Thanks to all you folks' help I got my trans in and ready to roll last night. Now, I have a 318 with a single Garret turbo in a draw thru setup, with a Holley Boost referenced 750 on top. I have a digital ignition with boost retard, and a digitial wideband a/f gauge. All that being said, what should I shoot for for a baseline on my setup? I will be running a max of 9 lbs of boost. So, how much timing retard should I set up per pound and from what initial number?, and what a/f number should I shoot for at idle and what number at ____ RPM? Thanks guys, just don't want to shell my goods first fire!

No boosted guys surfin today?!?!

whats the full specs on the engine? how much does the car weigh?

idle should be 14.5

to make it safe at wot low 12s and go from there. a egt would be good to have too.

Bone stock 1970 318 with all new consumables. Top shelf, studs, rod bolts, head gaskets etc. Stock manifolds modified with flanges on top to turbo loop in front of motor. Pretty stock 70 Cuda, manual brakes. Your right, never thought about an EGT. So 12 should be considered my low A/F ratio threshold eh?

low 12s is to start off with not what it will want, but you have to start somewhere, and you will have to run it and see what it wants.

whats the compression at?

8.7 Comp. YOur talking 12 to 1 A/F right? Any insight into how much timing to retard per pound of boost? I think I have it at 12 initial and 36 at 2500 right now (unboosted).

Bring it back 2 degrees per pound of boost and adjust it up from there. Detonation will scatter the pistons so don't go crazy. 12:1 is best for safe power.

Keep the carb to intake tract as short as possible. Be VERY careful with every connection and running ANY kind of boost gauge. You will be pushing a fat fuel/air mix through the gauge. If you get a vacuum leak (boost leak) then you will be blowing an explosive fuel/air mix through the leak. You don't need that fogging the exhaust manifold. Car go boom.
Remove any worm gear style hose clamps that will see boost. Replace them with higher strength T-bolt hose clamps.



A stock style 318 should live without a problem under that boost level. I'd think you could see around 300 rwhp max. Probably closer to 250. Either way, it'll wake up the car and make for some fun.

Your current timing curve sounds good, I would run between 1-1.5 degrees of retard per pound of boost.

For a/f at idle, do whatever the car runs best at, don't be too concerned with an acutal a/f ratio.

For a/f at WOT, the boosted guys typically run in the 11.5-low 12's range. Running overly rich helps to surpress detonation which is why they typically run a bit richer than ideal, at least to start with.

Thanks guys, great tip on the clamps, one of those things you wouldn't know except for experience. I am drilling and tapping directly into the under carb (ie boosted) aluminum housing for my boost gauge and also barbed fitting for ignition sensor and carb input. I will thread sealer it up well.

Your right about my goals, up here at altitude, (9000), what was once a fun car just sucks! This is kinda my test platform, once I get the bugs of the turbo system worked out, I am going to build a full tilt 318 and put the system on that. Maybe shoot for 450 hp up here in the mountians.

Hey, just wanted to tell DaytonaTurbo and Feets genuinely thank you. A few months ago you two gave me the insight and confidence to take this on, and now that I am almost done, your helping me across the finish line. Really, you guys are much appreciated for your knowledge and willingness to share.

I think feets would say that you've just reached the starting line, not the finish line. The real work in making it drivable now begins!

lol, your right for sure!! at least after this weekend though I will be able to turn the key again!

But you right, and you set me up perfectly, fella's get ready for me to use up some bandwidth in the next couple weeks buggin you!!!

Are you kidding? He's running draw through. Even I could tune that in an afternoon with enough time for a run to Hooters. Plop a carb on a turbo and go.

If he was running blow through things would be different. Putting the turbo first really complicates the tune. That's when you have tuning issues. It's also where you start making power.

One thing he will have to watch out for is the altitude. 9000 ft is ugly. Temps tend to drop. When the turbo starts sucking air through that carb on a cold day he'll have to be careful. It can lead to carburetor icing. Hopefully it's relatively dry when cold up there.

While feets is correct about the t-bolt style hose clamps being superior, many guys in the 4cyl turbo world have run the regular worm type clamps(myself included) and they do work. But we all know too well how easy those worm gear clamps strip out if you horse on them barely too tight.

For the uninitiated:

Draw through turbo:





Blow through:

lmao! Plop on a carb!!! Hopefully a simple system to get my feet wet and build a functioning fun system. Car will stay in the garage when anything close to icing temps are present!!

There's a reason they don't run draw throughs anymore...

Anyhoo, A/F and timing on a boosted engine depends alot on compression ratio, inlet air temp (right before intake valve), cylinder head chamber design, cylinder head material, and of course largely the fuel you run.

As a rule of thumb though low 12s is the absolute lean limit IMO for most home built boosted applications. And that's low boost IMO (6psi or less). Most people run in the high 11s, and when you start really pushing the boost (20+) more like high 10s.

Timing is the same, it's relative to how much boost and how well cool your inlet temps are. Rule of thumb though aim for 25 or less under boost. More boost and less octane means more timing retard.

In my shop right now, lovin wrenchin and lovin life!!!! I have no blow-off valve. Was just gonna watch the boost gauge real close until I learned the characteristics of my system. Am I nuts?