Cams for VX Race motor

[Testament]

I am putting together the head for my VX131R racecar, the head is from a carb argenta, mildly ported with 44mm/38mm stainless valves and bronze guides. I have CC'ed the head, all chambers were 50cc =/- 0.5cc. I am not sure what CC the VX pistons are, I haven't measured them yet, but I am guessing this will give a compression ratio somewhere in the range of 7.5-8:1 . Now I have a choice of cams at my disposal, I have pairs of
130TC cams
Argenta carb cams (same as 132 2L I think)
Beta 2L cams
VX cams

I have 30mm flangeless vernier pulleys to time these up with also.

Which cams would you suggest I go with? from reading your book and posts around this site I'm thinking either both 130TC cams or 130TC inlet/VX exhaust. Or possibly buying an even bigger aftermarket inlet cam and running that with the 130TC exhaust cam?

[Guy Croft]

What header and fuel system?

G

[Testament]

header will be 4-1, to be made when the engine goes in the car, so I can't tell you exact specs. I haven't decided on the carb yet, I have a 40IDF (32ch) I could use, but was also considering going to 44IDF or maybe an IDA, I don't think a DCOE would fit straight off the blower in the 131 engine bay.

[Guy Croft]

OK,

according to my notes the std Vx piston has a dish volume 7.5cc.

I'd go 40IDF 32mm chokes, use the 130TC inlet and the std Vx ex cam, header 36".

I have not done with the 40 IDF (plenty good enough setup though) I've done numerous on 45 DCOE like yours and seen up to 190bhp at the wheels. I figured lately that 45 DCOE might not be any better than 40 DCOE (up to some level of tune) but have no figures to prove either way.

If you change to a competition inlet cam (GC IIB or 3A both been used with great success by me) be careful with piston to valve clearances and come down to a 30mm or even 28mm choke.

There is a strong argument for using high-lift-at-tdc cams (big overlap) on blown engines to encourage blowing-down, but few, incl me have been inclined to try it out!

GC

[tmvolumex]

I have built 2 street VX engines that both utilized "long duration" cams. I built a 1756cc VX engine with 8 to 1 compresson, Alquati 40 -80 cams (300 degree duration), 40 DCOE Weber, Anza header and 8.5 PSI boost. Guy has photos of this engine in his tuning book. That engine was 175 hp at the crank. I installed the engine in my 77 Lancia Scorpion / Montecarlo and I put 150,000 miles on it. Despite the long duration cams, the engine had lots of low end torque and idled smoothly at 850 RPM. I later built a 2 liter engine with similar specs that I estimate to be over 200 hp at the crank. The 2 liter engine has much more torque than the 1756, as you would expect, but it also has the same docile behavior until you open the throttle. Both engines continue to increase in horsepower to redline (and beyond), which is 7,000 RPM. Positive displacement superchargers "tame" long duration cams as they prevent / reduce intact track reversion. Even though both intake and exhaust valves are open at the same time, reverse flow through the intact tract stops at the supercharger, the rotors are in the way and act as a positive stop. You will never have a fuel air mixture spitting out of the carb, like you can have on a normally aspirated, long cam duration engine.
tmvolumex

[Guy Croft]

good post Tom,

and your knowledge has helped a lot of people including me because you proved out the 40 sidedraft before me!

Re:

You will never have a fuel air mixture spitting out of the carb, like you can have on a normally aspirated, long cam duration engine.

.. only provided you run small chokes. There is a lot of high pressure back leakage outboard from the Roots blower. Run the chokes too big and the engine will never pickup whatever you do to it.


GC

[Testament]

Those are some impressive outputs, a great encouragement, thank you Tom

I've decided I won't be using the 40IDF as these are a pair and I will probably fit them to my 124 coupe at some point. This means I will buy a new carb for the VX engine, so I have a choice to go either a new 44IDF or 48IDA. can you see any benefit going to the IDA? the price difference is not great, and they are generally advertised as a racier carb (doesn't mean alot I know). IDA parts are definitely easy enough to come by here as they are very popular as induction for rotary engines in New Zealand (rotaries have a large following here). I think with the 44IDF there are chokes available down to 30mm choke, and for the 48IDA down to 34mm (standard is 37mm). or do you think the IDA will simply be too big.

I've just been calculating the compression ratio for this motor and it seems to be coming out higher than I thought it would be? Do the VX heads have a much larger combustion chamber as well?

When I calculate it using the tool on the Ross pistons website I get ~8.25:1

What I was caluculating on
bore - 84mm
stroke - 90mm
deck height -0mm (to be determined in reality but as a starting point)
Distance From Top of Top Ring Groove to Deck of Piston - 10mm
compressed Gasket thickness - 1.7mm (OE thema turbo gasket is 2mm uncompressed, not 100% sure if this is correct)
head volume - 50cc (buretted volume)
piston dish volume - 7.5cc

[Guy Croft]

I have att a CR calculator which is Excel, you can put in your own bore, CR parameters etc. I have set it up at 84mm bore with your gasket of 1.7mm and for flush piston although you can play around with comp and deck height/machining.

The Vx head is 55cc or so - and can end up more if you do valve-seat work.

Given the cams you have readily aval I would use the 44IDF with 32 chokes with the 130TC inlet cam and the prod Vx ex one. If you go to a comp inlet cam you'll need to go down to 30mm chokes (and depending on how radical the cam is sometimes smaller which would mean a smaller - 40 - carb).

G

[Fingers]

Not sure if I can be much help, but I'm running a 45 DCOE on my VX coupe with a GC manifold. I'm using 30mm chokes, as recommended by Guy I also have his 3A inlet cam and the car is a completely different animal. A lot more torque and also a lot more top end power, I can't recommend the 3A cam enough and had no valve-piston clearance problems. I certainly noticed a difference fitting just the carb, but the cam was the icing on the cake. I'd be really interested to hear how you get on, and especially how you find a 4-1 exaust, I still want to fit one to my coupe but have a lot of other projects on the go.

[tmvolumex]

I am not sure about other manufacturers of head gaskets for Fiat / Lancia boosted applications but the Spesso Volumex one has a compressed thickness of 2mm not 1.7mm. This change makes about a .2 point difference in the calculated compression ratio for a 2 liter. In addition, be sure to use a head gasket for a non reversed port configuration with your Volumex head i.e. early configuration. Don’t use an Integrale head gasket, as the coolant holes in the gasket, are oriented for reverse port head configurations. On this site there is a post of destroyed turbo engine because of using the wrong configuration head gasket.
I am guessing that you are planning on using your Argenta, carb to VX supercharger manifold. Make sure that the carb you select has the correct fuel float orientation for this application. If it does not, your will engine will flood / starve depending on the direction of the corner that you are driving through. DCOE's can be mounted in any orientation relative to vehicle travel, thus their ability to be used on inline or transverse engine installations. Take a look at your stock Argenta VX carb for the correct fuel float pivot orientation.
Tom

[Testament]

Just to clear things up-
the 131R had a VX engine setup in it previously which I have most of the parts from (it is not a volumetrico, it just had a Lancia VX engine fitted), but I am building a new engine for the car now, using an argenta engine and, parts from the VX engine and other parts that I have obtained.

-the Block and the head are from an argenta 2L carb engine. regular engine, not the VX version.
-the argenta head has been mildly ported with 44/38 SS valves and has bronze guides fitted. I've burreted this and all chambers are 50cc +- 0.5cc
-I have a set of NOS Volumex pistons that are being fitted and I am using the Crankshaft from the VX motor that came with the car.
-Cams, I have a pair of 130TC cams I have been planning to fit (although going to the bigger inlet cam sounds like it is probably worthwhile), Previously I thought I also had the VX cams that came with the VX motor that was fitted to the car, but I had this wrong, the car had regular 2L cams fitted.
-I am going to use the Thema (reverse port) gasket, I have compared this to a couple of old style gaskets and the holes do match up, and match up with the head and block. Some of the coolant holes are smaller than on the old gaskets, so I will carefully enlarge these to match.
-the old setup in the car had some kind of 2 barrel simulatneous opening 36mm weber off a renault v6 or something strange. this is getting binned and I am going to goto a 44IDF by the looks of it, this will be mounted on a custom adaptor to the supercharger inlet in an inline configuration. I don't beleive it matters if these are mounted 180degrees either way as long as they are inline as these are commonly used on VW boxer engines with a carb mounted each way around. There is simply no room to mount a DCOE, there is only 120mm clearance to the inner guard from the supercharger inlet.
- the 4-1 exhaust is going to be fabricated, you won't "find" one off the shelf anywhere that I know of in NZ at least.

thank you
Tom

[tmvolumex]

Oh, I understand your setup now. I thought you had a Argenta Volumex engine installed in your 131R. The Argenta Volumex was an inline, straight up engine, not the tilted over 20 degree, transverse engine that came in the Beta Volumex's. If you had a Argenta VX carb to supercharger manifold you could use a Weber DCNF carb.
Tom

[robert kenney]

All,
I picked up on this part of Guy's post regarding lift @ TDC thus blow down on supercharged racing engines. I hope this is a good place to write this.

There is a strong argument for using high-lift-at-tdc cams (big overlap) on blown engines to encourage blowing-down, but few, incl me have been inclined to try it out!

I would love to hear what you have heard on the subject. This is a regular talking point around the campfire at the track.

I have built a few blown (roots type and high helix supercharged) racing engines in both gas and methanol applications for drag racing. The wisdom behind blow down is sound advice for a force fed gasoline (petrol) burning engine when compared to methanol. The blown engines I work with do not have any means to cool the air charge other than fuel so this is a more important item.

With gas as you all know you run an AFR on 12-1 about and create a lot of heat you want to keep under control. The lift @ tdc allows the positive manifold pressure to blow air and fuel through the combustion chamber to cool it and the associated components heading off detonation.
Lets say for relative discussion on a gas engine with modern large lift integral lobes and duration of 275 degrees @ .050 lift I would run 110 - 108 lobe centers. Along with that 8.5 - 1 compression and 15 -17 # of blower on 100 octane fuel. This would not require any timing relative to boost adjustments (boost retard).
Running the same engine with 112 lobe centers I would need to tame things quite a bit. Compression/ timing and better fuel.

An engine running on methanol likes 114 - 116 lobe centers to minimize blow down with duration around 290-300 @ .050 tappet lift. Methanol runs a 5.5 approximately AFR and along with its lower volatility loves heat to make good HP. Excessive lift @ TDC cools too much. If you can't generate cylinder heat you can't win races. When the tune up is right I can lean .005" and pickup a tenth of a second @ a 7.60 ET. Works out to be about 100 horsepower.

These are based on my interpretation of results on the track tuning and the knowledge highly experienced tuners.
Sorry to ramble and I hope I was coherent enough to put my thoughts in a readable form.

Robert Kenney

[Testament]

I'm in the process of designing the header now, and I am tossing up on the pipe diameter. the head has 38mm Exhaust valves - do I go with 1.5" pipes ~ same diameter as the valves, or is it worth going to a larger pipe (1.75"?) with the higher flow on a supercharged engine? My gut feeling is it's safer to stick with something smaller and keep the velocity up even if it does start to strangle the top end over 6000 or 7000rpm - the rest of the exhaust system will probably be 2.25" with one or two straight through mufflers/resonators then side exiting in front of the right rear wheel, so there shouldn't be much other back pressure in the system.

Length will be 40" or as long as I can fit while keeping all 4 pipes the same length and still being able to install in the thing.

[Guy Croft]

Rather late reply, Xmas to blame, sorry.

Primary diameter 3mm bigger than valve throat diameter on all 8v units that I've done seems to work fine. That usually works out about the same as valve diameter which is 38mm in this case, 1.5". I have not tested this as such but achieved very high power on 1.5" ID, doubt if there is much gain to be had going bigger (based on my own exp in this particular case) but I definitely would not go any smaller.

GC