Road Rally Engine Potential Spec

[Peredur]

I'm currently building a road rally car and am considering the following spec engine build:

1.4 SR/1.3 block + crank
1.3 rods
12st Pistons (+0.5mm if I can find any)
1.4 SR Big Valve Head (already have this)
AST 3 or NVO 63 cam
Weber 38 DGAS carb on custom inlet (road rally rules, 2 chokes etc)
4 branch

Any suggestions or observations? I might need to pocket the pistons with such a high lift cam and I'm not sure how high the compression will be using the 1.4 head.

Pic here of the head, the valves are quite large :d

http://i1279.photobucket.com/albums/y528/Peredur_Wyn_Davies/Head_zpsc4da6c29.jpg

[Royston]

On my SR I has 31mm inlet and 39mm exhaust valves, as a precaution I had the piston pockets opened up to permit the valve Head to enter the pocket of the piston as they were too big/wasn't enough clearance.

On my build with a mild 270 cam there were masses of clearance, bit it depends on you cam/lift/duration.

http://img.photobucket.com/albums/v697/1297cc/DSCF0982.jpg
Big valve left, standard right

[Stuart]

Lift at tdc will be your limitation, but in order to get contact you need to be running a silly 305deg or more cam.

[_Jake]

Good luck finding 1200 pistons i had to import mine from the fritz, i have a 1300 bottom end here if you interested

EDIT; http://www.ebay.co.uk/itm/Mahle-Kolben-fur-Opel-Corsa-Kadett-1-2-S-Neu-/380594331167?pt=DE_Autoteile&hash=item589d309e1f i got mine from here. Arrived within a week, cant complain really

[mowgli]

you can reuse a 1400 block with a minor rebore to fit 1200 pistons, but you also need 1300 rods, as the gudgeon pins are bigger..

why not get a 1400 16v bottom end. do a quick measure & if the cam isn't too crazy, it will save you a load of money. don't the oval boys do something similar??

[Peredur]

Initially the plan was to use a 16v bottom end but I was told by a friend that the compression would be too high and the pistons don't have enough metal on the crowns to machine cutouts, hence why I thought the 12st piston route would be better :confused:

[_Jake]

12st is a high compression engine anyway, unless your using a 1600 head like me your going to have to machine the pistons down to get it sensible from what i can gather. I was supposed to start building my bottom end next weekend but since i wrecked my car it will have to wait a while, speak to mowgli he knows :)

[mowgli]

the compression will be similar on the 16v to the 12st. its down to fitting some softish valve springs & doing a dummy head build to measure the valve lift. considering the 12st was designed with big enough cutouts to survive a cambelt failure, which i managed at 75mph once, the cutouts are a bit of an overkill. you might be pleasantly surprised, as long as you time it right

[Peredur]

I want to fit a fairly lairy cam to get the best of the head so the 12st route looks a bit better due to the cutouts mentioned. Would I be able to fit the 12st pistons as they are into the block after boring or would I definitely need to machine the crowns?

[meritlover]

one observation for starters would be the potential for cracks forming between the inlet and exhaust valve seats.
what is controlling your sparks and why is there not any decent management on that list?

[mowgli]

I want to fit a fairly lairy cam to get the best of the head so the 12st route looks a bit better due to the cutouts mentioned. Would I be able to fit the 12st pistons as they are into the block after boring or would I definitely need to machine the crowns?
the 12st has pockets of about 4mm from memory. but you will be getting around 11:1cr without machining.

if you wanted to machine them down, then the 1400 8v bottom end suddenly looks very similar.

the reason we did the 1200+1300=1400 conversion back in the day was simple... they hadn't launched the 1400 at the time.

[Peredur]

Thanks for that, so would there be any gains from running the 12st pistons over the 1400 bottom end?

[mowgli]

if you have a 1300 as a donor, then yes, because the 1200 pistons fit the rods. but running a car at 11:1cr is more for torque than crazee top end hp.... so the lairy cam might not be the best...and you would also need to run octane boosters & lead additives, & like meritlover has pointed out, decent spark control

if you want to run on super unleaded or even normal unleaded, a 1400 std bottom end will be pretty good. and with that head & cam, and a decent bloke to set it up, i'd guess you'd be around the 100hp mark with some very good torque too

[Peredur]

TBH I'm not after all out BHP, I'd much prefere a torquey driveable engine,

[garyc]

Why not run a 14se, you can still get +40 pistons. And the head is better for a start.

I have got some 1300 rods if you need some.

[Peredur]

I've already got the head (square port), pic on the 1st page, and thought this build would be quite a good option

[gearbox90]

I would use the ast2 cam .

[Peredur]

Any particular reason for choosing the AST2 over something a bit more aggressive?

[Stuart]

Ast2 is a proven beast of a cam. The piper bp300 is the next best.

[gearbox90]

unless you are going solid lifter then there is no real advantage . i very well known vauxhall engine builder told me that ast2 would the highest to go on standard lifters , and tbh on road rallying you done want to agressive a camshft . I ran ast2 in my road rally nova and found good spread of power .

[_Jake]

Im going for an ast19 in mine so we can compare once theyre built ;) lol

[garyc]

Twin SU's on a custom inlet would be the way to go for me, or a big down draught dellorto.

[Stuart]

TBH I'm not after all out BHP, I'd much prefere a torquey driveable engine,
Ast2, cut print done.

[gearbox90]

Ast2, cut print done.
Agreed :thumb:

[Peredur]

Carb is going to be a Weber 38 DGAS downdraught, that's sorted,

[Peredur]

So, Would there be any better options than the 1200 piston, 1300 rods, route? don't mind a bit of working out and machining etc if it'll be a better engine in the end.
Also, I don't really mind putting solid lifters and uprated springs to deal with a race/rally cam.

[mowgli]

/\ for high compression, its pretty much the best way, whilst still using std components.

[Peredur]

Thanks for that Mowgli, what I wanted to hear without people getting into an argument about cams etc.

Budget high comp 1400 it is then!

[Stuart]

You can't have a wide torque band annnnd a silly mental cam on a simple 8v setup. If you are dead set on a rev monkey engine then simply build one and ignore any advice lol

[Peredur]

I'm not after a rev monkey but want a fair deal of power and torque hence looking for a slightly more peaky cam than the AST3 but not a full on race cam

[gearbox90]

didnt relise it was an argument about cams tbh . Just thought i would give advise from my experience with cams and road rallying but nevermind, use what you want . When you start to wonder why cars with less power than you are finishing higher up than you ;)

[Dave A]

Have to agree, road rallying is not all about ultimate power at all. With all the issues around noise ad driving standards at the moment I'd think twice about that "ultimate" engine if I were you, might not get to use it that much! Power rarely wins on a road event, even in wales, down here in the south west I can regularly finish in the top ten with a standard 1.3 sr engine.

[Peredur]

Ok, I realize I might have been contradicting myself, sorry guys :tard:

I'm not looking for the "ultimate" engine but want a solid powerful lump. Having navigated in a few different spec cars I have an idea of where the power is needed etc and think I could get away with a fairly peaky cam.

I'm not snubbing your advice (although it may seem like that) :roll:

Really, I'm looking to build the best I can within my (limited) budget :)

[Peredur]

Got some 12st pistons now, just need a 1.3 engine if I can find one!

[garyc]

There are plenty if you look hard enough ;-)

[philip]

Speak to rhydian @ james motorsport, he's down your end matey and has built a fair few 8v's for the road rally lads, most of them end up on my mates rollers and seem to be doing very well too.

[Peredur]

Rhydian is literally 2 mins away, went to school with him and his brothers haha, What rolling road would that be?

[dionbee]

AB From my guess Peredur.

[philip]

Yeah, andy + ade are top lads, used them past 9yrs