View Full Version : Building a better bottom end F7R
Just thinking about rebuilding the bottom end of the car and whilst a Megan is probably the one which will go in I'm wondering how to go about making it more relaible/more able to take more RPM.
I was thinking 172 Clio connecting rods as I think BenR mentioned there the same size etc but better built and lighter so thats a start but is it neccessary?
Same for pistons are stock pistons fine or will an upgrade to the BB high compression or whatever there called be better if so what sort of gains is it just a few LB and its just only for a true racing engine?
What about ligthening and balencing the crank.
Also what sort of cost are we talking about? Whats sort of RPM are you then safe with I'm running 7.2k at the moment which I thinks a bit high with a ligtened and balenced crank etc could I run say 7.5k as looking at the RR runs for the car the engine not loosing any power at the limiter so more rpm means more power without any loss.
clowo16v
31-10-2005, 00:49
I'd get the whole bottom end lightened and balanced as a start. Should cost around £50 at a decent engine shop.
Slithers
31-10-2005, 01:05
I'd get the whole bottom end lightened and balanced as a start. Should cost around £50 at a decent engine shop.
£50.00!!??!?!?!?!?
surely you mean 500? any sort of engine work that cost 50 squid on its tod would come back to haunt you, almost certainly.
My cranktrain was dynamically balanced for £50 :wink: on equipment that was intended for turbine blades (5x more accurate than the usaual gear).
Dont go to BBT for pistons! if you want some forged ones, i'll give you the details of where to get mine (Accralite...very good). as for conrods, H section rods are available, but doubt they are necessary for 7500rpm.
You have to remeber that it isnt just the bottom end thats limiting the max rpm, its the ability of the head (cams/valves) to flow at high rpm, the combustion chamber design to promote a fast enough burn to allow it, and of course the valve train for keeping it all together, and not destroying itself when you wind it up (lighter parts...less inertia forces blah blah blah).
You can also look at line boring the main journals so as to keep it all true, adn of course boring the cylinders to ensure a true bore, and good finnish.
If you want really high rpm, it would be necessary to have a steel crank that is counter-balanced to your reciprocating mass (piston+rod assembly)....assuming that the head flowed well enough to allow that sort of engine speed of course.
The problem with these engines is that they are far from "square"...i.e the bore is no where near the stroke. ideally you want a large bore with minimum stroke....=low mean piston velocity=higher obtainable engine speed. also more torque and the ability to fit larger valves.
Slithers
31-10-2005, 01:28
My cranktrain was dynamically balanced for £50 :wink: on equipment that was intended for turbine blades (5x more accurate than the usaual gear).
Dont go to BBT for pistons! if you want some forged ones, i'll give you the details of where to get mine (Accralite...very good). as for conrods, H section rods are available, but doubt they are necessary for 7500rpm.
You have to remeber that it isnt just the bottom end thats limiting the max rpm, its the ability of the head (cams/valves) to flow at high rpm, the combustion chamber design to promote a fast enough burn to allow it, and of course the valve train for keeping it all together, and not destroying itself when you wind it up (lighter parts...less inertia forces blah blah blah).
You can also look at line boring the main journals so as to keep it all true, adn of course boring the cylinders to ensure a true bore, and good finnish.
If you want really high rpm, it would be necessary to have a steel crank that is counter-balanced to your reciprocating mass (piston+rod assembly)....assuming that the head flowed well enough to allow that sort of engine speed of course.
Sorry i thought he meant forged pistons, lighter con rods, crank etc, when "entire bottom end" was mentioned.
Bit of crossed wies here by the looks of it.
yeah see wot u mean!! lol my pistons alone were over £500 by the time i had the blockbored to suit!!
Slithers
31-10-2005, 01:40
yeah see wot u mean!! lol my pistons alone were over £500 by the time i had the blockbored to suit!!
CHRIST ON A BIKE!!!!
500 knicker?!?!?, for the pistons?!?!?!, lol you is one nutter stan!!, fair game though man, i seen your engine pics and they look fookin mint lad.
Dont go to BBT for pistons! if you want some forged ones, i'll give you the details of where to get mine (Accralite...very good). as for conrods, H section rods are available, but doubt they are necessary for 7500rpm.
If you want really high rpm, it would be necessary to have a steel crank that is counter-balanced to your reciprocating mass (piston+rod assembly)....assuming that the head flowed well enough to allow that sort of engine speed of course.
The problem with these engines is that they are far from "square"...i.e the bore is no where near the stroke. ideally you want a large bore with minimum stroke....=low mean piston velocity=higher obtainable engine speed. also more torque and the ability to fit larger valves.
I don't want to go spend a fortune but if 7.5k is possible without going spending a fortune or if it will just mean its safer I'd be happy to pay. I know going to massive rpm is going to need a forget bottom end and I don't want to go pay that sort of bill.
Not that I'd go this far but would a 1.8 block and crank be a better starting point with a huge bore than a 2.0 block and crank or does the extra cc of the 1.9 diesel/Williams crank make up for the less rpm it could hold?
Stan I asked BenR but didn't get the answer I wanted to hear but what about bike power in the car? Do you concour that its just not suited to the weight of the Clio sheel and that only kit cars can go down this route?
Dont go to BBT for pistons! if you want some forged ones, i'll give you the details of where to get mine (Accralite...very good). as for conrods, H section rods are available, but doubt they are necessary for 7500rpm.
If you want really high rpm, it would be necessary to have a steel crank that is counter-balanced to your reciprocating mass (piston+rod assembly)....assuming that the head flowed well enough to allow that sort of engine speed of course.
The problem with these engines is that they are far from "square"...i.e the bore is no where near the stroke. ideally you want a large bore with minimum stroke....=low mean piston velocity=higher obtainable engine speed. also more torque and the ability to fit larger valves.
I don't want to go spend a fortune but if 7.5k is possible without going spending a fortune or if it will just mean its safer I'd be happy to pay. I know going to massive rpm is going to need a forget bottom end and I don't want to go pay that sort of bill.
Not that I'd go this far but would a 1.8 block and crank be a better starting point with a huge bore than a 2.0 block and crank or does the extra cc of the 1.9 diesel/Williams crank make up for the less rpm it could hold?
Stan I asked BenR but didn't get the answer I wanted to hear but what about bike power in the car? Do you concour that its just not suited to the weight of the Clio sheel and that only kit cars can go down this route?
it wouldn't move with a bike engine
edde the pink one is running a completley balanced megane bottom end (you have the whole thing balanced, crank, flywheel + clutch)
7800rpm limit
also, don't just "wack" new pistons in, you should really detail and balance the rods (by weighing them) and do the same to the pistons
edde the pink one is running a completley balanced megane bottom end (you have the whole thing balanced, crank, flywheel + clutch)
7800rpm limit
Thats why i said cranktrain....crankshaft, pulleys, bolts, fly, clutch cover etc etc
Edde,
i have to agree, a bike engines power/torque characteristics arent suited to a monocoque like a Clio. even if you got the weight down to kit-car level, the aerodynamics would play havoc! the one way you could do it if you wanted to, is to use TWO bike engines. even then tho, once you get on tarmac, i can imagine you will have transmission problems when you try to launch it.
clowo16v
31-10-2005, 14:52
50 quid for a full bottom end balance yeh. This entails weighing all the pistons and making them the same, detailing the rods to make them weigh the same, balancing the crank and lightening and balancing the flywheel.
See ya
Matt
Edde, check thsi lot out, someoen posted it on cs, dunno if any of ti is of any use?
http://search.ebay.co.uk/_W0QQsassZrichardwholt
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