ptwohey

Happy Memorial Day! I imagine this question has already been answered but my search has not found previous post so here it is again.

I'm rebuilding a 1969 DZ (Z28) 302 to as close to factory specs as I can including date codes. The heads on my engine were sold years ago and trying to find replacements has been expensive with poor results.

I did buy a pair of dated 186's from CA and had them shipped in to RI, The cast numbers are correct and the dates are perfect, but, these were machined from 1.94's to 2.02 and when the shop checked them out mentioned that air flow is not the same so my high end (over 6K) will suffer.

I've been told that all 186 castings are the same regardless of valve size so I'm asking what I need to do to make these heads work as designed with 2.02 intakes and 1.6 exhaust?

I found a full rebuild on youtube but nothing about the difference was mentioned.

Thanks.

cv67

Its not going to suffer with a 2.02 valve hogwash
Will putting a 2.02 valve in a stock head bring some noticeable gain, no.
Were they leading up to buying those "bad' heads from you? lol

If they are good and not cracked port those suckers well noone can see it
Doesnt sound like thats the shop to do it.

Local shop yrs ago took a set of AFR 180s, blasted the front of them,(you can also use a texture type paint then go orange over it, milled the (billboard ugly) logos off and using epoxy shaped the hump on the front, then sprayed them orange. That little motor made some GOOD power really oughta consider that its not hard and power gains....oh yeah! In person you really couldnt tell
perefect sized head for that 302 if youre winding it up

tpi421vette can get you a screamin deal on a pair
Keep the 186 for the next guy in the garage.

cardo0

I think I'm reading that shop has determined the throat area and maybe the ports for your replacement heads are different than larger valve stock heads and will not flow as well. The real problem is finding a competent head porter as most of the hacks that malinger on these forums just want your business and will hog them out for you and take your $$$ to. On the other hand it kinda reads like u don't want any modifications to the heads other than adding the larger vlvs. In that case you're stuck with what you got. If not look for head porter that can wet flow and port the heads. Won't be cheap or easy to find but u will get the optimum throat and port for your vlv size.

Hope this helps.

GUSTO14

Patrick, I suspect what the machine shop is referring to is the heads that left the factory with 2.02 intakes had their combustion chamber in the area of the intake valves un-shrouded. There have been a number of threads over the years that discuss the procedure. Here is one...
https://www.corvetteforum.com/forums...-02-valve.html

Tom Parsons (DZAUTO) is quite knowledgeable on these matters so I give a great deal of weight to what he says. This discussion relates to converting 461 (double hump) heads with 1.94 intakes to the 461's with 2.02 intakes, but I believe the issue is the same.

Good luck... GUSTO

7t9l82

The throat needs to be opened up to match the bigger valve or there is no real benefit. It's a simple procedure. Unshrouding the valve is worthwhile too.

Solid LT1

Chevy opened the throat below the valve seat AND also relieved the combustion chamber wall with a cutter......if you don't relieve the chamber wall there is no benefit to going to a 2.02 dos intake valve. Get David Vizards book on Small Block Cylinder heads for details. How original do you want the head......Chevy went to screw in studs and guide plates on the 70 LT-1 for a good reason......there were lots of warranty claims on the 302 motor from valve train problems that made them add the $20 cost of studs and guide plates in 1970. I have a 69 casting CE service motor pulled from my wife's 70 LT-1 that has 186s and screw in studs/guide plates on it.....so they started before the 70 LT-1 was released in 70....same motor is a "386" block casting......anyone looking for one? Also have NOS 1186 Z/28 crank/TRW USA +0.020/+0.030 Pistons for a 302 if anyone is interested.

ptwohey

Great information from all you supporters. You cleared things up for me. It makes sense that the 186 castings are all the same and the porting is the difference.

I read the Persons posting and see a note that hardened exhaust seats are not needed but the best date matching set that I have already has them so that's not a choice.

I saw several YouTube videos that also explain everything about porting so I'll check that out. I'll give the machinist a call in the AM and ask questions to make sure I understand what he was trying to tell me about the heads and valves and see if he was talking about the extra work rather than problems created by the first shop to work on these.

If I give up on correct dates I do have one D 7 9 from a 302 but the same engine also had a M 4 4 (is that December 4, 1974?) I could not find any info if 186's were still cast in 1974 but it was on the 1969 302 engine.

Thanks for all the information and I'll update my decision after I make one. I'm not looking to go racing but the 302 reputation is low torque but high rev's. I will be using this to pull the original from my Z28 to save it and still have the extra 302 to beat on and not worry about blowing it up and loosing originality. After this is done I will be selling the 2nd extra CE 302 to pay the bills, I hope.

ptwohey

I have made the decision to use the correct date coded heads , After I disassembled them I see that these were ported sometime in the past to the proper specs of a 302 so all is good. This porting was not completely visible with the valves were installed but what did show was the larger valves were not relieved properly but I will fix that.

I do need to replace all the guides and valves plus stronger springs for the high lift cam so the work begins.

gkull

Hogwash is putting it mildly. I had modified 186 casting heads on my vette for many years.

You just don't throw bigger valves in a head . You take out the old smaller diameter 1.94 inch seats and you install the larger 2.02 seats. I'm not going to do the math on valve area, but lets just call it a 10% gain in air flow.

The design of the valve stem makes a difference. Manley race and pro flow are a tulip design (smaller) in the port to impead less air flow.

One thing you do need to do is machine for screw in studs.

My memory is failing as to what i did on them 30+ years ago. but it seams to me that stock spring were tiny like 1.260 diameter. Well i opened them up to use 1.43 or 1.46 diameter springs. With good spring, screw in studs, chromemoly retainers I was able to spin my 355 ci to 7200 every day of the week. I had tranny and rear end problems, but my motor never failed

You do understand that modern heads flow considerably more than old time 186 no matter how much work you put into them?

Jebbysan

Make sure you have a quality shop do a five angle valve job on your heads and blend them in.....
Back cut the intake and exhaust valves.......
The stock heads leave a lot of power on the table......but if set up proper....they work well enough.....

My 66' Sting Ray had a ton of work in the heads......plus Ferrera 5000 valves....backcut, five angle....yada,yada......
They flowed over 240 cfm at .500 lift......and the low lift number were on par with an Edelbrock RPM head.....it ran VERY well.

But if original vibe is not necessary...bolt some Dart 180 Platinums on it and hang on.....

Jebby

gkull

I started out in the era of multi cut valve angle jobs. I tend to believe in modern radius valves with the single seat cut. all you have to do is hand lap them in and that is only if you feel like it. Modern equipment if often so good lapping isn't often required

ptwohey

The guy doing the machine work Ihas been doing this for 50 years and already did up a 327 that runs great. He had several choices of upgrades but understands that this DZ 302 is intended to be "as original as can be" with upgrades for today's gasoline because eventually it will be sold as a 1969 Z28 engine and the original 327-350 will be dropped back in the Vette.
If I was 20 years younger or my daughter comes around and gets interested in hot rods rather than C-130's and protecting our country a ground up build using new technology would be nice. I have several SB and BB cores sitting in the corner for that.
By keeping this 302 close to stock the resale value is hopefully higher than the cost I have into it.

Hardened seats, screw in studs and valve guides are usually acceptable to most dedicated GM enthusiast

I'll post the end results when I get them back. The next step is the short block that still has the original rotating hardware and never been bored. Hoping a re ring and bearings is all that's needed

gkull

If I get this correct you have a 69 camaro that came with a 250 hp 327. Then you had some mechanic hop the 327 to the 350 hp level. Now you think that by making it a clone Z-28 with a 302 motor that it will be worth more for resale?

There are lots of mods to get it close as a clone. The Z/28 was for the road racing fan. 4 wheel disk, Dual exhausts, special suspension, heavy-duty radiator, quick-ratio steering, special seats, and 15×7 inch rally wheels.

I sold my 67 RS/SS 350 4 speed a couple of years ago. I've been a long time Camaro and Vette owner. I never felt that the little 302 was a performer. It was made to compete in a 310 max ci road racing class. It's high compression, mechanical cam, and the dual four models were interesting. But very low power to weight ratio for a street car and lacking TQ because of the small ci.

cv67

302s , unless you have a 4.56 gear just too small a motor
Light car, enough compression good enough head they can run ok
OP noone can see whats under the valve covers. Believe me if someone were to pay for a clone 302 if they heard the heads had a great port job hes an idiot to protest it. Some take the original thing too far.

At least they sound good

What id give to own another 67 rs, first car only one I miss

Sold it thinking yet another M22 went bad, looking back it was simply jammed linkages. let it go for 1200.

7t9l82

The little 302 in the Z/28 was to meet trans am rules of the day. But only the geniuses at chevrolet decided to make the street version with a small engine chrysler, ford, Pontiac and even AMC had sense enough to put a larger engine in their versions.the 302 was a decent enough engine but it was at a disadvantage on the street. I know guys that ran 5:13-1 gears on the street to even the score.
The nice thing is most small blocks look much the same so you can build what you want and make it look pretty stock.

ptwohey

Sorry for the confusion about cars vs motors. I have 7 classics all with the original motors and drive trains including the Z28, it is not a clone. And the 327 - 350 is the 66 Vette. What I also have is extra engines for each car including 2 extra Z28 302's. I pull the original engines to protect the financial value of the drivetrain but build motors to the same specs so I can enjoy the cars and not worry about popping the original engine.

The issue with the 186 heads is because it was a short block when I got it and the second 302 heads are not dated the the block. Anyway, every thing is in order for now.

jim2527

50 years means nothing if he still has 50yo techniques and thought patterns. I'll take a guy who's been doing it for 10 years but uses modern techniques.

ptwohey

Thanks for the note and I can understand that totally but unfortunately my experiences with new technology and new shops has not been rewarding. I took a brand new 1969 CE 350 I found on eBay to the local shop who built a buddy's 850 HP BB to have it checked out His new technology totally ruined the originality of that engine when he decked the block and heads removing the VIN and needing special gaskets to reassemble it. That engine became just another OTC engine. If I want HP that is the type of shop to go to but for old stuff to be refreshed I go to the old timer with the old methods who built winning dragsters back in the 60's and still wins races today! He works alone without minimum wage apprentices and does not run a mill house machine shop. Sure, he does have a long waiting list but my wife says I can't die until my projects are done and I'm up to 150 years old at the moment

cv67

Those guys are hard to find. Mine was just like that, old timer one man shop simple equiptment but his know how carried him over the yrs. Machining excellent, perfect balance jobs. Retired few mos back. Tried a few of th emore expensive guys with the CNC machines. Their know how was extensive however an hourly employees or level of caring isnt
Had to take back a few valve jobs that leaked....now looking once again.
Decking machine cant really stop just short of the #s if you want a flat deck for a performance build doc whats there for the futyue deck it right and move on. What good is original if deck height is all over the place

ptwohey

I guess there comes a time in each of our lives when we kick our butts and mine has been bruised several. I was lucky enough to work in a well equipped prototype shop with several millers and plenty of tools. I had a set of screw in valve stems installed by a 3rd generation and very reputable shop. It was not a nice experience when I got the bill vs the ballooned quote and found out that a newbie did the job. What tipped me off is that the tops of each stem was a different height. The valve covers would not even fit! I worked with fellow pattern makers with experience going back to WWII showed me how to set the heads on a Bridgeport and do it right. The shop did apologize after I pointed out the problems but the price was still higher than the quote. That was the only time I was able to save the project.