Hi

I'm trying to get an idea what the compression ratio would be with 083 heads and a stock 83 350 with dished pistons. (truck engine)

original heads were 464624 with 74-76cc chambers
the 14101083 head has 64cc chambers I believe

Thanks

 

You'll need to know how much volume the dish has.
Use this calculator, there are others just search.
http://www.angelfire.com/fl/procrastination/motor.html

 

If those ar ethe most common factory dish pistons, then they're about 12cc; your CR with 64cc heads will come out somewhere in the 9 - 9¼:1 range.

 

Unfortunately the pistons are in the block they have an approx .100" dish plus reliefs for the valves.
Guess I should try to find a .040" compressed thickness head gasket. To replace the stock steel contoured 4.100" .020” compressed thickness one.

I have to run this on 87 pump gas. 9:1 to is about the max I should run I guess? I'm going to run TBI and don't want the ecm to retard the timing. I hear it really backs off the timing.

Thanks
Mike...

 

Yeah those are pretty much yerbasic factory smogger 350 pistons. Seen em a hundred times if I've seen em once.

I've put more than my share of 64cc heads (double-humps) on 70s smogger motors EXACTLY like yours, never ran into any trouble. In fact, people would be AMAZED; even leaving the old 2-barrel carb on their car, it would be like bolting on twice the horsepower. I used to love getting those in to do that to them, especially 400s, because I KNEW I'd have a happy customer. Every time, they'd come back from their trip around the block test-drive with a smile on their face, READY to write a check. The polar opposite to building a dome-piston motor with smogger heads, to get the CR up; those were NEVER satisfactory. It got by about 81 or 82 to where I would just refuse to even bother with doing that combo. I told people who wanted that built that they were just going to have to find somebody else to build it for them, they didn't have enough money to make it worth my while.

You'll come out about 9:1, maybe a tweek higher. No problem on pump gas.

Run a regular .039" composition head gasket. FelPro HS7733PT2

 

The pistons on your engine will be .025" in the hole and 12cc dished. IMO, you will be best off going with some 64cc chambers and a .016" compressed head gasket. That will put your quench distance at .041" which will be better than the .064" that the other head gasket would give. Proper quench will keep the engine from detonating and the a/f mixture burning properly within the chamber. 083s are not bad heads, but need some work on the short side radius. I would personally port the heads substantially. The stock cam in your current 350 is the same cam that came in the TBI 350 trucks. The 083s will need more fuel and more timing than the TBI heads to run properly. Since you are programming your own chips, I would recomeend a camshaft in the 204/214* area as stated before. I can also give you some tips on the timing table and some other aspects of the tuning the TBI chip to pull that much weight efficiently. You should also setup an adjustable fuel pressure regulator and boost the fuel pressure to about 16-18 psi to run the heads. The 350 TBI chip needs about 6* added across the board to combat the slower burn with the TPI heads compared to the TBI heads faster burn rate.

 

No way to tell that without mocking it up.

 

ITs a STOCK engine, stock pistons on 350s of that year and most other years are .025" in the hole.

 

Deck heights on factory blocks vary a good bit. Not to mention the stroke of a factory crank can vary. Saying that his pistons are -.025" in the hole is an awfully brave assumption.

 

I have measured atleast 100 small blocks, factory assembled ones. They have all been between .023 and .027 or so. .025 is VERY typical. If he wants he can measure it to make him happy.

 

I'm going to order the heads through a parts store.

What angle are the center head bolts on a 87 350 Camaro???

I found a listing for the 14101083 head by looking at a 87 350 Camaro it also listed the 14096217 casting with the 083.
Is the 14096217 head a bad one???

I may go Vortec depending on the price. no core new head can't see the price being great but I'll try.

Mike....

 

083 heads have 64cc chambers and will get your compression up around 9:1, maybe a bit higher. With a thick .039" Fel Pro "rebuilder" head gasket it will be on the low end of that range. If you want to use a thinner composition-type head gasket (much easier to seal up with old parts that might not be perfectly flat) GMPP sells one that's only .028" thick- that will get you up closer to a true 9.25:1. And the price is right- only about $35 a set. I've used them myself several times now and they work fantastic.

Agreed, those pistons have a total dish of about 12cc, including the valve reliefs. They're VERY common pistons for smogger era 350s. Likewise, I've always found them to sit about .025" in the hole. However, others have found they can sit significantly lower than that (.040-.050" or thereabouts). I beleive that to be true, although I've never run into it myself. If you look at some budget replacement pistons you'll see they have a shorter pin height (making them sit further in the hole). Typically the pin height on a stock 350 piston is 1.56" to make them sit .025" in the hole. Some of the budget replacement pistons have a pin height of 1.54" which would put them .020" further down at TDC (~.045").

Also agreed that swapping a set of 64cc heads on top of an old smogger 350 in place of the 76cc stock casting really makes the engine a LOT snappier. Just the difference between 8:1 and 9:1 compression really wakes up a motor in the low-mid RPM ranges. It really does feel like you strapped a second engine under the hood. And if you can swap out the old smogger cam for even a MILD performance cam you can really have a strong runner for very little money!

 

Hi

Just waiting for my 083 heads to arrive in the next 2-4 weeks.

 

Budget is limited now. I didn't plan on replacing the cylinder heads but couldn't bring myself to reuse the old 462624 heads
The stock cam and lifters will have to stay for now also.
I bought and was going to use an external fuel pump with my TBI conversion (Master E8153) rated at 10-14 psi 30gph. that pressure seems low to me!
What type of pump and regulator should I use???
I would appreciate tuning tips when that time comes, should I start with the stock bin that came with my ECM or use a different bin for a starting point. stock eeprom=ARJT (91 G20 350 Auto, EGR, TCC)
I plan to do some porting but don't what to wreck a set of heads.

Thanks.....

 

You need a pump that's capable of more pressure than that if you're staying fuel injected. TPI and other port-injected setups require 40-50 PSI. Even TBI systems you need about 15, but perferrably more in both cases since the fuel pressure regulator is going to keep the pressure down to where it needs to be at the injectors themselves.

 

I measured the piston to the top of the block and the piston sits back .027''

I'm thinking of using a frame mounted fuel pump a Master E2000
specs are 70-90 psi and 30-40 gph
The stock regulator I will modify so it can be adjusted.

Anyone know of some good choices for a TBI fuel pump above the stock 15psi.


Thanks

 

The pressure regulator in the TBI unit is capable of lowering the pressure of a high pressure port-injection type pump. In other words, if you get a 60 PSI pump (like for a TPI engine or similar) it'll still regulate it down to what it needs at the injectors themselves. Obviously, many choices are available both in-tank and externally mounted.

 

Hi Fast355

Long long time ago you mentioned about giving me some tuning tips for my 83 G3500 class C motor home.

I’m currently running the 83 350 with the stock cam ,TBI heads, factory TBI injectors and intake and a 1227747 with EBL flash.

Does the offer still stand? Thanks again

Mike.

 

Sure thing Mike. What are you having problems with?

Probably best if you start a post in the DIY Prom as it will get you more helpful responses.

Your setup is for all purposes a stock TBI 350.

Are you running manifolds or headers? If manifolds does your chassis run the factory tubular manifolds and catless true duals? Did you remove and cap off the smog pump(s) and air fittings in the manifolds.

 

Hi Fast
My motorhome came without cats but the original exhaust manifolds with air tubes were badly cracked so I replaced them with some without air tubes. Bought a set of headers but they didn’t fit unfortunately. Opened up the exhaust manifolds with a die grinder and port matched them to the heads.
I currently have 2-1/2” pipes running from the left and right exhaust manifolds past the transmission tail into a medium duty truck muffler with dual inlets and a single 3” outlet pipe that exits over the axle then out the left side.
I’ve never seen the factory tubular headers where they stainless steel? Heard they made factory stainless tubular headers for the 454.
I will start a new post to DIY prom again
I’m going to start doing some tuning with EBL Flash again. This time I’m planning on making changes to my timing tables when I’m started I only did VE learns with my WB.
Trying to find information on setting up timing for a heavy vehicle 10500 lbs plus
May use the timing table from the 91 G2500 I originally used when I started with WinAldl seemed to have more power.
Thanks

 

The advance curve for a regular G-van might have a little too much timing for the load your engine will sustain. I would look for a G30 van timing map. It is noticeably different. Generally you will want to limit the low rpm high map advance and increase timing slowly with rpm. Do your VE learning first while watching for knock. Once you get the VEs dialed in you can mess with the timing. Then go back and tweak the VEs.

 

Thanks I’ll look for G30 5.7 auto bin.