Mivec Owners Group

hi guys, just need ur opinion about this. i want to change my engine, just wanna to know if anyone can help me wif this..
if i got a 4g92 mivec head with a 4g94 block is it possible to match it. as there r from the same family.. anyone have done it b4??? or just match it with 4g93 block? it would be 1.8 mivec rite? and of course optional turbo kits are always available... anyone?
thank you

Yes it is possible i know of one that is going in malaysia

Unfortunatly the 94 is not a good motor performance wise, they max rev to 6500rpm, if you want to gain more power mod your 1.6 or do the 1.8 otherwise you will just be dissapointed, yes the 94 block will be a bolt on fit as its the same series engine

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CJ4A JDM RED MIRAGE RS RACE CAR

I dont know why people are so quick to jump on the 4g94. I know in factory trim they are a pretty plain jane motor. So are alot of factory motors. But factory standard motors arent what we're talking about. Lets compare apples with apples, Take a factory famed 4g63, in NA single cam form, 93kw and 139ft. (depending on spec). This is quite comparible to a 4g94 which has 92kw and 130ft.
With the 4g94 you have a solid iron block, simillar as a 63. Now with the ability to add a proper mivec head, some good aftermarket rods and pistons, a great rod/stroke ratio and even a turbo if you are that way inclined, you "could" be onto a winner.
Alot of peoples concerns with a mivec 4g94 is the long stroke and piston speed. Take alook at some of the stroked 4g63's, 100mm stroke is the norm for these. Yet they still rev them to a recommended 8k.
I think alot of the reason there aren't any/many hot 4g94's around is because if you decided to do up a 2.0 you would just go down the well walked path of the super 4g63.
Im never one to just say something is great or shit without some good proof. It could be cheaper to go down the 63 path if you were to do a 2.0, but whats the fun in doing the same old thing over and over again. Its cool to do something different, and hopefully pull it off.
Lets think outside the square, we're New Zealanders after all.

The problem is you will struggle to get a good rod/stroke ratio out of a 94, they redline at 6500 and they run factory forged pistons due to there terrible factory rod/stroke ratio, my na SOHC 4G63 galant daily redlines at 7500 due to the 4G63 having a really good rod to stroke ratio factory,

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CJ4A JDM RED MIRAGE RS RACE CAR

There is a pretty fast Colt/Mirage 4G94 Mivec in Jamaica which I've seen video footage of on Here or ColtUK. Class winning car on occasion and it's pretty good competition. I think his engine is heavily modified though.

The 4g63 does have a great rod/stroke ratio for sure. But there are maybe a few problems with what your saying. I would think the factory redline differences between the 63 and 94 have more to do with max piston speed due to the big stroke differences rather than the rod/stroke ratio differences. (btw they are 1.6 for the 94 and 1.7 for the 63.)

There are engines out there that have poorer r/s ratios but have a higher redlines. You and I both know a "built" 94 has no problem revving, and seem to be quite sucsessful and realiable.
For sure the 63 is a great motor. I dont think I'll ever see a 1000hp 94 mivec But like I siad before, who wants to do the same old thing over and over again?

what car are u driving sir???

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It's hard to make a life a life

All im saying is money and strength everything considered to build up a high power strong race mivec motor, you cant go past the 93, i had a mivec motor with a bad rod to stroke ratio and look what happened, you would have to heavily modify a 94 motor to get good power and reliability out of it and i personally dont think you will gain anymore power out of a 94 over a 93, the 94 you are talking about made 200hp and had a max rev of 7200, my 1800 made the same power and reved to 8000 easily but yes i understand what you are saying brad but the 93 is alot easier to get power out of, even the 1.6 for that matter

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CJ4A JDM RED MIRAGE RS RACE CAR

When its all said and done the 94 was not intended as a performance motor. You can modify anything heavily to make it go better, but at some stage you have to look at how much you are having to change and is that a good starting point afterall. Other motor options may have either achieved the same result with less expense and effort or for the same money acheived more.
A bore of 81.5mm and stroke 95.8mm is way out of sqaure, with such a small bore for a 2 litre you end up with a hugely long stroke, making for insane piston speeds and stress on internal components. No wonder they were apparently produced with forged rods from factory.
At 1.6 the rod ratio is surprisingly high for the 94 but lets bring the real numbers to the table and you can see that this only compounds the problem, the 94 has 152.9mm long rods. Thats 19.5mm longer than the 93 rods so you are adding mass in the length and suffering very high loads from the piston speeds produced by the extra 6.8mm stroke, which isnt ideal for a performance motor.
People will build what they like and providing they are happy then thats all the really matters on an individual case. But for me I would pick the 93 as the starting point for an N/A motor over the 94 as I believe the potential for better high rpm performance outweighs the small amount of extra displacement offered from the 94.
Agreed that the 4G63 is a super star motor too.

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96 Mirage RS

You guys need to look at what you're saying. You are contradicting yourselves. You are one one hand saying the 94 has a poor r/s ratio and it's one of the reasons you rate it poorly, then on the other hand praising the allmighty 4g93 which has, if you looked it up the worst r/s ratio of all, (less than 1.5)
And as for the piston speed thing, You'll find the "average" piston speeds of a 94 revving to 7600 is the same as a 93 revving to 8000. Not to mention again all of the 100mm stroker 4g63s out there revving to 8k+!!!
Oh, and you dont see the guys with super long stroker kits in their 4g63's and rb34's etc complaining, quite the oppisite.
As for costs involved in building a 93 compared to a 94. I cant see alot of differences really? A set of rods, pistons, arp's etc. All these costs would be much the same? Machine work, similar? Headwork, same?

Stroker 4G63 and RB34s are done with a billet steel crank - so lots of strength built in there, and necessarily shortened rod/piston assembly so less reciprocating mass. But 8000+ rpm on a modified bottom motor is not really that impressive when standard mivecs a red line at 8200 and modified motors run much higher, not to mention Honda engines etc

I do find all this talk of rod ratios amusing - its all just internet nonsense every engine is different and different engne builders have different thoughts on what is good.

As an former ford man the comparison with the Kent and BD series is obvious especially as they and the 4G9 series share a 81mm bore. The kent series and it BD derivatives all used 81mm bore and ran various capacities from 1000cc to 1600cc, all these were achieved with variations in stroke just as with the 4G9 series. Almost every capacity has been used in competition and highly developed with engines producing in excess of 100bhp/L from a 8 valve, which is good now but was really excellent back then. The 16v BD derivatives raised the game even further, with 150bhp/L from some race motors, all these were achieved by variences in stroke not bore, sure the short stroke 1100s etc rev higher than the 1600s but even those produce good power at high revs. People overbore the 1600 to get 1760 which again does good power but the only sucessful stroker I am aware of were built by ford for the 1972 London-Meixco World cup rallies, these were bored and stroked 8 valve engines, to 1840 if memory serves, producing a measily 140bhp but designed to run on the worst of fuels from around the world and at altitude (on carbs remember) without preignition or detonation problems. Ultimately a thicker wall alloy block was used to get 2000cc BDG (and overbores) and even 2.1 in BDTE form, all done by boring though. Between them these engines show that rod ratios are if not complete bunk then at best only a small part of the story. As with all engine tuning a holistic approach is required.

With the money ford were spending on motorsport in the 70s I am certain longer stroke engines will have been tried but the fact that they did not use them speaks volumes I would say.

I'm interested in building a 4G93 Mivec, hopefully there'll be an nice increase in low down torque as well as peak power, but personally I think a 4G94 will be pushing things too far and will ultimately require a billet or forged crank as well as uprated rods and more than likely custon cams to make it work. The capital outlay just doesn't seem worth while to me. The standard mivec cams make peak power well above the rev limt of a standard 4G94, and even forged items aren't indestructable they just raise te limits a bit.

Will for a start not all 63 strokers have billet cranks. Alot of stroker anythings borrow cranks from the same family of motor to get a bigger stroke. Also these stroker motors are up there, some winning their classes.
I know that mivecs like to rev hard, but thats not everything. The guy from jamaca proves that with his engine thats got pretty much the same power as camerons 20k motor, and he dosen't rev it as hard and he does'nt have the fancy quads either.
To dismiss the r/s ratio as an important factor is ignorant. I know alot of people will argue the perfect number for sure. but it is still a very important part of choosing a base motor.
Im building up a 94 with turbo, built internals, and standard cams for now. Im not going to be revving to the moon (a benifit of the turbo) my piston speeds and rotating mass forces will be down due to this, I got my 2 liter capacity and i got a better r/s ratio than a 93.
Everyones got a different opinion of whats good. Some people like imports some like v8's. Thats cool.
I'll see you at the strip or track or whatever having fun (oneday:)). Thats why we do this isnt it?

I agree with what you are saying about the stroker cranks there Spuds. There is no comparison to a factory crank. Unfortunately there are also plenty of examples with guys using the larger stroke factory cranks for a purpose that it wasnt intended for and breaking the crank.
It's also noteworthy as you say that the highest capacity the ford motors ran at 81mm bore was 1600. Thats something like the 77.5mm 4g92 stroke. The old 92 probably started its design process looking at successful models.
Ford certainly didnt feel that strokes heading out to any length to achieve capacity was the best move.
I wouldnt agree that the rod ratio is complete junk I'm sure there was consideration given when Ford was designing the engines. Either to modify the rod length, gudgeon pin height, or block height to maintain or achieve a desirable ratio. This would then affect the head port design, cam shaft profiles / valve timing etc. But we are on the same page motors are a complex system and it is absolutely a holistic approach thats required. Another motor example is honda's move with the B16B motor where they chose to go to the taller b18 block same crank and piston pin height and just increase rod length. THis change was all about the rod to stroke ratio.
Oh to have an R&D department with lots of people, equipment and a budget bigger then New Zealnds GDP....
Cam is a bit hot on the rod ratio thing at the moment as he ended up with a pretty average outcome with his last motor its fair to say.
Brad, in the built up 94 case you may strengthen the pitons rods and fasteners but this just leaves the crank and the block at the next two weakest links. You are talking about a turbo application though so your requirements are quite different to anyone else N/A motor, go and have fun with that I hope it goes well for you.

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96 Mirage RS

The sooner that somebody does it, the better.
Yes rod/stroke ratio tends to be more internet BS.

You can't win, shorter rods put more side loading on the bores but keep the piston a TDC for less time (maybe less prone to detonation). Longer rods do the opposite.

Steve

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6G72 mivec Twin TDO5 20Gs up and running.
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