Forged Piston Thoughts

[blastronaught]

I'm putting together a 1.6 Xflow running low boost (thinking 1bar MAX, 600mbar more like it) and a Renault R5 carb. Targeting the 150hp ballpark. Planning stock components everywhere else (cam, valves, rods).

Per the discussions on this forum, I'm going the forged pistons route with 8.5:1 CR (open to thoughts here, but from my research this looks reasonable for reliability). Burton's seems to be the only place offering any of the shelf, but the accralites are way too high CR (12:1). Plus, looks like I can save money going through JE Pistons here in the USA and not shipping across the pond. Anyway, since going this custom route and spending the money, anything I should add/change from the standard piston? General considerations I will forever regret not having considered?

[Dyno]

Pistons are indeed the only part that should be replaced in this engine. If you need to replace the valve, buy good quality ones like TRW items or any REC (UK).

About piston shape, if anything can help this piston not loading to much heat, I should say, use a flat top piston. But I have no idea how the KENT engine react to flat top pistons. Not been into KENT engine for a very very long time and never been deep into it. Maybe others know. Some engines did had this design as standard, no squish at all.

Otherwise, to lower the compression, piston can stay almost stock. I believe there was a 8,5/1 but not for sure.

[Graham]

kent engine works ok with a flat piston but need a lot of ignition timing, although perhaps that wont so much be the case on a boosted engine.

for sure i would of thought a flat piston some way down the bore would run a lot cooler and be a good move

[blastronaught]

That sounds logical enough, I'll relay the flat-top option to JE and see what they have to say. Hopefully I'll be able to save money too by not having them cut a dome out of the piston blank.

Graham, by a lot of ignition timing do you mean a lot of advance or just a lot of tinkering to find where things are happiest?

[katana]

Sorry - general query related to this....... I thought majority of x-flows were flat head / bowl piston types and thus benefited from reasonable squish performance to aid combustion. Wouldn't using a flat piston and a flat head be a retrograde step in terms of combustion? Surely forcing the mixture from the edges into a 'bigger' bowl in the piston (to lower the compression) especially in a turbo combination that isn't the best flow design - would be the better option? If having the expense of forged pistons, and having the bowl would be the better option, would then moving a 'oval or kidney shaped bowl more under the valves give an improvement in combustion? Views welcomed as every day is a school day.

[Graham]

i think the x/flow generated a reasonable amount if swirl as the inlet port directs the incoming charge at the curved cylinder wall. flat flat isnt as good from a combustion point of view, but the engine greatly benefits from the much lighter piston, poorer combustion can often be offset you more timing.

by way of comparison dave walkers twin plug pintos needed a lot less advance to make max power, only 22 degrees, but power wise it made exactly the same as the single plug ones

[fatboy slim]

nothing wrong with flat top pistons in a x flow turbo'd or N/A. the ultimate turbo x flow used pistons that were more or less flat tops as in the zakspeed capri. i used accralite twin cam pistons in my 1300 turbo as they had the thickest crown available so can take the heat and have the ability to machine a dish into if required. both my N/A 1660 and 1860 x/flows used std twinky pistons and both set times in speed events that are still to be beaten over 20 years later

[Dyno]

i think the x/flow generated a reasonable amount if swirl as the inlet port directs the incoming charge at the curved cylinder wall. flat flat isnt as good from a combustion point of view, but the engine greatly benefits from the much lighter piston, poorer combustion can often be offset you more timing.

by way of comparison dave walkers twin plug pintos needed a lot less advance to make max power, only 22 degrees, but power wise it made exactly the same as the single plug ones

I regular have Porsches 3,6 ltr on my dyno. All nice twin spark. Make approx the same Bhp on single spark as on twin spark. But need more advance. The only real benefit of using twin spark is the later advance and later advance mean less heat. Very important when you take a 2 ltr 120 Bhp engine design into a 3,6 Ltr with 250 Bhp air cooled engine. All Porsche race engines had twin spark and relative low compression ratio (round 10/1). For sure to combat heat. Possible twin spark has some emission advances to but can't say, don't measure EURO 6.

[blastronaught]

This may be too much to ask without having any data to look at, but would you all think that the heat-resistance benefits of the flat top would be offset by the need to run more advance? Or will it end up cancelling out any benefits, and I just have a lot of advance?

Maybe I should just tap 3 spark plugs per cylinder into the head (kidding).

[katana]

Just one thing - you shouldn't be having lots of advance with a turbo. If the swirl characteristics are good as Graham says then a boosted charge will end up with more retarded timing than NA........just a thought!

[fatboy slim]

had my 1300 x/flow mapped today. 259hp, 221ft @18psi. and all with flat head and twinky pistons.

[Graham]

had my 1300 x/flow mapped today. 259hp, 221ft @18psi. and all with flat head and twinky pistons.

[Dyno]

had my 1300 x/flow mapped today. 259hp, 221ft @18psi. and all with flat head and twinky pistons.

Very well done

[katana]

That's stout - nearly as good as some bikes..............................................its banter!

[fatboy slim]

thanks onyd, have yet to try it on track yet but it was a handful with only 190hp and 158ft . somehow i don't think i'll be needing the 5.3 diff that's fitted at the mo

[Dyno]

My advice, sell the diff before it's exploded !!!! Dyno graph? Full engine spec. ?

[fatboy slim]

gonna swap it for a 4.4. too technical to put pictures on here as it says i have to resize them????. oval port race head,roller rockers, gold ivey springs,ti caps,custom piper cam,accralite t/c pistons with unfinished crowns,approx 8.5 to 9CR, newly linered 1300 block as we cracked the original casting, oil squirter jets,robson steel rods, std crank,alloy flywheel,AP clutch,t25 turbo with gate set at 18psi, custom plenum with VAG throttle body,550cc focus injectors,s80 dta ecu,stainless manifold and 2.5" exhaust,decent intercooler looking at plot it has 120ft at 4k and 90hp. then at 5k its got 195ft and 185hp. will be interesting getting off the line with that

[Dyno]

gonna swap it for a 4.4. too technical to put pictures on here as it says i have to resize them????. oval port race head,roller rockers, gold ivey springs,ti caps,custom piper cam,accralite t/c pistons with unfinished crowns,approx 8.5 to 9CR, newly linered 1300 block as we cracked the original casting, oil squirter jets,robson steel rods, std crank,alloy flywheel,AP clutch,t25 turbo with gate set at 18psi, custom plenum with VAG throttle body,550cc focus injectors,s80 dta ecu,stainless manifold and 2.5" exhaust,decent intercooler looking at plot it has 120ft at 4k and 90hp. then at 5k its got 195ft and 185hp. will be interesting getting off the line with that

OK, F1 engine !!!!