Sigma-galant.com

Hey all, heres an exercise for all the astron specialists, I know there is lots of you on this forum!

I'm looking to build up a race engine for our sigmas, to run on a banked clay speedway track.

At the moment we run reasonably standard engines with balance shafts removed, lightened flywheels, some with webers. The engines run at full revs in 2nd gear pretty much the whole way round the track, the stronger engines can handle third gear depending on track condition.

Rules for this exercise - no efi, no turbo, budget needs to be reasonable

We are thinking the 4g54 + Tr magna head, plus the usual balance shafts/flywheel.

What sort of cam would you guys run?
Head work? What compression? Pistons?
Oil work considering the flogging these engines get?
Recommend a machine shop around brisbane/SE QLD to do the machining?



Look forward to your ideas!

Chris

Pic of track so you guys can see what I'm talking about

Hi ChrisE, welcome to S-G. Seems you already got a good grasp of the Astron engine going by your run down on what you've done to your speedway Sigma. First up, familiarise yourself with the noobs best friend on the site - the search function http://www.sigma-galant.com/search.php Check out our resident Astron mad scientists Cheaterparts and Superscan811. One has oodles of track experience and the other has had success with designing intakes from road bike quad carbie racks. There are tonnes of resource material on here that will serve as a solid guide to building what you want.

Welcome to the site mate

I didn't know sigma racing was still on? would love to come check them out. I'm located between browns plains and jimboomba

ChrisE wrote: Rules for this exercise - no efi, no turbo, budget needs to be reasonable
We are thinking the 4g54 + Tr magna head, plus the usual balance shafts/flywheel.

What sort of cam would you guys run?
Head work? What compression? Pistons?
Oil work considering the flogging these engines get?
Recommend a machine shop around brisbane/SE QLD to do the machining?

I will try to give you a run down on my race engine -- Its been very good for hillclimb and circuit work

I beleve you almost cant get to much weight out on the rotating parts on an astron
I only build the small bell housing pattern 2.6 so I can run the smaller 2 lt size flywheel
I make my own flywheels from 4140 steel so I can get them under 5 kg and the outter edges are milled to make the outter edge as light as possable

http://www.sigma-galant.com/viewtopic.p ... eel#p24148

my flywheel is lighter than the one in this old post
and I have a compete clutch assembly that weighs 2.3 kg
I have removed 2 kg from the crank shaft with some polishing and knife edging
the rods are still astron however the bolts are now ARP the beams have been polished and peened
balance shafts are gone of cause
and the crank pulley is an undersize aluminium pulley
I run a bored block up 0.60"
of cause there was a lot of care ballancing and assembling the bottom end

the top end has a little port work nothing special I just knocked the guides out and ground the lumps out around the roof of the port

tthem machined the guides down where they go into the port with a taper to cut down there shape
the valve were back cut and the seats were cut right to the edge of the valve

the cam I run was a Speco gride ( MS 344 ) inlet spec 45/71 ex 85/45 duration @ 050" 267 and valve lift 471"
the comp was set at 11.3:1 and it was happy to run 30 deg total advance with 98 oct fuel

twin DCOE13 webers with 41 mm chokes ( I had to machine my own chokes weber dont make them this size )

I made my own headers a 4 into 1 with 1 3/4 tube ( sorry cant remember the primary tube lenth )

I fitted a larger baffed sump with a crank scraper

the engine made 119.5 Kw at the treads ( @ 6100 rpm ) some time ago
and spins 7000+ in all gears without much trouble

Id use a ts magna m9 head as.it has a very small closed kidney.shape combustion.chamber for higher.compression..

It's been a lot of years since we last ran one of these on clay speedway tracks but will try my best to remember what we did.

The bottom ends are pretty much bullet proof, remove balance shafts and get the bottom end balanced with clutch, flywheel and balancer. Run some decent flat top pistons and zero the deck height. Run the conrods as they are unless cranking the compression right up.

Heads are not to bad in standard form so get the ports tidied up for flow and matched to manifolds. We ran the early Magna head but now I would go for the later M7 and take .040" - .060" off for compression or even better the M8 or M9 with the kidney chamber, cc'd to get compression wanted. You can run a 34mm core plug in the back so you can get away without having to run a magna cam with the seal to stop it leaking. Throw the hydraulic rockers in the bin and run adjustable's swapping out the adjusters with Porsche or very early mazda? ball end ones so that you have full load over the stem of the valve at high lift. Swap the springs between the rockers with some machined alloy tubing so they cant slide across. Block off the egr port at the inlet manifold side and weld up the rear water outlet to the same size as the sigma one, get milled flat and then you can run the sigma inlet manifold and not have all the stuffing around to adapt a magna one. The back of the head can be machined quite easily to take double valve springs if you want to go that far.

Run the oil pump out of a sigma or triton with the hydraulic tappets. Will give you good pressure as you are not using hydraulic rockers and will fit with out modification to the timing cover like the later magna one needs. As long as the block and head surfaces are both flat and the head is re torqued, std head gasket will work fine.

We used to run a billet cam designed by a well known speed car/sprint car driver over here but for the life of me I cannot remember the specs or even if the profile is still available. Whatever cam you get, don't be afraid to run the tappet adjuster lock nut on the underside of the rocker instead of on top (normally only needed if running a regrind). Run a thermo fan and not a clutch fan. Get rid of the advance and set static timing between 30 and 34 degrees. You can get the standard carbs to work quite well (we had to use them) but stay with the weber and match to the manifold.

We had quite a lot of success with a similar build at various tracks and a good placing in a state title against 6cyl's. Engine was very reliable and ran 4 seasons with problems and only a peace of mind freshen up before selling car. There is quite a lot you can do depending on class restrictions and money. I must say, I have had some fun playing with these heads for speed car application but that was a while ago now.

Cheers for the replies guys, lots to think about. no class restrictions here as its a private track but we may have to make some of our own rules up to keep it equal.

ChrisE wrote:Cheers for the replies guys, lots to think about. no class restrictions here as its a private track but we may have to make some of our own rules up to keep it equal.

thats simple first look at safety thats works out the first set of rules --- and then maybe work the classes into basic size of engines if you have enough to feild different classes

and leave the rest free - simple

no matter what rules you put in to make things equal , the smarter guys will work around the rules and still make a faster car and quite offen at a higher cost
the faster drivers will still drive faster