4g93 / 4g94 Frankenstein info - high rpm capability? maybe!

[unclepaulie]

Im not sure if this info is out there on the internet collated but i did some researching and number crunching:




so essentially swap a 93 crank into a 94 with custom rods: 1.76 rod ratio. not bad when you compare that to a Honda K20a engine.

if you're building a cammed 4g93 for a NA (or even turbo build) with aftermarket rods (or rods & pistons): hypothetically: use a 4g94 block, and longer than standard rods with a 4g93 crank and you end up with a motor which will want to rev more, and be more efficient down low.

now this is to suit an otherwise standard motor. essentially i was trying to make a SOHC 93 rev more with minimal outlay...cam, head clean up etc....





what is rod ratio?
tl;dr bigger number the better. bigger number the more the engine will be 'revvy'. Motorbikes and F1 engines are 2.0:1 and more.
read more here too

Can i use a 4g92M head? yeah sure. go for it. same issues as fitting a 4G92M head to a stock 94 block, but this bottom end might actually handle the RPM. search that yourself.



this is probably useless info? maybe? i dunno. maybe someone will decide to slap one together and send it.

 

[SDate42]

I’m at work, so no figures, just thoughts.

compression ratio might be well wrong for anything other than boost.

and the stroke to bore ratio is still not brilliant at the end of the day - way better than the 94 for sure.

where would you pickup custom rods from? Whats the length on a 63 rod 69 rod or even k20 rods?

 

[unclepaulie]

I’m at work, so no figures, just thoughts.

compression ratio might be well wrong for anything other than boost.

and the stroke to bore ratio is still not brilliant at the end of the day - way better than the 94 for sure.

where would you pickup custom rods from? Whats the length on a 63 rod 69 rod or even k20 rods?

oh yeah, fudge, thats a good point about the CR! so:

4g93: 9.0:1
4g94: 9.5:1
4g94 destroked w/ 93 crank: 8.87:1

so yeah boost definitely. or back to needing some type of domed top piston to bump it up for NA spec. there is a GDI spec 4g94 engine (factory 11.0:1 comp) that might have the right pistons for this. checking that out now.




could always over bore it a pinch? I guess? wouldnt be bad seeing that new pistons are needed.... But more work mean more $$$$ and then you figure: why not just go for an entirely different motor.



Any rod manufacturer should be able to make them. As they’re still 4G93/94 rod dimensions, just longer....there’s Chinese ‘forged’ I beam rods on

 

[donki]

Posting to follow with interest.

Overbore or oversquare is a good general rule of thumb - my audi's BxS is 84.5x89.0 (10:1) and has a supercharger on it at 14si, but it is also a very modern engine with direct injection etc etc etc etc.

For info, the biggest issue IMO with the g9x engines is the crank rod end's. High torque and high RPM tend to turn the bearing into pixie dust, so custom rods, solid caps and end bolts will solve some of that drama

 

[donki]

I'm also 85% sure some version of the 4AGE or something has aftermarket support for a perfect aftermarket piston if you bore/clean up the g9x block, and i'm slightly less sure that the CA18 or CA20 has the same rod specs..

 

[SDate42]

Also a pro for the crank swap, you can get forged higher or lower CR pistons, so you could head into the 7's for CR if you wanted or closer to 10 if youre staying NA. Lower CR will net you a more gentle peak cylinder pressure peak. Boost will compensate then for the lack of pressure.

You should end up with a very stable, strong, "high reving", 4G9x.
Would need a fairly large turbo and wastegate to make full use of this.

Posting to follow with interest.

Overbore or oversquare is a good general rule of thumb - my audi's BxS is 84.5x89.0 (10:1) and has a supercharger on it at 14si, but it is also a very modern engine with direct injection etc etc etc etc.

For info, the biggest issue IMO with the g9x engines is the crank rod end's. High torque and high RPM tend to turn the bearing into pixie dust, so custom rods, solid caps and end bolts will solve some of that drama

Reducing the spike in peak cylinder pressure will help the bottom end too. You'd be a fool to skimp on studs/bolts in the bottom while changing rods and pistons - but I'd be very curious to see how long stock gear would last on a setup like this

 

[unclepaulie]

Posting to follow with interest.

Overbore or oversquare is a good general rule of thumb - my audi's BxS is 84.5x89.0 (10:1) and has a supercharger on it at 14si, but it is also a very modern engine with direct injection etc etc etc etc.

For info, the biggest issue IMO with the g9x engines is the crank rod end's. High torque and high RPM tend to turn the bearing into pixie dust, so custom rods, solid caps and end bolts will solve some of that drama

thats why i compared it to the K20A which is kinda baseline for a modern, powerful, tunable, NA engine.

new hardware with the new rods and bearing would be a must, and probably head studs too if boosting it. would need to check out the crank see how that would hold up

Also a pro for the crank swap, you can get forged higher or lower CR pistons, so you could head into the 7's for CR if you wanted or closer to 10 if youre staying NA. Lower CR will net you a more gentle peak cylinder pressure peak. Boost will compensate then for the lack of pressure.

You should end up with a very stable, strong, "high reving", 4G9x.
Would need a fairly large turbo and wastegate to make full use of this.


Reducing the spike in peak cylinder pressure will help the bottom end too. You'd be a fool to skimp on studs/bolts in the bottom while changing rods and pistons - but I'd be very curious to see how long stock gear would last on a setup like this

8.87:1 comp isnt too bad in modern terms for a boosted engine, specially with the now new beefy rods in it....i'd be learning toward 12:1 for NA with E85.

strong and stable is the key take away. sure you rev a stock 93 or 94 to say 8ish/9ish rpm....but for how long. maybe this motor would go beyond that 9500rpm? i dont know. guess thats the exercise here.


i think the recipe would be:

4g93 head, ported to all heck
decently wild cam
4g94 block
4g94 pistons (open to swap to something else mentioned)
custom length rods (156.4mm)
all new bearing and ARP bolts, headstuds

the only problem with spinning this hypothetical engine to such high rpm is things like oiling, and clutch engagement, harmonics.... its really opening a deep worm hole of engine building...and an engine builder i am not haha

 

[DrB]

I'm building pretty much this exact setup, 92 mivec head, 93 crank in 94 block.

In regards to high rpm issues on the 93 I've spun it to close to 9k and the issue is valve train stability, valves bounced and shifted all the inlet valve seats.

 

[unclepaulie]

I'm building pretty much this exact setup, 92 mivec head, 93 crank in 94 block.

In regards to high rpm issues on the 93 I've spun it to close to 9k and the issue is valve train stability, valves bounced and shifted all the inlet valve seats.

ohhh this is awesome news! Please share anything you can / want to. I’d love to know more, just to absorb knowledge.

 

[DrB]

i was looking at using the 4g63 long rods, they are 156mm, which should get me in the ballpark.

 

[unclepaulie]

i was looking at using the 4g63 long rods, they are 156mm, which should get me in the ballpark.

yo @DrB any updates?

 

[Stancer]

I'm building pretty much this exact setup, 92 mivec head, 93 crank in 94 block.

In regards to high rpm issues on the 93 I've spun it to close to 9k and the issue is valve train stability, valves bounced and shifted all the inlet valve seats.

Also interested as I'm about to join a similar endeavour!