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Engine ?

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yellowroket

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just picked up an 87 C20 350tbi, th400, sf14 bolt rear w/4.56s. Never been around these engines before and am wondering do they have factory roller cams. What size heads, valves combustion chambers and such. It has a fuel pump block off plate on the side of the block, can you put a carb on it and run a mechanical pump. Also if carbed whats the max lift the factory heads will handle. Thinkin of building it up for my blazer
 
your best bet for the engine specs is to look at the number on the back of the engine block, top right behind the intake, and google search that number... that will tell you every thing you need to know.....

It is more than likely not a roller motor... probably a hydro cam and standard combustion camber (84cc I believe)....

The block off plate... yes you can remove that and do a fuel pump... you will need the fuel pump push rod and fuel pump... any parts place will have this, like summit of jugs.... make sure you get the adapter plate too (bolt 4 bolts to engine for the adapter, then the two bolt fuel pump)... I would stay fuel ingested though... my eldocrap spits and coughs if its not almost flat :mad:

good luck and keep us posted :D
 
yellowroket said:
just picked up an 87 C20 350tbi, th400, sf14 bolt rear w/4.56s. Never been around these engines before and am wondering do they have factory roller cams. What size heads, valves combustion chambers and such. It has a fuel pump block off plate on the side of the block, can you put a carb on it and run a mechanical pump. Also if carbed whats the max lift the factory heads will handle. Thinkin of building it up for my blazer
Click to expand...

Answer your first question, NO, the truck did not get roller cams until the vortec engine came out in 1996.

IIRC the combustion chambers on those are 60cc and have 1.94" intake valves and 1.5" exhaust valves.

Not all blocks are drilled for the mechanical fuel pump push rod. My factory 89 block has the block off plate but the block is not drilled for the push rod. Some of the blocks aren't even drilled and tapped for the bolts.
 
If the engine is out of a C20 It can have either 64cc 193 heads or 76cc 191 heads.
If it is a 4 bolt main it should have the 76cc 191 swirl port heads. aprox 8.2 to 1 CR
2 bolt main should have 64cc 193 heads. aprox 9.2 to 1 CR
To make sure what heads you have look in center of the lifter valley there will be a string of numbers ending in either 193 or 191 to positivly ID the heads.
Both have 194 int 150 ex.
Both are a swirl port design head with a early fast burn type chamber not as refined as Vortec heads.
These heads in stock form are only good to around 4500 RPM before running out of air. Because of the swirl port design and the interference it causes at high RPM/ air flow.
With a good port job they will flow a little over 5K.
They are very good heads for building low end torque. But if high RPM power is what you are after dont use them. Get a better head.
IIRC they will handle .480 lift with proper springs/retainers
 
Thanks guys lots of good info, im going to yank the motor out of the donor truck this weekend and will probably tear it down or at least start to. Thanks again
 
Hey guys well i finally got some time to tear into the engine. Its a 4 bolt main that must have been rebuilt very recently with the large chamber 191 heads. No sludge, corrosion in coolant passages nothin. Has new pistons, small inverted dome with 4 valve releifs in it. Short block is in perfect shape, the heads are a different story. The valve guides are shot!! I have a set of older 1.94 small chamber heads that i had reworked about a year ago setting in the garage. Question is one will they work on the later model block, and two if the compression with the 76cc heads is around 8.2 what will it be with 64cc heads. Im assuming it will raise the compression around one point, which would be just about right. Let me know what you guys think, i dont want to find out the hard way the swap wont work.
 
as long as you use the stock dished pistons you are correct. The 64cc heads will raise the CR aprox 1 point.

Older heads will bolt on the block no problem
But
The center 2 bolt holes on each side of the intake manifold/heads are a different angle on center bolt heads (TBI) than older heads/manifolds.
The TBI intake manifold will not bolt to older heads (Non centerbolt) without Elongating the 2 center bolt holes and grinding the surface where the bolt seats on the manifold a little.
If you are not going to use the TBI manifold. Then just bolt on a carb manifold and you are good to go.
You will also need an older HEI distrubutor if you go Carb.
 
I just did the math and the CR ratio will go up 1.071 points going from a 76cc head to a 64cc head with all else being equal.

This is assuming a 7cc dished piston, .020" deck height, and a .039" compressed head gasket.

Just to add, the compression ratio will be 8.480 with 76cc heads and 9.551 with 64cc heads using the above specs.
 
Thanks guys really appreciate the info! I was going to swap the TBI over but for now im just going to throw a carb on it. I picked up an HEI yesterday from a buddy of mine and a set of older style valve covers. Should have everything covered to start puttin it back together.
 
If you keep the stock cam. Dont put a big carb on it. The cam in TBI engines if anything, is anemic.
I recommend no more than 600 CFM max. 500 cfm would be perfect.
f you want to go with a better cam buy one that is computer friendly if you plan on swapping to TBI later.
Most computer friendly cams will run just fine with a carb.
 
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