6 replies to this topic

[robert.hedges]

Hi,

 

I'm starting a small bore reasonable spec engine build as follows:

 

lightly ported 12g295 head with standard inlets but overbore exhaust valves

1.3 Roller Rockers

Twin 1.25 SU'swith rams and pancake filters

SW5-07 cam (Purchased)

twin valve springs

A-Plus block

3.44:1 FD

 

Now the problem... I'm unsure which way to go, either flat top 1098 + 40tho with 1098 crank or flat top standard 998. Either way it would be using  Russell Engineering Pistons operating at CR of around 10.-10.5:1 (yet to be purchased)

 

 

I'm leaning towards the 1098 but that would add additional cost at this time through the crank and block work etc. where as if I stick with the 998 I can be up and running quite quickly and possibly look to change to the 1098 later when more funds are available.

 

The question is... I'm looking to have the dizzy curve modified to suite the engine build, but if I go down the 998 route now with modified curve will I need to have the dizzy re-adjusted to suite the 1098 later or will the curve be the same?

 

As silly as it sounds the answer to the question may sway me one way or the other as changing the curve later is yet more cost!

 

Any thoughts would be welcome.

 

 

[fwdracer]

Junk the dizzy - technolgy best left in the 1960's. Go to a Megajolt system and you can then tailor the advance curve to whatever engine you end up with, without spark scatter, points wear and all the other compromises a dizzy brings (Unreliability on wet days etc).

 

As for engine choice - 998cc unit all the way. The 1098cc is long stroke - a lazy engine with limited rpm potential - the 998cc unit will get everything out of your proposed cam/CR/Carbs.

 

If you are overboring anyway go to +80 Russell Eng Pistons tho' or use even more extreme sized +135 Calver pistons. You'll end up with a "squarer" 68mm bore/76.2mm stroke engine that will withstand decent high rpm  without reliability issues.

http://www.calverst....ore_pistons.htm

 

I've no affiliation with Calver ST - but race a 998cc unit, they are brilliant things and if I were to build a road unit, the biggest pistons and maybe even a 12G940 head conversion (pocketed block) would be my route.

[robert.hedges]

Thanks for your thoughts... hadn't seen these larger pistons.. very interesting.

[KernowCooper]

Speak to H&H Ignitions 01384 261500

 

the advance curves are very different on the 998 and 1098 and the 1098 needs to be correct to avoid terminal damage

[robert.hedges]

Thanks for that. Great knowledge.

[Spider]

My own experience with the 1100 engines has been good and unquestionably worthwhile over the 998s. You don't have to rev the 1100 as hard and have produced better results than the 998s, also I've found them in most states of tune more street drivable than the hotter 998s. 

 

Generally, boring the small bore block up to +0.100" oversize isn't a problem but going bigger than this, you may find fresh air where you don't want it, not often, but does happen. The bores at these bigger sizes do of course need to be off set.

[timmy850]

If you are overboring anyway go to +80 Russell Eng Pistons tho' or use even more extreme sized +135 Calver pistons. You'll end up with a "squarer" 68mm bore/76.2mm stroke engine that will withstand decent high rpm  without reliability issues.

http://www.calverst....ore_pistons.htm

 

Calver is selling Graham Russell's 68mm pistons. Have a read through this and the articles on his website

http://www.ausmini.c...php?f=2&t=87949

 

 

You can also get the accuspark blackbox unit, which uses your current distributor and can adjust the advance and dwell curves.

http://www.accuspark...uk/Blackbox.htm