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Chevy 186 head flow questions

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Re: Chevy 186 head flow questions

Postby ap72 » Thu May 20, 2010 11:49 am

I would keep the heads you have, and swap the pistons. Those other heads aren't that great, additionally there's still too much compression with decent piston to head clearance.

You can continue trying to find ways of ignoring the problem, or just fix it. You need different pistons, or race fuel (or E85 if its available).
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Re: Chevy 186 head flow questions

Postby chevyracer8262 » Thu May 20, 2010 12:07 pm

Well the problem with buying new pistons is that I would have to get everything rebalanced, cause I seriously doubt I can find another set of pistons the same exact weight as what I have already cause I bought everything matched and balanced. I know I screwed up when I bought this kit, but at the time I had bigger plans for all this.
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Re: Chevy 186 head flow questions

Postby chevyracer8262 » Thu May 20, 2010 12:21 pm

Man life can really bite.
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Re: Chevy 186 head flow questions

Postby Stan Weiss » Thu May 20, 2010 12:40 pm

chevyracer8262 wrote:Well the problem with buying new pistons is that I would have to get everything rebalanced, cause I seriously doubt I can find another set of pistons the same exact weight as what I have already cause I bought everything matched and balanced. I know I screwed up when I bought this kit, but at the time I had bigger plans for all this.


They do not have to be the exact same weight. If the new set of pistons is a little lighter you will be fine. Do a search here there have been a number of threads on using lighter pistons and not rebalancing.

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Re: Chevy 186 head flow questions

Postby Lockwire » Thu May 20, 2010 1:21 pm

Those pistons maybe could have a bowl cut in them. The deck ( I just checked one ) sonic tested .275 thick. Maybe you should check with a macine shop. You do need around 9.5. :)
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Re: Chevy 186 head flow questions

Postby robert1 » Thu May 20, 2010 1:42 pm

Put a set of .080" head gaskets on and you're at 9.5!!!
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Re: Chevy 186 head flow questions

Postby ap72 » Thu May 20, 2010 1:44 pm

Lockwire wrote:Those pistons maybe could have a bowl cut in them. The deck ( I just checked one ) sonic tested .275 thick. Maybe you should check with a macine shop. You do need around 9.5. :)


Not a bad idea. Maybe less costly than buying new ones and selling what you have.
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Re: Chevy 186 head flow questions

Postby BrazilianZ28Camaro » Thu May 20, 2010 2:29 pm

If you can deshurond the valves in the 186 heads would be a win-win. More flow, with a little less CR.
Retarding the cam would help also.

I believe the E85 will not blend evenly with pure pump gas with out a product that added to the gas can make the E85 suitable for adequate blend.
70% gas +30% E85 would raise considerably the knok resistence of the fuel.

Here in Brazil our pump gas is in reality E22 (22% anhydrous alcohol about 110 octane) blend in all 87,91 and 95 octane pump gas. The effective octane of the E22 is higher than pure gas because the alcohol mixed.

As a example , a Buddy have a 77 Chevy Opala that I wrench, 151 Ci N/A, 268 ADV DUR CAM, 109LCA,mirror polished chambers/ valves, .048 quench, 11.3:1 CR, 2700 lbs, 3.54 gears. Timing is 22-36°+10° vaccum advance.

I'm sure this little engine see high loads at low rpms with that relativelly heavy weight (for the size of the engine).

To our surprise, It runs REALLY FINE with "87" pump gas E22. :shock:
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Re: Chevy 186 head flow questions

Postby steve25 » Thu May 20, 2010 3:29 pm

The combustion chamber in those latter casting number low comp heads you posted about make less power out of the same givem amount of air flow.

Remember an engine is nothing more than a air pump, 260 cfm thru a 180 cc port along with a 9 to 1 comp and a cam of no more than 222 duration on the intake side will make for great power thru a 2500 rpm wide power band.
I would with out question give up 12 HP at 6200 to have 20 more HP at 4500.
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Re: Chevy 186 head flow questions

Postby Solid LT1 » Fri May 21, 2010 1:36 am

If you have enough time to waste you can make a pair like this :lol:

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Re: Chevy 186 head flow questions

Postby chevyracer8262 » Sat May 22, 2010 11:13 am

Those 492's look awsome. That's the plans we have for my 186's right now I'm working on the first intake and exhaust port then we're going to do the valve job and flow them to see where I need to improve to get them to flow where we need. Have you flowed those 492's to see what they flow?
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Re: Chevy 186 head flow questions

Postby Mike Rogers » Sat May 22, 2010 11:47 am

If they are true factory 186 heads and they have not been man handled like porting and milling they bring a good dollar to the wright guy looking for them that is doing a z28. I had a set that had the wright date and sold them for $1500.00 done so don,t be to quick to start porting them.
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Re: Chevy 186 head flow questions

Postby Solid LT1 » Sun May 23, 2010 1:18 pm

Intake port sizing was left at Fel Pro #1204 stock gasket size because a real Z/28 intake is going on them and they don't have much room for port matching to anything bigger. I'm finishing up on valve job, spring seats right now and would expect final numbers in the 230CFM (@ 24" vacuum) flow in the 0.500" lift range, not spectacular but much better than stock ports. Exhaust should be in 190CFM (@24" vacuum) at same lift (based on previous efforts I have done.) Motor is a stock appearing 350 LT-1 Chevy.

The other poster is quoting $1500 for a set of 186 castings, maybe 2 years ago but not now $250-500 for a pair of heads on Fleabay seems the going rate right now in this economy but, if you don't need original looks, I would definatley sell those heads and buy a current set of RHS or Dart heads to replace them, you would be far ahead of the game doing this in the first place.

I just spent 2 hrs grinding a set of valve spring locators down from 1.45 to 1.42 diameters to fit spring seats of these heads. Many people give no thought to cutting spring seats out to a 1.55" diameter, I won't because these old heads are very thin in upper casting and your getting pretty close to water even using the 0.060" shim method like in the Isky catalog. With RHS or Darts, the casting is much better material and quality than these old Chevy castings. Someone should really license from GM the "camel hump" exterior design and make some modern castings for us old school motor guys, I'd pay $800 for a set rather than having to deal with some of the issues I deal with in reworking these old castings.

One last step is machining the valve cover gasket surface so it dosen't split VC gaskets apart, something I never seemed to have problems with in the old days but, I think gasket composition has changed greatly in these times (like no asbestos in materials :lol: ) Just a few hours here, and a few there and pretty soon your talking some real $$$ and efforts being wasted but, I enjoy making something better that it was when it left the factory.
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Re: Chevy 186 head flow questions

Postby chevyracer8262 » Mon May 24, 2010 6:43 pm

Well my 186's already have a ton of machine work done to them and are no where near stock condition. I had originaly planned on going with a set of RHS heads but due too financial reasons I had to opt out and a buddy of mine gave me these heads in the condition their in now. Hopefully we'll be able to flow the ports that I've ported this weekend. So far, they've had alot of porting done to them, they're machined for 1.42" dia springs, 2.02"/1.60" valves, reamed for press in guides, screw in studs and guideplates. They used these heads on his brothers 350 race engine.
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Re: Chevy 186 head flow questions

Postby chevyracer8262 » Thu May 27, 2010 4:18 pm

When porting the 186 heads how much can you grind on that bolt hole protrusion just before the bowl area in the intake ports without going through? I've got it ground down pretty good but I'd like to make the runner a little straighter by laying it down some more. so far I've got the intake ports matched to a felpro 1205 gasket, raised the roof .100" at the intake face, and tapred it straight back to the valve guide, ground on the pushrod pinch area some, but not a whole lot and started bowl blending the intake bowls. I had to go up to the 1205 because my tunnel ram intake ports are that size already.
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