what compression ratio on a boosted 1600 bug engine

[advinnie]

Hi all. I have a fresh build 1600 beetle engine with about 2000 miles on it on running a pair of dell 40 carbs and it runs just fine but i got bored so decided to fit an AMR 500 super charger to it but have some questions.

The cam i am running is a Scat C35 which required the CR to be raised to 8.5:1 CR. Now im planning on running 10 psi boost , Is this static CR to high?
The supercharger set up will be a draw though set up using a Weber DCOE 40.

I will be running a 123 Distributor so i can control the timing advance and retard but i take it that i still set the max WOT advance to 28-32 BTDC and retard 1 psi per psi of boost?

Also should i connect the crack case breather back into the carb or is this a bad idea?

Any help would be great.
Thank you

[Bruce.m]

Without an intercooler you’re limited on boost anyway. 5-7psi. So the compression ratio isn’t a problem as such.

[advinnie]

Ok so 10 psi is a no go?
I will have to find a different size pulley to lower the boost

[Bruce.m]

Well, maybe. If you can add an intake temp sensor and monitor the temps. The warmer the air is, the less dense so it reverses the benefit of boost while increasing the onset of detonation.

[Clonebug]

With a drawthrough you will get intake cooling from the Venturi effect.
I've read some see up to 100*F cooling which is as good as a decent W/I system.
A blower will heat the air even at cruise so the draw through's cooling will help. I feel the best thing to do would be to invest in a quality ECU and Crankfired ignition that allows you to monitor and/or log a few important sensors that you should add.
IAT
CLT
Timing
Boost

I catch flack every time I mention intake temps on that other site but my experience in the 50,000 plus miles I've been turboed proves to me that 130*F. is a critical intake temp.
You will need to retard timing a fair amount once you get to that temp.
I've seen cruise temps that high in California and had to change timing since my maps were made for 80* ambient air temps.

[risk]

Here is a cheap way to monitor intake air temp. M6 threads too, so easy to plug off later.

https://www.adeptpowersports.com/trail- ... PwfQ&gQT=1

[advinnie]

That link is blocked

[BugUgly]

$57? not bad for a sensor that can handle air-cooled temps.

[advinnie]

That link is blocked for me. Can someone post a photo of it so I can see what we are talking about please

[V8Nate]

Here it is

Sent from my SM-S918U using Tapatalk

[advinnie]

Thank you for that. I will see if I can find something like that in the UK

[risk]

It's for motorcycles, but the actual sensor is M6 thread so you could easily tap a hole in your intake pipe or end casting. One of the versions on that website is just the gage and sensor, no water pipe tee.

I vent my crankcase to a breather box with AN10 lines from fuel pump block off and alternator stand, then atmosphere via a 2" dia filter from Moroso. I would not vent hot oily crankcase gases back into the carb in a boosted application.

I wonder if an intercooler plate sandwiched under the supercharger, with forced air from the heater outlets of the fan shroud would drop temps effectively?