BlownCorona

BlownCoronas 1971 Toyota Corona

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what kind of compression are we talking?  
would avoid running a thick head gasket if you can, 
got a close up picture of the combustion chambers?   maybe able to take some material out.

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10.5:1 with stock stuff. 

I could get it down to around 9.2:1 with machining the pistons a little. And a 1.5mm cosmetic gasket. 

The combustion chamber is hemi design. I did think about taking some material out but I have no idea about that side of things. 

Cooper gasket and o ring block didn't seem a particularly cheap option. 

 

1584539556_images(12).jpeg.a93bf376d241c5c5e01eed688047aa8c.jpeg

Just a pic off the Internet but the same head. 

As for the piston, I assume I could machine a chamfer on the dome the same angle and depth as the valve relief pretty safely, wouldn't want to take any off the top though especially if building for boost. 

 

935330635_8826188262Pistons.jpg.aa2a8e0c3448e4ec6674770e50e45bf6.jpg

Piston on the left is what I've got. 

Another option is 20r pistons, they look to have a very small dome and might be the key. But I'm struggling to reliabley compare them. 

1806413572_71QdoegBdL._SL1500_.thumb.jpg.634c8388472e4648d7ddb91616e67901.jpg

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Is it possible to deck the pistons domes down?

We have copper sheet and could cut a gasket if needed, just the design is tricky, you need to ensure you get sufficient clamping force on the copper.

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I don't think I can deck the pistons any useful amount, they would get too thin real quick. 

It's a closed deck block so clamping force would probably be OK, but have heard of issues with fluid sealing with copper? 

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Yeah they tend to weep as its quite hard to get the copper to yield evenly/everywhere.

When I was looking at making one, I considered etching away non clamping areas similar to a standard gasket.

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Your  1.5mm cometic gasket and piston skim idea  should work fine      9.2  still up there for a supercharger  but good gas, tune and fuel. should be all good if you aren't going to run all the boost. supercharger bit harder on the engine than turbo.

would avoid copper gaskets. will be chasing leaks forever

 

some flatop/less domed pistons and normal thickness gasket, to make use of the little squish area prob best option

doesnt look like much opportunity to take material  from the chambers going by that picture 

 


 

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Nah with the hemi head I didn't think scooping material from the head would work. 

Not sure if I'm comfortable with 9.2:1 especially when I was aiming for 8.5:1 but I'll see what I can dig up flat top piston wise. 

I do have an even higher compression head here that could either make an angry N/A engine or maybe work well with zero deck pistons. And a standard gasket, standard gaskets have been reported trouble free even up to 30psi

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Have also considered moving to a turbo since I have the supercharged crown which is a keeper. 

How much softer on the engine would that be? If its negligible then I'd rather the blower simply because I think they are much cooler, even if they are way worse haha

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Superchargers are pretty hard on them at low rpm witch is most of the issue

i remember talking to marsh about his engines and he said with PD blowers he gets them as close to 8:1 as he can.

in saying that though, that’s on carb v8’s with odd intakes.

multi point injection has huge jump on that tuning wise

 

personally I’d be pretty gutted if you ditched the charger :(

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Likewise. But I'll just approach it methodically. 

I think the 20r piston will be the ticket I just need to get my hands on one. Entire quality 20r piston kits can be had out of the states for $150usd 

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will have higher cylinder pressure for same power with supercharger  vs turbo.   taking power directly from the power stroke to drive the supercharger.
plus as above, forcing air in at low rpm  especially non intercooled  is a recipe for knock.     once engine is spinning faster can get away with more.

its a balance of a lot of things.   boost, fuel quality, air temp, compression ratio.   going from 9.2 to 8.5 compression ratio honestly isn't that big of a change, run a psi or 2 less boost and your back in the game on the 9.2 engine

turbo is just easier as need less power in the cylinder to make the same power at the crank.   and can do things like ramping the boost up at high rpm where engine less likely to knock

 



 

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(assuming it stays boosted) its getting intercooled this time around. itll also not be running that much boost. i was keen for 7-8, but would be just as happy with 5-6 in a reliable engine that i wont really have to stress about. its not remotely about power for me. ive had fast cars and i still only drive them at 50kmh. having the blower is 100% about the style the feel and the noise they make. but i also doing want to install it and only make 1psi because itd be technically supercharged. does that make sense?

i either want a reliable engine making some boost. or id rather not bother. 

 

its still got the clutch on the blower so i could get it up via the ecu to switch on at say 3000RPM or something to mitigate that low RPM problem. however id need to setup a bypass system as i doubt just getting the engine to suck air through an undriven sc is ideal. even though it happily does it? cant be good for fuel economy. 

for what its worth, and this may change your answer.

if these 20R pistons are what i think they are it would be cheaper to build the 8.5 engine, than the 9.2 engine. it would also be bolt together and go with zero machining required. except for perhaps some valve reliefs. the 9.2 engine relies on the assumption of being able to cut the entire circumference out of the 18RG pistons dome and also the cometic head gasket is a 92mm bore vs the current and stock 88.5mm bore so thered be weird dead space in there. a stock gasket is 1.2mm though so most of the deccompression comes from cutting the pistons. 

turbo does interest me. and so does the thought of being nicer to the rare engine. 

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20r pistons sound like a plan then.  i was more saying don't get caught up on .7 compression ratio than going either way.

sounds like will work all good to me,  with that boost,compression plus being intercooled.   assume  98 octane fuel?
just dont want to get into the situation  where have to retard the timing too much.

the estima? vans the sc14's come on have a big stepper bypass valve,   1.5" diameter.    can run with the charger clutch off when cruising and have the valve open.   could even use it to bleed off some boost at low rpm if you happened to run into knock down there. not the best way to do it but is an option

 

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yup, the crown i have is also factory sc14 with the big bypass valve. works awesome for cruising around but its an ugly and bulky system. could probably be hidden away though. 

i just saw on the LCEengineering website that the 20r pistons are not currently available. have sent some emails so we'll see. if they arnt available ill have to revisit everything as most of the other piston kits for the 20r i can find look like economy cheapie things which probably will end in tears. 

initially i was hoping to use 95 octane as 98 is a complete pain in the ass to buy in chch. however NPD are offering a steady supply of 100 octane and seems like there a new station popping up daily. interested in your thoughts on this? 

 

 

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100 sounds amazing.   

can get away with a bit more on 98 than 95.   just  have to try it. tune with knock detection

an example:  going from 95 to  98.  let me run another 4psi boost and gain 30kw  on a 1500cc engine

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shit thats a big difference, as in like 75% of my desired boost pressure. 

i got interested in running their 100 fuel when a colleague said his tuner couldn't get his cammed up blacktop levin to detonate with it. also a tuning shop in timaru did back to back to back test with 98/avgas/npd100 and found the avgas and npd very similar (no lead though) and they were making more power on the sr20det with less boost than on 98, so it definitely lets you get away with more timing. 

my main concern was availability.  but that might not be such a problem anymore, though not all npds are carying 100. however at this point, harder to get fuel trumps grenading a motor. 

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