cams, head work, or high compression pistons?

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AlessioDF

Re: cams, head work, or high compression pistons?

Post by AlessioDF »

vandor wrote:Hi,

It all looks very nice!

> 8mm dome pistons (10,5:1/10,6:1 CR) 84,60mm

8mm dome pistons are more like 10:8-11:1 CR. Did you measure all the volumes to see what the actual CR will be?
Or does the VX head have larger combustion chambers?

> 3) BC1/BS61 Cams (26/66 - 272°- 9,54mm lift)

You probably know what those cams were the same as in later models, but Fiat changed the valve clearance for cam timing measurement purposes, so on paper it seems like later cams are much weaker.

8) Single Plane (bigger ports) Fiat Argenta 120i intake manifold

Argenta 120ie was fuel injected, so it's likely from Argenta 110.

Yes Argenta 110 manifold...my fault!
CR should be around 10,5:1-10,6:1 because of VX head has bigger chambers: they're very close to Abarth 130TC Strada (Ritmo in Italy), almost 52cc instead of 45/46cc as in my old 124 CC1 head. So static compression should be lower than 10,8:1-11:1..
I can just think what's likely to be but I've never done precise calculations..
About cams I know that my old one are like 15/55 but 9.9 lift, while CC (1592) are 15/52 with same lift: almost equals BC1 power and speed...108bhp vs. 110bhp (with dual 40's). Incredible: isn't it? Most of people think that the magic is just in dual 40 Weber and 26/66 camshafts....

Excuse me for my elementary english, but feel free to write everything you want, I'll understand!
vandor
Posts: 3996
Joined: Sat May 23, 2009 1:23 pm
Your car is a: 1971 124 Spider
Location: Texas, USA

Re: cams, head work, or high compression pistons?

Post by vandor »

> CR should be around 10,5:1-10,6:1 because of VX head has bigger chambers: they're very close to Abarth 130TC Strada >(Ritmo in Italy), almost 52cc instead of 45/46cc as in my old 124 CC1 head.

All 2000cc engines I am familiar with have 52-53cc combustion chambers, that is what I used when I calculated 10.8-11:1 CR for the 8mm dome pistons.
I recommend measuring the actual volumes to see what the real compression ratio will be, otherwise you may have a nasty surprise once the engine is running.
Csaba
'71 124 Spider, much modified
'17 124 Abarth, silver
http://italiancarclub.com/csaba/
Co-owner of the best dang Fiat parts place in town
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FiatMac
Posts: 290
Joined: Sat Aug 01, 2009 1:14 pm
Your car is a: 1982 2000 Spider
Location: Salisbury, North Carolina

Re: cams, head work, or high compression pistons?

Post by FiatMac »

vandor wrote:
All 2000cc engines I am familiar with have 52-53cc combustion chambers, that is what I used when I calculated 10.8-11:1 CR for the 8mm dome pistons.
I recommend measuring the actual volumes to see what the real compression ratio will be, otherwise you may have a nasty surprise once the engine is running.
Csaba,
AllessioDF's engine is an 1800cc. Using a 2 liter head with 52-53cc camber volume and 8mm dome pistons I would estimate the CR to be 10.1 to 10.3.
Stan McConnell
Retired Mechanical Engineer
Salisbury, North Carolina
82 2000 Spider (driving)
78 124 Spider on the rotisserie
76 124 Spider parts car or possible Lemons racer
83 parts car
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