF is the point of full boost at 2000rpm on an engine designed to spin 7000rpm+ anyways?

[NewyorkKopter]

so theres no lag lol

[2.2 Straight six]

Originally Posted by NewyorkKopter

so basically
bigger engine= less lag with bigger turbos
smaller engine= more lag with bigger turbos

also wats the diffrence between a flat and wide powerband??

yea, matching turbos to engine size/exhaust flow will relate to turbo lag.

flat isnt to do with the powerband, the powerband is the range in revs at which point the engine is at its peak power:

e.g. you have an engine making a maximum power of 400bhp

a wide powerband means there is a big range at which the engine is making maximum/almost maximum power within the two point on that given range.

so, it makes ~400bhp between 6500 to 7500rpm, then the maximum powerband is 1000rpm (6500-7500=1000) but this varies between engines and setups.

the "flat" refers to the power/torque curve (for definitions of bhp an torque search for the thread on it) a flat curve means its not very steep, or has a shallow gradient. a tall curve means its steep, or has a tall gradient.

hope this is right an makes sense.

[CBFryman]

Originally Posted by NewyorkKopter

Centrifugal s/c's do exist. lol theyre just like a turbo execpt they power off of the crank. and also like a Turbo they are more focused toward higher end rpm here's a link to sum article about themhttp://www.coloradocobras.com/whippl...rchargers.html

also can you tune your turbo or twin turbos to make full boost a 2000 rpm and all the way upto redline(lets say its 8,200 rpm)??

i know what a cyntrifical superchargers is...i was talking about boost drop.

[2.2 Straight six]

you mean the boost drop where halving the rpm cuts the boost down to 1/4 ? i cant see that as being true, i mean if its spinning twice as fast it can draw in twice as much air. so how would the boost drop to 1/4 of the amount ?

i think that if you double the rpm, you double the boost. if you halve the rpm, you halve the boost.
so its in a constant ratio.

[CBFryman]

basic mechanics says boost stays constant as airflow dobles when RPM doubles causing engine air consumption to double.
however im not a cyntrifical compressor expert so depending on the impellers compression map it could be true though i doubt it.

[nissanfanatic]

so theres no lag lol

First your definition of lag is wrong.

Second, you don't honestly think a powerband can last for 5k on an average street car do you? Factory cars make full boost by 2k. And they suck for top end power.

[nissanfanatic]

That rule only applies to positive displacement compressors.

On centrifugal compressors, boost increases as the square of the speed of the compressor wheel. Flow can increase phenominally without a large increase in wheel speed. AKA dynamic compressor.

[454Casull]

I'm pretty sure a turbo sized too small can cause flow restriction (backpressure) at high speeds, causing a drop in redline.

[2.2 Straight six]

oh, yeah. too small a turbo will create back pressure an wont do the engine any favours. it wont just cause a drop in the redline, but without anywhere to go (if the wastegate isnt up to the job) then you could blow something up, either having exhaust forced back into the engine, or blowing exhaust manifold seals/gaskets...

..i dunno. i haven't tried over-boosting recently.