Got a quote from Jethot yesterday to ceramic coat my exhaust manifolds and downpipes $900, I'll just bite the bullet and do it.

 

I am a restoring a Jag XJ12 Series One. Probably a bad idea but I have always liked the car and I have restored a few cars so I have some idea of what I am getting into. My unrestored car on 4 carbs is probably making about 200hp so I too would like to get towards the magic number. A solid 400hp would do me fine. However, after having read this thread I did the basic math for the Jag V12 Brake Specific Fuel Consumption - the number that is possible based on the energy in the fuel not the way the engine is put together and it comes in at around 380hp. Are people running larger injectors? If so what size? I would like to know what is mathematically possible before I start shovelling money in. I am going down the throttle body Motec route with the engine build.

 

Not a bad idea. These cars are wonderful especially the V12.

TWR managed 330hp from a road going 5.3HE with only exhaust and intake mods, they bolted the GRPA exhaust manifolds and downpipes and CAI from OTR and K&N air filter.

The 5.3L needs to rev to make power (or turbo), if you can stretch to stroking the V12 with the same mods 380-400hp is doable in HE. But with a big increase in power across the entire RPM band.

I was just re-reading Allan Scotts book, as I am in the process of building my spare engine to 6.7L. Anyway one thing I noted he wrote was the 5.3L needed smaller intake runners for the street, but the 6.0L worked really well with the stock intake.

Cheap V12 engines come up from time to time and buying a fuel injected one will give you all the FI bits to ditch the carbys.

Those carby manifolds were woeful. You could cut the carby mount off and braze a 100x100 aluminium box section to make a plenum and use Commodore TB's on the front. You could use Commodore injectors and 2 DFI units to run dissyless. Just thinking outside the square.

 

Well, as there are several types of torque figures, just saying '250 torque' isn't helpful. NM? Lbft? Mkg?

Secondly: horsepower and torque on their own say nothing about the useable power. 250 nm at say 6000 rpm vs. 800 nm at 2500 rpm... As an example.

My old C30 had 185 nm at 4000 rpm. A 2.0l engine with 145 hp. The same size turbodiesel had 320 nm at 2000 rpm and 136 hp (100 kw). So, what one was faster?

Both had a 0-100 kph (0-62 mph) figure of 9.4s. But then the 2.0l petrol wirh less torque and a massive 9 hp more power would outrun the diesel. Vmax (220 kph vs. 210 kph) and 0-200 kph (0-125 mph) were faster.

So just stating a torque figure and hp figure won't say much at all.

So, given a 3500 lb car and wanting to drive it as an everyday vehicle, I'd look at the 800 hp engine. A 250 nm engine would be enough to drive the car (my XJ8 has 310 nm) on a daily base... And an 800 hp engine with no torque is what is a great thing can be. Wankel engines had no torque and still were banned from F1 racing as they would beat all current normal 4 strokes.

So for me: hp all the way, torque is for people who can't change gears

 

Ron is in the USA so all those figures will be ft/lb. The 800hp F1 engine makes its peak power at near 20000rpm not too usable in a road car.


Torque and HP are not separate things. HP is a man made measure, Watt came up with the idea of 1hp = 33000ftlb/min. So HP is a measurement of torque over time.

Acceleration is A=F/M where F = torque at the tyres and M = the mass of the car. So to accelerate a car faster you need to increase the torque at the tyres. This is simplified as there are other factors ie rolling resistance etc that need to be factored in. Torque at the tyres is a simple calculation of the gearing. A Dyno measures Torque at the tyres then via the gearing and tyre rolling diameter entered by the operator can calculate engine power and torque.

There are ONLY 2 ways to increase HP

1 increase the RPM with the same torque
2 increase torque

Increasing torque across the RPM band will increase the HP band

eg 300ft/lb @ 3000rpm falling to 200ft/lb @ 6000rpm and 150ft/lb @ 6500rpm

300*3000/5250= 171hp
200*6000/5250= 228hp
150*6500/5250= 185hp

Assuming the same linear torque curve
450*3000/5250= 257hp
300*6000/5250= 342hp
225*6500/5250= 278hp

Assuming the same vehicle the 2nd will accelerate faster in all areas.

 

Both HP and torque are related... But you can't just go by two numbers without their relations... That was what I tried to show with my comparission regarding the two engines shown. 320 vs. 185 nm... Technically the 320 nm engine should thrash the 185 nm one but it doesn't... Of course the gearing and when how what can be produced are important factors, but as said, just showing some numbers and saying 'pick' doesn't work.

I prefer hp over torque, as engines without high torque ratings (like the Honda S2000 engine with 2.0l displacement and 270 hp (iirc) or the 1.3l 2 rotor wankels in Mazdas 13B engines) can be a joy to drive and scream more when you rev them high

 

Thanks for the replies. The point I was trying to make is that regardless of the engine mods there isn't enough useable energy from the fuel with the stock size injector. Does anyone run 400cc injectors or above. It's the only way to get enough fuel into the engine to make the 500hp number.

 

Excellent description Warrjon. well said !

 

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Diam, you mention 13B Mazda rotary cars ,well i owned a 1987 Turbo, with later engine 13B 1993 large single turbo, it made on wheel dyno 420 WHP at 7500rpm, but dyno operator said in 3rd gear with rear end 4.11 reduction made 1000 ft lb torque at tires, but it calculated out to 3.75 lbsft torque at E-shaft(crankshaft). actual vehicle weight 2750lbs, not 3500/3800lbs.

lets put some reality into the subject, on the hiway, when driving at 50mph in 5th gear, you race another car, my car whould just bog down and do nothing!

to have any chance of catching up to other car(fast), you would need to shift down to at least 3rd gear(where some torque is available), the reality is by the time you have taken the nesassery moves, off throttle change gears , back on the throttle,and brought boost back up, other car is gone! been there done that.

now lets go at it again, this time both cars 50mph, i,m already in 3rd gear. and on the boost, he is in 4th but has 500 torque, be a great race, but only usable on a super hiway when there is no end of road,(USA Interstate,Adobahn,etc).

if other car has 800 torque you would never catch him, my RX7 showed 165mph max,only 375 torque.

800 torque has potential for over 200 mph easily!

i'm just saying i been street racing for over 60yrs, win some and lose some,
but a lot of fun, and lot of learning, what works what dont!

BUT nothing beats cubic money, at least for long!

I LIKE TORQUE, HP can be what it is, a number.

 

Nice RX7 mate! I meant - torque for the 13B - without a turbo... There you need to rev the guts out... But again, nice RX7!

 

como, it would take a lot more than higher flow injectors for a 500hp Jag V12, fuel is no good without air to support it, at proper A/F ratio.

 

TWR used XK 4.2 injectors in the GRPA car. Injector flow rates are usually rated at 43psi. Increasing the fuel rail pressure will increase the flow rate from the injector and as a bonus provide finer atomization.

Standard HE injectors are 18.25lb 192cc,

Commodore Supercharged injectors are 370cc these will work.

Ron's right TWR only just got to 500hp from the race car before the end of its life. If you want to make power from the V12 I would suggest buying Allan Scott's book there is a lot of technical information in there about the R&D on the race car (and the TWR road XJS) that can be used to build an engine.

 

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Diam, a good video on you tube!

two new cars from BMW, petrol BMW M3 vs Diesel Alpina D3, a factory comparison of the two cars!


check it out good stuff.

 

as i remember PRE-HE injectors are 300cc using 38psi, so another reasonable idea! so jack up the pressure and just may do the trick, but not to forget its always about tuning,como!

 

Had some down time today. So I thought I would get my 6.0L heads and look at the flow through the exhaust valve/port. I was not interested in CFM all I was looking at was turbulence and how it could be reduced. A reduction in turbulence will naturally increase flow anyway.

I lifted the valve to 9.5mm, 0.375".

The first 2 pics show the thread vibrating considerably. In the next pic I smoothed the flow into the seat with some water based wood filler. You can see the difference in the 3rd pic where the thread is rock still, indicating no turbulence. The last pic there is still some turbulence but its much less than pic 2. I think if the lip circled in red was profiled then the turbulence would be further reduced.

 

Warrjon, interesting work!

by looking at that chamber shape, what if it were possible to shave the head around .100 thousandths,(around 2.5MM) would it not put the inlet valve deeper into the bore, and reduce a lot of that shrouding metal around the exhaust valve?

altho it may bring up cylinder head thickness, also chain tension, and how thick is the deck surface?

but along with your chamber mods, just may get that hi turbulence thing to work!

you say someone is rebuilding your engine , just may hold off on piston selection until you are sure,of compression numbers and piston to valve clearences!

i chopped .050 thou. off my heads pre-HE, with no ill effects just to get the valves deeper into the bore!

also that turbulence is there to control detonation along with full use of the burning fuel! you may not worry about MPG, but NOT be nice to have detonation while just driving at light cruise!

just some thoughts on the subject!

 

WOW this is the worst thing I have seen since I polished my first valve....
I did it all wrong...
so much design has to go into tumble and swirl and when you start messing with things like this even though a smooth flow is great for moving air over external surfaces you are now in a confined resonate chamber...

now I know there are design short comings limiting the V.E. of our HE heads ... but Smoothing out the FLOW right there might counter intuitively reduce drivability and greatly increase the fuel demand.... might as well go to pre HE HEADS....
http://www.eng-tips.com/viewthread.cfm?qid=63761

Or start from scratch I prefer modeling new head design base on the matchless G50 head and new pistons and Cam profile too as they have to be a matched set to work correctly
THAT combo arrives at 50 hp from 499cc under 7000 rpm...

 

by the way;

that is a very good shape for the top of the exhust valve, were it is rounded over on the top.

wonder if only 6.0L ford engineering did that small mod, it has become a must do on a lot of race engines in past 10years.

pic of a 1929 Chevy in-line 6 , hi-turbulence combustion chamber , patent went to Buick shortly after GM purchased Buick!

but i have worked on many of those old chevies, and close to half 1/2 had cracked exhaust seats and into the water jackets= JUNK because of heat build up in the small exhaust chamber, notice inlet almost touched the piston top induced swirl/turbulence.

just some useless trevia about hi swirl.turb chambers.

 

Thanks Ron, it's always good to get another opinion. Nothing is cast in stone yet.

My engine builder is Norman Lutz who has a world of V12 experience and has built an 800hp NA V12. He is using Chevy 305 KB pistons with very thick crowns the ability to machine some off the top to adjust clearance to 1.3mm. This will also reduce the crevice volume to advantage.

Laying the chamber walls back to open the path for exhaust. Funny you mention planing the head to the intake valve I was originally against this but might just re-consider it.

I have not seen inside a pre-HE exhaust port but the HE has a very sharp short side turn, seats on both intake and exhaust are better than most stock SBC I have seen.

I have a lot of experience in Flow measurement having worked in a Military Calibration laboratory, lets hope I can put some of this knowledge into improving the HE head somewhat.


I have some clear acrylic which I plan to make a transparent cylinder so I can see if there is any port induced swirl. I will be concentrating on low to mid flow on my homemade flowbench.

I think the biggest challenge in starting with a stock head is keeping CR up unless the capacity is increased. When you look at the HE heads, it seems Jaguar just took the flat head and machined a pocket. This has sharpened the short side radius on the exhaust. I am not sure if this is where the power is lost as my understanding most of the power comes from the Inlet port. If the exhaust port is restricted it will provide pumping losses and cost torque.

 

Spent some time looking at intake flow characteristics today.

What was interesting was the direction of flow into the cylinder was totally different than I had expected.

Looking at the head from underneath (head upside down) I was expecting air to flow anti-clockwise. What was unexpected that it was clockwise and flowing greatest from the bottom of the port, you can just see the thread. Very little air was exiting opposite the spark plug.

This was at all valve lifts and high and low flow.

This pic is for illustration only (at 4mm lift) it was too difficult to take a pic with the setup. When I tested it both valves were in place and the cylinder. What the pic does illustrate VERY clearly is the shrouding of the intake valve at mid lift. Maybe this is the issue with the HE head not the exhaust valve,,, food for thought............

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