help to make a 9.5 ratio on a 3.2 rb30/26 block stock

[krysto_77]

Hello everyone ,

I am currently building a 3.2 L with an RB26 cylinder head my block is stock and I will run E85 and E100
My mapper who is Romain Levesque from dear RaceCAL LtD (former syvecs technical director) asks me to make a ratio of around 9.5.

so after reading a lot of topics on it
I found pistons with a CR 9.0 and 10.0 expensive IRP
what direction would be taken to achieve a ratio of 9.5 without having to plane the block by 2mm or to do it a minimum, but to be able to play with the thickness of the cylinder head gaskets

thank you in advance for your response

[r32-25t]

Custom pistons or machine the crown of the 10:1 piston down 

[Lithium]

12 hours ago, krysto_77 said:

t of topics on it
I found pistons with a CR 9.0 and 10.0 expensive IRP
what direction would be taken to achieve a ratio of 9.5 without having to plane the block by 2mm or to do it a minimum, but to be able to play with the thickness of the cylinder head gaskets

thank you

I'd verify how invested in exactly 9.5 he is if it turns out to be a massive amount more effort to go 9.5 vs 9.0 or 10.0.  He may have just said that as a suggestion not realising it'll be a huge deal to go specifically there when half a point either side isn't so bad.

[krysto_77]

5 hours ago, Lithium said:

Je vérifierais à quel point il est investi exactement dans 9,5 s'il s'avère que cela demande beaucoup plus d'efforts pour passer à 9,5 contre 9,0 ou 10,0. Il vient peut-être de dire cela à titre de suggestion, sans se rendre compte que ce serait une grosse affaire d'y aller spécifiquement alors qu'un demi-point de chaque côté n'est pas si mal.

 

[krysto_77]

yes you are right, indeed it is for information only.  there is not much difference being at 9 or 9.5 or 10.  but when I see that you have to plane the block by 2mm if you have taken (example) CP piston which means that you end up with an 8.2 with the rb26 cylinder head.  hence the question I ask is what would be best to achieve what he is asking me.  take pistons in 9.0 or 10.0 to avoid planing a famous 2mm on the block knowing that I worked on the dome of the cylinder head which became total hemispherical

[GTSBoy]

47 minutes ago, krysto_77 said:

but when I see that you have to plane the block by 2mm

Which is a thing done by no-one ever. Not even remotely a good idea.

I would run an engine with 10:1 these days. Good management and fuel compared to the early 90s when these boat motors were designed & built.
 

[r32-25t]

1 hour ago, krysto_77 said:

yes you are right, indeed it is for information only.  there is not much difference being at 9 or 9.5 or 10.  but when I see that you have to plane the block by 2mm if you have taken (example) CP piston which means that you end up with an 8.2 with the rb26 cylinder head.  hence the question I ask is what would be best to achieve what he is asking me.  take pistons in 9.0 or 10.0 to avoid planing a famous 2mm on the block knowing that I worked on the dome of the cylinder head which became total hemispherical

You will need custom pistons made, the combustion chamber is to modified for any off the shelf piston to give a good compression ratio 

[krysto_77]

Thank you for your answers 👌

[Komdotkom]

It's also worth noting that the static compression ratio needs to be considered in conjunction with your camshaft specification to ascertain the dynamic compression. 9.5:1 is fine with stock cams but if you're running 288's then you'll be pumping 120psi and it'll be a dog.

[krysto_77]

11 hours ago, Komdotkom said:

Il convient également de noter que le taux de compression statique doit être pris en compte en conjonction avec les spécifications de votre arbre à cames pour déterminer la compression dynamique. 9,5 : 1 convient aux caméras d'origine, mais si vous utilisez des 288, vous pomperez 120 psi et ce sera un chien.

I see what you mean !! 👍

so I drive with E85 AND E100 my cylinder head and full supertech with 270° camshaft and 10.25 lift

this weekend I spoke with my mapper and he told me 10 ratio would be even better

so I went to set up a setup with :

3.2l crankshaft from expensive spool import with a stroke of 91mm

Nitto or IRP connecting rods length 152.5 mm

and piston irp ratio of 10

after having the information near spool import the setup did not work because of the crankshaft which is 91 mm 

therefore the assembly mounted in the engine block will come out 1mm high above the cylinder head gasket surface

so I have to review the construction of the lower engine

low IRP is Italian I am French I wanted to limit the costs because as they are in Europe I do not have customs fees to pay 🤷‍♀️

[Komdotkom]

You can probably just purchase the crank, rods and pistons from Spool Imports as a package.

[krysto_77]

Il y a 20 heures, Komdotkom a déclaré :

Vous pouvez probablement simplement acheter la manivelle, les bielles et les pistons auprès de Spool Imports sous forme de package.

Yes indeed ; They offered it to me, I'm waiting for their quote 😉