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(Very) High comp N/A engine - camshaft selection?

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Hi all,

I'm sharing my build that's been put a side right now but that doesn't mean I think about it.

I'm rebuilding a 2 litre Peugeot engine. XU10J4RS is the engine code.

It's 16v, 86x86 and produce 163 bhp (120 kW) stock. Right now I run a stock engine with retarded intake cam. 48 mm ITB and 4-2-1 exhaust manifold. Its now makes 195 bhp (143 kW) at 7900 rpm and still got the stock 195 Nm at 6500 rpm (instead of 5500 rpm stock)

Now to the new engine.

New engine is so far:

88 mm pistons, 92 mm forged diesel crank, 164 mm rods (original 158), Oversize valves (31.5 mm exhaust and 35 mm intake), I got a dry sump that will be used. Will be using the 48 mm ITB and 4-2-1 exhaust manifold as well.

The spec will be thrilling 16:1 compression ratio and I will be running E85. Right now I'm thinking of buying race E85..

The piston to head clearance is going to be 0.96 mm

The pistons is custom made and I did a little miscalculation with the dome. I thought I needed to modify the combustion chamber volume to fit the oversize piston but the dome was made after original chamber. It's a copy of the WRC piston with some small changes.

Therefor the new engine is 16:1 instead of 14.7:1 as calculated but I still think I can pull this off.

The engine is not prone to knock and have a pretty good combustion chamber.

Now to the question; I need a camshaft and this insane build. I know its a bit late to select camshaft when the rest is already ordered but I need to adapt to the new stuff.

Max RPM I'm thinking about 9000 rpm and max power at 8000 rpm. I'm hoping to produce at least 250 bhp (184 kW) but I don't see that as a problem due to the previous engine produced 226 bhp (the ITBs and stock 4-1 exhaust manifold, 98 gas, 12:1 CR, 2.04 litre)

I need some help with what to think of when choosing cams. Should i go for the longer duration and a bit lower lift and a bit more duration and higher lift?

See the spreadsheet picture added. I also attach some of the cams I've found of the shelf.

I might forgotten something and if you have questions please ask.

Take care!

Attached Files

For 9000 rpm and CR 16:1 you would want the cams with longest duration available. As for the valve lift- you need to take the head to the flow bench and find the maximum valve lift where airflow stops increasing. For instance if the airflow does not increase after 12 mm valve lift there is no sense to go for a camshaft with 13 mm valve lift or higher.

It looks like the stock head will continue to flow after 0.5" lift.

Its not my head in the attached file and I will get a port job done on my head. But as far as I know the lift will be a result of the airflow.

What about duration. is the 300-310 (at 0.1mm lift) the way to go or should i get a custom with more duration?

I know this build is something more than what everyone use to build.. Is here someone with experience?

Attached Files

One big problem with direct acting followers is the diameter limits what you can do with the camshaft profiles before running too close to the edge and compromising reliability.

TBH, I would contact the support departments of the manufacturers I had it narrowed down to, and see what they recommended for my application - including the rest of the valve train. I'd also make sure I know exactly what I intended to use the vehicle for, and the gearing I was going to use - that last is quite important and I've seen some unhappy results when folks built 'peaky' engines and tried using them on stock gearbox and diff ratios.

So the green line in the flow bench graph is the ported head? it flows less than the stock head and everywhere less than 0.45 in lift. If those are backwards, then you can see that the red line isn't going to flow much more with lift above 0.5 in.

Nope, they are two different, stock, cylinder heads for two different engines - I think he was using them simply because one was his head's flow curves/details.

Thanks for the replies.

The pictures is two different flow charts of 2 different heads. And as I said the head will get a job. I will also change from hydraulic lifters to mechanical.

The lift I think I got, as much as possible depending on the limits of the flow and any mechanical limits.

I've searched around and it's basically only Honda folks who build crazy N/A engines (I know its not 100% true but it feels more common). They got both rocker arms and vtec. But I've seen a lot of camshafts that got 260 degrees duration on vtec and even some of the dyno graphs they don't find the peak, they need to rev 1000-2000 rpm more to find the peak.

How will the overlap between intake and exhaust affect the performance? It's possible to retard the intake cam a bit to move the torque curve. But then the overlap will get smaller.

Regarding the gearbox the final drive is changed from 3,95 to 5,23. At 8k rpm the max speed is 217 km/h with 195/50-15 in 6th gear.

But yeah, in the end the best might be that I contact a cam manufacturer but I want to learn and get more knowledge. I've been searching information for 4-5 years now and this is the first time I'm reaching out.