4g61t.org

QUESTION


a stage 2 or 3 cam the 10.5:1 cr would give me enough clearence between valves and pistons?

the 12v engine has already 10.5:1 cr right?

and If I install the 12v head in my 8v engine, would have a problem?

i know I can do that, I saw the head gasket and I didnt find difference

_________________
Stock Sucks...!!
Mods List:

Custom cold air intake
Iridium Sparks
NGK sparks plugs wires
2" exhaust and moffler
ACCEL Coil
240cc inyectors
52mm TB
K&N filter
Elantra BRAKES ( upgrade )
195/50 R15
2.5" lowering springs
Ate. brake Fluid

QUESTION:

Why the hell did you repost so many times? lol

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91 Colt Hatch
4g15 12V 5-Speed
Getting parts for 63t swap.

Fixed.

I was wondering why the posts were disappearing as I was trying to delete them too. Flying Eagle you were obviously quicker on the draw!

OT: I beleive the 12v motor has the same 9.2:1 CR that the 8v engines have. However the 12v motors already have flat-top pistons which is compensated by the fact that the 12v head has larger combustion chambers which brings the CR back down again.

The only stock parts combo that provides the 10.5:1 CR is the X1 flat-top eye-browed pistons with the EFI 8v 4G15 head that has the kidney shaped combustion chambers. If we're talking Hyundai engine codes that means you want a G4AJ block and G4DJ head.

i was thinking, is these 12v pistons:

http://www.b2b-piston.com/auto-piston/ajmitsu-081.htm

and these for a 8v:

http://www.b2b-piston.com/auto-piston/ajmitsu-307.htm

allmost same specs, if i get those pistons as upper shown, would i rise my CR?

correct me if i?m wrong.

EDIT

what are these :

http://www.b2b-piston.com/auto-piston/ajmitsu-119.htm

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**Hyundai performance**

ok

xrl8 thanks, but how can I make 10.5:1 cr with a 12v head?




the 12v engine has 10hps more than 8v engine right? just because of the 12 v.?

should I keep the 8v head?

_________________
Stock Sucks...!!
Mods List:

Custom cold air intake
Iridium Sparks
NGK sparks plugs wires
2" exhaust and moffler
ACCEL Coil
240cc inyectors
52mm TB
K&N filter
Elantra BRAKES ( upgrade )
195/50 R15
2.5" lowering springs
Ate. brake Fluid

To get a decent increase in CR with the 12v head I think you would need a slightly domed piston. For example the stock 4G67 (1.8L) pistons in my Lantra are domed to make up for the lack of piston diameter (compared to a 4G63) but which is also somewhat offset by the slightly smaller combustion chambers of the "1.6L" marked heads.

I'd guess you would need to use a customised/modified piston from another engine that shared similar specs to the 4G15. There are however alot of factors that must be considered in selecting a suitable piston eg. wrist pin type and size, compression height, skirt length etc. A task best left to an expert engine builder IMO.

I'd say your best bet would be to contact RPW since they are the only people I know of that bother with serious mods to the 4G15 8v, 12v, 16v motors. RPW customised a set of aftermarket hyper-eutectic pistons for my 4G61T motor which gave me flat-top pistons. Check my avatar.

As for keeping the 8v head - that is certainly a consideration. I had a balanced 4G15 bottom end, X1 pistons with a professionally ported 8v head, deshrouded valves and ported/matched inlet manifold and that setup was an awesome IMO (for a 1.5L at least ). It's not like 8v heads cant be worked even more with larger valves and such. Plus, while the 12v heads may have a little more peak power the 8v heads give better mid-range torque which with these motors is more usable given their under-square geometry means they will never be a hi reving motor.

do have an idea of gains you got?

or timeslip?

best bet is work with the 8v head, i guess.

_________________
Stock Sucks...!!
Mods List:

Custom cold air intake
Iridium Sparks
NGK sparks plugs wires
2" exhaust and moffler
ACCEL Coil
240cc inyectors
52mm TB
K&N filter
Elantra BRAKES ( upgrade )
195/50 R15
2.5" lowering springs
Ate. brake Fluid

Heh, no I didn't have cash for things like dyno tunes back then and to be honest I couldn't keep the stock KM162 gearbox in one piece long enough to risk taking it to the drags. I broke 2nd gear twice and 3rd gear once as well as couple of shift rails and a finger control - that gives you a little bit of an idea what a 10.5:1 8v motor's torque is like.

Let's just say that it certainly gave the 5.slow brigade a run for their money.

sorry i didnt get the last part....


anyways, if I change the head for a 12v, should I replace the ecu?

I guess that for a race car, i need more peak power than mid-range power, right?

i really want more power, i will start to think and research how can I get a 10.5:1 with a 12v.


could I just reduce the height of the head to get the 10.5:1 ? i dont know the correct word for that.

is there something like standars to get some specific CR reducing the height?

_________________
Stock Sucks...!!
Mods List:

Custom cold air intake
Iridium Sparks
NGK sparks plugs wires
2" exhaust and moffler
ACCEL Coil
240cc inyectors
52mm TB
K&N filter
Elantra BRAKES ( upgrade )
195/50 R15
2.5" lowering springs
Ate. brake Fluid

You can shave the head which will increase compression - but only marginally. You cant go too far other wise you will have problems with the valves hitting the pistons. Plus then your cam timing goes out which may or may not need to be corrected.

If you are setting up for purely track racing then there may be a slight advantage going with the 12v head. If you going for autocross/spirited street driving then the 8v would be my choice for its superior midrange.

I think the 12v ECU would be unnecessary with a head swap but probably desirable.

oright, thank you, my goal is to have the car for a race use only, at least for 1 or 2 years.

12v head would be better.

if I shave the head as much of heights difference between the stock 8v pistons and x1 excel pistons, would I get a 10.5:1 cr with the 12v head?

i have never mesured, but i guess is like 1mm right?

or can anyone can give me an idea, which pistons should i try to get 10.5:1 cr in the 12v head?

thanks for all the help, xrl8

_________________
Stock Sucks...!!
Mods List:

Custom cold air intake
Iridium Sparks
NGK sparks plugs wires
2" exhaust and moffler
ACCEL Coil
240cc inyectors
52mm TB
K&N filter
Elantra BRAKES ( upgrade )
195/50 R15
2.5" lowering springs
Ate. brake Fluid

If you add some 1mm oversize pistons to that equation you might see a CR of 9.5:1 but it wont be anywhere near 10.5:1. The combustion chambers of the 8v EFI heads are ALOT smaller than the hemispherical chambers of the 8v carb'd heads which is the reason the CR goes up so much when you use the X1 pistons.

Shaving the head, larger pistons etc only has a small effect since you are only skirting around the edges. The key to large CR changes is the piston/combustion chamber combo. Make a significant change in either of those and you will see large gains. It's easy to go down in compression via use of a thicker headgsket but going up is always difficult.

ok.. but i didnt want to mean oversize pistons, i tried to mean, shave the head 1mm for example....

to raise the CR. instead start to look for a custom 10.5:1 pistons in the 12v head.


there is no other 1.5L 12v engine with a higher compresion pistons?


sorry for all the questions, but i have planned to modify my engine, like 1 and a half month from today.

_________________
Stock Sucks...!!
Mods List:

Custom cold air intake
Iridium Sparks
NGK sparks plugs wires
2" exhaust and moffler
ACCEL Coil
240cc inyectors
52mm TB
K&N filter
Elantra BRAKES ( upgrade )
195/50 R15
2.5" lowering springs
Ate. brake Fluid

I dont think the head will take a 1mm or 40thou shave. Mr Piston would be introduced to Mr Valve at or before that point me thinks!

Your only choice in trying to attain a significantly higher compression is to get some custom pistons.