V6 Strong modification

[Jim K.]

If you use more than the 3liter stroke (72.6mm) the THS rods will hit the 3liter block (12 or 24v) in several places.
The 12 and 24v blocks are different basically because of different length head studs, water pump, knock-sensor bosses, some engine mount studs, oil-squirters, tensioner and other detail differences. The crank is not a problem, they are basically interchangeable.
Venolia used to have 98mm pistons.
Jim K.

[Gabor K.]

Jim K. a control question: I considered buying these rods to be used in a 3.2GTA engine. Are you saying that with its longer stroke the THS rods cannot be used? In the THS ad. its mentioned that all the V6 rods are the same?

Does anybody have any idea of the rev limit of the 24V engine with original parts? In other words at which point is it necessary to change the rods and the oil pushers?

Also on the original rods of the 24V engine there is an oil squirting hole to improve cooling. When changing to special rods this squirt dissapears. Is it of any consequence?
Any views about this?

[slyalfa]

I can give some info on the oil squirting hole.
All the V6 motors after such and such date and S/N added oil squirters in the block.
I do not think any of the 24V did not have them. So the hole in the rod is no longer needed.
Also I think the hole in the rod can cause them to fail. One of the mods that used to be done is to weld up the hole and grind the surface smooth when preping the OEM rods.

[FMG_V6_btb]

As Jim K suggested in another thread, better than weld the oil squirter hole in the rod (which can cause an important strenght loss due to the change of crystalline properties of the rod material in the weld point and surroundings) it is better to fill and close it with epoxi resine for metal.

I'm not sure that all 24 valve engines are fitted with oil squirters in the block, I think this feature was introduced in the 24V besides the chain driven oil pump and the belt tensioner installed in the place of the oil pump-distrubutor toothed pulley (there are also 12V with squirters in the block). So it is important to check if your engine has this feature.

I suppose the THS rod profile doesn't differ so much compared to the original Alfa rod, in any case I think it can be take some material from the block or liner without problems, I have seen many liners with machined neck lines for the rods.

About rev limit, I have no information, but I suppose 7500-8000 could begin to be potentially dangerous.

Paco

[slyalfa]

yes when the S came out is when the squirters started so any 12V after that had them and I think that is before any 24V. I think they also changed the RPM of the oil pump at the same time before going to the crank type. on both 12V and 24V as the dizzy was not driven off the pump any more they changed the gears so the pump would spin a bit faster. I am guessing to make up for the flow of the squirters.

[FMG_V6_btb]

Hi again!!

As I told, I have bought some V6 engine parts, among them there is a set of OEM rods; I have measured and modelled one for analysis purposes.

Following, it can be find some screen shots of the analyzed rod.

Simulation conditions were the following:

-Engine speed: 6300 rpm
-Piston bore: 98 mm
-Stroke: 78 mm
-Power at simulation conditions: 449.5 HP
-Peak pressure: 109 bar @ 13 deg ATDC
-Piston weight (Complete with pin and rings): 550 g
-Inertia force @ 13 deg ATDC:16016 N
-Gas force @ 13 deg ATDC: 82149 N
-Resultant normal force on the rod: 70556 N
-Inertia bending torque in the rod: 55 Nm
-Rod material: Alloyed steel (elastic limit: 620 N/mm2)

Most relevant result: the maximum stressed area is the orange coloured one, with 580 N/mm2 which is near the elastic limit of the material. The safety coefficient is 1,07 which is very low for the application (2 is the recommended for cyclic stressed parts, as the rod is).

The following step will be the simulation of a THS rod (approx. because I have no accurate dimensions) in the same conditions, and see the maximum stress.

Paco.

[slyalfa]

I have a set I could take a few readings if you let me know what you want.

The big end seems too good? the stress tests I have seen before show a lot on the big end. how did you do this? did you sim it on 2 round rods that are a bit smaller?

[FMG_V6_btb]

All depends on the scale of the result colours (stress), but usually you will see more stress in the big end when the rod is submitted to extension (due to inertia forces of the alternating masses and the rod), the avobe represented case is rod compressión 13 deg. after the TDC of the firing cycle.

About THS rod dimensions: thickness, shape... it's complicated because to be accurated, I need a fabrication drawing, so if you can and want to spend a little of time...I can send you a sketch without measures to you put them on it.

Paco.

[ALFA-75-MAN]

Love the thread but with 400 plus hp unless your on a track or on private property where are you going to drive? It simply doesn't make sense to modify and drive on normal streets.

[FMG_V6_btb]

The answer is the same that a ferrari owner can give you if you ask him... not all is speed, acceleration makes more adrenaline to flow, is when you really can feel the power (and weight) of the car.

I would like to build and sell a small serie of the car (everything depends on the investors), that's why I need the car passes emmisions regulations, and be homologated.

All the car testing and tunning will be carried out in circuits, some test in the proving grounds of IDIAD@, and others in the Circuit of Catalonia (were F1 and GT cars race). The following picture is a general view of IDIAD@ test tracks.

Paco.

[ALFA-75-MAN]

Okay but at least find a track that has some turns this one looks like an oversized oval.

[85gtv6]

Paco,

Could you re-run your OEM rod finite element analysis for say a 250hp 3.0L engine to determine at what RPM the rod fails in tension due to reciprocating acceleration forces and suggest a safe maximum engine speed? This would be a big help to us since there is a lot of controversy about what the safe maximum rpm is for a typical N/A street or track engine.

I am guessing that you would have to determine the fatigue strength of the rod material and then vary the RPM in the simulation until this fatigue strength equals the stress.

If you do this, when I have finally removed my old 2.5 I'll take it apart and post some pictures of the failed rod.

Also, I noticed that you modeled the rod material as alloy steel with an elastic limit of 620mpa (89,900 psi). The 3.0L rods that I have (US 1991 164L 3.0 12V rods) look to me like cast steel but I am not an expert. If they are cast then the tensile strength could be much lower than the compressive strength. I don't know what these strengths are but maybe you have some info on this.

Thanks for your help,

Jeff

[FMG_V6_btb]

Hi Jeff,

Yes, I can run again the simulation with those parameters (250 HP, in a standard N/A 3.0), and assigning a fatigue strength to the rod material, as you proposed (not easy, because we don't know exactly the material the rods are made).

As you mentioned, I selected an alloy steel with a elastic limit of 620 MPa, which IMO could be similar to the used by Alfa Romeo or other manufacturers of standar rods, but maybe somebody could contribute with more accurate information that we can use in nexts simulations.

About the rod manufacturing process, I'm 99% sure all Alfa rods are forged, at least the ones I have here...

As I said, I will perform the simulation, but I will not be able before middle of next week... I hope you will be patient

Paco

[newalfisti]

Quote:

Originally Posted by FMG_V6_btb The answer is the same that a ferrari owner can give you if you ask him... not all is speed, acceleration makes more adrenaline to flow, is when you really can feel the power (and weight) of the car. I would like to build and sell a small serie of the car (everything depends on the investors), that's why I need the car passes emmisions regulations, and be homologated. All the car testing and tunning will be carried out in circuits, some test in the proving grounds of IDIAD@, and others in the Circuit of Catalonia (were F1 and GT cars race). The following picture is a general view of IDIAD@ test tracks. Paco.

[goats]

PAco et al
Reading this thread makes me realize how utterly ignorant I am with respect to engine design, terminology, and system concepts! Keep up the great work and please keep posting on your project as it is very informative for me and I am enjoying learning about this. I apologize in advance that I can not contribute but hopefully I can watch from the sidelines!