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Wet sump stealing BHP? (K-series)


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How much of an affect can a wet sump have on bhp on a high powered k-series?


I have a circa 230bhp engine spec making 214bhp. Engine spec is:

VHPD engine with fully ported head & throttle body

1444 cams

Titan PTP throttlebodies (not swan neck type)

32.5mm inlet / 28.5mm outlet valves

New liners / piston rings

Power speed 4-2-1 exhaust with CAT in silencer


It was mapped at emerald, throttle was checked as fully opened, timing and compression was all fine. We even did a run with no ITG filter to check. The injectors were at 90% duty. The engine had approx 750 miles on it since rebuild (this was the 2nd RR session after a blocked CAT in the original VHPD exhaust was the suspect. I changed to power speed and re-visited emerald).


Torque was a little bit down everywhere so it's a consistent loss. The cat is a 200cell high flow cat. I need this for MSA rules in sprints / hill climbs. I hadn't heard of wet sump wind age losses until recently. Could this explain a drop in torque over all the rev range?


Link to my RR results.




The run with the large hole in the midrange is the same engine spec but with the blocked CAT (75% collapsed standard Caterham 4-1 cat)


Any ideas where the missing bhp is?

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I don't have a record of the compression pressures but it was done by Dave at emerald and he wasn't concerned with the results at the time. It's on my to do list to re-check myself to get a note of the values.


between the two runs the whole exhaust system changed. 1st run was the Caterham VHPD standard primaries which fed into a standard Caterham cat (4 into 1) sitting in front of a raceco silencer. The Caterham primaries are 1-1/2" and the new power speed exhaust used on the 2nd run is 1-3/4". It is also a 4-2-1 rather than a 4-1 with the Caterham exhaust.


Picture of 4-2-1 power speed exhaust fitted



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There is a difference between pressure and ratio. Latter is a static measurement - volume of head chamber, gasket, valve pockets and distance piston is down the bore at TDC as a ratio of swept volume.


Absolutely critical to get BHP and avoid detonating the engine. Covered in great detail in one of David Vizards books (tuning the A series) though applicable to all engine builds.



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They were timed by DVA and rechecked by Dave at emerald. Dave at emerald measured them at 146 / 126 thou, although he did say his vernier wasn't too accurate as it was slightly bent to get the vernier in the correct place to take the measurement. Dave also said he has never seen an issue with any timing from DVA engines and trusts implicitly that he would of got it spot on.
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The 2:1 portion of the 4:2:1 looks very long.

All the ones I've seen in use are about half that length.

However, I don't know what lengths would be optimal.


Windage can have an effect. Most setups at your level have dry-sumps, so it's much less an issue normally.


You look to be running the standard EU2 electrics - the coils can be quite flaky and can tend to break down, especially at higher revs. You could look also look into the R101 wasted setup, although both R500s I had were fine on the EU2 setup.


I have a 2180 inlet cam, which can release a few more HP, if you are interested?

I was going to put it on my R500, but have since sold the car.


Cheers - Simon


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The two runs were done approx 3months apart but on the same rollers (emerald). The only difference was an extra 500miles run in and the new exhaust. Because the old exhaust had a blocked cat the load sites were completely different so the whole mapping session was re-done. There was a large increase in torque in the midrange with a slight tail off of at high rpm's which was to be expected with a change from 4-1 into 4-2-1.


@simonpa yes I agree the exhaust 2 into 1 section is quite long. It's a standard power speed design as used on quite a few k-series. But it does choose the lengths differently to the k- series 4-2-1 collector that swaps out with the Caterham cat.


Thanks for the info on the cams, I would rather try and sort my current situation if possible as their must be an underlying reason to the loss in torque across the rev range? I suppose a cat and wet sump may be enough for the reduction? The problem is most people who have this configuration don't have a wet sump or a cat so it's hard to compare like for like. Is it a known phenomenon that wet sumps steal bhp? Has anyone got experience of bhp gains changing to dry sump?

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There are lots of posts on various forums for windage, but not much hard data.

it looks like a few percent loss is common.


It's pretty obvious that c crank running in air (or partial vacuum) is going to move a lot more easily than one running through a viscous fluid. However, once you compare that to splashing through moving oils and froth, things get a lot more complicated.


I should imagine that there will be a slight difference between running an old-style rubber sump gasket and the newer one with the big shelf areas that look like they will send more falling oil onto the crank, but maybe stop oil in the sump from sloshing the crank as much..

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