6A12/13 - To forge or not to forge?

spetz · Post by **spetz** » Thu Dec 22, 2011 9:46 am

Hi guys,

I really am tempted to undertake this project, so much so that I feel it is just a matter of time before I at least attempt to build this engine. I expect that I will start in about a year.
This is of course subject to "possibility". And I have 2 options.
1. Use 6A13TT rods, cryo, shot peen, ARP rod bolts etc, and use 4G92 MIVEC pistons (assuming they work) and have a "OEM bottom end" and save the money for other mods and hope to make impressive NA power for an essentially standard bottom end.
2. Go forged bottom end, possibly may be complete overkill and unnecessary. May not give much of an improvement besides a slightly higher compression ratio and the power figures may be disappointing for a "forged bottom end" application.

Please give your thoughts and reasons behind. I like the idea of option 1 (it seems to be big in the Honda community, to make big power on OEM bottom ends) however forged rods/pistons these days are not so expensive, and it would be horrible to build the engine only to blow it up from a bent con rod or something.

From the research I have done though, it seems the OEM bottom end should be fine to spin to the current FTO rev cut.

BearOnFire · Post by **BearOnFire** » Thu Dec 22, 2011 9:24 pm

Not to forge. Variable valve timing engine generally have very strong internals.
What kind power estimate you reaching for?

spetz · Post by **spetz** » Thu Dec 22, 2011 11:49 pm

Well the idea is to get it together using just stock parts (heads, intake, headers, cams etc), so power will be pretty low initially as because of the extra 500cc peak power would probably be under 7,000rpm , but it will have more torque everywhere.
And then modify it in stages. The power output will mostly depend on the cams used which will depend on the internals. Obviously if OEM internals are used then the standard FTO rev limit of about 8,200rpm will be used and I would get cams which would give peak power around 7,800rpm so the power will not be huge.
If forged internals are used I would get cams to make peak power around 8,800rpm so I would hope for at least about 180-190 front wheel kw.

According to my calculations, if the engine can make 250nm of torque at 7,000rpm, and 230nm at 8,000rpm (assuming this is peak power rpm) then it should make 260hp at the flywheel.
Of course, on the other scale, if it makes 250nm @ 8,500rpm that would equal almost 320hp at the flywheel.
So it is just speculation and it all depends on the parts used and how well they work together.

If I were able to start the project I would from today, but the problem is I am outside of Australia until October 2012

Post by **Bennoz** » Fri Dec 23, 2011 8:31 am

Nothing wrong with option 1, its the same type of combo I've used worked engines in the past. Old school motors with 12:1 comp ratio & filthy lumpy scatter cams, never bent a rod.

With option 2, have you checked the price of forgies lately? Cheap as chips. That full set of six rods & pistons my old man got for his Patrol only cost him $1400. Guy who made them up in QLD reckoned he could do the same price for a set for me.

My only question about the whole arrangement is, where are you going to find cams that give you peak power at 8,800rpm?? I've had mivec cams at grinders all over Sydney & everyone of them looked at them blankly, then gave them back to me & told me to buy an Evo.

If you do find someone that will put a grind on 4 billet sticks, the billets alone will cost ya 2 grand... and if you're gonna spend that kind of coin on cams, spend it on the bottom end.

spetz · Post by **spetz** » Fri Dec 23, 2011 10:02 am

Yes forged internals are very cheap these days that it seems stupid not to get them just for peace of mind. Considering I would still need new pistons (even if from Mitsubishi, I think they are $75 each) and shot peening, cryo'ing the rods, rod bolts etc, the difference between OEM bottom end and forged bottom end is becoming negligible.
That being said, in all reality the rev limit would probably be kept as stock (8,300rpm) and the forged bottom end would not give me any additional power.

It may sound silly but somehow doing it on an OEM bottom end is very appealing to my emotional side, but stupid to my logical side. I would like the result to be comparable, rather than overshadowed by K24/20 builds.

I had cams priced at $1,700 for billets by Tighe. Other places can copy them and I was thinking I would send them to the US for even better pricing.

I have been reading about the negatives of oil squirters under the pistons especially when used with forged pistons and thinking that if I go forged internals and use a 6A13 SOHC block which doesn't have the squirters the build may end up being cheaper still.

BearOnFire · Post by **BearOnFire** » Fri Dec 23, 2011 11:39 pm

http://www.cartuningtips.com/engine-tuning
Not opposing to the idea at all. Misubishi did what they could to find a balance for power and drivability. Many mechanic always suggested forced induction for healthy power increase for our engine,run the risk going backwards with serious NA tuning.
RPW 6a12 engine is a foundation to work on.

spetz · Post by **spetz** » Sat Dec 24, 2011 1:16 am

I think that article is way too general and surely does not hold truth to highly tuned engines like MIVEC motors.

It is easy to go backwards in NA tuning, but don't forget there is an additional 500cc in the 6A13 which will boost torque substantially

4G9XRR · Post by **4G9XRR** » Sat Mar 03, 2012 9:29 am

Do buttom end. At least new stock rods. Oem mitsu rods used specially with high ks are proned to rod stretch, resulting on positive deck height (piston stick out of block).

If mivec 4g92 pistons fit probably better buy b16b pistons. Only mod that will is to reduce the size of piston skirt and increase diamter of small end rod bush from 19 to 20mm. Cc of b16b piston is ideal for NA use very close to that from CP or Arias forged units.

Also you need to look at areas such as oil clearance (way too tight) to much grab and use the right oil to suit.

spetz · Post by **spetz** » Sun Mar 04, 2012 9:47 am

I wouldn't want to use Honda pistons in the motor, so it would either be forged/aftermarket, or parts from Mitsubishi so as to have a claim at "OEM bottom end".

The thing (as mentioned before) is that forged parts are so cheap these days that if I need to buy new Mitsubishi parts and/or get them modified, I would be better off spending that money towards forged rods.
For example, maybe a new Mitsubishi rod + cryo treating it + shot peening + crack testing etc would cost similar to a custom rod

4G9XRR · Post by **4G9XRR** » Mon Mar 05, 2012 12:53 pm

I agree but if budget is a limiting factor then using parts that are compatible will not harm the set up.

Yes forged is cheap but the fact that the chinese has flooded the market with diffrent types of rods, makes it hard to select doesnt it. Personally would get some aluminium rods from BME used them with all the engines I built, works a treat on both NA and FI set ups. Price is quite reasonable for custom too, less than a grand shipped to Australia.

spetz · Post by **spetz** » Tue Mar 06, 2012 8:26 am

It isn't so much that I think using Honda pistons would harm the setup, but rather I just would not be happy knowing there are Honda pistons in there. I know it sounds a bit stupid but considering the engine is MIVEC it is "competing" against VTEC YO!!!!! and resorting to using Honda pistons just does not seem like the right thing to do especially on a hybrid engine which possibly has never been built before.

With the rods, according to members of a VR4 forum, people achieve 400-450hp at all four wheels before rods let go, and have revved safely to 8,000rpm.
These are power figures which the engine will never get close to, but rpm figures would hopefully surpass 8,000rpm.

As for pistons, the 4G9X pistons are 81mm, with the same wrist pin diameter and in the DOHC 4G93 it revs to 7,500rpm with an 88mm stroke. The 6A13 only has a 80.8mm stroke so pistons speeds would be lower, and the R/S ratio is better as well which I think in theory means the 4G9X pistons should be strong enough. It would mostly be a matter of finding the ones with the correct CR

4G9XRR · Post by **4G9XRR** » Tue Mar 06, 2012 10:43 am

From what I have learnt from building engines theories are good but they are not always the same when laid in a practical point of view.

I know what you mean but like I said marely a suggestion considering budget is a main concern.

By the way if you get cp and wiseco to make you a piston the dome profile is extracted from the b16b and they modify the valve pockets to suit a tighter quench area. You can verify that with my pal in race engineering in the USA, buy plenty of CP pistons from him. Mr John Pimentel, email him more his a very helpful bloke when it comes to pistons etc..

Rods I can understand what you mean but all is an assumption with stock rods. Unless they are new I would not use them, considering they are cast rod stretch is a big factor I am sure you have seen a similar scenario in mivec.co.nz

spetz · Post by **spetz** » Wed Mar 07, 2012 8:36 am

If I were to do pistons, I would do rods as well. So it's a case of both or none.

This build, if it happens, is still at the very least a year+ away from even commencing and in that time I am not sure I will still have this enthusiasm for it.
Cars are getting so cheap these days that spending for example 10K on an engine when that money + the sale of the car could buy something like an Evo makes it hard to commit financially to such a project.

What motivates me though is that I really want to build an engine by myself, and this seems like a good step

4G9XRR · Post by **4G9XRR** » Wed Mar 07, 2012 11:08 am

Yes you can buy an evo or other exotic releases. But it is also a good achievement to build your own ride and constructing a diffrent weapon usually involves money.

Either way be a sheep or be diffrent.

Technikhaus · Post by **Technikhaus** » Wed Mar 07, 2012 4:27 pm

All in all though,
the FTO is better looking imo :p

spetz · Post by **spetz** » Thu Mar 08, 2012 8:00 am

To be honest I think the looks are questionable. The FTO looks good from the front but the rear half looks unbelievably horrible. Also it is much heavier.
And at the time I did the conversion FTOs cost 20+ k to buy so doing a 6A12 conversion was more cost feasible.

4G9XRR, I think that both arguments can be justified. You can say that doing something different is worth the effort/money, but you can also say that the best bang for buck solution is the way to go. Plus the end result is important, so a 6A12/13 Lancer may be fast, but it'll never be faster than an Evo with some mods.

By the way, what do you think the chances are of someone building this engine who has never built an engine before? Taking into account time is not a factor

4G9XRR · Post by **4G9XRR** » Thu Mar 08, 2012 8:38 am

From experience and witnessed this you can make any car as fast or faster than an evo.

If the evo did not have a turbo you would probably just keep up with it. The 4g63 is a mini me of the 4g93 twin cam both use hydrualic lifters and really sh*tty puny cams from factory. In saying that it runs a pretty high boost, I dont think its quite a good comparison personally.

This reminds me of an american joint back in the early 00's comparing a 20grand k20 swap conversion vs a stock evo 8. Lol

spetz · Post by **spetz** » Thu Mar 08, 2012 9:18 am

I agree that it wouldn't be "too" difficult to beat a stock Evo, but an Evo with some basic mods will be a different matter.
Taking into account the limitations of a FWD setup that is, as well as limitations of an NA setup.

Do you have any experience with the 6A12?

payaya · Post by **payaya** » Fri Mar 09, 2012 8:18 pm

Where are you getting these rev cut figures from? It's not 8200 rpm or 8300 rpm.

GR - 8250 rpm

GPX - 8500 rpm.

Taz · Post by **Taz** » Fri Mar 09, 2012 11:02 pm

dunno where your getting the 8500 from, driven a gpx and my gpr and neither have gone to 8500, cut off is pretty much bang on 8250, definitely no higher than 8300 - factory might say 8500 but it aint

FTO AUSTRALIA