CHOOSING A TURBO AND FUELLING FOR YOUR VR6

[RBPE 198]

(Please bear with me on this thread, there's a couple of A5 books i'm going through that I wrote (which are barely legible), plus several hard drives and I need to resize a lot for here too! I'll update it in due course).

So, if you're deciding to turbocharge your VR and are not sure what to choose I have added a little information for you to have to hand:

The following were worked out for the 2.8 24v motor. I'm going to add the 12V and 3.2 engines and also various VE's, rev limit's and peak torque values to work to depending on the state of tune of your set up. A good tuner will tell you that you should always work to peak torque values and i'll add the variables for different states of tune depending on specs.

Engine: 2.8 (170.8 ci), 7000rpm max rev limit, 93% VE and inlet manifold charge air temp of around 100 deg F I think I used for the calcs - tuners will tell you to aim for less than 40 deg C temps of your charged air (which is about 100 deg F).

To get a rough estimate of HP you times the lbs/min by 10. I also chose a peak torque value in calcs and plots of around 5100rpm which is generally what it is for lower boost levels or heads with less mods, basically a good point of reference for a road cars peak torque when going FI.

STD 2.8 24V 93%VE

40 LBS/MIN = 10 psi/ 0.68 bar of boost

45 LBS/MIN = 13 psi/ 0.88 bar

50 LBS/MIN = 16.1 psi/ 1.1 bar

55 LBS/MIN = 19.2 psi/ 1.3 bar

60 LBS/MIN = 22.3 psi/ 1.51 bar

65 LBS/MIN = 25.4 psi/ 1.72 bar

70 LBS/MIN = 28.5 psi/ 1.93 bar

75 LBS/MIN = 31.6 psi/ 2.15 bar

80 LBS/MIN = 34.6 psi/ 2.35 bar

85 LBS/MIN = 37.7 psi/ 2.56 bar

90 LBS/MIN = 40.8 psi/ 2.77 bar

95 LBS/MIN = 43.9 psi/ 2.98 bar

100 LBS/MIN = 46.9 psi/ 3.19 bar

So from the above list you can see that to flow roughly 70 lbs/min, which is roughly 700hp, you'll need to run around 1.93 bar of boost on a fairly standard 24v 2.8 engine with a commonly regarded VE of 93%.

These are the same as above except the Volumetric Efficiency (VE- Efficiency of your engine) is increased to 100% which is what to aim for at least with a race spec engine. If anything, it gives you an idea as to how much less boost you need to flow a certain amount of air as your engine gets more efficient (smoother pipe work, ported and polished, big valves etc).

2.8 24v AT 100% VE:

40 LBS/MIN = 8 psi/ 0.55 bar of boost

45 LBS/MIN = 11 psi/ 0.75 bar

50 LBS/MIN = 14 psi/ 0.95 bar

55 LBS/MIN = 16.8 psi/ 1.15 bar

60 LBS/MIN = 19.6 psi/ 1.3 bar

65 LBS/MIN = 22.5 psi/ 1.5 bar

70 LBS/MIN = 25 psi/ 1.7 bar

75 LBS/MIN = 28 psi/ 1.9 bar

80 LBS/MIN = 31 psi/ 2.1 bar

85 LBS/MIN = 33.8 psi/ 2.3 bar

90 LBS/MIN = 36.9 psi/ 2.5 bar

95 LBS/MIN = 39.8 psi/ 2.7 bar

100 LBS/MIN = 42.5 psi/ 2.9 bar

I have also done some rough plots on the ever popular Honeywell-Garrett turbochargers to give you an idea of what size of turbo to use.

If you are new to such things then just note the far right hand plot and where it corresponds on the left vertical axis. The left axis is boost and as 1=0 psi (basically you are at ambient/outside air pressure) you simply subtract one to get the boost level in bars (e.g. 2 on the left axis is 1 bar of boost, 3 is 2 bars of boost etc).

To get psi rating you simply times the bar of boost by 14.5 so 2 bar of boost (3 on the left axis) is 29psi.

Twin turbo plots (max flow halved so times bottom flow rate number by two to get max flow rate in lbs/min)

These are popular with the HGP/HPA type of TT conversions, ideal for low boost/power applications but as you can see start to run out of efficiency when going for bigger numbers. Anything over 20psi or so they struggle.

Larger turbo's have been used, from GT2860's to 2871's and even the 3071 below.

GT3071R for Twin turbo set up

As you can see there can be a lot of surge issues as the boost is increased, with them highly inefficient above 1.5 bar of boost or so. I will always maintain that a good single turbo set is better and especially seeing as the VR's can use an inline type of exhaust manifold to slave all the gasses from the cylinders in a short length (like a log type of manifold). More highly tuned engines will shift the plots right somewhat negating surge on the larger TT set ups.

SINGLE TURBO PLOTS:

GT3076R:

GTX3076R:

GT35R:

GTX35R:

GT4094R:

Garrett's T series are also commonly used, there are few flow graphs available but they tend to use a 75mm or 76mm Compressor blade (like a GT30R) and 65mm turbine (in-between the GT30 & GT35R's turbines). The larger TO4R/Z turbo can flow a lot more and has a 74mm turbine but I'd use a DBB if looking for anything over 55lbs/min/550hp IMO.

So the following plot is suitable for the T04B/60-1's mainly and not T3/T4 - 50/57/60 Trims or TO4R's, in my opinion I would not bother with T3/T4 trims as they are a bit too small and if flowing the levels a TO4Z can flow I'd look at a DBB unit for a road car.

This final one gives you a bit of an overview of the maximum flow rate under certain boost levels using a fairly standard 24v VR6 plotted on a GTXR42.

As a guide i'll say the following;

Twin turbo - They can become hugely inefficient at higher boost levels so choose a single turbo if running over 20psi or so..... unless you've a heavily modified engine or you're not looking for a road car. It is rubbish about less inertia and so on due to the fact that you're getting half the flow on, as an example; a GT25 or 28R's 53mm turbine compared to the 60 or 68mm turbine of a GT30 or GT35R, it'll depend on the material of the turbine, displacement, VE, gas speed etc.

You have the set up for an inline manifold so no need to use a TT set-up on a single head engine in my opinion and I have yet to see a VR running higher pressures come anywhere near as close to a single turbo unit's figures for a road application on the dyno's. The peak torque value is always higher up the rev range and quite often lower!

Single turbo - 55lbs minimum imo, the 65+lbs of a GT35R will get you a bar of boost about 3.5k rpms although there are many variables. For a decent low pressure unit I am a fan of the T3 60-1, 0.82ar, will see you over 500hp all day long and provided you don't go over 1.5bar is all the turbo you need for the price. However, there are also modified units such as Turbonetics that are designed to be high pressure units based on the 60-1 compressor but, as you can see, it doesn't take a lot for a VR6 flow past 50lbs/min!

FUELLING:

I'll update the fuelling aspects soon using 12V, 13.5V & 14V references with the popular Walbro 255 & 400 ltr pumps as well as Bosch 044 and Aero A1000. I'll also go into detail about the injectors, duty rates, pressures etc from 440's to 2000's.

[Daverse 175]

Good info there! Although too late for numbers, it reminds if being back at college! haha

[FishWick 21]

Excellent post!

the 65+lbs of a GT35R will get you a bar of boost about 3.5k rpms although there are many variables.

Yep, that is spot on!