Hi every one, my Rapid zetec conversion aint gonna happen in the forseeable future so can anyone tell me what cam/ carb with give me the best performance out of my Rapid 136????

Many thanks

Crazyphill

Hi every one, my Rapid zetec conversion aint gonna happen in the forseeable future so can anyone tell me what cam/ carb with give me the best performance out of my Rapid 136????

Many thanks

Crazyphill

Can worms of....need I say more. Are you after ultimate performance and sod the reliability....if so then the carbs are a pair of 40 DCOEs. Cam wise.....who konws....you may gain a bhp or 2 by running a race cam, but unless your engine is set up for it with the right ignition curve and carburation then its a waste of money. Speak to Autosprint about cams....he has done a few SKoda engines. I believe he currently recommends a 295. Kent and Piper do a 285..all are regrinds with nothing new available.

Get the head ported and a decent exhaust would be my advice....speedpro in cz got me a nice exhaust (not talking Ashley off the shelf stuff) and it enhanced the performance throughout the rev range.

Hi,

Im running a Kent SK3 cam in my 136 Rapid. Its a 295 duration cam, with a powerband of 3000 - 6000 rpm, done by Autosprint in Birmingham.

I had to make a stepped key to the full inlet lift at 105 degrees

Its a nice cam, a little lumpy at the bottom end, but comes on cam and revs well, and seems to match the standard cogs quite well.

Im running a ported MPi head (basically just the standard ports cleaned up and polished) with a 4 branch exhaust from Speedpro in CZ. The MPi does flow better than the stock head, but comes with stupid honeycomb springs that are not easily interchangeable, due to 7mm valve stems (the standard head runs 8mm), and bounce after 5500rpm.

Carbwise, Im on the replacement weber (30BCIS) upjetted to suit. The inlet manifold will take most weber carbs (think 28/32 or 32/36 from a ford pinto) but will need opening up to suit. Anything bigger (38 DGAS / 40DFAV) seems to overfuel at the bottom end.

I've also got a set off bike carbs to try too..

The standard dizzy wont advance much after 5000 rpm, so either needs modifying or goto megajolt.

Like normal engines, they are not cheap to tune!!

If you're just going for power, and presuming you've got a 5-port head, an up and over manifold and single Weber.

I thought the 136 had an 8 port ???? i'd better check now i think!!!! And yes i am looking for power!!! And its gotta go better than the 125 i had out of me estelle taking into account the dodgy speedo reading!!!! lol

O and Kieran, what do u mean about a stepped key???

The 136 is an alloy 8 port head

Because the cam sprockets are keyed to the shafts, and because you cant get a vernier pulley off the shelf, the only way to adjust the cam timing to get it spot on is to make a stepped key, to inch the sprocket into the right position.

How did you get 125?? the speedo's only read to 110.... The best i've had is is "H" from the "MPH" at the bottom which was 118 according to my satnav.... private test track, downhill, wind behind etc...

Edited 7 September, 200916 yr by Kieranzxt

Twin 40s are what you need then.....but it will cost....a lot! A nice compromise is a Weber 32/36 (£20 from Ebay) which I had set up for me at a rolling road and for which you can get new jets. That combined with a ported head, exhaust, decent ignition curve and mild cam netted me 90bhp. With a hairier cam it might have made 95bhp......but it went reasonably quickly and pulled through the range.

I think £80 quid setup at bogg bros and bike carbs is a better bet (fixed price, no matter how long it takes).

Skofast might be able to get you a steel twin weber inlet off the shelf over in Czech. I use a kent grp a cam, some mini dual valve springs (I think they are super sport) with caps made to suit. A mpi head ported with even bigger valves (36 or 37 inlets and larger exhaust). 4 into 1 exhaust. A 136 dizzy with lumi fitted and mapped to the cam. Uprated oil pump with large oil cooler. Lightend and ballanced bottom end. Uprated grp A clutch cover. Larger pistons (just over 1300cc). This engine will tick over at 500 rpm and rev to 7500 rpm, but most of my gear changes come in at 6500-7200 rpm. It drives quite well as a road car. 10.5 :1 compression, also set liners up to the max setting and use higher head bolt torque. Large pulleys. Electric pump and larger fuel line.

Speedpro in cz will supply all sorts of goodies, but something like the twin 40 inlet will be a couple of hundred quid delivered (its about £155, then you need postage and the banks always charge £20 foreign money transfer because Speedpro dont take cards)...then you need carbs, 2nd hand - another couple of hundred, then airfilters and linkage....thats another hundred. Then you need to get them jetted and set up. I would reckon you can probably do it for £600 if the carbs are close to correctly jetted. Not cheap!!!

Rsimps....did you modify a standard oil pump or is it a different uprated item? I need to do something about the oil system when I build the engine for Snotty.

You put a stiffer spring in there or place washers under the spring.

"HP" oil pumps are a waste of time, money and ultimately power. Reasoning:-

Pressure is a different thing from flow. Block the pump outlet and you can get near infinite pressure with enough power driving the pump, but you have no flow.

An HP pump increases pressure in the galleries by maybe 2 or 3 bar. The places we need pressure and flow are the main and cam bearings, where hydraulic thin film effects give something like 2_000 to 3_000 bar, so the HP pump might add 1% to pressure where it's needed.

pressure will increase flow to a degree. Fluid flow is pretty much like electrical flow and pressure like voltage. The pressure is the driving force and as oil goes through the galleries there is a pressure drop. An increase in pressure therefore can increase flow particulary at the end of the flow path. Its a sensible thing to do for a few pence and one that every works team did in period. Also run a grade up in the oil (I use 25/50 Vavoline racing) and fit a big oil cooler if you are thrashing it.

replace voltage with current. ie if you blow water down a pipe to fresh air, you start with a presure and it drops to 0 when it flow to air. Like you start with 12v and at the other end, earth you get 0v.

You put a stiffer spring in there or place washers under the spring.

That sounds like the pressure relief valve not the actual pump?

Which gives you higher pressure. ie it relieves at a higher pressure so the oil going round the engine is at a higher pressure.

Flow is directly proportional to pressure. Viscosity is indirectly proportional to flow. The radius of the gallery is to the power 4. Basically if you double the radius you get 16 times the flow.

Its not as simple as that, there are frictional loses in the gallery surface and oil and the oil needs to be the correct viscosity to do the job at the bearing end and the pump needs to be designed to pump the oil of the correct viscosity. If you just follow the physics/engineering calcs using 4-1 oil would increase the flow, but in reality the pump design would not pump it, it would probably cavitate the oil and it would not work as a very good lubricant.

Use a new pump too! That's about the best you can do without redesigning the engine. You could try limiting flow to some areas, make sure the gallery to the bearings is not on the load side to help the oil flow on things like the crank journals (ie pluging one side of a cross drilling). These are general comments on engines. pretty much known about for the last 100 years.