I acquired a 305 that came out of an 89 vehicle, from VIN portion of the block numbers. It has 187 heads, peanut like roller cam and dished pistons. I am assuming an L03 engine. Also assuming 9.3:1 comp. ratio. LG4s with 416 heads had a 8.6:1 with dished pistons. On this board there are many claims that 416s are 58cc chamber heads. What is the chamber size of the 187s? 51cc? Has anyone cc the 187s? They do look tighter than 416s, not as square shaped and the plug is set deeper in the head.

 

187's were 58cc. Factory LO3 pistons were flat tops with 4 valve reliefs.

Are the pistons you're looking at really dished, or just have these 4 crescent-shaped valve reliefs?

I picked up an '87 LB9, thinking I'd use it as the base for my mods. Turned out it had one 187 head and one 081 head. After the heads came off, I discovered it had .040"-over dished pistons. I was going to live with that and the S/R Torquer 305 heads when I discovered the block had cracks in the lifter valley (probably why it was rebuilt, but the cracks weren't fixed).

If the pistons in your engine really are dished, it could have been rebuilt with dished pistons (the stupid vaccine isn't universally required yet).

 

The '89 pistons are definately not oversized and are factory. I am assuming they are dished because they are not like '85 and '86 pistons I have been working with lately. They have the valve reliefs just the same as the flat pistons but are also dished in about a quarter inch in from the outer chamfer.

Could it be an '89 305 that is not a L03? Then it would not be listed as 9.3:1.

Why, by the way, does the L69 list as 9.5:1 and the L03 9.3:1 if they both use 58cc chambers and the same pistons.

 

Sounds like dished. Could be from a truck or van. Or, stock-size replacements.

I'm not completely sure about the reason for the change of CR rating, but I know my LG4 had a steel shim gasket. I understand later engines use a thicker composition gasket (but I don't know that for certain).

 

Don't want you to think I am rubbing you five7, but I checked the boards here on the pistons since we went to that. Seems L03s came with dished pistons. One of the threads has links to photos and it is exactly what I have. That puts this back to the heads. I guess I will check the chamber sizes (crudely) to make the comparison. I will mention here what I find if you are interested.

 

I measured roughly 5.5cc larger chambers on the 416 than the 187. After failing with a liquid test (old, leaky heads), I did a dry measure using measuring spoons. 1/8 tsp. was the smallest I used. Who said home ec. would be a waste of time? I am not saying this is exact, but there is a noticeable difference. Again, very noticeable around the intake valve and spark plug. Also, the 187 does not have that depression in the roof of the chamber like the 416.

 

Still doesn't sound right.

Got links to those LO3-dished-pistons threads?

 

Sure, here's one

https://www.thirdgen.org/techbb2/sho...hreadid=194623

This thread has one photo and a couple links.

Funny, the guy with the photo says they are flats but looking at piston #6, it doesn't look to be so.

My thing here though was to find out the chamber sizes of these heads that I have.

 

I remember disassembling a Chevy 305 from a 85 Pontiac and it had completely flat pistons. There weren't even valve reliefs.

What compression did the Chevy truck L03's have? I thought they might have had 8.5:1

 

Uncle. I'll defer to those with more experience in the later years.

But, the .040-over dish of that '87 LB9 of mine is much deeper than what is shown in those pics (no valve reliefs, as a matter of fact). My '86 LG4 pistons were as described, flat with reliefs.

'87-up, all 3rd gen V8's had 9.3:1 CR - it could be that the factory put a small dish under the combustion chamber (note that valve reliefs are still there).

FWIW, '82-'84 LG4's had dished pistons and 8.5:1 CR; while L69's, '85-'86 LG4's and LB9's had flat-tops and 9.5:1 CR - all with 416 58cc heads.

This all begs a question, though: Why do you want to know about these 187 heads? I believe I can say without fear of contradiction that those swirlports are performance garbage.

 

Just covering as much info as I can find on these heads. Rumor has it is a good head for low end. I'm building a 305 for a 4x4 Sonoma. I have little use for power over 4000 rpm with this truck. I am looking for air velocity more than volume. Thing is I am not using pistons like those used with these heads. Like to know the volume of the chambers to calculate the compression if it turns out I decide to go with these heads.

 

Oh these are great 4x4 heads. The swirls generate good low end response, but sacrifice top end. Port the exhaust side improving the line of sight and these heads will do what you want for off-idle torque; especially when you combine them with a high lift, low duration cam.

 

Here you can see the difference of the chamber at the surface. 187 is definately tighter here.

I'll try again.

 

Photo again.

 

After reading that the swirl ports don't swirl, I decided to try the ol' water hose experiment. The top images are the swirly head. They swirl water from the hose anyway. It also would seem that they would be less affected by the valve. Note in the upper right image how a good portion of the water makes its way all the way around and shoots out into the neighboring chamber. The 416 does what other heads I have tried this on does. It hits the back side and jumps straight out with minimal swirl.

I also did a verticle measurement of the intake port. The minimum height of the port was near to 2" while the 416 minimum height was around 1-3/8". I found it funny that most people mention the horizontal tightness of the port but overlook how much taller they are.

 

I'm the one who posted the pics and 57kid is exactly right. As you can see they are flat top with 4 valve reliefs. They are 58cc chambers. I dunno what else to say, except look at the pics.

 

The piston thing again.

Taken from the silvolite website. They make replacements.
#1449 1976-86 3.06." dia. head recess .09" deep.
#1466 1982-86 Flat head with four valve reliefs.
#1493 1987-94 3.10" dia. head recess .040" deep with 4 valve reliefs.

http://www.beckracing.com/slvpg27.htm

http://www.beckracing.com/slvpg28.htm

I dunno what else to say, except look at the pics.


Since I started this thread, I have learned that the comparison that I originally made can not be done that simply. I was unaware of the piston change.

As long as I have become this involved with deciding on which heads I will use, I will continue the investigation and get out the heavy grease, seal the chambers and do an accurate fluid test of my own.

 

Follow up to the 187 intake port investigation. If anyone is interested.

I recently took a peek in the plenum of an edelbrock torker II and notice a familiar shape. The openings to the ports inside the plenum are very similar to the tightest area in the port of the 187 intakes.

Upon measuring the plenum side port openings I come up with an average size of 13/16" by 2.20". I then proceded to the heads. I measured the height just before the bowl which seemed the shortest and it also had the tightest width. The tightest width is at the top of the port. That width extends about half way down and then begins to widen as it continues down. This spot measured at around 13/16" and very close to 2"

So even if the head port didn't begin to widen, the difference is up to 10% in area. If you were to use the head port in the manifold plenum I would think you would still have a real good manifold. Edelbrock says the torker II provides power up to 6500 rpm on small blocks.

The width of the port at the top does decrease as you procede in to the bowl area but at this point you are in the swirl inducing area and there in no longer a port floor.

I am not saying this is an exact comparison to performance potential but I believe this should help eliminate the ports in the head as its problem, if there is one. I would think any problems would have to be found over the valve.

Other heads that I understand have similarities in port design. 1) LT1 aluminum: I have read they are narrower at the top of the port than the bottom. 2) LS1: "cathedral" ports, tall and skinny.

 

After playing around a while, I came up with a consistant fluid measuring system. I am satisfied with the results.
The chambers I tested averaged 55cc for the 187 and 58cc for the 416.

 

Jeez. I never really paid attention to these threads about the LO3 piston, but I guess I should have.

Using the piston pic that 25THRSS posted in the other thread, you can clearly see they're dished. I lightened the pic so you can actually see them.

See the ridge on the outside edge of the piston face? That makes them dished. The area in the center of the piston is recessed, and is considered dished. I have similar pistons from a LO5. They are dished. No matter how flat they look, they’re dished.

 

HOLY CRAP. what a dirty core.

must have been out of a caprice taxi cab.

 

you know what aj, you are right. I never even saw that tiny edge before. They're not dished much, but they are dished. That would also be one reason why the heads came out to only 55 cc. If I remember correctly those pics came from an 89 L03.