trackday 2.0 with 2.4 head?

[gt350ta]

Hello everyone,

I'm starting to build my trackday 2.0 cih engine.
My plan is to fit forged pistons giving in stock 2.0 about 10:5 - 11:1 cr from Venolia and then fit 2.4 head.
Pistons should give then about 9.7:1 cr. From my calculations in "CIH numbercrunch" program from opeltuners the dome of venolia piston is about - 9 cm3 .
Then milling the head 1mm down from 103mm to 102mm height ,that should take from head volume about 5 cm3 ,which would give about 52-53 cm3 2.4 head (stock is about 57). That should bump cr to about 10.5:1, which is enough for 300 12.1mm valve lift camshaft with solid lifters and 100 octane fuel.
Sorry for all these "should" & "about" but I need any suggestions here.
Off course before any action taken I will measure my 2.4 head volume and height first. I’m just asking if this is idea good.

The other option is to install 1.7 or 1.5 head (I have all parts needed) but head job for larger valves, better airflow and unshrouding near inlet valve will cost me the same as set of forged pistons.
Any other ways I can go?

The rest of parts are:
- 1.9 block bored to 95mm
- lightened 1.6 crank (is it cast or forged item?) balanced with lightened to about 7 kg flywheel and clutch cover
- pre 73 forged rods
- polished rocker arms
- modified Weber 32/36 DGAV or 38 DGAS (which ones better?) with modified intake manifold for start, later twin 45 dcoe (I can get twin dellorto 40 from alfas for cheap, but read somewhere they are not good for performance use)

My plan is to achieve 150-160 hp to stand chance against Alfa GTV and BMW e30 1.8is.

Sorry for my english, still learning.

Best Regards
Przemek

[Aardvaark]

Good luck with you project. Keep us informed on your progress.

[ggl]

Back in the day I built a somewhat similar engine

2.0 bored to 96, non-forged flat top pistons
1.6 "street ported" head fitted with 42/37 vales with slimmed down stems and skimmed 1.5mm
1.7 forged rods, polished and balanced
300 degree cam with 12mm lift (sorry, that's all I can remember as this was a few years ago)
Stock 2.0 crank, balanced
Lightened and balanced flywheel
(yadda yadda yadda)

On dual 40 DCOEs it put out 148hp and on 45s it put out 156 hp (flywheel)

I made a conscious choice about running flat top pistons (cheap) and putting the money towards a proper head job instead as I couldn't afford both. I had to be a little careful about over revving it but on the other hand the stock valve train isn't too happy about those high rpm's either so I felt it was a decent compromise

[gt350ta]

So I guess I have to go for dual webers for 150 hp. Or maybe go for a 350 Holley? They are cheap on ebay. Or the inlet manifold is the restriction whatever carb is used?
Another question: how will this 2.4 big exhaust valve behave on 2.0 engine, isn't 40mm to big for 2.0?
And can anybody give me any directions how to modify rocker arms, I can polish them and smooth all edges, but here in Poland we don't have any specialist for shot peening.
Thanks for any help.

[opelnut10]

Originally Posted by gt350ta So I guess I have to go for dual webers for 150 hp. Or maybe go for a 350 Holley? They are cheap on ebay. Or the inlet manifold is the restriction whatever carb is used? Another question: how will this 2.4 big exhaust valve behave on 2.0 engine, isn't 40mm to big for 2.0? And can anybody give me any directions how to modify rocker arms, I can polish them and smooth all edges, but here in Poland we don't have any specialist for shot peening. Thanks for any help.

The biggest problem with the 2.4 head is finding a carburated manifold to fit it. I would modify the 2.0 head with bigger valves and maybe a street port job. As far as rocker arm modification you can cut the side rails down which will take some weight off (take the arch out of them) A 350 Holley will not be enough to get the HP you are looking for, a 500 CFM is a better choice. My 1.9 + .060 overbore with Chevy valves (1.84&1.50) with 12.5 to 1 compression, 1 3/4 inch header tubes with 3 1/2 inch collector and a Cannon manifold with a 500 Holley and big cam made 185-190 HP at the flywheel.