20 valve compression question

[20 valve]

if im keepin my 20 valve aspirated but want to modify it , do u think it makes sense to go from 11:1 stock compression to maybe 12.5:1 ?

[Kwanza]

Originally posted by 20 valve
if im keepin my 20 valve aspirated but want to modify it , do u think it makes sense to go from 11:1 stock compression to maybe 12.5:1 ?

Not for a street car... You'll just detonate to death...

[thespud]

Increasing compression Ratio is not good... but I would say, that if you wanted to keep her Naturally Aspirated, you could always put on bigger cams, MWR Big bore kit, Larger (330cc) Low Impedance Injectors, and maybe even Stoke her to 1.8L (to become a 7A, essentially). I have even heard of people stroking the 4A's to 2.0L. Of course, If you wanted to stroke her, a port and polish would also be good.

[Kwanza]

Originally posted by thespud
Increasing compression Ratio is not good... but I would say, that if you wanted to keep her Naturally Aspirated, you could always put on bigger cams, MWR Big bore kit, Larger (330cc) Low Impedance Injectors, and maybe even Stoke her to 1.8L (to become a 7A, essentially). I have even heard of people stroking the 4A's to 2.0L. Of course, If you wanted to stroke her, a port and polish would also be good.

I personally wouldn't go the stroker route just because the possible torque gains won't make up for the possible horsepower loss. Oversquared motors don't rev well... and considering this is a 4AG 20V... it *needs* to rev.

Also, increasing compression is a good thing... but he just wants to much. I wouldn't go more than 12:0:1 on a street car simply because you'll be constantly fighting with detonation... but you guys overseas do have better octane fuel than we do in the US...

[thespud]

^^ But then the 7A-GE 20v Hybrids have more horses... stroking to 1.8L is EXACTLY the same as a 7A block.

And i meant that, raising the CR that much aint good.

[Kwanza]

Originally posted by thespud
^^ But then the 7A-GE 20v Hybrids have more horses... stroking to 1.8L is EXACTLY the same as a 7A block.

Not exactly... but I get what you mean. The 4A block is too small to use a stroker crank the same size as the 7A so it'll need to be modified. The 7A block has a taller deck than the 4A. Simply using the 7A bottom-end would work... but horsepower numbers aren't exactly staggering for 7AGE hybrids. Maybe like 10 hp more in the top end and a better torque curve... Most of the club4ag guys who have done 7AGE swaps and the ones I've driven don't have as good of top-end power as built 4AGs IMO... they just make a better torque band.

[Pineapple]

Can the 4A-GE be over bore to 1.8L or 1.7L? Maybe that'll be better then high CR.

[boroEF]

the stock cr is high enough as it is. if you are going to take off the head regardless, then just do valve jobs or something...and do your own P&P... and get a hold of some decent cams. maybe 262s or something.

[Kwanza]

Originally posted by Pineapple
Can the 4A-GE be over bore to 1.8L or 1.7L? Maybe that'll be better then high CR.

The 4A/7A blocks are too small to make such large bores. You might get away with 1mm or so... but you can't bore out those blocks a lot...

[Pineapple]

Hmmm could we use 4A crank with longer rod on 7A bottom to reduce stroke? The 7A won't rev because of longer stroke.

[Kwanza]

Originally posted by Pineapple
Hmmm could we use 4A crank with longer rod on 7A bottom to reduce stroke? The 7A won't rev because of longer stroke.

Then there will be no point. The stroke is what makes the displacement in the 7A block. It's not that the 7A won't rev... it's just no suited to rev. Unless you upgrade rods or something...