14 replies to this topic

[Ade-Cooper]

Hi folks,

Just pondering the idea of having my spi head remastered-

Question is - what's the typical prices if taking to a local machinist and what specifications?

Firstly I dont want to walk in and not have a clue what I'm asking - thus asking on here and not face to face where I can blush ? and not wanting to be ripped off either.

Many thanks

[Turbo Phil]

I’ll assume as it’s an SPI it’s a road engine and mildly tuned ? I’ve written the following on that basis.
The chances of your average machine shop having a clue how to modify a cylinder head properly are minimal. Generally they’re ok for getting heads skimmed and maybe the seats recut, but not usually much else.
Unless you’re planning on taking it over 6,000rpm (or going forced induction) on a regular basis the standard road spec valves and iron guides are fine, don’t be conned into paying out for race valves and bronze guides for a road motor. Have a 30deg back cut applied to the inlets and 3 angle seats cut in the head.
Use the standard 29.4mm exhaust but fit the larger 35.6mm inlet valve (with the port throat opened to suit) have the guide boss ground away completely, and for a road motor on a mild cam simply tidy/smooth the ports out with no real enlarging of the inlet port required. The exhaust port can be opened a little, but don’t get carried away. The chambers will need to be opened out/cut back a little to deshroud the valves, especially around the larger inlet. The chambers will need to be measured and the head skimmed the appropriate amount to restore the compressor ratio.

Avoid any company that try’s to sell you all the bells and whistles (unless it’s a full race engine ?) offers to polish the inlet ports or doesn’t ask for your engine spec and intended application.

Phil.

[Fast Ivan]

this needs pinning

[Ade-Cooper]

I’ll assume as it’s an SPI it’s a road engine and mildly tuned ? I’ve written the following on that basis.
The chances of your average machine shop having a clue how to modify a cylinder head properly are minimal. Generally they’re ok for getting heads skimmed and maybe the seats recut, but not usually much else.
Unless you’re planning on taking it over 6,000rpm (or going forced induction) on a regular basis the standard road spec valves and iron guides are fine, don’t be conned into paying out for race valves and bronze guides for a road motor. Have a 30deg back cut applied to the inlets and 3 angle seats cut in the head.
Use the standard 29.4mm exhaust but fit the larger 35.6mm inlet valve (with the port throat opened to suit) have the guide boss ground away completely, and for a road motor on a mild cam simply tidy/smooth the ports out with no real enlarging of the inlet port required. The exhaust port can be opened a little, but don’t get carried away. The chambers will need to be opened out/cut back a little to deshroud the valves, especially around the larger inlet. The chambers will need to be measured and the head skimmed the appropriate amount to restore the compressor ratio.

Avoid any company that try’s to sell you all the bells and whistles (unless it’s a full race engine ?) offers to polish the inlet ports or doesn’t ask for your engine spec and intended application.

Phil.

 

 

Thanks Phil,

 

Really helpful reply, gives me some information to take to my local machinist.

 

The SPI has standard manifold, but RC40 single box there after, K&N top filter and some 1.5 rockers to go in at some point (that's why thinking of having the head done when doing rockers)

 

The only other concern is the SPI management itself, reading through the forums the ECU will adjust to the differences in head and high lift rockers - as you cant tune the standard ecu  - would this be right??

 

Also what kind of prices am I looking at for the head work? (estimate as I know everywhere will be different) looking on line they vary from £1200 - £600 would this be about right?

 

Many thanks 

[Fast Ivan]

 

I’ll assume as it’s an SPI it’s a road engine and mildly tuned ? I’ve written the following on that basis.
The chances of your average machine shop having a clue how to modify a cylinder head properly are minimal. Generally they’re ok for getting heads skimmed and maybe the seats recut, but not usually much else.
Unless you’re planning on taking it over 6,000rpm (or going forced induction) on a regular basis the standard road spec valves and iron guides are fine, don’t be conned into paying out for race valves and bronze guides for a road motor. Have a 30deg back cut applied to the inlets and 3 angle seats cut in the head.
Use the standard 29.4mm exhaust but fit the larger 35.6mm inlet valve (with the port throat opened to suit) have the guide boss ground away completely, and for a road motor on a mild cam simply tidy/smooth the ports out with no real enlarging of the inlet port required. The exhaust port can be opened a little, but don’t get carried away. The chambers will need to be opened out/cut back a little to deshroud the valves, especially around the larger inlet. The chambers will need to be measured and the head skimmed the appropriate amount to restore the compressor ratio.

Avoid any company that try’s to sell you all the bells and whistles (unless it’s a full race engine ?) offers to polish the inlet ports or doesn’t ask for your engine spec and intended application.

Phil.

 

 

Thanks Phil,

 

Really helpful reply, gives me some information to take to my local machinist.

 

The SPI has standard manifold, but RC40 single box there after, K&N top filter and some 1.5 rockers to go in at some point (that's why thinking of having the head done when doing rockers)

 

The only other concern is the SPI management itself, reading through the forums the ECU will adjust to the differences in head and high lift rockers - as you cant tune the standard ecu  - would this be right??

 

Also what kind of prices am I looking at for the head work? (estimate as I know everywhere will be different) looking on line they vary from £1200 - £600 would this be about right?

 

Many thanks 

 

 

that's correct - the ecu will adapt to the tuning all by itself, its really good like that. there is a limit but I don't think you're heading that way, there are alternatives though should you need it.

Prices do vary wildly, but I would stick to either AC Dodd, Kieth Calver, and though I haven't used or seen his work turbo phil above comes highly recommended

Also worth speaking to the aforementioned regarding the rockers

[ACDodd]

What turboPhil says is bang on.

Ac

[Cooperman]

Phil,

 

That is about the best explanation of how to get a significant improvement from a head that I have ever read. Well said and it should be pinned as a reference for everyone.

[Ade-Cooper]

Thanks guys, thanks Phil for the info! Much appreciated

[Turbo Phil]

Thanks guys, thanks Phil for the info! Much appreciated

No worries.

Phil.

[mini13]

And this is why Phil is my goto guy for head work, Straight up, Good work, Good pricing, and a nice guy to deal with.

[markking]

Thread revival :)

Is this all relevant for a 1275 carbed engine/head also?

Such a great explanation it would be great to use as reference when going to/talking to the machine shop.

[Turbo Phil]

Yes it’s relevant whether carb or injection.

Phil.

[Tones61]

The only other concern is the SPI management itself, reading through the forums the ECU will adjust to the differences in head and high lift rockers - as you cant tune the standard ecu - would this be right??

Also what kind of prices am I looking at for the head work? (estimate as I know everywhere will be different) looking on line they vary from £1200 - £600 would this be about right?

Many thanks
[/quote]

The standard ecu will self tune up to approx 85/90 bhp

Edited by Tones61, 11 March 2020 - 07:24 PM.

[Turbo Phil]

The standard ECU can’t be reprogrammed, so power is limited in regards to this.
Head prices vary dramatically, I sell what most would consider a “stage 3” head for £595 on an exchange basis. It’s pretty much what I described above.

Phil.

[croc7]

Phil, off topic but I didn't know what or where Cumbria was located.  Looked it up on line, glad that I did, really interesting history.