I need some camshaft guidance on a 2.0l racecar

Matt Monson · 04-09-2008, 01:03 PM

Hello:

So this isn't for me. This is a customer's car and he's asked me to help him make a decision. My specialty is transmissions. If you tell me what the engine does as far as power and redline etc. , I can set up a transmission for you. But this time we need to go the other way and decide what the engine needs.

This is for an FIA 2.0l vintage race car. I just finished building a short ratio gearbox with basically airport gears in it. It's running C G J O S and for the time being an open differential. This is a new car and a shop that is building their first Porsche vintage racer. He's expressed a desire to keep the redline at 7000rpm for longevity and hopes to get two seasons out of the first engine while they develop the rest of car. They are keeping the compression ratio in the mid-9's for the same reason and it will be run as a single plug engine. Because of FIA rules they are running Solex carbs. He's indicated that 170-180chp will be fine for this first round of development.

So, what do you think they should run? I figure the options are basically
1. Solex grind
2. 911E grind
3 911 S grind
4. 906 grind
5. Other ideas?

I am thinking they likely want the Solex or the 911E grind but am unsure of the subtle differences between the two. I think the 911s and 906 will be too peaky and for an engine with another 1000-2000rpms higher redline. Any help or guidance you can provide is greatly appreciated.

kenikh · 04-09-2008, 01:17 PM

7000 RPM redline decides it; no race cams (or even S cams). I'd use a mod-E or something similar from John Dougherty.

304065 · 04-09-2008, 01:41 PM

Supercup 102. Ask John (camgrinder).

And remind your customer that he's going to be a sheep in among the wolves. . . FIA 2,0 spec motors in race tune produce at least 220 HP.

CGJOS is interesting, 904 mainshaft?

Matt Monson · 04-09-2008, 02:45 PM

Yep,
NOS 904 mainshaft.

I think this guy has a bit of an idea what he's in for but just wants to play it conservative early on. However, not really a "conservative" gearbox there aside from sticking with the open differential...

Brant · 04-09-2008, 03:49 PM

I'd talk him into bumping the redline to at least 7200 and putting S cams in it at a minimum.

built like that, the motor will last for years and years

at colorado altitude he is going to be really disadvantaged
I know this because I'm living it with 147hp at the rear wheels with 9.8:1 compression, single plug, huge 34mm venturi's, and FJOSV

the venturi's gave me 14hp at the loss of all of my midrange below 5,000rpm
but the gearing allows me to keep the motor above 5,000 all of the time.

He is really going to be underpowered in the colorado vintage scene
most of the 2.0's are about 200hp to the rear wheels.

its fine that he knows this, but its really not going to hurt his longevity to build it as a stock S engine

Matt Monson · 04-09-2008, 04:00 PM

Quote:

Originally Posted by Brant

I'd talk him into bumping the redline to at least 7200 and putting S cams in it at a minimum.

built like that, the motor will last for years and years

at colorado altitude he is going to be really disadvantaged

I kind of felt the same way about it but since it was kind of outside my area of expertise, I wasn't sure if I should push him to go up to 7200 or maybe even 7500. I think I will talk to him about it.

As for the altitude, he's in the UK, so he's not going to have the same challenges we face in that respect. I am shipping him the tranny and a '65 RHD rolling chassis that I had. He asked about the cams and a few other things as a sort of "while you are at it could you..." sort of request.