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juha_teuvonnen
Juha Teuvonnen

(7 posts)

Registered:
02/16/2011 04:56PM

Main British Car:
Rover v8 build: 4.0 block, 4.0 pistons, 4.6 crank and rods, 3.9 heads
Posted by: juha_teuvonnen
Date: October 20, 2011 05:22PM

Hi All,

I am contemplating the following Rover V8 build: 4.0 block, 4.0 pistons, 4.6 crank, 4.6 rods and 3.9 heads. I was told that 4.0 pistons combined with 4.6 crank and rods will yield a compression ratio somewhere in the neighborhood of 10.9:1, which IMHO is a bit high. I am wondering if I use the 3.9 heads (37 cc) instead of 29 cc 4.0/4.6 heads, what will be the compression ratio in my build?


juha_teuvonnen
Juha Teuvonnen

(7 posts)

Registered:
02/16/2011 04:56PM

Main British Car:
Re: Rover v8 build: 4.0 block, 4.0 pistons, 4.6 crank and rods, 3.9 heads
Posted by: juha_teuvonnen
Date: October 20, 2011 06:06PM

I did the math based on [en.wikipedia.org]

With stock 4.6 pistons,rod and crank, assuming
bore=94 mm
stroke = 82 mm
Compression ratio Cr=9.35

We get
Chamber volume Vc = 68cc

According to clever and resourceful folks on discoweb, with 4.0 pistons, 4.6 rod and crank, the Cr turns out to be10.9, which in turn means that the chamber volume turns out to be Vc ~ 57.27

If we slap a 3.9 head instead of 4.0/4.6 on that puppy we increase the Vc to approximately 65.27

Which yields us a compression ratio of approximately 9.71

While 9.71 != 9.35 it should be workable with premium gas only, especially given the fact that GEMS has knock sensors and knows (how to/when to) retard ignition timing and enrich the mixture.


Phillip G
Phillip Leonard
Kansas City
(395 posts)

Registered:
02/03/2008 04:12PM

Main British Car:
1992 MG RV8 Rover 3.5

Re: Rover v8 build: 4.0 block, 4.0 pistons, 4.6 crank and rods, 3.9 heads
Posted by: Phillip G
Date: November 04, 2011 09:40PM

You guys are amazing,.

Are you all former GM & Ford engineers ?

Where'd you come from ?

keep them on the track,

phillip g
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