[TRADERMIKE 2012]

Originally Posted by steve25

I have had both the 360 hp 2 bolt main 428 and the 376 hp 4 bolt main motors and the pistons where the same dish type.

Mikes answer: I wonder if on the 1967 428 ci HO with 4 bolt main as I have with YK code if the HP goes up to 390 as in 1968 and 1969. "D" Port Heads and YK code- meaning Automatic with 4bbl Included. I have seen Photos of a Flat Top Piston with Recess for Valves. What are those used in?

[tekuhn]

Basically, the 428’s used the same heads as 400, so they had to dish the pistons to achieve the desired CR. The 455 used it’s own head castings (with larger chamber volume), so it had flat top pistons with valve reliefs like the 400’s.

[SD455DJ]

Originally Posted by TRADERMIKE 2012

Mike: Would like to see a Photo of the 1967 428 CI HO Piston Top. I have the Pontiac 1967 "D" Port Heads on the HO YK Code 428 ci Block. That is if you can and have access to that Block and it is 1967. I have never seen the 10.75 CR Piston and I have read there was a Lower CR Piston version used on the Big Body Vehicles. Since I have never had my Heads off the Motor, I am curious to see the difference between them. I have seen photos in Books but I can't distinguish between Low and High compression Pistons. All that I read is that the Low CR is Dished to Lower the CR. So, if you can provide the Two Photos showing both Low and High CR Pistons for 1967 428 CI HO Piston's, would be beneficial to my current research, thanks. Mike out.

TraderMike, The 428HO is a '68 WJ code (manual) for a '68 Catalina 2-dr post coupe my brother is restoring currently. I believe Steve25 is right on with only one dished piston used on the 428 for all 3 years. I don't recall the CC's now. When Dan rebuilt the engine, he used flat-top Icon or Diamond forged pistons to achieve a true 10.75 compression ratio. The dishes would have dropped it down to low 10's. 428's used the same head as the 400's (670's in '67 and 16's/62's in '68/'69). Their combustion chambers all measured in the 72-75 CC range, so needed dished tops to lower. Pontiac went with dished pistons on the 421/428 rather than have specific head castings, like they did for the 455. In the 60's Pontiac adjusted compression ratios by swapping different heads. I attached a copy from the '68 and '79 parts catalogs of the 428 piston P/N's. I see the '68 catalog lists different P/N's for the '67 & '68 428's while the '79 catalog list only one for all 3 years (most likely superseded P/N's over the years to one common part) and most likely very minor differences between the '67 and '68 pistons to notice.

(Got tree'd by tekuhn!)

Dennis

[TRADERMIKE 2012]

Originally Posted by SD455DJ

Trader Mike, the 428HO is a '68 WJ code (manual) for a '68 Catalina 2-dr post coupe my brother is restoring currently. I believe Steve25 is right on with only one dished piston used on the 428 for all 3 years. I don't recall the CC's now. When Dan rebuilt the engine, he used flat-top Icon or Diamond forged pistons to achieve a true 10.75 compression ratio. The dishes would have dropped it down to low 10's. 428's used the same head as the 400's (670's in '67 and 16's/62's in '68/'69). Their combustion chambers all measured in the 72-75 CC range, so needed dished tops to lower. Pontiac went with dished pistons on the 421/428 rather than have specific head castings, like they did for the 455. In the 60's Pontiac adjusted compression ratios by swapping different heads. I attached a copy from the '68 and '79 parts catalogs of the 428 piston P/N's. I see the '68 catalog lists different P/Ns for the '67 & '68 428's while the '79 catalog list only one for all 3 years (most likely superseded P/Ns over the years to one common part) and most likely very minor differences between the '67 and '68 pistons to notice.

(Got Tree'd by tekuhn!)

Dennis

Good Info., thank you. Now, I don't see the words "HO" included in your documents that you sent for one thing says 428 only plus you mentioned that your brother had to use a Flat Top type version Piston to reach 10.75:1 CR. So, I ask "How did the Factory provide Vehicles with 10.75 CR using the Pontiac 1967 "D"- Port 670 Head 428 ci HO (YK) in my case unless they were using the Flat Top version like the 400 ci Engines. I have learned they would have installed the "Y"-branch Exhaust system under the Special Equipment order. There are 1045 YK code 428 ci "HO" Manufactured in 1967 only. Someone sent a list of Special Equipment like dual springs, special dist., higher pressure oil pump, "Y"- Branch Exhaust. In the Brochure it is mentioned that 10.5:1 CR and 10.75:1 CR were available upgrade options to the Big Vehicles in 1967. I can't help to think that the Flatter Top Piston would have been used to achieve 10.75:1 CR to arrive at those results. We are excluding any dealer upgrades like Royal Bob-catting the Engine here. Since the Dish is to lower the CR on the Big Vehicles. Problem is I don't know what Vehicle my 428 ci went into because it is installed in my 1979 Pontiac TA today. Your thoughts please, Mike out. P.S. On your Brothers Pontiac 428 ci "HO" 1968 WJ code (manual) for a '68 Catalina 2-dr post coupe Engine "What is the Factory stated CR with those Dished Pistons, see the Brochure". I would think the CR would have been 10.75:1 and if it could put out that CR "what type of Pistons were used to obtain 10.0:1 or 10.5:1 CR"? Also, the Pistons in the Photos look like the Dished version or low compression version?

[b-man]

All 428 pistons used were the same, the combined volume of the dish and 4 valve reliefs was 11ccs. This allowed Pontiac to use the same heads on 428 and 400 engines and maintain the same compression ratios.

The 428 compression ratio came in two different flavors, 10.5:1 and 10.75:1，there were no low compression regular fuel or 2-barrel economy versions of the 428. The difference in combustion chamber volume would be a scant few ccs at best. Either the heads were milled a little to reduce their volume or slightly thinner head gaskets were employed to get to a theoretical 10.75:1 from 10.5:1. The pistons were all the same 11cc dished ones no matter what.

Keep in mind that the actual real world compression ratio on these engines were roughly a half point (or more) lower than the advertised numbers.

The 421 engines did not use a dished piston to maintain the same compression ratio of the 389 engines that they shared cylinder heads with. They had 4 very large valve reliefs to get the added volume needed. Consequently the 389 pistons had 4 very small reliefs.

1964 421 piston on the right, same year 389 piston on the left. There’s no reason other than increasing the piston head volume for the larger 421 valve reliefs. Both engines utilized the same heads (both 1.88”/1.60” and 1.92”/1.66” valves in ‘64 depending on engine options) and same valve lift camshafts.

[TRADERMIKE 2012]

Mikes observation: After reviewing your 1967 only info. I see three different numbers for the 428 ci Piston. I think 1) 10.0:1 CR = Dish Piston + 75 cc Cylinder Volume + Thicker Head Gasket.
2) 10.5:1 CR = Dish Piston + 75 cc Cylinder Volume + a Reduction in Head Gasket thickness.
3)10.75:1 CR = Flat Top Piston with the Valve Relief + 72 cc Cylinder Volume + thinnest Head Gasket thickness of them all.

After that is where a Dealer like Royal could use that thin copper head gasket in their kit to raise the CR one point along with their other Tricks.

Mike is speculating here, tell me your view!

[TRADERMIKE 2012]

Originally Posted by b-man

All 428 pistons used were the same, the combined volume of the dish and 4 valve reliefs was 11ccs. This allowed Pontiac to use the same heads on 428 and 400 engines and maintain the same compression ratios.

The 428 compression ratio came in two different flavors, 10.5:1 and 10.75:1，there were no low compression regular fuel or 2-barrel economy versions of the 428. The difference in combustion chamber volume would be a scant few ccs at best. Either the heads were milled a little to reduce their volume or slightly thinner head gaskets were employed to get to a theoretical 10.75:1 from 10.5:1. The pistons were all the same 11cc dished ones no matter what.

Keep in mind that the actual real world compression ratio on these engines were roughly a half point (or more) lower than the advertised numbers.

The 421 engines did not use a dished piston to maintain the same compression ratio of the 389 engines that they shared cylinder heads with. They had 4 very large valve reliefs to get the added volume needed. Consequently the 389 pistons had 4 very small reliefs.

1964 421 piston on the right, same year 389 piston on the left. There’s no reason other than increasing the piston head volume for the larger 421 valve reliefs. Both engines utilized the same heads (both 1.88”/1.60” and 1.92”/1.66” valves in ‘64 depending on engine options) and same valve lift camshafts.

Mike wants to know: Do I figure a total of 72 cc - 11 cc valve relief to get 61 cc in the "D"-Port Bath Tub.

[SD455DJ]

Yes, Pontiac listed 2 different head gaskets for the 428:

9790910: (0.038”) 68-70 400/428 H.C.; 69-70 400 HO/RAIII/RAIV
9790911: (0.048”) 68 400/428 Sm.Va.; 70 400 2V; 71-73 400
9785654: (0.038”) 67 400/428 H.C./HO
545055: (0.038”) 70 455 All
489029: (0.042”) 73-74 400 All
488575: (0.042”) 71-76 455 All

The 9785654/9790910 at .038" crushed and 9790911 at .048" crushed.

Dennis

[lust4speed]

Originally Posted by TRADERMIKE 2012

Mike wants to know: Do I figure a total of 72 cc - 11 cc valve relief to get 61 cc in the "D"-Port Bath Tub.

You are going the wrong way with your math. You have to add all voids to get the final combustion volume. So using your numbers, 72cc plus 11cc plus area for the head gasket plus the distance the piston is down in the hole plus a few other smaller voids like the area around the piston circumference to the cylinder wall down to the top ring (the last one most don't worry about unless using a piston with a large chamfer).

[tekuhn]

Originally Posted by SD455DJ

(Got tree'd by tekuhn!)

35 years ago, that used to be my specialty!

[TRADERMIKE 2012]

Originally Posted by lust4speed

You are going the wrong way with your math. You have to add all voids to get the final combustion volume. So, using your numbers, 72cc plus 11cc plus area for the head gasket plus the distance the piston is down in the hole plus a few other smaller voids like the area around the piston circumference to the cylinder wall down to the top ring (the last one most don't worry about unless using a piston with a large chamfer).

When I have read about the 428 ci Motor Piston size Bore and Stroke it said 72 cc and screw in studs, so I thought that volume was complete for the "D"-Port Head for 1967. I see what you mean though, don't forget the "Quench"- Fire Front. Is that the correct word? Squish, something like that. Zero Deck, the Piston is at the Top of the Block because it was milled so?

[TRADERMIKE 2012]

Originally Posted by b-man

All 428 pistons used were the same, the combined volume of the dish and 4 valve reliefs was 11ccs. This allowed Pontiac to use the same heads on 428 and 400 engines and maintain the same compression ratios.

The 428-compression ratio came in two different flavors, 10.5:1 and 10.75:1，there were no low compression regular fuel or 2-barrel economy versions of the 428. The difference in combustion chamber volume would be a scant few ccs at best. Either the heads were milled a little to reduce their volume or slightly thinner head gaskets were employed to get to a theoretical 10.75:1 from 10.5:1. The pistons were all the same 11cc dished ones no matter what.

Keep in mind that the actual real world compression ratio on these engines were roughly a half point (or more) lower than the advertised numbers.

The 421 engines did not use a dished piston to maintain the same compression ratio of the 389 engines that they shared cylinder heads with. They had 4 very large valve reliefs to get the added volume needed. Consequently the 389 pistons had 4 very small reliefs.

1964 421 piston on the right, same year 389 piston on the left. There’s no reason other than increasing the piston head volume for the larger 421 valve reliefs. Both engines utilized the same heads (both 1.88”/1.60” and 1.92”/1.66” valves in ‘64 depending on engine options) and same valve lift camshafts.

Mike Thought:
I always wondered "How come they put Valve Reliefs on both sides of the Pistons". They are to lower the CR. I thought they would be only for 4 Valve per Cylinder DOHC Engines. I knew that the Wrist Pin on the Piston was off set for less pressure on one side of the Cylinder wall so you only need 2 valve reliefs. Always learning, thank you for sharing.

[tekuhn]

There are four valve reliefs so that the piston can be used on either side. Otherwise, you would need two different pistons for right and left. You couldn't just flip a 2-relief piston over for the opposite side due to the pin offset.

[TRADERMIKE 2012]

Originally Posted by tekuhn

There are four valve reliefs so that the piston can be used on either side. Otherwise, you would need two different pistons for right and left. You couldn't just flip a 2-relief piston over for the opposite side due to the pin offset.

Mike reply:
Got you, there is more than one reason. It has been a long time since I built My 327 ci Chevy Motor from scratch. I took the Motor from a 1969 Chevy Impala and had the work done in the machine shop, had a friend Port and Polish the Heads. Make a long story short it got stolen after my hard work and saving every last penny as I was learning the Carpet Trade. I was to install it in a 1967 Chevy Flat wind shield Van. Ended up Buying a Brand New 1979 Dodge Van and making $153.00 monthly payments plus insurance.

[TRADERMIKE 2012]

Originally Posted by TRADERMIKE 2012

Mike Thought:
I always wondered "How come they put Valve Reliefs on both sides of the Pistons". They are to lower the CR. I thought they would be only for 4 Valve per Cylinder DOHC Engines. I knew that the Wrist Pin on the Piston was off set for less pressure on one side of the Cylinder wall so you only need 2 valve reliefs. Always learning, thank you for sharing.

Mike wants to know if {Originally Posted by b-man}
The info. you posted about the 428 ci Motor is coming back to me, as I too have read that in the past. Brings up the question of: "Did a 1967 390 HP version 428 ci 670 "D"-Port Head ever exist with "Smaller Valves" in a "Full" Body Pontiac Built on the Factory assembly line"? (Non, Bob-Cat Edition) As, I believe I've read about in the past. I am aware of 390 HP on 1968-69 428 ci because of the round port Head design upgrade, upgraded Cam and "Y"-Branch Exhaust.

[Kenth]

ALL 1967 400/428 #670 heads uses 2.11" - 1.77" valves. no such thing as "small valve #670 heads.

NO roundport heads ever on fullsize Pontiac´s from factory.

[TRADERMIKE 2012]

Since I was going by memory and I don't have the Article at hand, I would ask this: "If one was to use a previous 1965-66 Head with the smaller Valves that fit the 1967 428 ci Engine (with the smaller Valves) would that increase the HP or CR on the 428 ci given you use the same Carb. and Exhaust?

[tekuhn]

Originally Posted by TRADERMIKE 2012

Mike wants to know if {Originally Posted by b-man}
The info. you posted about the 428 ci Motor is coming back to me, as I too have read that in the past. Brings up the question of: "Did a 1967 390 HP version 428 ci 670 "D"-Port Head ever exist with "Smaller Valves" in a "Full" Body Pontiac Built on the Factory assembly line"? (Non, Bob-Cat Edition) As, I believe I've read about in the past. I am aware of 390 HP on 1968-69 428 ci because of the round port Head design upgrade, upgraded Cam and "Y"-Branch Exhaust.

The highest HP 428 in 1967, was 376HP. For '68-'69, the highest HP was 390. The '68-'69 engines used the new open chamber head design, but none of them were "round port" heads. The only 428 that did not have the large 2.11"/1.77" valves, was the '69 360HP 428 that used #46 heads with 1.96"/1.66" valves.

[TRADERMIKE 2012]

Can someone give me their best guess about my Engines HP: I have a very strong 4 Bolt Main Armersteel Crank and it is very clean inside the Engine. I have a mild build on a 1967 Pontiac 428 ci HO "YK" code Tri-Power Intake that is up jetted, new "041" Cam, new Hydraulic Johnson Lifters, new Chrome Moly Pushrods, new 7/16 Rocker Studs, new Oil Pump, new 6 AL MSD Ignition with a rebuilt Electronic Distributor, Functional Air Induction and a new Timing Gear that has been Advanced to 109 C/L .

Coated Headers inside and out plus their wrapped. Exhaust travels through 3" Collectors to about 2" pipes and 2.5" Exhaust exiting through the Rear Diffuser (No Mufflers). Engine sits in a 1979 Pontiac TA that weighs about 4000 lbs. Has 3.23 Gears in the Rear End Posi- traction 4 Wheel Disc. Brakes. TH 400 Trans. is in front of the Gear Vendors Unit. Commanded by the B+M Shifter with the button on the Grip for the GV. Starting with the 376 HP from the Factory, I would be satisfied to be getting one HP per Cube?

I have never had it Dynode, but I have had it up to 130 MPH on the old Cam when it was worn. I know this current Cam "041" is designed for even more top end. So, at this time, I don't have the speed rated Tires to even try to surpass 130 MPH.

Also, I just remembered I have installed a Hughes HD Torque Converter and have yet to try It, as I am finishing up this project that I have found myself grossly intertwined in doing. The answer should be in terms of 1967 ratings please.

[P@blo]

Originally Posted by TRADERMIKE 2012

Can someone give me their best guess about my Engines HP: I have a very strong 4 Bolt Main Armersteel Crank and it is very clean inside the Engine. I have a mild build on a 1967 Pontiac 428 ci HO "YK" code Tri-Power Intake that is up jetted, new "041" Cam, new Hydraulic Johnson Lifters, new Chrome Moly Pushrods, new 7/16 Rocker Studs, new Oil Pump, new 6 AL MSD Ignition with a rebuilt Electronic Distributor, Functional Air Induction and a new Timing Gear that has been Advanced to 109 C/L .

Coated Headers inside and out plus their wrapped. Exhaust travels through 3" Collectors to about 2" pipes and 2.5" Exhaust exiting through the Rear Diffuser (No Mufflers). Engine sits in a 1979 Pontiac TA that weighs about 4000 lbs. Has 3.23 Gears in the Rear End Posi- traction 4 Wheel Disc. Brakes. TH 400 Trans. is in front of the Gear Vendors Unit. Commanded by the B+M Shifter with the button on the Grip for the GV. Starting with the 376 HP from the Factory, I would be satisfied to be getting one HP per Cube?

I have never had it Dynode, but I have had it up to 130 MPH on the old Cam when it was worn. I know this current Cam "041" is designed for even more top end. So, at this time, I don't have the speed rated Tires to even try to surpass 130 MPH.

Also, I just remembered I have installed a Hughes HD Torque Converter and have yet to try It, as I am finishing up this project that I have found myself grossly intertwined in doing. The answer should be in terms of 1967 ratings please.

What kind of work has been done to your heads? If stock d-port I'd expect similar performance but if ported to roundport flows then you could safely say you would have similar performance to such.

There was a figure posted that one cfm of intake head flow was good for two horsepower (actually it is closer to a 1.9:1 ratio) so if you have everything right a stock 208 cfm intake port can support 416HP. Since power comes from heads if you flow at 250cfm you can potentially make 500hp.