Found some of the guff I posted before
Well, that would be some engine! 100hp was generally regarded as good but that was some time ago.
Don't know about the setup you're asking about but some comments and observations you may want to consider.
Cylinder head - a lot of tuners just used slightly larger inlets with stock exhausts but you can fit larger inlet and exhaust valves. They use a 7mm stem diameter so you 'may' be able to modify valves from another engine - cut down the head and machine a new collet groove. I've lost an engine from a valve pulling through the standard collets so you may want to use aftermarket ones - AFAIK, they use a standard 7 degree angle and you can purchase generic machines ones. At one stage, I was considering checking out what was available for the old Mini engines that may be useable as they use high rpm with aggressive profiles.
There isn't much meat under the valve seats so you may have to use longer valve springs to get the required rate - the valve length can be machined to suit. If you do this you're going to get some funny angles for the rocker, esp' with a reprofiled, rather than new core, camshaft. I didn't play around with this stuff but the SB chev' pushrods seem to be the same ball end size, if so, a custom set would be just the thing - esp' as you should then be able to correct the rocker alignment by filling the guide channels. You may also find the rockers hit the breather 'box' if the head is machined to far - this drove me nuts checking the valve clearances until I realised what was happening. There is a chance you'll run out of thread on the rocker studs for the crimp nut to hold, I machined a couple of mm off the bottom of the lock nuts in a lathe.
Another problem is that the studs can pull out of the head under heavy spring/high rpm use, you can use the old SB Chev' technique of carefully drilling through the head into the bottom of the stud and tapping a pin into it to lock the stud in place - not for the clumsy, alternatively you can get special studs machined with the oilways drilled but this should be very expensive. i would assume you'll be running a four branch exhaust manifold so you'll also need to get the gap between the centre ports filled in and plug the heat risers - I partially tapped them and screwed in plugs that reached the port.
I'd also given some thought to the possibility of fitting shafts to use Mini rockers and an auxiliary oil feed.
Timing chain is only a single row and I wasn't able to find a heavy duty/duplex kit but they're supposedly quite strong - would have been fun making up a gear drive, though.
Conrods are supposed to be pretty strong but I lost an engine when a big end cap broke - something I've never heard of happening on any engine before so I expect it was a manufacturing flaw. If you've the budget, custom aftermarket rods may be a good idea as it opens up some more possibilities for pistons, such as an overbore using forged Ford Lotus pistons with the dome machined off.
I would expect the crank to be OK.
Flywheel - you may want to lighten it but it's pretty good already. However, you may be well advised to have the flywheel/crank machined for additional dowels.
For the carbies, a 45 or 48 downdraft is the best bet on a suitable manifold but it'll stick through the bonnet - I'd expect the best option will be a throttle body on a sidedrsft manifold.
Gearbox isn't up to it - I've broken several second gear sets and the constant mesh gears with a mild engine. I know there used to be a stronger, straight cut close ratio gearset from, I think, Jack Knight in the UK but I suspect they're no longer trading. I know off a couple of people using the Toyota starlet 5 speed box on a modified belhousing - no details though.
Dif' 'should' be up to it if it's in good nick and the tyres aren't too grippy.
Radiator should be upgraded with a triple row core and you may need to look at an oil cooler.
Rebush the distributor and use a luminition kit - better would be to use mapped ignition with the throttle bodies.
All in all, I expect the 126hp was using a turbo', probably built around a reworked low compression head from a bedford van, etc.
forgot, car looks good - have you thought about widening the rims to 6", still painted with the pie dish covers?
« Last Edit: May 10, 2007, 10:25pm by gordo »
Well, that would be some engine! 100hp was generally regarded as good but that was some time ago.
Don't know about the setup you're asking about but some comments and observations you may want to consider.
Cylinder head - a lot of tuners just used slightly larger inlets with stock exhausts but you can fit larger inlet and exhaust valves. They use a 7mm stem diameter so you 'may' be able to modify valves from another engine - cut down the head and machine a new collet groove. I've lost an engine from a valve pulling through the standard collets so you may want to use aftermarket ones - AFAIK, they use a standard 7 degree angle and you can purchase generic machines ones. At one stage, I was considering checking out what was available for the old Mini engines that may be useable as they use high rpm with aggressive profiles.
There isn't much meat under the valve seats so you may have to use longer valve springs to get the required rate - the valve length can be machined to suit. If you do this you're going to get some funny angles for the rocker, esp' with a reprofiled, rather than new core, camshaft. I didn't play around with this stuff but the SB chev' pushrods seem to be the same ball end size, if so, a custom set would be just the thing - esp' as you should then be able to correct the rocker alignment by filling the guide channels. You may also find the rockers hit the breather 'box' if the head is machined to far - this drove me nuts checking the valve clearances until I realised what was happening. There is a chance you'll run out of thread on the rocker studs for the crimp nut to hold, I machined a couple of mm off the bottom of the lock nuts in a lathe.
Another problem is that the studs can pull out of the head under heavy spring/high rpm use, you can use the old SB Chev' technique of carefully drilling through the head into the bottom of the stud and tapping a pin into it to lock the stud in place - not for the clumsy, alternatively you can get special studs machined with the oilways drilled but this should be very expensive. i would assume you'll be running a four branch exhaust manifold so you'll also need to get the gap between the centre ports filled in and plug the heat risers - I partially tapped them and screwed in plugs that reached the port.
I'd also given some thought to the possibility of fitting shafts to use Mini rockers and an auxiliary oil feed.
Timing chain is only a single row and I wasn't able to find a heavy duty/duplex kit but they're supposedly quite strong - would have been fun making up a gear drive, though.
Conrods are supposed to be pretty strong but I lost an engine when a big end cap broke - something I've never heard of happening on any engine before so I expect it was a manufacturing flaw. If you've the budget, custom aftermarket rods may be a good idea as it opens up some more possibilities for pistons, such as an overbore using forged Ford Lotus pistons with the dome machined off.
I would expect the crank to be OK.
Flywheel - you may want to lighten it but it's pretty good already. However, you may be well advised to have the flywheel/crank machined for additional dowels.
For the carbies, a 45 or 48 downdraft is the best bet on a suitable manifold but it'll stick through the bonnet - I'd expect the best option will be a throttle body on a sidedrsft manifold.
Gearbox isn't up to it - I've broken several second gear sets and the constant mesh gears with a mild engine there was a redesign when the remote got it's bracing and that was supposed to be stronger. I know there used to be a stronger, straight cut close ratio gearset from, I think, Jack Knight in the UK but I suspect they're no longer trading. I know off a couple of people using the Toyota starlet 5 speed box on a modified belhousing - no details though.
Dif' 'should' be up to it if it's in good nick and the tyres aren't too grippy.
Radiator should be upgraded with a triple row core and you may need to look at an oil cooler.
Rebush the distributor and use a luminition kit - better would be to use mapped ignition with the throttle bodies.
All in all, I expect the 126hp was using a turbo', probably built around a reworked low compression head from a bedford van, etc.
forgot, car looks good - have you thought about widening the rims to 6", still painted with the pie dish covers?
« Last Edit: May 10, 2007, 10:25pm by gordo »
Depends how hot the summer is over there - I found even a standard car to run on the hot side when driven hard on the open road but with a triple core, it would sometimes drop the temperature - even on hillclimbs, etc. Use it with an electric fan - I had mine wired to be off, on or via the thermostat control - handy for cooling it down between runs.
If I was building another engine, I'd deck the block to zero or -10 thou for better quench and it'd mean less off the head.
BTW, you can take quite a lot of the ports EXCEPT at the exhaust ports at the block side of the outlet, however unless you've a spare head and/or experience, I'd recommend leaving that to someone familiar with the head.
I also used Kent HD single coil valve springs with a 1mm shim under them.
The stock cam' isn't that bad, don't go too wild if you replace it as they get a bit gutless at low rpm.
Couple of other things to get back on topic.
Standard GM friction plate is made of a relatively thin metal - I've had a couple fail due to cracking, however the aftermarket ones, eg Repco, are quite a bit stronger, they've a better friction material too!
The aftermarket pressure plates also seem to be a bit better but if you're a real concern, such as when forced induction is used, then you should be able to get a custom one built with a heavier diaphram spring. I've heard of using two diaphrams springs in other applications but ...
You may also want to look at the engine mounts, I've ripped a couple but that was probably due to old age, as much as abuse. Back in the day, you could get heavy duty replacement rubbers but I'm not sure about now. Keep an eye on them if you're not using a different mounting system.
I'd recommend modifying a sump for wings (should clear the strarter but beware exhaust clearances) and a baffle as I found in hard braking the oil would move forward enough to lose oil pressure - even overfilled by a litre. If you do this, best thing is to bolt the sump to an old block to prevent distortion while cutting and welding - once that happens, it'll never seal!
I'd also a long writeup at this site, but it's been through some changes and seems to have gone - however, it's also got a 1256 tuning section that may be of interest.
www.chevettes.com/info.php - however, I wouldn't follow their guide as, IMO, I had better results doing it my way!
