building the 6.5 liter motor, im almost ready to order the pistons and I want to know what's the highest compression safe to run on a street motor? they made one with 10:1 has anyone ever gone higher? my goal is about 80hp per liter, 520hp total 80(6.5) = 520. im going with a cam possibly like the isky xm5 regrind. because I don't want to run out of cam at high rpm.

and for the dish, im gonna want a oversized valves, and im thinking of shaping the dish similar to the BMW "bathtub" shape. so it thoroughly swirls the mixture.

anybody have any imput?

 

I would talk to the piston manufacturer - they should be knowledgeable on what type and shape of dish works best.

 

Have you ever spoken with Glenn Bunch? He raced a V12 E Type in the 70's. He put one of his race engines into a customers car of mine. The car was a monster.

http://glennbunch.com/car-history/jaguar-xke

 

any thoughts on compression?

 

just read his articles, he ran 11:1 compression with webber carbs. in 1976 so he was using a stock dristrubtor setup, (plastic trigger wheel). good info there, he doesn't have a contact.page, does anyone have his information?

 

Without any other data to go on, I'd be inclined to simply mill a hemispherical-like bowl into the piston, allowing for a quench ring around the outer diameter.

The shape of the bowl won't have much effect during the intake stroke anyway, but as the piston approaches TDC, the quench ring would force the mixture into the bowl creating a great deal of turbulence in that area.

One other thing to consider is that a symmetrical bowl in the center of the piston may not be the most effective. Something like an offset bathtub to place the plug over the center of the bowl might be a better way of getting a more even burn and reduce pre-ignition.

Keep in mind that your can get far more imaginative than the guys who did this stuff before CNC and Pro-E and Solidworks was available.

 

yeah, I hear ya on that. I am looking at the design rob beere had which looked like three overlapping circles

 

Just out of curiosity, why are you only going to go to 10:1? With aluminum heads and a good quench zone, you could easily go to 11.5 or a bit higher and still run pump fuel.

For example, I have a Chevy 350 with iron Vortec heads that is at 9.6:1 running on 87 octane regular. If I were to equip that same engine with an alloy version of that head, I could go to 10:1 or maybe a little more on regular gas easily. With good mapping on the ignition, pre-ignition is a lot more controllable.

As another example, a common Hyundai sports and 11.5:1 ratio - on regular fuel. Mazda's direct injection engine is running 13:1.

10:1 was a failrly high limit when this engine was first done in the early 70's, but they didn't have the microprocessor advantages we have now.

 

If you really want the best performance and high compression, consider running E85.

 

not for nothin my dads 69gto ran 11:1 in 69 stock with the ram air 4 cam. I just need to have the correct shaped piston to handle the mixture.

 

E85 is only viable if you can get it at a reasonable operating cost. Here in central FL, the nearest station that has E85 is almost 20 miles from my side of Orlando. In traffic, that could be a heck of a commute.

You can certainly make a lot of power on E85, but you have to burn a lot more of it. I suppose it depends on what part of the US you are in, but here in FL there is little to no difference in the price of E85 vs. regular gasoline. In effect, that makes the price of E85 a lot higher than gasoline because of the decreased economy.

Anyway, at least here, it would be stupid to burn 2 gallons of fuel each way to go fill up. If you live in Minnesota or Iowa, it's a whole different story.

 

Quench and swirl are the keys, I think.

 

Manufacturers spend very large amounts of time and money optimizing combustion chamber, valve layout, piston shape, and CR to meet various goals including power and fuel economy. (Toyota probably optimizes for fuel economy and low-end torque, Kawasaki probably optimizes for max-RPM HP.) All of the research that goes into this suggests that it might not be as easy as you think.

I don't mean to discourage you - I want to see your project kick butt! But often times, when it comes to determining what will happen when you start changing the features of the combustion chamber, you're just making wild guesses. With that being said, consider sticking with what you know has worked well on other Jag V12 engines. Just a thought!!

 

I've got drawings of what rob beere uses, so I need to have them translated (written in german) and then I can get a custom set made

 

And therein lies the heart of the problem. Unlike a small block Chevy, very little ahs been done on the V12 Jag. And while Rob Beere may have attempted something, there is little or no basis for comparison on whether it was a truly the most effective solution.

You can probably count the number of running 7 liter Jag V12's on one hand, so I applaud Calvin's attempt at building one. Uncharted waters, indeed!

 

yeah you're.tellin me. and rob beeres sells the pistons shapped like.the old twr ones. three cicles the center.being a.dish and set off to one side 7mm to make it centered on the spark plug

 

If they're proven performers, they sound like the ones you want! I'm guessing they're not cheap. Maybe you could go to one of the piston manufactures, show them a picture, and ask them to make it for you? I know Probe used to make very affordable custom pistons. Probe isn't my first choice for a forced induction application, but I'd use them all day on an NA setup.

 

yeah the hp rating I am going for is like the same as a 200hp 4 cylinder. so I really don't need super high strength pistons. but I plan to send the diagram of the crown to everyone and make sure somebody can do it

 

I Joined this forum because I thought people should know if they ran E85-R you could increase the compression much higher and the jag head might be ideal, the XK120 certainly would have been. With an ethanol blend you could go higer than 10.1 . 20 to 1 is the highest I would recommend you will get more power but you will get better fuel economy than petrol . The engine runs clean, you do need better fuel pump and quality injectors.

 

I Joined this forum because I thought people should know if they ran E85-R you could increase the compression much higher and the jag head might be ideal, the XK120 certainly would have been. With an ethanol blend you could go higher than 10.1 . 20 to 1 is the highest I would recommend you will get more power but you will get better fuel economy than petrol . The engine runs clean, you do need better fuel pump and quality injectors.