Cold air intake box

SeanDezart

Well-Known Forum User
IMO Sean, your tester is only going to be right if the TB diameter with the trumpet is the limiting factor on air flow for the engine. With a 45mm body, its more likely the limit is elsewhere.

Thx, interested to hear opinions - this is the first dyno test before any running in. Once run in, it'll be dynoed again and programmed definitively.
 

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SeanDezart

Well-Known Forum User
Why? they make much nicer noises after that :)

And some make bigger noises than desired after - I prefer longevity.

why do low? I guess if you map it higher and set a limit after the power drops away? Just for a bit of overrev?

It'll be mapped to the max limit, maybe 7500 (?) and point taken for the overrev but as a 95% road car, 6800 is more than enough power from an L31.....it's mostly about torque for acceleration - not top speed.
 

jonbills

Membership Secretary
Site Administrator
peak acceleration comes from peak power and gearing. If your power peak comes at 7500 for example, you'd be mad to set a limiter lower than that. If you have a limiter at 8000, you can choose whether to rev to 6800 or 8000. if you have a limiter at 6800, you don't have a choice.
 

SeanDezart

Well-Known Forum User
peak acceleration comes from peak power and gearing. If your power peak comes at 7500 for example, you'd be mad to set a limiter lower than that. If you have a limiter at 8000, you can choose whether to rev to 6800 or 8000. if you have a limiter at 6800, you don't have a choice.

I think the key word here is 'peak' ! This is not a competition car, no time attack, drag runs, hill-climbs.....just a road car with perhaps some track-day fun once or twice a year with nothing to prove.

Let's be clear, it'll be mapped, dyno-run and a graph presented which'll determine peak power, torque and the drop off - eiither a smooth falling away or sudden death ! From that I'll decide at which revs to set the cut-out which I'm anticipating to be at 6800 as I have no shift light. I have Speedhut gauges but preferred the classic look of no LEDs (see photo).
If I had a steel billet crank, I'd probably go higher....but that would be over-spec for a road car.

I always believed that acceleration derives from toruque, top speed from power - over-simplified I know as quite correctly gearing plays a huge part. I have a stock-geared S13 box and a Scooby 3.54 LSD. If later, I want to swap out the diff I have spares but MZR runs these with no compliants.
 

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Rob Gaskin

Treasurer
Staff member
Site Administrator
Does the longer stroke of the 3.1 (LD28?) crank make it more fragile at high revs than the L28? I'm assuming so.

I used 7k on my track car for 10 years and without a damper.
 
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jonbills

Membership Secretary
Site Administrator
I think the key word here is 'peak' ! This is not a competition car, no time attack, drag runs, hill-climbs.....just a road car with perhaps some track-day fun once or twice a year with nothing to prove.
SeanDezart said:
it's mostly about torque for acceleration - not top speed.
my point was that that acceleration comes at peak power.
SeanDezart said:
Let's be clear, it'll be mapped, dyno-run and a graph presented which'll determine peak power, torque and the drop off - either a smooth falling away or sudden death ! From that I'll decide at which revs to set the cut-out which I'm anticipating to be at 6800 as I have no shift light. I have Speedhut gauges but preferred the classic look of no LEDs (see photo).
If I had a steel billet crank, I'd probably go higher....but that would be over-spec for a road car.
I agree, that makes sense and from that initial graph, it's going to be a monster. I have the same Speedhut gauge setup.
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SeanDezart said:
I always believed that acceleration derives from torque, top speed from power - over-simplified I know as quite correctly gearing plays a huge part. I have a stock-geared S13 box and a Scooby 3.54 LSD. If later, I want to swap out the diff I have spares but MZR runs these with no complaints.
Well, clearly power and torque are very closely related. power = torque * rpm/5252. So yes, acceleration derives from torque. Via power. Power is a measurement of how much 'work' can be done in a unit of time. Accelerating a car is 'work'. Therefore, by definition, the more power you have, the more accelerating you can do. I think the power from torque at low revs (like in a turbo diesel) where it comes just above idle is more accessible. I mean, I think my 525d might beat my Z over the first 30 yards on the high street, but after the first 30 yards my Z will overtake. And if I take the trouble to launch the Z at 4k rpm, it'll beat the diesel over the first 30 yards too.
 

jonbills

Membership Secretary
Site Administrator
HP determines how fast you'll hit a brick wall, torque however defines the distance for which you will drag the wall with you
Sounds catchy, but not true. It's the mass of the car that determines the distance you'll drag the wall with you after impact. (Assuming the wall is draggable, which of course most aren't :) )
 
Sounds catchy, but not true. It's the mass of the car that determines the distance you'll drag the wall with you after impact. (Assuming the wall is draggable, which of course most aren't :) )

and the torque will help move that mass.

Anyway, i've had it printed on t-shirts now with big, massive Z's on it.
 

SteveK

Forum User
BHP is a number derived from Torque and RPM and as such it can easily give a false picture of the engine (good or bad) and can become fixated upon (keyboard racing) if you are going to use BHP then look at the area under the curve and the curve shape.
A more robust way to compare engines is BMEP

BMEP (psi) = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)

The PSI number is purely theoretical and doesn't relate to actual cylinder pressures but gives a clearer picture of the engines ability to make power

A good number for a single cam 2 valve is around 200 plus.
 

SeanDezart

Well-Known Forum User
A) seanie (the girl), can't afford to restore her Z a 3rd time so doesn't want to max out the engine.

B) she still has no idea of peak power...250bhp?

C) any guesses based upon those curves and your VB theoretical peak rev ranges ?
 

AliK

Vehicle Dating Officer
Staff member
Club Member
A) I think the Loubitins will have to match the Z colour - but I agree Seansie, don't over-rev too much and don't let Franky bully you out of your Loubis. There's a lot to be said for longevity instead of ultimate HP if this is not a race about car. Are you using forged pistons / rods?

B) With no real info about your cam etc and going with pure gut feel, I have you north of 250 and south of 270 once properly ran in (and by that I mean a good 5k miles) - what is your cam spec?

C) I think you have lovely curves Sean x
 
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