54 replies to this topic

[Cooperman]

I was kinda assuming that it would already have a strengthened centre main anyway.
But, yes, here is only so much you can do to a NA engine if you still want it to be road-driveable.
If the car is not being used for competition where 1/10ths of seconds count and where class/capacity issues don't exist, then forced induction could be the way ahead. With a turbocharger it's easy to get over 115 bhp at the flywheel with only about 8 psi boost pressure. You do need to beef up the diff though as the very high torque when the turbo comes in tends to wreck the standard diff pin.
To do that would require new pistons and a lower compression head (i.e. bigger combustion chambers). Also revised ignition timing with a slower advance cure would be vital.

[racingbob]

yes your engine sounds like fun at the moment and you would know

if reliable, spend your money on suspension thats where the enjoyment is

in driving for track day, oh and brakes and tyres. hoosiers are great

[jamiestevenbell]

i already have a full negative camber kit and adjustable spax and hilows, and yokos. At the moment i dont really want to consider the turbo route, and its has a xpin diff fitted and if i decide to have more work done ill be having a centre main, i might be asking too much then but wouldnt there be much of an increase in power by going to the med monster head with my cam? Cheers guys this helps much appreciated

[Cooperman]

i already have a full negative camber kit and adjustable spax and hilows, and yokos. At the moment i dont really want to consider the turbo route, and its has a xpin diff fitted and if i decide to have more work done ill be having a centre main, i might be asking too much then but wouldnt there be much of an increase in power by going to the med monster head with my cam? Cheers guys this helps much appreciated

Just changing the head might give you a couple of bhp. The problem is that it is easy to get from, say, 70 bhp to 90 bhp, a bit more difficult and expensive to get from 90 to 100, still more difficult to get from 100 to 110, and after that you will find that the cost of each extra bhp is huge, the driveability reduces and the need to frequently rebuild becomes hugely increased.

[mike.]

I think your 2 options to get a noticeable increase in power are either a really fancy head (7 port, twin K, KAD) or forced induction.

If you've got the money and don't like the idea of forced induction, then a fancy head would be a really nice addition to your engine and I think your current gearbox would cope with the increase fine, although the clutch may need looking at.

Forced induction really is worth thinking about though for a road engine, as the nice thing about it is you don't need to rev high to produce good power. So you can keep the engine within its standard rev range. Another thing is, as long as your transmission and compression ratio are good enough, you can up the boost for more power. So when your just pottering around you can run it on low boost, maybe making 120bhp and not putting too much strain on the components, and then when your out for a blast crank up the boost valve and make 170bhp.

[jamiestevenbell]

ye well im tempted for a 7port fuel injection, and i believe it has an uprated clutch as the pedals alot heavyer than a friends on his mini, driveablitiy isnt too much of an issue for me as i barley ever use it in the week its simpily a nice weather car, has anyone here got a 7port head? or do you know anyone that has that i could get intough with regarding this?, and does anyone here have one of the med heads that uses there offset valves and all the trimmings? if so how do you find these. cheers guys

[mike.]

The injection alone would give you a decent increase it driveability at least and combined with a 7 port head would make a great weekend blast engine.

I know theres a number of people who run the specialist components 7 port head on the turbominis forum, its the preferred 7 port head over the cheaper cast ones you can get, as its had a lot more development put into it and is CNC machined by SC.

Theres a thread at the moment in the turbo section about 7 ports. I know wil h has one and so does turbo phil, there are others too, Matt his name is but i'm unsure of his username...

[jamiestevenbell]

ok wel are all the people you know running the head turbod? I suppose i should be happy with what i have lol but i just want more, i suppose thats the way it will always be though!

[mike.]

Yeah most I know of are turbo'd to be honest. But the way the head performs is no different to running it N/A and the advantages the SC head has over the cast 7 port heads still apply. The SC head is already machined ready for injectors and has a fuel rail as far as I know, so then you just need a megasquirt set up to control the fueling. So it is simpler to get going than the cheaper 7 port's.

This is a quote from mini13 on the SC heads when I was asking about the advantages they offer over the cheaper cast heads:

'well with the pierce/ minisport heads the porting is to large, mainly because it tapers out fast to meet the 40 dcoe flanges, as you cant add metal back in you'll never beable to get the porting as good as the SC head, that dosent mean the peirce ones arent worth while though....

reaistically topend power is going to be similar with the SC one having the edge, but the low down power will be significanty better on the SC one due to better gas speed and port effeciencys.


as an example with the sc head a 998 has made 178hp on 18psi of boost, with room for improvement. '

[jamiestevenbell]

ok thanks this may be the way i go then! is there much benerfit going fuel injection over webbers as i may be able to get a set of webbers that are literally 1000miles old at a good price! and i also think 7 port heads look epic lol

[Sam Walters]

ok thanks this may be the way i go then! is there much benerfit going fuel injection over webbers as i may be able to get a set of webbers that are literally 1000miles old at a good price! and i also think 7 port heads look epic lol

If you plan on making any more power, change the pistons. Those slipper pistons arnt ideal to say the least.


I do suggest going turbo. Its not the head that makes the power on that engine its the gt17 turbo strapped to the back. 250hp has been made on the 5 port.

Id invest the money into the turbo route and select some new pistons for your engine.

Overall its going to be cheaper and its going to yield more power. I wouldnt wind up the boost past 12-14 psi as this is 140bhp on a well sorted engine with a gt17. Your drop gears will be okay aslong as you are sensible, diff the same. Beyond this power level youre looking at a new gearset.

[mike.]

Theres no point paying all that money for a 7 port head and not running it injection. The main advantage of them is how well suited they are to injection.

Using the parts from other cars, I don't think injecting it will cost as much as a set of webers and then the tunability you'll have will be great. The good thing about injection is you can tune the fueling and timing perfectly for your spec across the whole rev range and for different loads on the engine. You can't do this with carbs and a dizzy.

With injection you'll be able to improve the drive ability of the car and make the cam less lumpy too.

[jamiestevenbell]

hm still not too keen on turboing i know it will be cheaper but i much prefer n/a and i have been looking on specialist components website and hav had a quick look at the bmw 16valve head and there doesnt seen much difference money wise between that and 7port has any one here got one of them? Would there be much difference driving/performance wise between the two heads? Thanks

[Turbo Phil]

The 7 port will be the cheaper conversion as you can use your current rockers, ex manifold, cam & you don't need to do any block mods or run pistons with valve cut outs. It's pretty much a bolt on conversion with no machining needed.
Fuel injection won't yield anymore power than a well set up pair of Webers, what it will do is allow you to have complete control over the fuelling increasing driveability & economy.
The SC heads are a much better design than the others available. I have one sat in the garage with most of the other bits to build a new Turbo motor.

[jamiestevenbell]

you dont fancy sellin the head thats in your garage do you? Lol and on specialist components website they do a bmw conversion kit where they do all the machining and provide the required bits for just under 3k