NA rally head

[mbrallying]

Just after you guys opinions on the right head for my rally 2.6

Its time over christmas to get stuck into the rebuild, which means finally building a good head for it.

I know m6-m7 are the best, but whats the best way of modding them for higher comp (no higher than 10:1). Is it ok to take that much off the deck and not worry about timing chain tension and cam timing, although not too worried about timing as I was going to run an adjustable gear anyway, aswell as early model rockers and cam.

Or is there other ways to up the comp??

Or should I run the higher comp head to start with (m8-m9? please correct me if I'm wrong)

And also what are the tips for getting the most out of them, porting, valves, matching???

Any info greatly appreciated.

Thanks in advance guys

Mark..

[galantgrunt]

Hi mb, There are lots of factors that effect compression and if you want to be accurate about your 10.5:1 be prepared to do lots of measuring, more than once have a look on the net there are calculators you can use. There are a number of ways to raise compression you can deck the block, use dome top pistons, or like you said take some off the head.

Zero deck height to start. I am not sure if the later magna's used a head with smaller combustion area or if they used dome top pistons to raise the compression? I am sure someone will know.
Just something i have noted with these engines is that high compression is not necesarily a good thing as far as making lots of power. The first engine i built had around 10.5:1 with twin webers and was making 130bhp this was using the old series one head with series 2 flat top pistons. The problem was i could not get any advance into this engine using premium pump fuel without it pre detinating. However yours been a rally car you may be able to run race fuel.

The engine Im running at the moment is setup for a turbo uses the m6 head and magna bottom end and series 1 forgies. I decked the block heaps and the head to get it up to 8.5:1 compression and guess what it makes exactly the same power as before without the turbo. However, it now runs injection. I put this down mainly to the better flowing head and being able to run heaps of advance.

I know there are a few people on this forrum with big hp na cars and id be interested in what they say is a good compression ratio for these NA engines. Obviously there will be differences for the types of fuel used. What is a good comp ratio for say Premium pump fuel, race fuel,

[mbrallying]

Thanks mate

My engine now sounds almost identical to yours, I run flat tops with a series 1 head on 45's and it makes 122bhp. Thats pretty close to yours hay!! Although I think my comp at the moment is somewhere like 9.5:1 which is perfect for us as we do only run pump fuel.

I'm mainly going for airflow, if I can use the best flowing head to start with and then bring the compression up to where mine is now I'd be happy. But if not, I'd rather try and get the best flow out of the higher comp head (i think m8-9 I can never remember) and make sure all the cam timing and stuff is nice and reliable, as the thing will be revving a bit.

The magnas with higher comp still run flat tops, and the heads have a kidney shaped combustion chamber.

And I'm only doing the head at the mo. The bottom end is staying for now.

Mark..

[Rally_2.6LC]

Hey mb,
Talk to Superscan811 on here.....he is building a high power engine (although he is going high comp too but thats through other things).
He is using a M7 head and doing some mild porting (using a die grinder) on the intake just to get the air to flow a bit better around the valves and then going oversize titanium valves that have been shortened (out of Nascar cars).
See if he can put up a picture of the intake of his head for you.

Im no expert on the heads and compression, however my original 2.6L that was built by an apprentice at Coltspeed used TP magna block, 2L Jap spec head (the rare one) and forged flat top pistons.....i was told this upped the compression to around 10 or 10.5:1 (thats just what ive been told so dont quote me on that please haha) however this sounds identical to what your running so maybe it is lower.

One last thing, are you going EFI with this or staying webers? because (im sure you realise this already) but the inlet stud pattern is different and doesnt match the series 1 heads so you will need a new manifold or adaptor plate made up.


Cheers Matt

ps is your white GC coupe the one I keep seeing at the Night Owl Classic each year??? Ive got the brown GC 4 door......

[mbrallying]

Yeah matt thats me, we do zero for the guys every year to help them out.

I am staying with the webers for now (at least the next 12 mths) and pending some funding booms would love to build a quad throttle body manifold in the nearish future. But the five link rear end and gearbox conversion are definately higher on the list at the moment.

Thanks for that info its all a big help mate.

Mark.

Ps saw some fotos from the cruise the other day, looking good mate. I caught up with the guys before they left newcastle to say g'day.

[cheaterparts]

I'll jump in if its any help

my circuit car is running 11.2 to 1 with a magna head machined 3 - 3.5 mm with flat tops
and runs BP98 pump fuel with webers and runs fine on 34 deg total advance - it of cause also runs a fair bit of cam duration which in turn drops the effictive comp ratio
so far I have run 119.5 Kw atw or ( 160 hp atw ) @ 6100

I have a bigger cam for it and will need to up the comp some more with the new build

machining the head for 10 to 1 is not a problem sorry I cant remember off hand how much to take - keep in mind that every mm you remove from the head or deck retards the cam about 1 deg - (2 deg crank)

there is enough adjustment for the cam chain slack but check the distance the adjustment plunger comes out of the oil pump while dailing in your cam and fit a spacer to the plunger
to stop it going back 14mm or 9/16 flat washers do the job - I however turn up an aluminium spacer for my builds

as for getting the best from a M6/7 head bigger valves are the best thing thumb of rule
says that a round inlet port should be about 80 % the dia of the valve
so a M6/7 has about 42 mm ports - 50 mm x 80 % = 42
so the std 46 mm inlet would be better inlarged 4 mm there how ever not enough room in the head
you can get 47 mm inlets and 39 exhuasts in 21/4 stainless these do help
other than that match the ports to your inlet clean the ports up

the other thing if you are running 45 mm webers I machined up 41 mm chokes for my car
these still pull ok down low but do run out of breath up high you will need to run as big as you can get in 45s

hope that is some help or at least food for thought

[Rally_2.6LC]

Thanks cheater that actually helps me with my build as well.

As for still running webers, if you have an astron 1 head now, and you want to still run webers you will need an adaptor plate for the astron 2 manifold as some of the studs are different........there was something I read somewhere about the rear water jets being bigger on the astron 2 heads and needing to do something to the manifold if running an adaptor plate.
Check the "For Sale" section as there was a manifold with stud holes to suit both heads, this will give you an idea for the starting point.



Cheers Matt

ps ide like to have my LC running for Night Owl next year, but again wether funds permit and if I can get it engineered or not, the 2.6L aint the problem, its the 2 seater and battery relocation and switch pannel ive put in

[mbrallying]

Thanks cheater thats everything I need to know.

One other question I was going to ask you was, I saw a photo of a quad magna throttle body manifold you made and was wondering if that was a success? I do know that the 45s are getting a bit lazy on the 2.6, so this idea to me sounds great, and something my budget may be able to handle.

Any info and/or wisdom on this would be great.

Thanks again

Mark..

[cheaterparts]

One other question I was going to ask you was, I saw a photo of a quad magna throttle body manifold you made and was wondering if that was a success?
Mark..

I still havn't used them but will go on shortly - I had them on the engine and almost fully wired up but there was a dyno shoot out across the road from the factory I was in .
(I won the 4 cyl NA class the year before) I was not going to enter as there was the ECU to set up then a mate turned up with his 944 and was winning so the webers were quicky fitted back on more so just to beat him - ( which I did )

I hope to get the donk out over Xmas to build it with some new faster bits and that will include the quads

[mbrallying]

What ecu are you going to run? I'm very interested in this now 8oD

Sounds good mate, good luck with the build.

You'll have to let me know how it works out.

Mark

[cheaterparts]

What ecu are you going to run? I'm very interested in this now 8oD

Sounds good mate, good luck with the build.

You'll have to let me know how it works out.

Mark

I have a delfi ECU off a gen 3 - I had to make up the crank angle wheels and still have
to do 1 for the cam
but the reason I went with the delfi is that they are cheap they run seq spark and fuel std
and run multi coil std and are fully adjustable
my dyno guys have the gear to set up gen 3 and do so all the time

[Rally_2.6LC]

I wouldnt mind seeing a photo of this quad throttle body setup.

[webby]

I believe this is the setup Cheater was on about?

[Rally_2.6LC]

drool.......................

[cheaterparts]

drool.......................

from a thread on quads in workbench - gen chat

How'd you do the manifold for that setup Cheater?

well the end plates are just cut out of 10 mm aluminium plate - with holes bored and
mounting holes taped
the runners I machined from round aly bar stock they have a 3 deg taper and are 50 mm at the tb end tapering to 43 mm at the head - that of cause makes it easy to blend into the head for the port match
then I welded it up
the injector mounts were hand done with a drill and die grinder
you also may notice that the TBs have been machined to take the short trumpet lead inns
which I also machined from bar stock
the linkages are off the shelf after market bits
the total cost of materials was under $ 300 not counting time