RAdams

It is an MDX block, yes. With different pistons.

You're basically upping the compression ratio on an MDX motor with new pistons, slapping on some higher-flow heads with nicer cam profiles and jamming it into a car that's lighter than the intended application.

Torque (lots) from the additional displacement and horsepower from the cams, compression ratio and redline.

If that's not the formula for fun I don't know what is.

Sypher

Thanks, but I've heard tha misery loves company, so you might be trying to trick me...

JSuppi

damn thats a nice chuck of change, maybe something i'll look at doing after my extended warranty runs out and I can have some fun

Now the big question, let's see who's going to be the first one to do this mod and then stick the SC on it (with the headers, etc.). If it all works, that's going to be a beast.....

astro

jesus christ...
I said in the first thread, that I have the money, and I'm ready to buy the full package right now...still nobody has spoken to me...

GET A HOLD OF ME.

bullaculla

The compression is too high to safely add the S/C. you'll blow the head gasket.

typeR

ive been sending them emails telling them to watch out for you Robb...i told them your check'll bounce...because i want mine before yuo get yours ...you rich gotta have everything bastard

Closer

They already mentioned that the pistons can be changed for lower compression.

MDX-S

They turbocharged S2000's to 8PSI on 11:1 C/R, so have no fear

bullaculla

Trust me, I really want your kit! BAD! i just dont want to be the first to bolt on an S/C. I have already talked to a few shops abiut doing the work. Acura dealer won't touch it!

EricL

So, just to be clear, this package is just the modified MDX short block (pistons, balance, etc...)

As here is the item and pic of the factory stock MDX block:

http://www.acuraautomotiveparts.net/...SMISSION+ASSY.





With the MDX short block coming in at around $994...

Modified MDX Short block only (no heads)?

With the modified rod ratio, the intake velocity/charging at lower speeds in going to fatten the torque up quite nicely, but, it's hard to know how much porting and polishing the "complete" kit got to keep the torque and power up at the top end too.

Rod Ratio "stuff":

http://hometown.aol.com/vilinss/tech.html

AcuraTLSFan

When you use the Type-S pistons with a block with higher displacement...doesn't the compression ratio decrease instead of increase? Compression Ratio is the ratio of the volume when the piston is at the top position compared the the volume when the piston is at the lower position. Can someone explain to me why i'm wrong?

typeR

i understood them not to be type S pistons...

acuraboy_RENAMED

u're theory is correct but u're making the assumption that the type S rods and crank are being used as well. they are not and that's why this kit has the compression numbers it does. i believe a shorter rod is being used (more strength) and that a seriously re-worked crank is also being employed. the crank is where u're getting the increased travel/throw of the piston. so the piston is being pushed through a greater length of the cylinder versus a stock MDX setup. the greater distance traveled - higher compression.

or something like that.

i stayed at a holiday inn express last night

EricL

1. I believe the crank gets some chamfering to make for "better lubing" (as to SERIOUS work -- I don't think so).

2. The compression ratio is based on:

CV (cylinder volume) # the volume that is SWEPT by the top of the piston
CCV (combustion chamber volume) # the area above the piston at TDC (AKA unswept volume)

CR (compression ratio) = (CV + CCV) / CCV

3. The "slugs"/"pistons" are changed from the MDX to different pistons that allow for less compression (than with the MDX slugs) (Note: I can’t know for sure, since I haven’t seen the pistons, but I’ve included some math that will predict combustion chamber volume and compression ratio and the change in them (based on the pistons and wrist pins being identical). I’m making a guess, but based on the increase in compression with a 7mm increase in stroke, the compression would increase from 10:5 to 11.26.

4. IF the MDX pistons (at top dead center) LEFT the combustion chamber volume (as it was with a stock CL Type S), the compression would be increased due to the increase in stroke. The "swept" area is increased with the shorter rod (in the MDX) and longer stroke of the crank. If both sets of pistons were flat top pistons or the Type-S pistons were reused (if that was even possible) the change in compression ratio would be from 10:5 : 1 to 11.26 : 1.

Ok, first some specs:

< --------------------------- >
CL Type S
CL
Bore and Stroke: 3.50 in. x 3.39 in. (89 mm x 86 mm)

Type S compression ratio: 10.5: 1
CL compression ratio: 9.8: 1

Total displacement (just for checking purposes): 3210 CC 3.21 liters

< ------------------------- >
MDX
Bore and Stoke: 89 mm x 93 mm (That is a stroke that is 93-86 = 7mm longer in the 3.5L engine (MDX factory short block)
Total displacement (just for checking purposes): 3471 CC 3.471 liters
MDX compression ratio: 10:0: 1


Derived figures (see math below for equations to get the values):

MDX combustion chamber volume (CCV) = 64.22 CC (based on 10:1 compression ratio.



So, how about some math?


First, figure the “swept” volume (not including the combustion chamber volume:

(We just need the area of the bore x the length that the area is swept)

Pi r^2 = Area = Pi * (8.9cm/2)^2 = 62.21 cm

Volume = Area * stroke = 62.21cm^2 * 8.6cm = 535 cc (cm^3)

Now just to check, we take the 3210 CC that Acura gives for total displacement and divide by 6: 3210 / 6 = 535 cm^3 = 535 cc for each of the 6 cylinders in the V6.

Time for the combustion chamber volume (CCV): [ CV = chamber volume, and CR = compression ratio ]

CR = (CV + CCV) / CCV and CCV = CV/(CR – 1) [CR = 10.5, CV = 535cc (for stock 3.2L CS)]

CV = 535cc / 9.5 = 56.32cc (So, the combustion chamber volume is now found for a stock CLS

Now, let’s assume that the combustion chamber’s volume stayed the same with the MDX slugs (the volume removed or added at the top of the piston would have to subtract or add the same volume as the original CLS slugs did). (A flat top piston for both would make this a no-brainer).

The volume is now going to be greater with the stroke increased from 86mm to 93mm (+7mm).

Volume = 62.21 cm^2 * 9.3 cm = 578 cc. (This is the swept volume in an MDX or 3.5 type s)

Just to check 578cc * 6 = 3.468 liters (and is close enough to the 3.471 liter spec given in the Acura MDX website blurb)


Ok, I’ll assume that a miracle occurs and the MDX piston is designed to keep the combustion chamber volume exactly the same; this would allow for an increase in CR.

CR = (CV + CCV) / CCV = (578 + 56.32)/56.32 = 11.26 : 1 (With MDX pistons with same volume removed or subtracted from combustion chamber or if assuming both pistons are flat topped (they aren’t).

AND, lets check the math so far with the values I’ve obtained for a 3.2L CLS (no mods)

CR = (535 + 56.32)/56.32 = 10.5 : 1

If both sets of pistons were “perfectly” flat (flat top pistons), this would be done and one could assume that the stock block would give an increase in compression ratio from 10.5 : 1 to 11.26 : 1. (That’s assuming a bit, but it would be easy to see that it would be possible to have a compression ratio that is a bit to high for 91-octane and would probably move the requirement up to 93-octane. There’s probably a 2-percent gain there (5HP or so as well).

The pistons in $2500 conversion kit claims to have a compression of 10.85 :1. The combustion chamber volume would need to be reduced from a 3.2L engine (metal would need to be removed from the “slugs” when compared to the OEM 3.2L Type-S pistons (sitting at TDC). The change in volume to get the 10.85 would be CCV = CV / (CR-1). Solving for CCV we get: 578 / 10.85 – 1 = 58.68. The “new” pistons would have to “account” for a 58.68 – 56.32 = 2.36 cc increase in chamber volume (if the Type-s were flat top pistons, the pistons would have some small cut outs in the top.





Finally, if anyone wants to see if you can get some 0.050 oversize pistons, you can bore out the 3.2L to 3.3L and the 3.5L to 3.6+L …

As a note – with the shorter rod and longer crank, you are getting the piston speed to increase by around >10% and this causes the increase in lower and midrange torque/HP. The piston moves faster and gets the air moving quicker. The downside is the air speed at higher RPMS requires the heads to flow even more air – that’s one of the trade-offs…

The mean piston speed is also going to be greater at a given RPM. (This means there is more relative wear) Note: given the tranny situation, I wouldn’t worry about this AT ALL.)

Finally, a shorter rod doesn’t always mean more strength – it depends…

bullaculla

Damn!!!its all sooo clear now!
j/k! good work! I'm sure it will help a lot of people! I just want to know how soon I can order one!

acuraboy_RENAMED

yes of course it depends...everything "depends" but since i didn't introduce anything such as material or design and just length then it can be said that a shorter rod is a stronger one. take anything around u? if it's shorter its more difficult to bend no? a handful of full length pasta is easier to break than a handful of half-length pasta. then same goes for a 1x4x12 vs a 1x4x8.

u're using a cl (mdx-same thing) block with shorter rods and still getting 3.5L of displacement. how is that not substantial crank work?


anyone have a spec sheet for this mod kit? rod/crank/bore #'s??

EricL

If you look at that one aspect and compare identical I beams, the longer one is going to "bend" more. Unfortunately, that is not the only issue that is going on. The piston speed is increased and this will result in increased reciprocating stress. There are other issues as well...

IMO, I'd worry about the slushbox before worrying about the rods launching through the hood of the car or block!

However, someone could expect more wear in the engine (all things being equal) at a given gear and road speed. (Drive a car all day at 5K RPM and see how long it lasts relative to a car that "loafs" along the highway doing 1500 rpm...)



THE MDX block comes with different rods, pistons, and crank (at a minimum). The crank has a longer throw. Why are you assuming that Honda/Acura (or whoever) ground the CLS crank? Or looking at your last question, you seem confused. Bottom line -- the MDX crank is used and is not re-ground


The kit is basically a MDX short block (with some pistons and some clever beef-up with different pistons (to keep the compression ratio close to the stock CLS ratio) and some mods to enhance reliability (oil pump, chamfering, etc)




The bore is the same as the CLS and is 89mm.
The stoke is that of an MDX and is 93mm (I provided the figures in the math above).


Look at the MDX spec sheet for the bore and stroke if you don’t believe me. (then compare them to the CLS; you will see that the bore is identical, but the stroke is increased..

bullaculla

I went to a local shop today and showed them the pics of the kit. They quoted me $1600-$1800 to do the swap. Do I need to buy a head gasket kit? I cant re-use them can I? That is probably going to be another $600!

acuraboy_RENAMED

[QUOTE]Originally posted by EricL
[B]


THE MDX block comes with different rods, pistons, and crank (at a minimum). The crank has a longer throw. Why are you assuming that Honda/Acura (or whoever) ground the CLS crank? Or looking at your last question, you seem confused. Bottom line -- the MDX crank is used and is not re-ground[QUOTE]


because MDX-S posted that in one of the 3000 other threads on this

EricL

[QUOTE]Originally posted by acuraboy
[B][QUOTE]Originally posted by EricL



THE MDX block comes with different rods, pistons, and crank (at a minimum). The crank has a longer throw. Why are you assuming that Honda/Acura (or whoever) ground the CLS crank? Or looking at your last question, you seem confused. Bottom line -- the MDX crank is used and is not re-ground

Quote:

because MDX-S posted that in one of the 3000 other threads on this

http://www.acura-cl.com/forums/showt...threadid=75247


$2500.00 buys you:

NEW race-prepped short block assembly displacing ~3.5L.
10.85:1 compression High Performance Pistons.
Weight matched rods with radiused crank journal oil ports.
Modified (volume enhanced) oil pump.
Full upper end gasket set (FR/RR heads and plenum)


-- Radiused crank journal oil ports == Chamfered oil ports--

EricL

I'd buy new head gaskets -- but that's what I've always done. Opinions vary...

$0.02

EricL

Acuraboy:


BTW, I notice you asked earlier about just using an MDX block. There have been at least a couple of people who have done this.

The advantage of the $2500 "kit" is:

the parts have been beefed-up

AND

the pistons are custom "slugs" that allow a slight bump in compression relative to the stock CLS compression ratio...

acuraboy_RENAMED

ideas about using the lined fel-pro gaskets (with the metal rim that requires the head to be machined to receive it)?

acuraboy_RENAMED

and yes EricL, that' the thread where MDX-S mentions the shorter rod taking care of the engine's weakest link as well as achieving 3.5 via crankshaft throw.

i think another advantage of the $2500 kit is that it's cheaper then trying to find a new OR used MDX block.

any idea how these blocks are prepped? honed, aligned, jbm?

MDX-S

The blocks are new, and nobody delivers a better finished block than OEM Honda when it comes to Hone, line bore, etc...

The Head Gaskets are included in the Head sets which come with the $2500 kit.

Thanks.

acuraboy_RENAMED

how much would it be to have the block prepped anyway?

MDX-S

To be clear, no one does this better than Honda....so why pay 300-400.00 more to have a machine shop screw it up?

acuraboy_RENAMED

sorry..don't mean to question u - especially considering that i have ZERO experience with honda blocks. just never heard of a block coming from a casting plant that was basically perfectly straight and clean of burrs. but if u say so jefe...
thanks for the assurances

bullaculla

Thats all I needed to know! I call the number tomorrow!
you still got any left? The PM said 2.