4.6 crank, rods + 4.0 pistons

russell_ram · Post by **russell_ram** » Wed May 23, 2007 10:00 am

Gav,

10.1 with 4.6 pistons, 11.63 with 4.0 pistons.

These go down to 9.5 (4.6) and 10.8 (4.0) with composites.

Unless you want to run LPG I would have thought the composites/4.0 pistons at 10.8 is a good compromise.

Russ

ihatesissycars · Post by **ihatesissycars** » Wed May 23, 2007 10:04 am

Thankyou Russel, you're a star!

Lpg, no but nitrous yes so i need to choose a c/r i guess thats a good compromise as you say.

Decisions. . . .

kiwicar · Post by **kiwicar** » Wed May 23, 2007 10:09 am

Hi Gav
what cam timing are you planning on using?
how far down the bores will the top of the pistons be?
Mike

ihatesissycars · Post by **ihatesissycars** » Wed May 23, 2007 10:53 am

Bore and piston measurements will be standard rover measurements whatever they are. Cam timing, yet to figure that out. The only compromise towards using nitrous will be a lower c/r, everything else will be geared towards max n/a power.

kiwicar · Post by **kiwicar** » Wed May 23, 2007 2:06 pm

Just asking as the two biggest factors determining CR with those fancy new heads of yours will be when the inlet valve closes and the squish band. If you are using "normal" rover dished pistons you will have to use a lower CR than if you use "reverse dome" style piston (see je pistons catalog" with a big squish band. you also need to consider if there is enough clearance between the head and the top of the piston now the head has a proper squish area, probably OK with a comp gasket but you will need to check with the tin gasket 40 thou min.
Mike

Post by **katanaman** » Wed May 23, 2007 2:18 pm

standard heads still have a squish area so the piston/head clearance will remain the same. That's not to say it couldn't be made better by decking the block but if you running lowish compression then that's not a good idea.

ihatesissycars · Post by **ihatesissycars** » Wed May 23, 2007 2:53 pm

As Markli says i believe squish and head to pistons clearances should be unaffected. The heads were made to be a relatively simple bolt on not an all out thing requiring modifying of everything else on the engine to accomodate them.

I will be getting cut outs put in the pistons anyways as i intend to run a large cam and the vlaves are bigger too.

kiwicar · Post by **kiwicar** » Wed May 23, 2007 4:27 pm

I thought from the post further up Gav was talking of 10.8 to 1 comp with 4.0 pistons, I would call that fairly high on 95/97 octane gas and nitrous.
I would say was faily high to use without considering clearences, and I did qualify it all with the reference to tin gasket which the 4.0 pistons were not designed to be used with.
Was just trying to help avoid an unecessary expense.
Mike

Post by **katanaman** » Wed May 23, 2007 4:53 pm

To the best of my knowledge the deck height is the same on all engines there for the piston head clearance is the same. New heads don't change any of this what so ever which looked to me like you were inferring. I would say this means that tin gaskets don't cause a problem clearance wise but will compression wise looking at russells figures. Admittedly this is an assumption on my part as there are more than a few cross bolt bottom ends with old type (larger combustion chamber) heads on and tin gaskets.