How can you work out if a turbo is going to be laggy on a cossy?

can it be purely worked out from some specs and a comp map?

 

You can get a rough idea from the flow etc, but you can't really tell the response etc, until you get it on the dyno. This is why turbos are developed on engine dynos, that way you can experiment with all the variables .

 

Can usually tell pretty well by engine and turbo spec, especially if can cross reference with other engines with the turbo (even if totally different types).

Got something in mind Ryan, if so post up, should be able to give you a fair idea.

 

my t61r

P trim 84 exhaust.

will get other spec's off the turbnetics site.

engine is your billet crank, billet rods, cosworth racing low comp.

cams would be suited to turbo, just getting CR, and port sizes

 

Get a compressor and turbine map for it as a bare starter, then dig out a YB powergraph from a motor similar spec to the intended to get approx airflow figures....

How do you know that if you dont know if the turbo suits the engine?

 

cams suited to the turbo?! without knowing what the cams are i wont know if the turbo suits it, lol.

and depends what "suits" means, cams are all swings and roundabouts, higher boost threshold and more peak, or less peak and lower boost threshold.

without knowing cam n head specs, its hard to know, cams make a HUGE difference, esp when going big.

2litre?

T61R is similar in characteristics to GT35R TBH.

 

yes still a 2 ltr steve.

stu, im asking for someone else, cause there too lazy to do it

CR is 7.5

Inlet ports are 26mm

Current Cams are BD16 & BD14

 

Compression ratio is completely wrong for a start .

 

Whats the lift and durtation on BD16 and BD14?

Compression dont seem wildly out to me, tho id go a lil lower and boost the fuck out of it.

 

thats what i said.

but its what the engine builder has done it to

 

well spec it yourself then, job done, only you to blame, thats what ive done

lift and duration of BD14 and 16s? Or dont people even know

 

not my engine steve.

will see if i can find out on the cams

 

BD14 lift 8.9mm / duration 247°
BD16 lift 10.1mm / duration 265°

 

so any clearer? or still clear as mud

 

...on those specs about 4.5k spin up...not bad at all really!

 

what you mean by spin up?
boost starts? or hits full boost by?

 

i would think starts steve, cant ever see it making full boost at 4.5k

would love it to though

 

Id say it will be boosting way below there, but should have decent amounts of power (ie over 250bhp) by 4.5k, possibly 4k, shoudnt be too bad TBH, but full youd see by no more than 5 idve thought.

 

cheers for the advice steve, just trying to convince the new owner that the car will be a monster and not a lag monster.

also said it will piss 550bhp

 

Ryan,
But on a 2 litre lump it WILL be a lag monster , and contrary to whatever Phil says, the c/r will play NO part in spooling the turbo up any quicker.

My engine is 7.5:1 and below the boost threshold (3k) it is more dull than a wet weekend, even though it makes a 15psi by 3150rpm and full boost by 3500rpm....

 

Doubt be much/any worse than a decent RS500 spec engine, so yeah, thats still technically laggy as fuck, but for the size of the engine its acceptable id say.

EDIT to say snap with mikes comments

 

Mike high comp dont help spool up when did i say this? Hi comp gives better off boost responce...CAM choice helps spool up!

4.5k should be max boost on a 35 type roller bearing.

 

so it should be your average engine lag then, with more than your average BHP to match