Compression ratio and smog levels.

[Ziegelsteinfaust]

A friend of mine scored a Grandpa fresh 1982 D150 with a bad motor. Yes a brand D truck.

Well it has a 318, and he has scored a 318 roller block too. I know the roller cam will help power, and not effect smog levels. If you don't go crazy obviously. Modern catalytic converter will help power, and well being new helps too. Along with he has been perfecting every part in the engine for optimal DD street power.

So what about going from less then 7.5-1 to 9-1 compression ratio. I know the brand D Magnum motors had the higher compression along with our own Vortec small blocks.

How badly does it effect smog? We're trying to find a happy zone, and not have a problem motor. My worry is the carb will do something I can not mentally account for. As the later Vortec + Magums had over 9-1, and port fuel injection. Where as TBI engines had 8-1 or something like that.

He needs to sell his Diesel truck to get some money, but also loose the payment. Wife's pregnant unexpectedly is the reason, and he wants to be ahead of the curve.

[truckster]

I'm running a 5.7 Vortec with roughly 9.7:1 compression and a Quadrajet. No problem with emissions tests.

[Ziegelsteinfaust]

What kind of tests do they run in Utah?

Is it like California where you have a function test where they test ppm of pollutants?

[truckster]

For older vehicles it's a tailpipe test.

[Bigdav160]

Everything else being equal, increasing compression should reduce hydrocarbons and carbon monoxide but potentially increasing oxides of nitrogen. A good catalytic converter should help with that

[Dead Parrot]

A lot of stock motors from that era were 8.5 compression. 9.0 shouldn't be a problem. If the NO busts limits, you can retard the timing a bit which should lower NO but may raise HC. As others have mentioned, the modern catalytic converters have done wonders on allowing engines to be tuned more for power. An advantage the folks in the late 70s and early 80s didn't have.

Be sure to check the emissions rules on what is allowed and required. Some places seem to be real picky and others don't really care.

[Ziegelsteinfaust]

He wants something that is not lazy like the old smog era stuff along with poor fuel economy. Basically his goal is Magnum or Vortec like performance.

So it sounds like nothing to be worried about, and it will be fun to see what he gets out of the engine.

Thanks for the help

[burnin oil]

A thought is build it with the higher compression but using a thin head gasket. If emmissiins become an issue then install a thicker gasket to slightly lower the compression.

[Ziegelsteinfaust]

Originally Posted by burnin oil

A thought is build it with the higher compression but using a thin head gasket. If emmissiins become an issue then install a thicker gasket to slightly lower the compression.

While Yes it does work it does not move enough compression around to make a effective change. Depending on the bore size. You can move from 9.2 to 9.0-1. Anymore you start hurting quench, and quench is effective for smog control too.. Unless you are right on the edge in function.

The brand D heads are open chamber heads "or atleast the ones he has" which is something I have no experience with going around smog testing. Typical GM heads of the smogger era are D chamber which do provide effective quench. Not as much as Vortec, LT1, or LS heads. Just compared to open chambers.

Brand D had a lot of open chamber heads, and a few closed chambers. He has been looking for closed chamber factory heads, but as of right now he is seriously looking at speedmaster aluminum heads. Which are aluminum redone stock heads with better chambers, and a good option if you want a Magnum or Vortec like engine.

We were texting at work yesterday, but it seems like he just wants a Magnum engine. With a couple bolt-ons to maximize economy, and the power package. It has enough power for his needs, and will give him the least problems when he can least afford it. He is a Brand-D guy, and very familiar with the 93+ variety. A Magnum I thought was a option, but the differences are just to much. Atleast at this time with what we can do, and find a machine shop willing to do. Then depending on how far he goes on the 318. He will either match or exceed a 5.2 Magnum.

Either way I am curious to where it ends up as I want a Burb, but I can usually only find smogger eras in my price range.

[burnin oil]

I dont do smog Era motors but I do know that a good tight quench is a good thing. I would zero deck it and run whatever piston that is closest to a flat top that hits the 9:1 ratio. That should be a pretty good setup and allow it to be slightly decompressed if needed. Being this isn't a runner of a motor I would run whatever head has the best low flow and velocity numbers. He wants it to grunt so make it a stump puller. Who cares if the heads are maxed out for this application.

On a separate note be prepared to do some computer tuning. I did a rering on a 03 jeep 4.0 and moved the cam 4 degrees. Computer did not like it at all! It ran alright at 1/4 throttle buy sucked above that.

[Ziegelsteinfaust]

Basic plans following my old format was 9-9.2 to 1 with a near zero deck height. I only had 2 smogger builds. Both were known combos to me. The brand D, and open chambers throws a curve.

No computer on the D150. It has a thermoquad of some sorts.

[burnin oil]

Thermoquad. Perfect. Open chsmberd are fine. You need the flat tops and smaller heads to make the open chamber heads work. You want to keep quench on the tight side. Basically you will try and use port velocity to keep the fuel suspended and blown around the cylinder. Not to bad. Big ports will kill you on smog. When emmision testing I would do a tune up with hotter plugs. And captive discharge MSD box would help also. Basically anything to ensure a clean burn if you are worried about smog. I am lucky and live in an area where half the cars running around have the check engine light on.