Using older heads on a serpentine engine

[ITVRI]

I have an early set of ported stage three heads that I would like to install on my Chimaera Serpentine engine but have observed that the mounting bracket in the older heads has one bolt hole less.
I believe it is possible to install an older set of heads on the newer engine.
Has anyone gone through the process and can advise about how to go about mounting the power steering and alternator?
The heads are 34cc will this make a big difference to the compression ratio?

Edited by ITVRI on Thursday 15th December 17:09

[900T-R]

ITVRI said:

The heads are 34cc will this make a big difference to the compression ratio?

Yes. Serp heads have 28cc combustion chambers as per standard (st preserp 36cc IIRC).

Roughly, the bowl in the piston tops (without valve reliefs) is like 85 mm across and 4-5 mm, deep. Volume is pi x r squared x h, makes 3.14 x (4.25 x 4.25) x 0.5 = 28 cc - so the combustion chamber volume in the heads make about half the total combustion chamber. Which - again very roughly - makes the difference about a full point, so from 9.5:1 you would drop to 8.5 or so.

All extremely quick and dirty calc from visual memory so I could be about 100% off , but you get my drift as in what sort of proportions you should think...

Edited by 900T-R on Friday 16th December 10:38

[OleVix]

900T-R said:

Yes. Serp heads have 28cc combustion chambers as per standard (st preserp 36cc IIRC).

Roughly, the bowl in the piston tops (without valve reliefs) is like 85 mm across and 4-5 mm, deep. Volume is pi x r squared x h, makes 3.14 x (4.25 x 4.25) x 0.5 = 28 cc - so the combustion chamber volume in the heads make about half the total combustion chamber. Which - again very roughly - makes the difference about a full point, so from 9.5:1 you would drop to 8.5 or so.

All extremely quick and dirty calc from visual memory so I could be about 100% off , but you get my drift as in what sort of proportions you should think...

Meaning: These heads will work fine for a turbo/SC build but not for a NA engine

[DangerousDerek]

OleVix said:

Meaning: These heads will work fine for a turbo/SC build but not for a NA engine

OP if you decide they are unsuitable please give me first refusal

[900T-R]

Please make your own calculations based on actual observation at the piston end of things before deeming a combination (un)suitable for your purpose.

I just made my quick back of a fag packet calculation based on assumption in order to demonstrate whether the difference is likely to be significant, which it is.

[blitzracing]

The composite head gasket is your extra combustion space as I understand it?

Edited by blitzracing on Friday 16th December 17:56

[ITVRI]

Cheers for your thoughts and help.
I undertook some more research and by my calculations the heads are rated at 34.5 cc from the original 29cc which has changed the ratio by 6cc and moves the compression ratio from 9.35 to 8.6:1
While this appears quite low I came across a calculator showing Compression Ratio vs HP difference.

After entering original HP (210) and compression ratio (9.35) and entering in the potential CR of 8.6:1 it shows only a 5 HP loss which I think I can live with considering the benifits would be 25-30hp once I match them to a 45mm manifold with shortened flared trumpets.

Calculator here
http://www.bgsoflex.com/crchange.html

I was surprised that the compression ratio change of 0.7-0.8 is only a 2 percent gain (or in my case loss). The unknown is the cam overlap and how this might exacerbate it.
I suppose I could just use the tin gasket instead of the composite one.

Edited by ITVRI on Saturday 17th December 00:41

[N7GTX]

Perfect for one of these:

[Dominic TVRetto]

ITVRI said:

Cheers for your thoughts and help.
After entering original HP (210) and compression ratio (9.35) and entering in the potential CR of 8.6:1 it shows only a 5 HP loss which I think I can live with considering the benifits would be 25-30hp once I match them to a 45mm manifold with shortened flared trumpets.

...

I was surprised that the compression ratio change of 0.7-0.8 is only a 2 percent gain (or in my case loss). The unknown is the cam overlap and how this might exacerbate it.

5hp (true or not) is only a single facet of the car's performance, in this case peak power - lowering the compression will affect the performance across the entire rev range, and therefore will have a far bigger effect on the driving experience than that figure taken on its own merits would suggest .

Having lowered the compression ratio by 0.5 on my other car (albeit a 2l turbo), the effect was immediately noticeable in terms of pickup from lower revs - something used regularly in day-to-day driving and therefore always making it's presence felt...

Also it may be worth checking the actual compression of your engine, as it is conventional wisdom around here that some of the Rover model's engines compression ratio's were lower than advertised - so you might end up with a low 8.x CR with those heads, which would exacerbate the aforementioned effect on performance.

Food for thought maybe...


Dom

[Graham]

if you use the tin gasket rather than the thicker composite would this not bring the cr back to where it was. the reason the later heads have a smaller bowl is because of the thicker gasket...

[Dominic TVRetto]

Can you deck the block on a 4l, or is there no room..?

[Sardonicus]

By

Dominic TVRetto said:

Can you deck the block on a 4l, or is there no room..?

Yes you can and less material removal when compared to the cylinder heads to acheive your desired CR