A different engine configuration ... constructive comments please!

[belize1334]

If you reduce displacement while keeping the dome volume the same then the comp ratio will drop. Comp ratio is found by dividing the dome volume by the displacement + dome volume. With 2.4L and 11:1 comp the dome volume is 0.24L. If you then drop the displacement to 2.1L the new comp ratio will be (2.1+0.24)/2.1 = 9.75:1. Of course that's a guestimate since most engines aren't actually 2.4L but rather 2.375L or whatever. Still, you get the idea.

 

[cheekychimp]

So assuming I am crazy enough to sleeve this block down to a 2.0 litre displacement what compression could I expect if I used 2G pistons or even Evo spec 9.0:1 CR pistons?

 

[belize1334]

If you sleeved it to run OE pistons and did a FULL destroked long rod 2.0L with 88mm crank then you'd get the same CR as before. You've changed the geometry but the displacement is the same so the CR is the same. On the other hand if you used a 92mm crank then you'd be bumping the displacement and that will change the CR.

You can always figure out the new comp ratio if you know the old comp ratio and the displacement for which it was intended. You have to assume that the rod length will be correct so that the piston rises to the same final height. Then the dome volume is the same in both setups. We start there.

CR = (disp + dv)/dv = disp/dv + 1 --> dv = disp /(CR - 1).

Then we calculate the new CR...

CR2 = (disp2 + dv)/dv = disp2/dv + 1 = (disp2/disp)(CR - 1) + 1.

So, if we assume that the old displacement was 2.02L (first overbore pistons, 88m stroke) and the new displacement is 2.113L (same pistons with 92mm stroke). Then we can get the CRs.

Starting with 8.5 we get CR2=(2.113/2.02)*7.5 + 1 = 8.85. Starting with 9.0 we get CR2=(2.113/2.02)*8.0 + 1 = 9.37. This of course assumes that you use the appropriate HG to achieve the intended CR. If you use a thinner HG you'll bump that value just like you would with a normal build.

 

[cheekychimp]

I wish I had paid more attention at school /ubbthreads/images/graemlins/shocked.gif

Thanks. So essentially I can be sure in this case that apart from the head gasket whatever CR the pistons are rated for in a 2.0 litre 85mm bore and 88 mm stroke is what I'll get in the new build. That makes things simpler.

I think I'm going to do this. I don't think it will be amazing but I think it will work and work well and live a long time and for a stock car that's what it is all about.

 

[belize1334]

So you're talking about using Mitsu pistons and an 88mm 4g63 crank in a G4CS block with 156mm rods to make a long-rod 2.0L? Basically not worrying about displacement gains but just banking on the longevity of the long-rod?

If it were me, and considering that you have to use custom rods anyway, I'd drop the OEM pistons and sleeving and use stroker pistons and 162mm rods. Basically you get 6mm from the destroke ((100-88)/2=6) and another 6mm from the lifted wrist pins in the stroker pistons. Then you'd be uber long-rod at 162/88 = 1.84 AND you'd have 2.1L to boot from keeping the larger bore of the G4CS. I know that you want to use OEM pistons, but once you're using custom rods it's not an all-oem build anyway and you could do the above for CHEAPER than the machine work for sleeving the block.

 

[cheekychimp]

Quote:
So you're talking about using Mitsu pistons and an 88mm 4g63 crank in a G4CS block with 156mm rods to make a long-rod 2.0L? Basically not worrying about displacement gains but just banking on the longevity of the long-rod?



Yes, exactly! Believe me, I do understand everything you have said about displacement etc but you have to remember I've done all of this on my other car with the FFWD Connection 2.3 stroker with aluminium rods and ceramic coated pistons etc etc etc. I want this engine to start and live forever because that one inevitably won't. Not if I'm going to wreak every last cent of enjoyment out of it /ubbthreads/images/graemlins/devil.gif

I appreciate your advice on the other issues. I may well PM you for help when I get started. I keep looking at Magnus' dry sump kit. MUST resist the dark side!!!!

 

[belize1334]

Remember, also, that I've never built an engine. I'm happy to contribute whatever I can to the topic but I'm not an expert. All I have is a strong background in math and HOURS UPON HOURS of internet research on the various engines that others have built.

 

[cheekychimp]

At least you are honest about that and more than likely when you do actually build an engine it will turn out to be an absolute stonker!

I was just thinking actually. If you did go to the trouble of sleeving the G4CS block and using a much better cylinder wall material as Toybreaker suggested; I wonder if there is enough room to make the sleeves thick enough that you could rebore to 87mm at a later stage and build the 2.1 litre super long rod anyway?

 

[belize1334]

I was actually unable to get a straight answer on this when I was talking to the machinist. Once a block has been sleeved, how big can it be bored before the sleeves become too brittle to hold-up. What is the minimum wall thickness for the sleeve itself. Perhaps the block could be bored to 87mm and then a sleeve inserted which would subsequently be bored down to 85mm giving a 1mm wall thickness. Then if you decided you didn't like it the sleeve could be pulled leaving you with an 87mm bore block. Would the sleeve be happy with that thin a wall? What about 2mm wall thickness. Would the block be happy at 88mm bore? That's 0.060 overbore for G4CS which is 0.120 overbore for a 4g63... seems a bit thin between the cylinders... I just don't know about that...

 

[misterfixit]

I doubt you could pull the sleeve without trashing the bore it was in. Manufacturers will generally offer up to 1mm over on dia (mitsu offer 0.25/0.50/0.75 and 1.00 over). For the motorcycle industry its also common for the aftermarket to offer these sizes and additionally +1.5m and +2mm. In the car world i'd assume this is the case but i'll do some digging to confirm. Assuming the G4cs block is the same length as a 4g63 and tha water cavities are the same id say we could happily over bore a 4g63 block to take g4cs pistons.

Didn't the later spacewagons come with a 4g64 sohc 16v motor?

As for the stability of the pistons in the bore. this has lots to do with the size and area of the skirt, and also with the piston pin offset.

I do not understand the issue with not wanting to use wiseco forged pistons I have one in two of my dirt bikes and they are fine. If the piston pin is offset in the correct direction and the skirt is adequate as long as the hone on the bore is correct there should be no issue. The hiootter turbo engine is supposed to run with more clearance to the piston so youdon't get sticking on the skirt.

But the material in the forged piston is more homogenious with a much better grain structure. A cast piston will be more porous and less well controlled material wise. Also you have to make sure the correct rings are used (hi chrome for running with cast iron bores) and visa versa for plated but life should be simple with these engines no funky platings to deal with.

I think there can be alot of variability between machine shops and machine house quality. The bore is only going to perform as well as it was made.

On the sleeving answer no one can really know except the guy who drew it as to how much safety factor was built into the wall thicknesses. but if the cores used to cast it are the same from 4g64 to 4g63 then we can safely go 1mm over the 4g64 standard size.

Rich

 

[Romanova]

Paul, didn't you have a FFWD motor... what happened to it?

 

[cheekychimp]

It's in the other car. I bought another VR4 and I want to do something a little less hardcore this time.

 

[mountaineerjeff]

ok, so i really didnt want to let this info out, purely because im selfish.

this is what i had planned for my mirage turbo.

if you take a 4g61 crank, and a 4g63 block, long rods, and evo pistons.

You now have a motor with very low overhead. and a red line that that could never be reached. i full built drag head would still top out before the bottom end.

I thought of this because of its application in the mirage. it was being built to run down turbo supras.

now this motor would have a displacement of 1.7 and a rod ratio of 2.1 much higher than any other combos.

the fun part is this can even be taken a step farther and applied to a 4g64 block upping your displacement to 1.8 (maybe 1.9 havent done the math recently) and give you an even higher ratio, and the longest rods possible if used with a higher pin height piston.

I just personally didnt think the extra displacement, or rod ratio was actually needed.

so there the cat is out of the bag. the easiest way to build a motor that will rev to 12000+ for way cheaper than anything else.

 

[cheekychimp]

Jeff,

I really appreciate this info, but how do you think this engine will effect the bottom end response. I imagine a 1.7 in a full weight VR4 might be a bit sluggish but going the 4G64 route with the 75mm crank if it really is a 1.9 might be an option with some higher compression pistons. have you done much research into this yet?

Paul.

 

[mountaineerjeff]

yea ive looked into it pretty hardcore, I was really trying to keep it on the DL but im in the process of selling the mirage, and plan on a bit of a different route with the vr4

alot of slowboys tests dont even show a loss of torque when going to a higher rod ratio. so the torque difference would be less than the difference between a factory 2.4 and 2.0. if you wanted to go to the 2.4 block then you would probably have to get custom pistons at which you could increase the power and CR. but from how i read it seems like to get what you really want you should do the evo pistons in a 63 block. that away you only have to by rods, which you might be able to get used. instead of pistons and rods done custom. and yea you probably will suffer a little down low. but these are gonna be compared to a built 2.0 or a built 2.4 not a stock one. I beleive that when done you will still have much more than stock which is plenty, taking into consideration youre looking into top end. there are give and takes with anything, but what im saying is the loss will still leave you with more eft over than most setups start with

 

[AWDnoobie]

Im not sure if im going to add info that would be usefull, but ill give it a try. Has anyone thought of using a a head from a Hyundai sonata dohc 92 to 96 i think. If im right it has a 1g intake, 2g runners and smaller combustion chamber. Im not sure how well it would work for a long rod stroker, but in my theory it could help for flow and top end.

If my info is bad flame away

 

[mountaineerjeff]

this info is not wrong, just slightly off topic. head choice can will and has been argued about forever, we're simply talking about bottom end

 

[turboaddict]

all of this is great in theory but it is alot of work for just running a 16g. in my mirage I am dropping boost from 35psi to 25psi beginning at 6500 and 10psi of boost lost by anything north of 7000rpm. Also please don't mess with the amg manifold if you are going to run an evo3/2g head just use the evo3 intake manifold(and for god sake sell the amg to me. also you are going to loose some bottom end with the longer rod. (if I under stand your setup of stock pistons, and aftermarket rods) the reason is the rod angle with the longer rod is not as great and thus torque goes down. this is how you can rev higher; to regain this people were going with the 92-94mm crank to overcome the loss and then some.

Again I am not trying to piss on your campfire but a stock 2.0 will be perfectly fine with what you are trying to accomplish and last for a long time. (it seems that you are trying to hard. or just think too much about what could be (as most of us do). I myself dream of a 4g61t with 11-1 compression on E85 for power and mpg's.

 

[turboaddict]

another thing, there is a big point of diminishing returns on rod-to-stroke, the 4g61 is a a 75mm stroke and a 150mm rod this is 2 to 1 and anything beyond this is a waste of time. Also for reference my jdm 4g61t in my mirage pulled like a freight train to my limiter of 8800.

 

[mountaineerjeff]

yes there is a point where we will not we the gains of a higher ratio. however that point is above 2.0:1 the point in going to the 2.0 block is to allow a larger bore, along with a common piston. the 2.1:1 ratio that is then achieved is still not 'too high'