Which pistons/rods/crank ?

[macdeb]

Maybe looking at beefing up my engine a little. It's a pretty healthy 450 with a piper 285 cam, head work, 10.5:1 comp' ratio etc and pushes 285hp at moment n/a. was looking at forged pistons [which are best suited] rods [whats' best, 'H' or 'I' section and what's the difference?] and maybe a stroker 4.8 crank as advertised on a V8 tuner site, or go double dosh and get a steel crank. Looking to make it pretty strong/reliable.
Already have thoughts on clutch and engine management. Thanks for any constructive input.

Edited by macdeb on Thursday 4th February 22:03

[Boosted LS1]

I'd get the pistons custom made in the US this allows you to spec the material, pins and ring pack etc. I and H beam describes the cross section of the rod. Some people say the I beam is stronger but for a road going car it won't make any difference what you have. I'd consider weight first and definately go for stronger bolts. As for the crank, stock one would be sufficient unless you want to spend mega bucks on a mega heavy steel item.

[spend]

Drop the big end size and have your crank offset ground you'll get better than 4.8. Buy cheap carillos and then get forged pistons made to suit the rod length + pins and compression you want. Easy

[Slow M]

macdeb said:

Maybe looking at beefing up my engine a little. It's a pretty healthy 450 with a piper 285 cam, head work, 10.5:1 comp' ratio etc and pushes 285hp at moment n/a. was looking at forged pistons [which are best suited] rods [whats' best, 'H' or 'I' section and what's the difference?] and maybe a stroker 4.8 crank as advertised on a V8 tuner site, or go double dosh and get a steel crank. Looking to make it pretty strong/reliable.
Already have thoughts on clutch and engine management. Thanks for any constructive input.

Edited by macdeb on Thursday 4th February 22:03

Macdeb,

Sounds as though your combination is pretty strong/reliable already (and a damn fine looking engine bay, BTW).
What you should do truly depends on what you're after.
Are you trying to max out the power and raise the rev limit or are you looking for more torque at lower RPM? Remember that as you approach the limits, you'll generally sacrifice some reliability.

If it were mine, I might consider the following:

• a slightly more agressive cam
• consider some port work to the intake/heads.
• modify your exhaust headers to be closer to equal length.

You'll need to have upgraded injectors as your power numbers climb.

If you're looking for a lot more power, I would not do without a forged steel stroker crank, use "H" beam rods with big bolts (SPS-Carr) and either a lot of cylinder head work or a new set of heads.
There are a number of pistom mfgrs that put out a high quality product. Look for who can supply the part you need without it being too custom as price will vary accordingly. (Probe, J&E, Wiseco, Cosworth, Arias all immediately come to mind but there are more)

Another thing to keep in mind is that the remainder of your powertrain is built for the transmission of a particular load. I'd look to others who have built up their car with identical clutch, transmission, differential, axles... to determine what the load limits for those components are.

Best,
B.

[macdeb]

Mike, Dave, Bernard, thanks for help so far [and for compliment].
Firstly, I'm looking for more torque [320 dead flat curve from 2.5 to 4.5 revs at moment n/a]. The heads are big valve and have been ported/matched with inlet and flared alloy trumpets. Exhaust have pre-cats removed/replaced with non-reversal cones and are ceramic coated in and out except for main cat of course which is on outside only. I 'occasionally' use Nitrous [only 50 hp, ignition is retarded] not often, just now and then and want to make sure it can handle another 50 [100 total real world] so I'm also thinking total seal rings and wired heads [nothing worse than when you do 'give it some' having the thought in the back of your mind, is it gonna let go] It does drive very nicely at the moment and mechanically whisper quiet which I like so piston choice is important. [only 13k miles on car] I'm keeping the car but want just 'a bit more' and peace of mind when I use it, if that makes sense. I've already upgraded the brakes and suspension and as stated will be changing clutch. I thought the T5 box was good for 450hp peak [correct me if wrong] so 400 peak should be ok? [nitrous is fed through a progressive controller so is introduced in stages rather than one big hit]. Bottom line is I'd like a stronger, reliable motor which I use 99% n/a, but will withstand a 'hit' now and then without drama. Thanks again.

Edited by macdeb on Friday 5th February 22:00

Edited by macdeb on Friday 5th February 22:05

[Boosted LS1]

^ What pistons have you got in there, forged or cast? For your intended application I'd go for custom forgings with thicker top ring lands and a TS file fit ring pack as you've mentioned. Upgrade the rod bolts if they aren't already arp 2000's whatever, or replace them as a precaution anyway. Jobs a goodun! If the nitrous arrives to early you'll kill cast or thin ringland pistons. Better to have it arrive late and use more of it to get the torque back.

[spend]

Begs the question of 'is it really worth it' for putting an occasional 100bhp shot on top of a 283bhp motor? I'd consider spending your money on making the ecu and the control systems uber gas friendly first if you just want reliability.

[macdeb]

Don't use the gas until after 3k revs, where's best to source the pistons/rods Mike? Will probably go for a Megasquirt system.

[Pupp]

Why the urgings for forged pistons? Sure, they *might* be stronger in ultimate terms, although that's not such a given over modern hypereutectic castings as it once was, but they come with a weight premium and all the potential issues associated with their strange thermal expansion qualities and the resulting clearances that have to be run. Having destroyed more than a few forged pistons in bike engines over the years, I'd not be so hasty to go that route now...

[dbv8]

Im going out on the beer just now Mac.... will stick my 2 penny worth in later.

+ 1 for Megasquirt2 btw. Contact Phil at extraefi 'daxtojiero' for a bargain full package.

[Boosted LS1]

I used to use hypereutectics in cosworth engines. They were hard as nails and ran with tight clearances. Problem was they were brittle and detonation would soon kill them. The forged pistons I use are often lighter then the pistons they're replacing and they'll always have a solid skirt design. As for clearances, they don't seem to rattle when cold or at least not enough for me to notice.

Any of the US guys can make them for you. I wouldn't bother with a UK company, the service can be dire.

[hiltonig]

got mine from diamond pistons

[Slow M]

macdeb said:

Firstly, I'm looking for more torque

Increase displacement.

macdeb said:

I thought the T5 box was good for 450hp peak

Torque breaks stuff. Usually big grunt and big grip destroy parts in between. It is when your tires hook up that something will break. Max HP is usually at a part of your rev band when the acceleration has slowed and is less dramatic.
As far as what pistons to use, I have been recently convinced that hypereutectic pistons would work well enough as long as you control detonation.
Have a look at this thread. The OP is a GM powertrain engineer.

Best,
B.

[crispian22]

you want more power mac?????

nutter!

i still have a chuckle to myself when i think of the way your car left mad jons cirby for dust on the way to wythall that time

[macdeb]

Quinny said:

I find all this quite interesting... But I'm unsure of which direction you're taking..

You say you want more torque

My view on that is the best way to big Torque is through big CC... A lot of the recommendations above lead ie lighter stronger, components lead me to think "REVS"

All well and good buiding an engine that revs like fk, but if its more Torque spread through a 2k to 5k ish rev range, that you're after, I think you could be heading in the wrong direction...


My Tuppence worth

Hello bloke, What I'm after first and foremost is a strong reliable engine [not that I've had any problems so far]and thought that whilst I'm at it it seems a shame not to increase the torque through displacement for use under most circumstances n/a. Not looking to increase revs. Any increase in top end if I wish at any time would be taken care of via a shot of gas

[macdeb]

Boosted LS1 said:

I used to use hypereutectics in cosworth engines. They were hard as nails and ran with tight clearances. Problem was they were brittle and detonation would soon kill them. The forged pistons I use are often lighter then the pistons they're replacing and they'll always have a solid skirt design. As for clearances, they don't seem to rattle when cold or at least not enough for me to notice.

Any of the US guys can make them for you. I wouldn't bother with a UK company, the service can be dire.

Mike, Having some made sounds like a lot of time, is it? Are there any of the shelf items that would suit?

[macdeb]

hiltonig said:

got mine from diamond pistons

What spec' are they/ are they sourced here or over the pond? Thanks.

[macdeb]

crispian22 said:

you want more power mac?????

nutter!

i still have a chuckle to myself when i think of the way your car left mad jons cirby for dust on the way to wythall that time

Glad you liked it. Next time I wanna see me coming back before he gets there

[Boosted LS1]

macdeb said:

Boosted LS1 said:

I used to use hypereutectics in cosworth engines. They were hard as nails and ran with tight clearances. Problem was they were brittle and detonation would soon kill them. The forged pistons I use are often lighter then the pistons they're replacing and they'll always have a solid skirt design. As for clearances, they don't seem to rattle when cold or at least not enough for me to notice.

Any of the US guys can make them for you. I wouldn't bother with a UK company, the service can be dire.

Mike, Having some made sounds like a lot of time, is it? Are there any of the shelf items that would suit?

I wouldn't think so. US firms usually make pistons in about 4 weeks. Order 9, it's nice to have a spare. Oh, somebody mentioned peak torque etc, this is when detonation is most likely to kill occur imo and is when the piston crowns are under the most cylinder pressure.

[tinker-27]

hi mac come and see me and have a chat,