8V turbo cam timing with 130TC cams

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SteveNZ

8V turbo cam timing with 130TC cams

Post by SteveNZ »

Hi

I have a Tipo with a Croma based 8VT engine, Delta IAW efi and 130TC cams fitted. I have done nothing other than just fit the cams and make sure the clearences are close to stock 130TC specifications. The cams have been fitted as if the engine was a 130TC. i.e. inlet cam is actually running the exhaust now as its a reverse port engine. Turbo is stock Croma T3 but will be upgraded to a T3/4. Something that is adiquate for around 200wkw (300+HP).

It runs well but I would like to get the best from this simple combination. I will be looking for a good mix of driveability and top end power. It is a street car but I mainly use it for short sprints and hillclimbs etc.

So my questions;

1 What cam timing should I run
2 What valve clearence should I run
3 Does it make any difference which cam is used for the inlet (or exhaust), or are they close enough to call the same?

Thanks in advance :D
Guy Croft
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Post by Guy Croft »

Hi Steve

First thing I'd say, it's always better to run less lift on the ex than inlet on a turbo. You won't lose power, but you'll get better throttle response and less fuel wastage. Turbocharged and supercharged engines have so much higher cylinder pressure during the firing cycle than normally aspirated ones that they can get away with milder exhaust cams. I've driven turbo cars with like- for-like cams, before and after I changed the ex cam and the difference in performance is quite marked.

I'd be tempted to ditch the 10mm lift 130TC cam on your ex side and get hold of an ex cam from an 8v turbo model, eg Delta Turbo 1.6 with 8.6mm lift, if the worst comes to the even say a 131 1600 with typical 9.5mm lift.

Running clearances should be set at 0.4mm inlet 0.45mm ex +/- 0.05mm

As for cam timing You could run a wide range of FL combinations, all will have slightly different effects, none liable to be bad, so to speak, eg: both at 110 deg (ie and carb models Delta Turbo 1600), inlet 103 with ex 107 etc. I wouldn't go outside the envelopes of 103-110 inlet and 105-110 ex.

I would go for a proven combination of inlet full lift (FL) at 107deg after tdc and ex 110 after tdc, like the 8v Integrale.

As far as the engine is concerned, and ignoring the turbo for a moment, opening the inlet earlier at 103 FL for example, rather than 107 gives more lift at tdc and would tend to give more upper rpm power by increasing the overlap. The penalty will be less effective filling of the cylinder beyond BDC; because of course the air doesn't just stop flowing in at BDC, it has filling momentum. And also the more lift at TDC, the closer the valves get to the pistons.

Opening the ex valve later, ie: FL at 105 BTDC rather than 110, again gives more overlap, and extends the effective power stroke (tends to get more energy from the exhaust stroke).

One might think perhaps that a combination of 103/110 might be a handful with so much overlap, but I doubt in on a 2 liter engine, 1600 maybe, but it's very 'trial and error' unfortunately. The normally aspirated (n/a) engine is much easier to tune, because we know we have to put in a lot of overlap to get power. Because on a turbo unit the air is blown in under pressure, the effect of alterations to cam timing is more difficult to predict.

The effect on the turbocharger from early opening exhaust valve is that we get more energy (heat, pressure) to the turbine.
Overlapping doesn¢ž¢t do much for the turbine directly, but indirectly the scavenging of the cylinder by that means is very beneficial to the combustion cycle as a whole, as much for a turbo unit as a normally aspirated one. And of course a longer inlet cam phase gives better filling.

(BTW if you have not seen it I¢ž¢ve been talking lately about the purging benefit from cross-flow in the GC V/W under ‹Å“all the power is in the head. Part 3¢ž¢)

I hope this is useful.

GC
SteveNZ

Post by SteveNZ »

Thanks Guy, yes thats a lot of help. I'll think it over.

BTW, I do have a Delta turbo i.e. cam. Would that be the best choice, ive got a few others to choose from too.
Guy Croft
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Post by Guy Croft »

That's perfect, 8.6mm nominal lift. I wouldn't bother looking for anything higher really. I know that choice won't hold you back or catch you out.

GC
SteveNZ

Post by SteveNZ »

Ok cool

Here is my current dyno plot. I hope to add a new one when I have adjusted the cams.

yes I also have to fix the boost spike.
Attachments
2L 8V croma turbo engine, 130TC cams, 8V Integrale management. 136kw @ wheels, 10psi boost
2L 8V croma turbo engine, 130TC cams, 8V Integrale management. 136kw @ wheels, 10psi boost
tipodyno2.jpg (90.54 KiB) Viewed 8940 times
Guy Croft
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Post by Guy Croft »

So, Steve, 136kW, if I read it right, x 1.34 = 182bhp?

That doesn't a bad result at all, 8v turbo at 15- 10 psi manifold boost - last year's engine I presume. Do you have power and torque plot vs rpm somewhere?
But I know you are doing a new setup, don't worry too much about the old one!

GC
SteveNZ

Post by SteveNZ »

Yep, 182HP at the wheels :D

No RPM scale unfortunately, however the boost spike is around 2500-3000rpm somewhere. I believe the plot goes up to 6000-6500 somewhere. Even though the torque is taking a dive at high RPM it pulls very freely to 7000 rpm. The original Croma would go totally flat at 5500rpm.
SteveNZ

Post by SteveNZ »

There is no debate over using a 130TC inlet cam in a turbo engine. Its a good (cheap) upgrade. However there is some confusion over which exhaust cam to use when paired with a 130TC inlet.

A 130TC exhaust cam is not recommended. So, just for the record, which factory cam would you choose for the exhaust? There are a lot to choose from, 105TC, other 1600 or a stock turbo cam have all been suggested.

As stated I have a pair of 130TC cams already fitted. I really don't care if the 130TC exhaust cam is not ideal. I just want to make sure its not detrimental to top end power, or some sort of reliability issue. I am more than happy with everything else.

I'm sorry if these questions are a little pedantic but I am very curious to know. Thanks :D
Guy Croft
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Post by Guy Croft »

She'll run OK with a pair of 130TC but the lower-mid torque ought to be better with lower lift ex.

For lift figures on 1600 cams refer to my book - I think you have it? Front section details the lifts on n/a and turbo 1600's etc.

GC
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