Tech Q: Compression SWAP

[toysrus]

Basically, I'm trying to pre-determine with your help what the compression ratio might be after using the DASH head, with the Sonata bottom end and maybe Evo II pistons ?

The DASH 12V SOHC, Bore/Stroke 85mm x 88mm, compression unknown....?

with the bottom end of a Sonata 2.4L SOHC, Bore/Stroke 86.5mm x 100mm and comprssion ratio of 8.6:1

1: Can I use the Evo II pistons, with just different/custom rings (i.e. what material/quality are the Ralliart ones made from) and what reliabilty problems or other issues will or can arise by going 0.75mm oversize in the radius of the rings ?

2: Now, how would compression be changed, firstly from using the DASH head with the 2.4L bottom end, it will rise but by how much, and then how much lower will it go after using the Evo II pistons which had a comprssion ratio of 8.5 on the DOHC evo's but set on a SOHC DASH (maybe different size) combustion chamber ?

3: What other options on custom pistons are there apart from the common hypertectic and forged and what are their properties ?

ta

[MrBishi]

I'm struggling to work out what your go is.
If you are serious about using a T88 then you will need a bottom end that revs to at least 8500rpm (I hope you agree). This means you will need billet rods and custom forged pistons. Not having 1st hand experience with the 2.4L cranks I'd be dubious about its ability to survive such high RPM.

Don't plan on building this tough motor using rods out of a N/A family car and non-forged pistons.

If you really want to get your Cordia doing 10s why not copy what the Yanks have been doing for years in their DSM Eclipses etc. Run the tried and tested route for HP & speed rather than re-inventing the wheel.

[toysrus]

True, I agree on the billet rods and forged pistons, how many companies make forged pistons apart from JE, any here in Australia (Wiesco or something) ?

Any recommended brands/manufacturers from past experiences on forged pistons and billet rods ?

ta

[Starion VR4]

yes wiesco does make a 2.4 Litre piston that is 8-8.5:1 compression, the crank does need to be nitrided for strenght, and the eagle conrods for a 4G63 6 bolt crank are the same ( i have all the above) and VR4 head.

[toysrus]

Satrion VR4, the DASH engine can't be stroked to 2.4L with the 2.0L bottom end can it ? Are you using the starion bottom end ?

[NXTIME]

You dont use the 2.4L crank in the 2L block. The 2.4 has a 100mm stroke as opposed to the 88mm stroke off the 2L. Use the complete bottom end off a TE Magna or Nimbus 2.4L. Instead of the Dash head, use a VR4 as the DASH head wont flow the amount that you are after. The larger capacity 2.4L will have more torque but wont be able to rev as high as a well built 2L DOHC. For a Cordia, Im would tend to lean towards a heavily worked @L DOHC as the 2.4L will make it harder to launch with the FWD set up of the Cordia.

For pistons and rods, take a look at some of the US shops and you will find that you can get a set of weisco or JE pistons and some billet rods for $11-1200USD plus shipping and taxes.

[NXTIME]

yes, the g63B and g64B have the same conrod sizes. The difference is in the stroke and bore.

[toysrus]

Thanks for the info NXTIME, what if I was to say I am considering selling the T88 when it gets here and switch over to a FP Red turbo as by the looks of things it would fit but very tightly and if I really want this doing 10s without going into DOHC teritory then I might just do the switch, plus I should make enough off the T88 to pay for the FP Red itself anyway :D

I've also got a custom 2nd Hand LSD Cone type (used on a rally cordia) on it's way which aparently is made/ or adapted for most vehicles for $1200 from somewhere in Brisbane, anyone know the place or have heard as I want to speak with them in regards to any mods which might/should be done to avoid having to get an auto with a stall convertor (about $5K)

So do you think I can pull of a 10sec with a DASH head or is that just as unrealistic as the T88 ?

I wouldn't be able to find a set of STANDARD Weisco or JE pistons if I were to use the DASH head would I.....or do I just have to use the g64B head gasket and how would the compression be changed by using the DASH Head instead of the VR4, doesn't the DASH have a smaller combustion chamber ?

[ProZac]

Your question (1) is a bit strange... if the bore of the 4g64 is 86.5mm, and the evo pistons are 85mm, there is absolutly no way you could use them, you can not have the rings doing the job of the piston. I would suggest you get some custom pistons made up, slightly larger than 86.5mm, then bore/hone out the block to accept them with the right clearance.. that way you know your starting with a good seal.

[Starion VR4]

Wiesco makes a piston for a 2L(4g63) engine with the 2.4L crank in it, no i won't rev as well as a 2L engine as the engine is oversquare, 85mm bore, 100 mm stroke but the torque will be better and as a result the turbo doesn't have to supply as much air EG 7000RPM air equivelant. We all seam to forget that with a turbo, torque is basically what we achieve through higher dymanic compression ratio. basic performance work revolves around the fact that higher compression ratio gives more torque right? With a turbo you are really fooling the engine into believing it has more compression ( due to boost). Summery, Dick Johnson Sierra when he 1st started tried to run 10.0:1 compression ratio with 20-30 PSI boost, as a result the engine had a narrow power band and would destroy it's self after 30 min racing right? In the end he ran 7.5:1 and 30-40 psi and the whole package survived and was easier to drive.

[NXTIME]

Starion VR4, you are correct. You CAN use the g64b crank in the g63b block, but you will need custom pistons and rods, and Weisco does make these. The eg of Dick Johnson is pertinent as it shows that power and torwue is made by using the correct mix of total compression based on the balance of static plus boost compression. Most (if not all) manufacturers now use higher compression (albeit intercooled) engines with their turbo engines, whereas the 80's saw most turbo engines using lower compression (eg Starions 7.6:1).

toysrus, as a point of reference, the fastes DASH engined car that I know of down the 1/4 is a 10.9 ET by a 70's Lancer by a workshop who have been playing with Mitsubishis eevr since you were in nappies. However, note that the lancer would have been much lughter than a cordia to begin with, and it is also RWD.

This is not a discouragement in anyway. However, if you were going to all this trouble, why not go for the 16v head and be done with it as very few people will really care if it was a 12V or 16V.

[SIRIUS]

if u were going to go with the dash head i dont think youll be able to run evo 2 pistons anyway seemin as they run 16v head...valve clearances wont line up if u use them on a 12v head