Mi16 Forge Pistons

[Dj_mini 7]

Im goining to have a l&b bottom end, arp rod bolts, logmans head, cat cams, 4branch exhaust and throttle bodies. My question is am im goining to any gains over the standard pistons with bigger valve cut outs over the slighly over sized foge pistons that qep sell? Is it worth the extra £550?

Cheers Dan

[easypug 0]

If your spending all the rest as you are forged pistons aren't really a big out lay. In fact its probably one of the cheapest things on your list...

Edited January 7, 2006 by easypug

[Jonmurgie 2]

It's a question you shoudl really ask Matt @ QEP mate, he'll be able to advise you correctly.

 

As I figure it with the Mi you only need forged pistons if:

 

1. Your running a Turbo/Supercharger

2. Your running wild cams and require more valve clearance

3. You can afford it

 

There may be other reasons... if you don't NEED to have them for the spec of CatCams your using (whic spec are you going for BTW) and if your current pistons are OK then I guess you'll be OK without them

[Dj_mini 7]

I think the cam number he sugested was 49005281 does that sound right?

My standard pistons are in good condition i was just interested if people thought it was nesscesary / worthwile for gains to change them.

[base-1 17]

Is it a road car?

[DrSeuss 0]

although there are other ways of doing it, another advantage of forged pistons is the raised compression ratio. Skimming the head produces some odd effects and you can't skim the mi head that much anyway.

[boombang 2]

Realistically you will only need them on an engine running high compression, needs the ability for machining for greater valve clearance, or very high revving engines.

 

Forged pistons should be lighter than standard pistons (stronger, therefore don't need so much material) - obviously good for revving as less force on rods and crank.

[Jonmurgie 2]

I think the cam number he sugested was 49005281 does that sound right?

My standard pistons are in good condition i was just interested if people thought it was nesscesary / worthwile for gains to change them.

 

Looking at the CatCams site I think you mean the 4900528 as they are the wildest cam you can go for before going to solid lifters etc.

 

As to whether it's necessary/worthwhile for gains... they themselves won't gain you any BHP, you use them because of other modifications, as stated...

 

Really, just have a chat with Matt @ QEP on Monday and he'll be able to best advise you as to whter you need to bother with Forged Pistons or not

[smckeown 1]

unless building a race engine why bother ?

[Miles 331 1 Cars]

There's not enough info on your engine spec to say what you will be needing, But if your planing on using over 7500rpm I would use Steel Rods without a doubt and change the big ends every 5k miles if on the road and use the Longman big end bearings

[Jonmurgie 2]

Miles, interesting you mention the use of Steel Rods... other then oil starvation issues I've not heard of the standard Mi rods letting go at upwards of 8000rpm... are you saying 8k rev limit should be a concern on standard rods?

[Dj_mini 7]

Its mainly for track use but i will use it on the road but not much prob just to get to the track.

 

I was going to have a limiter of about 7500 id rather have slightly less power to make the engine more reliable rather than running 8000rpm and spend mega money to do it.

 

Miles why use longmans bearings are they softer than the standard one to reduce crank wear?

[Robsbc 0 1 Cars]

I have Omega high compression forged pistons on my Mi16. They were fitted as a total package (cams, headwork, longman 4-2-1 manifold, throttle bodies, 40mm trumpets etc..) from Skip Brown Cars.

 

I could have not had them fitted but on their advice if i was prepared to put up with the increased oil consumption these pistons would contribute to increasing low down torque compared to one of their conversions without them (because of increased compression they give).

 

Most of the Mi's that have been on Emerald rollers have produced low than expected figures most around the 170-180BHP mark and around 140lbft for torque. Most of these conversions are admittedly been bolts on parts from various sources but I had a complete package as mentioned earlier my 1.9 Mi engine achieved 212BHP @ 7124rpm and 162lbft @ 5878rpm on the same rollers.

 

I have a friend with a 2.0 S16 engine visting Emerald on the 20th this month he's having Cat Cams (biggest you can fit before requiring solid lifters), 3 angle valve seats mated up to Jenvey throttle bodies & modfied GTI-6 manifold. Will post the results.

 

Rob

[Miles 331 1 Cars]

I know I keep going on about this but the big end wear very quicky in Race/Tuned engines and the rods around the big end are a weak point, I can show pic's of rods broken in various places so a Steel rod helps overcome this,

The Longman big ends are made from a different material (Can't spell the name!!) and are softer than the Eco friendly ones now sold

[veloce200 3]

The Longman big ends are made from a different material (Can't spell the name!!) and are softer than the Eco friendly ones now sold

 

I read something about bearings once before. It's an interesting subject - I think the main aim of a racing bearing is to be more sacrificial in that its easier and cheaper to replace these than an expensive crank. I'm not sure what type the OE bearings are but this link is good..Federal Mogul bearings

I think the main aim of a road bearing is long life but if starved of oil they will quickly wreck a crank. Anyone know anymore about the different bearing options ? Be good information to post hear for people building their own engines. I expect the racing bearings are avaiable in more sizes too - I remember only being offered one size when I changed the big ends in my engine after the oil pump chain slipped off and sheared off the pump sprocket! Before I knew what had happened I was back in the pits with massive big end knock. I think the standard crank has a surface hardening but maybe not when reground?. I had to clean off the bearing material off the crank with some fine emery cloth(!!) and fitted new shells and amazingly the engine has been going for 2 yrs of hard use since!

[Super Josh 4]

I have Omega high compression forged pistons on my Mi16.

 

Rob, are you running these with standard rods? Assume you've big inlet valves for that kind of power too?

 

 

 

 

Josh

[Robsbc 0 1 Cars]

Rob, are you running these with standard rods? Assume you've big inlet valves for that kind of power too?

Josh

 

Yes to both questions...

[Dj_mini 7]

Miles what you said about crank wear couldnt be more true picked up my crank from logmans to day an they said the mains had gone oval so they had to grind it bit of a shock as the engine has only done 68k.

 

I also got my bearings from them they use upratted big ends but standard mains in there builds so went with that.

[petert 587]

As I figure it with the Mi you only need forged pistons if:

 

2. Your running wild cams and require more valve clearance

 

This is really a catch 22 situation. The bigger the cam, the more valve to piston clearance you'll need, so the bigger the pocket. The bigger the cam, the more CR you'll need. Bigger pockets means less CR however, so you start to chase your tail, thus the need for a raised dome to increase the CR.

 

If it's just a hot street or mild track car, I'd advise skimming the block and liners to maximise the CR and squish height with the std. pistons. This will give approx. 10.8:1 with a std. head gasket. Otherwise, forged pistons are an excellent solution for repairing worn liners. I can't imagine there's too many original liners left in the world that are any good my now.

 

If you're looking for a cheap solution for a track car, it's possible to hone the liners for 0.003" clearance with the std. pistons, provided you know someone who can hone liners correctly. They usually end up out of round. Otherwise talk to Matt at QEP about some Wiseco pistons. I designed some 11.25:1 pistons a few years ago for Wiseco, which have a 2cc dome. They're excellent value for money.

[maxi 36 1 Cars]

I have Omega high compression forged pistons on my Mi16. They were fitted as a total package (cams, headwork, longman 4-2-1 manifold, throttle bodies, 40mm trumpets etc..) from Skip Brown Cars.

 

I could have not had them fitted but on their advice if i was prepared to put up with the increased oil consumption these pistons would contribute to increasing low down torque compared to one of their conversions without them (because of increased compression they give).

 

Most of the Mi's that have been on Emerald rollers have produced low than expected figures most around the 170-180BHP mark and around 140lbft for torque. Most of these conversions are admittedly been bolts on parts from various sources but I had a complete package as mentioned earlier my 1.9 Mi engine achieved 212BHP @ 7124rpm and 162lbft @ 5878rpm on the same rollers.

 

I have a friend with a 2.0 S16 engine visting Emerald on the 20th this month he's having Cat Cams (biggest you can fit before requiring solid lifters), 3 angle valve seats mated up to Jenvey throttle bodies & modfied GTI-6 manifold. Will post the results.

 

Rob

 

 

Rob, what sort of oil consumption did they say to expect with the forged pistons over std??

 

Maxi

[Daz_C 8 1 Cars]

Rob, what sort of oil consumption did they say to expect with the forged pistons over std??

 

Maxi

 

 

Its around half a litre to 500miles I think. It may be 1000 though ! Not drove mine that regular over the last couple of years, I just top it up when needed. It also depends on how you drive it. If you spend all your time with your foot to the floor chasing your nose then it will be as above but if you totter about as if your Gran is in the passenger seat then it will be less. !

[Robsbc 0 1 Cars]

Rob, what sort of oil consumption did they say to expect with the forged pistons over std??

 

Maxi

 

Like DAz_C said 1 litre per 1000 miles but it was more liek a guess from them as their raace cars get their oil change after each event so they don't notice the oi lconsumption as much as a daily road car.

Edited January 14, 2006 by Robsbc