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HondaHunter
 Post subject: 4g15 Pistons
PostPosted: Mon Apr 28, 2003 12:28 am 
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do all years of 4g15's have the same CR or did a certain year have a higher CR than the others?

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xlr8
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PostPosted: Mon Apr 28, 2003 8:54 pm 
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I have seen 2 types of piston for the 4G15. The dished items from the EFI 8v and 12v engines and the flat-top pistons that the carby engine (and perhaps what the 4G15-16v uses as they are 'eyebrowed' for a 16v).
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socrateez
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PostPosted: Sun May 11, 2003 5:57 pm 
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yeah, ive seen 9.2:1 and 9.5:1 ratios listed for different years in shop manuals

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xlr8
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PostPosted: Sun May 11, 2003 9:11 pm 
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No, that's not what Im saying. The EFI pistons must be dished because the combustion chamber of the EFI head (eg 8v) is alot smaller (kidney shaped) than the combustion chamber of the carby head which is hemispherical. The 2 motors in fact have the same static CR. Combining the flat-top carby pistons and the EFI head gives a much larger CR increase than 9.5:1, more like 10.5:1.
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socrateez
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PostPosted: Mon May 12, 2003 6:26 am 
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possible upgrade? Or do you think the compression ratio would be to high?

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04' Olds Alero
91' Colt GL hatchback
4g15 12valve 5spd.
4g37 TB, MAF & Injectors. 4g37 ECU
Ported & polished & custom CAI w/K&N filter
5* Cam retard, 7*Ignition advance
2-1/4" catback w/flowmaster muffler
89 GT brake and suspension swap
Lots of little s#@t
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xlr8
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PostPosted: Mon May 12, 2003 8:28 pm 
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This is no 'theory'. The first motor I ever built used the exact same setup Ive been talking about (4G15 carb block, 8v EFI head). Lets just say that I broke a number of KM162 transmissions with that setup... :( :twisted:

Before that I had the original motor fitted with a Weber 32/36 DGV carby with a ported and matched intake & 2" exhaust. The induction noise was great! :)
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socrateez
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PostPosted: Tue May 13, 2003 6:28 am 
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what about 12 valve head?

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04' Olds Alero
91' Colt GL hatchback
4g15 12valve 5spd.
4g37 TB, MAF & Injectors. 4g37 ECU
Ported & polished & custom CAI w/K&N filter
5* Cam retard, 7*Ignition advance
2-1/4" catback w/flowmaster muffler
89 GT brake and suspension swap
Lots of little s#@t
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HondaHunter
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PostPosted: Tue May 13, 2003 5:16 pm 
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xlr8 will the rpw 12v head header fit onto the 8v head?

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I live my life 1 repair at a time.
Nothing matters...not my crew...my bills, nor my friends drama...
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socrateez
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PostPosted: Tue May 13, 2003 7:15 pm 
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good question honda hunter. I know the bolt pattern is the same. The 12 valve head has big rectangular ports while the 8 valve has small round ports.

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04' Olds Alero
91' Colt GL hatchback
4g15 12valve 5spd.
4g37 TB, MAF & Injectors. 4g37 ECU
Ported & polished & custom CAI w/K&N filter
5* Cam retard, 7*Ignition advance
2-1/4" catback w/flowmaster muffler
89 GT brake and suspension swap
Lots of little s#@t
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xlr8
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PostPosted: Wed May 14, 2003 11:26 pm 
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Im pretty sure that the exhaust ports are the same from 12v to 8v, it is only the inlet ports that are different though you may be right as Im not sure. Dont confuse the 8v carby head with the 8v EFI head. The EFI head has much larger ports than the tiny carb head (and completely different combustion chambers).

I cant be certain that you could use the flat-top pistons with the 12v head as I have never tested the valve-piston clearances. I dont like the 12v head in any case as a 8v head gives a much broader torque spread across the rev range. IMO the 1468cc of the 4G15 simply hasn't got enough capacity to properly take advantage of the extra breathing of an extra inlet valve. The resulting slower charge velocity does not effectively fill the cylinder resulting in poor burn efficiency and less torque.

[start rant]
Consider the marketing of the engine, noone nowadays would buy a new car that isn't "multivalve". The customer might not know what it means but they know they have to have it. Marketing scum know this and demand the engineers produce "multivalve" engines on all models no matter how effective or ineffective it might be just to promote better sales.
[end rant] :)
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HondaHunter
 Post subject:
PostPosted: Thu May 15, 2003 12:44 am 
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Quote:
Dont confuse the 8v carby head with the 8v EFI head. The EFI head has much larger ports than the tiny carb head (and completely different combustion chambers).

lol dont worry i wasnt...so 4g15 head, g15 bottom end, rpw street cams, porting, 1.8TB, RWP header, 2.5in exhaust should bring the 1.5L to about what say ~140-160?

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Nothing matters...not my crew...my bills, nor my friends drama...
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xlr8
 Post subject:
PostPosted: Thu May 15, 2003 3:55 am 
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I think more like 120-140 with those mods with the addition of a standalone ECU. Although ultimately in this case we are more interested in what torque you are getting and how flat the curve is throughout the rev range. A 2" mandrel exhaust is more than enough as the torque response relies heavilly on exhaust back pressure in a NA engine.

If you want more you would have to look at a quad/twin-throttle manifold and go for a wilder cam (at the expense of bottom end). A 2" mandrel exhaust is still sufficient. After all, we are only talking about a long stroke 1.5L here. :wink:
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socrateez
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PostPosted: Thu May 15, 2003 6:40 pm 
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I know what you mean about the 12 v head lacking torque. Ive basically tuned mine to take advantage of the hp. Mainly 3500-6000 rpm seems to be the sweet spot. This aint no drag racer but on the highway itll eat a lot cars up. If i tune it for the best low end torque. top end suffers dramatically.

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04' Olds Alero
91' Colt GL hatchback
4g15 12valve 5spd.
4g37 TB, MAF & Injectors. 4g37 ECU
Ported & polished & custom CAI w/K&N filter
5* Cam retard, 7*Ignition advance
2-1/4" catback w/flowmaster muffler
89 GT brake and suspension swap
Lots of little s#@t
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socrateez
 Post subject:
PostPosted: Thu May 15, 2003 6:45 pm 
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Got in a 90 galant gs at work. engine smokes. I'm going to see what my boss wants for it. 4g63! Nice rebuilder project for the colt. Its hard to find these engines in salvage yards that havent eaten the valves. All the good ones are already sold before theyre out of the car. Plenty of other parts for them though. :D

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http://members.cardomain.com/socrateez
04' Olds Alero
91' Colt GL hatchback
4g15 12valve 5spd.
4g37 TB, MAF & Injectors. 4g37 ECU
Ported & polished & custom CAI w/K&N filter
5* Cam retard, 7*Ignition advance
2-1/4" catback w/flowmaster muffler
89 GT brake and suspension swap
Lots of little s#@t
Top
   
Reply with quote  
socrateez
 Post subject:
PostPosted: Thu May 15, 2003 6:48 pm 
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Quote:
Im pretty sure that the exhaust ports are the same from 12v to 8v, it is only the inlet ports that are different though you may be right as Im not sure. Dont confuse the 8v carby head with the 8v EFI head. The EFI head has much larger ports than the tiny carb head (and completely different combustion chambers).

I cant be certain that you could use the flat-top pistons with the 12v head as I have never tested the valve-piston clearances. I dont like the 12v head in any case as a 8v head gives a much broader torque spread across the rev range. IMO the 1468cc of the 4G15 simply hasn't got enough capacity to properly take advantage of the extra breathing of an extra inlet valve. The resulting slower charge velocity does not effectively fill the cylinder resulting in poor burn efficiency and less torque.

[start rant]
Consider the marketing of the engine, noone nowadays would buy a new car that isn't "multivalve". The customer might not know what it means but they know they have to have it. Marketing scum know this and demand the engineers produce "multivalve" engines on all models no matter how effective or ineffective it might be just to promote better sales.
[end rant] :)
What would be a realistic expectation for the 8 valve carb engines output after similar mods?

_________________
http://members.cardomain.com/socrateez
04' Olds Alero
91' Colt GL hatchback
4g15 12valve 5spd.
4g37 TB, MAF & Injectors. 4g37 ECU
Ported & polished & custom CAI w/K&N filter
5* Cam retard, 7*Ignition advance
2-1/4" catback w/flowmaster muffler
89 GT brake and suspension swap
Lots of little s#@t
Top
   
Reply with quote  
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