Power

As you yourself said on the other thread, you can't compare until you have like-for-like. You're talking other engines

I'm eagerly awaiting the results from your twin turbo. As you keep saying, dyno plots rule.

By your own arguments, how is it possible to get over 500hp from a RB25DET with a stupid cast exhaust manifold? Same number of cylinders, same capacity.....

I think the throttle is a restriction, yes,. it's the smallest 'ole in the intake tract (assuming an uprated turbo -capable- of 300+ ). I think the intercooler is a problem for its sharp angles and Just because the downpipe is bigger than the sum of the turbo inlets doesn't necessarily mean it's not restrictive.

But I'm no expert. Not managed to get a decent figure out of the TT DeLorean but that really does have crap manifolds, and at the moment, a crap intercooler.

If the main restrictions are the exhaust manifolds and ancillaries then extracting power would be relatively simple. Do the cylinderheads flow well, has anyone had them on a flow bench, is there enough room for the valve sizes to be increased? If the bottom end is strong enough to take the power your more than half way there. Although it's a single overhead cam there are many engines that are making extream levels of power (and torque) that are more primitive in design. Sure 350 is a lot of horsepower but im suprised the limits arent being pushed a little more. How much torque do the 300hp example produce. And what is the internal diameter of the exhaust manifolds?

As far as I can tell (and I have one of the more developed engines) the manifolds leading to the turbo are a big problem as well as the siting of the turbo at the front of the engine.
Hopefully Davids twin turbo effort will sort all this.....but if you havent actually been in a GTA its difficult to portray how fast a tuned one actually is. Mine had about 270bhp before its (currently not quite complete) rebuild and was very fast! On straigh (ish) events it was quicker than pretty much everything. Big piles of torque (over 300lbs at 3000rpm), low weight, rear engine/drive and good aerodynamics make for a very fast car.
For the first time ever I'm going to agree with Martin and say that much more than 300bhp in a GTA would be too much I think. 400bhp would be fine for straight line stuff but I suspect the chassis in standard form wont cope well with so much power round corners. You'llend up needing to add roll cages and strengthening...........and better brakes, and gearbox.

By your own arguments, how is it possible to get over 500hp from a RB25DET with a stupid cast exhaust manifold? Same number of cylinders, same capacity.....

'Stupid cast manifold'? What has what its made out of got anything to do with how it flows?

Come on Martin... The RB manifold has 6 ports (and this is a 24v head so the ports are double the size of the 12v GTA) and a collected area far larger in volume than on the GTA, its a common cast design to most turbo cars.

With the PRV, firstly the primaries on the GTA manifold are actually smaller than the exhaust valve before them, they then all join at a collector which is the same diameter as only ONE of the primaries, and then continues that diameter for an extra foot and a half of length!! Even on a GTA Atmo the manifolds are far better flowing than the turbo manifolds, but even switching to mandrel bent manifolds gains around 15bhp, and this is naturally aspirated. Turbo manifolds would choke the engine, even without any additional boost/manifold pressurein the mix...

I think the throttle is a restriction, yes,. it's the smallest 'ole in the intake tract (assuming an uprated turbo -capable- of 300+ ).

Pretty sure you'll find the outlet to the turbo is smaller (only 48mm) and as the inlet valves open one at a time, and they are only running 6mm lift and 44mm in diameter, they may be a bit more of a restriction than a 55mm diameter throttle body

A 55mm throttle body can flow 470cfm of air before it even causes any pressure drop (ie air flow goes over 300ft per second)

The intercooler on the GTA is not a restriction, in all the years I have been experimenting with GTA turbos with different setups/ configs I did manage to measure pre and post figures using two gauges and only witnessed around 0.5 psi drop across the core up to 15psi..and cars running my chargecooler system have an even lower drop - but they havent magically gained lots of hp through that 'drop' in restriction....

470CFM of flow on 'gasoline' at a 12:1 ratio for instance is good for 360bhp, on ANY ENGINE, it makes no difference!

Even if the body becomes a slight restriction at higher flow, it can be just overcome with more boost. It is not the max limit it can flow, its just the rate of gain for flow is not in relation to the increase in boost (ie not as efficient), but it doesnt just flatten off (or drop off) like the manifold turbine inlet pressure, which cannot be overcome with more boost, as you are simply increasing manifold pressure by running more boost. Thats the vicious circle of turbine inlet pressure.



If throttle body size seems an issue, the 1.5l F1 engines running 4 bar of boost made over 1200bhp using 50mm piping..



Or in the real world, this biturbo A610 made nearly 500bhp at just under a bar running a standard Safrane 55mm throttle body (the same as on the GTA) and standard Safrane inlet manifold.

[stephendell]

I'm hoping the throttle isn't a restriction as I'm using a 55mm one on my own engine.

I'm guessing if a PRV with 2 throttle bodies running 36mm restrictors can hit 550+ BHP then surely a PRV with a single 55mm and greater surface area should be capable of at least the same.

Total area of two 36mm restricted throttle bodies = 20.35 sq cm.

Area of one 55mm throttle body = 23.75 sq cm

Or have I done the maths wrong

Nope, thats perfectly correct, and even 4 cyl rally cars run over 300bhp with a single 34mm restrictor.

What 1/4 mile times and terminal speeds have been achieved, or are you guys not so much into that?

Its not that people arent into it, it just most havent had tuned cars or got round to doing it..

The other 'issue' is your going to be needing to go into forth, to pull a terminal over 100mph, and the GTA Turbo box is hindered as the ratio from 3rd to 4th is overtly long, whereas the atmo box has better spaced transition...

GTA's are very good for 60ft times, though the cog snatch from 1st to 2nd if hurried can be a problem.

Oh I see, would there be anyone with there alpine heading to the pod, shakespeare etc this year?

Someone mentioned earlier that the 'boxs are only good for up to 350, what is the box of choice or modifications needed to cope with more abuse/power. Does the standard box have a LSD?

I imagine the 60ft's are pretty good even on the standard cars due to the configuration of the car, in your experience below 2 seconds?

[Alpineandy]

Mr Smith is a 1/4 mile fan.
He's planning to check his car as soon as he's comfortable it's sorted.

I'd be interested to hear if he thinks it'll beat his skyline times.

Oh I see, would there be anyone with there alpine heading to the pod, shakespeare etc this year?

Someone mentioned earlier that the 'boxs are only good for up to 350, what is the box of choice or modifications needed to cope with more abuse/power. Does the standard box have a LSD?

I imagine the 60ft's are pretty good even on the standard cars due to the configuration of the car, in your experience below 2 seconds?

You can pull 2 with little effort on road tyres. Slicks should see 1.7-1.8's.

You can't measure a box in hp, only in torque, so 350lb/ft would be a safe limit, but this could equate to 400bhp if you managed to maintain that torque up to 6000rpm. It depends on how it is delivered too, and the slip factor of the tyres/clutch and whether the peak is low or high up in the rev range.

Ill be doing a pod run this year, weather permitting, and even if the conditions are not good it will hardly affect the terminal speed which is always the best judge of power.

[Alpineandy]

You can pull 2 with little effort on road tyres. Slicks should see 1.7-1.8's.

My A310 was doing 2.2 despite me being very gentle with the clutch.

[stephendell]

I imagine the 60ft's are pretty good even on the standard cars due to the configuration of the car, in your experience below 2 seconds?

On Monday wasn't Simon T discussing launch time/measurements/info gathered from his sprints?

Who Simon 1G TAylor

Some hillclimbs and sprints record times off the line and I can confirm the GTA is pretty good. 2 years ago at Harewood (car wasnt too far from standard then) I was second only on launch 250ft to the Evo iv that broke the production car class record and yet my placing 60 something seconds later was 5th and some way off 2nd and 3rd places (Evo and Skyline)