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If it's not really about tuning or wiring. Then it belongs in here.
Hi all, I am building my 4.6 2v which will be running a sx300 72mm turbo on pump gas and wanting to know what would be the best cr to build it. Was thinking about 10:1 but would like some feed back and thoughts from you guys, looking at pushing the power up reasonably high.
How much boost? 91,92 or 93?
Aussie, so E85 or RON 98, I expect.
Going to depend on a shed load of variants - a sgeneral rule, more boost = less compression, better charge cooling = more boost/compression, better response = more compression, etc.
There is a LOT of information you need to know before even thinking of that - and as the short block is one of the things everything else will be limited by, and it's a hassle and expensive to redo, you need to know pretty damn near what you expect to end up building around the short block - heck, is the power going to be boost or rpm generated, or both?
Thanks for the replies, 95 octane is all I can get here. Engine will be built good for 1000hp but will only be tuned to what I can make with 95 octane being the limiting factor to make reliable power. Maybe I should just do some more research but I'm thinking low cr and higher boost will keep a cooler charge than higher cr lower boost for the same power. Just want to make the right choice before I send a heap of coin on rotating assembly and heads
Using a Ford crank?
Not sure what you mean about keeping the "charge cooler" - it won't affect the air charge temperature, as such, but if you mean the pressure, and hence temperature rise, during the compression stroke, you're correct.
I'm not too familiar with that engine, but elaborating on Max's question, how familiar are you with that engine's weak points -not just the crankshaft, but rods, pistons, cylinder wall thickness, deck and head thickness, head bolt/stud clamping, breathing, parts availability, etc? I would assume the "2V" refers to valves, rather than venturiis as Ford sometimes did, and it was later produced in 3 and 4 valve versions for a reason, breathing, and so you may need to address that as well, maybe fit better heads?
Power is a result of torque and rpm - if the peak cylinder pressure (torque) is a limiting factor, you may be able to increase rpm a little to counter that.
If I were you, I would have a very good think about using that particular engine and whether it isn't a better idea to use a different one - just because it's what you have shouldn't really be a factor.
If you do decide to go ahead with it, consider water and/or methanol injection when under boost to reduce the temperature rise in compression and slow combustion speed.
I’d also consider your intended use; for example if circuit racing higher boost pressure means more charge cooling required to which there’s usually a hard limit. In that case it’s better to go for the lower boost, higher compression, higher revving option. For street or drag use heat soak isn’t so much of an issue so dropping the cr and increasing boost is a valid option and often am easier route to big numbers. It’s worth thinking ahead to future mods too such as cam and head porting as this will mean more power for the same given boost level or less heat soak for the same power level.
All parts are paid for just the wait to get them sent off and arrive at home but its a full forged internals Manley crank, k1 rods wiscoe pistons, trickflow heads arp studs top and bottom, I've gone with a combo that will give a 10:1 cr so its all go, thanks for the replies all. The tuning will be the fun part as I've choose to reflash rather than a standalone. Sct software is what I'm looking at, going to have to recalibrate the bigger maf sensor ive brought and the 80lb injectors but once the are in check the rest should ok, also changed from a returnless to a return style fuel system.