# 389CI and Installing 400CI Heads



## PontiacJim (Dec 29, 2012)

Finally got around to another one of my "Pontiac Facts" projects. I am no engineer or Pontiac engine rebuild specialist, but I read a lot of material on our older cars and read assorted forum questions and answers and really get frustrated at times when so many will have an answer, but have no factual data, drawings, photos, or prime source documents you can look up and read for yourself. So much of our hobby seems to rely on a "person's word" for it. So take my project with a grain of salt, but I present some findings that may answer an often asked question.

The BIG question. *Can I use late model 400/428/455CI heads on my 389CI? * Never have seen any "FACTS," just those who say "yes," "no," or "depends" if you bore the cylinders .060" to the size of the 400CI engine. The piston crowns are different from 389 to 400/428/455 in that the valves were relocated differently in the 1967 and up heads due to the increase in valve size and valve angle was changed - so valve reliefs are different and using later heads with higher lift cams can cause valve-to-piston issues with 389 CI pistons.

I purchased a stock bore 389CI Mellings cylinder sleeve from Summit. Stock bore is 4.0625. I then cut a slice of the sleeve, deburred it, and painted it silver so it would be real easy to see the relationship between the valves and the cylinder wall of the 389CI.

Photo #1 - I pulled out my 455CI head that I have cited previously in another post (listed at the end of this topic) and a Felpro head gasket which has a bore measurement of 4.3". The width of the 455CI combustion chamber measured 4.20" at its widest. I used the dowel pin holes of the head to fit/align the head gasket just as if it was on an engine. Left the valves out for this shot.

Photo #2 - I placed the smaller 389CI sleeve section within the 4.3" head gasket. I centered it by using a combination of my flat bladed feeler gauges so the feeler gauge could work around the cylinder evenly and not move it one way or the other. *LOOK!* _The 455CI combustion chamber hangs past the 389CI standard bore sleeve section._

Photo #3 - View of the intake valve side of the combustion chamber and how it extends past the 389CI sleeve.

Photo #4 - 2.11" Intake valve and 1.77" exhaust valve installed. Looking straight through the 389CI sleeve section at the valves. You can see how the sleeve sets inside the combustion chamber scallops of the intake side and barely was even on the exhaust side. I cleaned the seats/valves so they sit flat and no debris to hold them off their seats.

Photo #5 - I lifted both valves up high enough to where the valve's side edge was even with the surface of the head - which would be the same as the block surface. Kinda close to the 389CI sleeve. Note the angle on the valve and how the back side extends beyond the head surface when the side of the valve is brought even to it. This is where the problem of the valve striking the piston top comes in and why you need the valve reliefs to provide the clearance. 

Photo #6 - I lifted the valves free hand to a point where you can clearly see the side clearance of both the intake and exhaust valve in relationship to the 389CI cylinder wall - not much space at all.

Photo #7 - Looking at the valves from the side. Talk about valve shrouding!


----------



## PontiacJim (Dec 29, 2012)

PontiacJim said:


> Finally got around to another one of my "Pontiac Facts" projects. I am no engineer or Pontiac engine rebuild specialist, but I read a lot of material on our older cars and read assorted forum questions and answers and really get frustrated at times when so many will have an answer, but have no factual data, drawings, photos, or prime source documents you can look up and read for yourself. So much of our hobby seems to rely on a "person's word" for it. So take my project with a grain of salt, but I present some findings that may answer an often asked question.
> 
> The BIG question. *Can I use late model 400/428/455CI heads on my 389CI? * Never have seen any "FACTS," just those who say "yes," "no," or "depends" if you bore the cylinders .060" to the size of the 400CI engine. The piston crowns are different from 389 to 400/428/455 in that the valves were relocated differently in the 1967 and up heads due to the increase in valve size and valve angle was changed - so valve reliefs are different and using later heads with higher lift cams can cause valve-to-piston issues with 389 CI pistons.
> 
> ...



Part 2

Photo #8 & #9 is a closer look at the very small clearances between the intake & exhaust valves as seen in the 389CI cylinder. These lifts are way more than the cam would open the valves. I did this to clearly show how little clearance between valves and a stock 389CI cylinder wall. I put a feeler gauge on that exhaust valve and got about .028" of clearance.

Photo #10 - As a comparison, you can see the clearances around the valves when seated in the 455CI head. The cylinder of the 455 is of course larger and when the valves are opened, far less valve shrouding.

Photo #11 - I scribed around the inside diameter of the 4.3" bore Felpro gasket while it was centered on the head. You can see how close the combustion chamber is to the head gasket.

In conclusion, can I put the later 400/28/455 heads on my 389? Yes and No. The important aspect here is the valves clearance between it and the cylinder wall. Stock valve size is 1.92" Intakes and 1.66" Exhaust. Stock bore size is 4.0625. The 1967 and up high performance heads used the 2.11" Intake & 1.77" Exhaust valves having a different spacing/location/angle than the 1966 and earlier 389CI engine.

A magazine article that covered how to upgrade the 389 to use the newest 1967 400CI heads and top end stated that you could bore the 389CI over .060" to that of the stock 400CI which is 4.120". You had to use the correct 400CI pistons with matching valve reliefs. The block should also be chamfered to that of the 400CI to match the location of the valves to improve breathing (unshrouding the valves). The use of a 400CI head gasket will help to located the correct areas on the block to add the shallow scallops. You also need to get the longer 400CI pushrods to match the heads.

If you were to keep the 389CI bore stock to under a .060" bore, you could not take advantage of the 400CI pistons' valve reliefs that would match the later big valve 1967 and up heads. Your options would be to keep valve lifts down so the valves do not hit the tops of the pistons because the 389 valve reliefs are in the wrong place. You can have a machine shop re-cut new valve reliefs in the 389 pistons to match the later heads. You can find some pistons made to be used with either 389 0r 400 heads - they will have 8-valve reliefs. If you want to lower compression to use pump gas, you can purchase a dished piston which may have a dish deep enough to clear the valves. Lastly, custom made forged pistons like Ross. Keep in mind that you are still going to have very little valve-to-cylinder wall clearances and you may want to at least add the small chamfer/scallop in the top of the block to aid air flow.

The next thing is the width of the combustion chamber extending past the 389CI cylinder. The heads I have on hand are later heads, 1972 and up. The width of combustion chambers are all about 4.20" to include the smaller valve 350CI heads. These heads are also much bigger in CC's than the earlier heads having on average 72CC's. So my thinking is that as long as you use a head having the 72CC's, which will be a 1967-1970 head, you will not have the gross mismatch of the wider combustion chamber of the 1971 and up heads when compressions were greatly reduced by making the combustion chambers larger.

Can you use the later 1971 and up heads on the 389CI? Sure, but since the combustion chamber is wider and will hand past the cylinder bore, the incoming air/fuel mixture is going to slam right into it and no doubt create a lot of unwanted turbulence and with it a loss of power (in my opinion). So I would add the intake/exhaust valve chamfers/scallops and bring them out to the edge of the combustion chamber walls to improve breathing. Valve-to-cylinder wall will still be an issue with regards to side clearance of the valves.

Will using the later heads with the smaller heads 1.96" Intakes and 1.66" Exhausts work better? I believe you will still have an issue with the wide combustion chamber width. The smaller valves will certainly be better for air/fuel flow because the valve will be less shrouded and they are very close to the factory 389CI valve sizes. BUT, you still have the issues with the valve angle difference that may cause valve-to-piston problems with stock 389CI valve reliefs - so that has to be checked based on your cam's lift and opening/closing points.

Check my post for more info on heads and chambers:









Pontiac Combustion Chamber Differences &amp...


PONTIAC HEAD DIFFERENCES 46 J312 - 350CI 4X 7H D143 - 400CI 4X 1H B163 - 455CI 96CC Press-in Studs 98CC Screw-in Studs 114CC Press-in Studs 1.96"/1.66" Valves 2.11"/1.66" Valves 2.11"/1.66"...




www.gtoforum.com


----------



## 67ventwindow (Mar 3, 2020)

Thank you. It helps those that have a 1964,1966,1967 GTO/LeMANS/Tempest all in one car. Great visuals!


----------



## PontiacJim (Dec 29, 2012)

67ventwindow said:


> Thank you. It helps those that have a 1964,1966,1967 GTO/LeMANS/Tempest all in one car. Great visuals!


Thanks. I like to tackle some of the Pontiac babble that seems more bumping gums than facts. I've heard so many answers to the 389/400 heads that nothing is ever definitive. There is one of my customers I deal with at work who is a Pontiac enthusiasts, owns a number of Pontiacs, to include the $high dollar race cars and a lot of exotic parts. He knows a lot more than me and has been playing with Pontiacs for a good 40 years. We always get going on Pontiacs when I see him - sometimes I can't shut him down when I have to really get going. LOL So I mentioned it seemed to me that the larger 400CI valves would strike the cylinder wall/block of the 389CI - unless you bored the cyl .060" to match the 400CI bore. He said no. So that was what sparked me - to prove out our conversation. So it appears the big valves will clear the stock 389CI bore by a minimum amount and would strike the piston crowns at any kind of big lift because of the different locations for the valve reliefs. However, the valve shrouding on the one side is horrible and you would want as a minimum, to add the corresponding 400CI cylinder bore scallops to match the valves as an effort to somewhat improve breathing - which is what was done on the smaller bore 350CI HO engine (3.875" bore).

That said, my thinking is that you might almost do better power wise on the 389CI with its factory heads/smaller valves and then go bigger on the cam versus installing bigger valve 400CI heads, keeping cam lifts low, and accepting the shrouding of the valves.


----------



## LATECH (Jul 18, 2018)

I have had a few 350 that had the chamfer at the top of the bore to provide "deshrouding" to the valves (Intake mostly)
but both side of the bore had it.
I have a 389 with 400 pistons in it. I have 350 heads on it to reach 9.5 to one so I never had worries about clearance
to the cylinder walls. And with 400 pistons I have the correct reliefs as well.
I milled .045 of each head (and intake face for intake interchangeability) to get to an 82 CC chamber
Built that motor about 10 years ago. It is one bad mammer jammer


----------



## bigD (Jul 21, 2016)

You mention several times about a big cam possibly causing a valve to hit a 389 piston. So, have you done any testing/measuring to see EXACTLY how much cam can be safely used ?

There would obviously be several variables, just a couple of which would be: piston top to deck height & head gasket thickness. You'd need to measure exactly how far the lowest portion of the valve faces are, from the piston tops, when the pistons are at TDC. I suppose this could be easily measured by using really light valve springs to hold the valves up, then mashing the valves down & measuring the distance to the piston when @ TDC.

Would be lots more work, but I suppose you could try different cams in the engine by using a solid lifter. By using really light springs & rotating the crank slowly, you could measure how close each cam came to pushing a valve into a piston.

Has anybody here done this sort of cam measuring for this later heads on 389 deal ?

The main reason I bring this up is that I seem to remember reading of at least one guy who ran 400 heads on a 389 & used a pretty decent size cam in it, without causing a valve to hit a 389 piston. No, I don't remember exactly which heads or cam was used. But I do remember that I was surprised that he could run that cam in that application, after all I'd previously read.

Would love to read any threads or other info about how big a cam could be used, or has been used, in this application.

Obviously, the particular heads used would be a major factor in this deal. Some heads would obviously put the valves closer to the pistons. Some heads have been machined down. Some have had valve jobs done, which changed the valve location slightly, etc.

I'll do a search & see if I can find info about the cams used in similar applications. If I find anything, I'll post a link here.

Here's all I've found, so far.

"670's will still work on a 389 even though the valve reliefs are different. Usually anything under .500 lift and there is enough valve clearance. Same setup in my 55, I run 91 or 93 octane whatever I can get."

Here's another opinion.

"With a stock 389 Pistons and its average .023" deck clearance and average head gasket thickness the 670s will have no issues provided the Cam used has a lift of less then .425" at the valve.

If the 670 heads have had a valve job done then .015" more valve lift can likely be run ."

IF this is true, the 068 & 744 cams should be OK. But, with all the possible variables, I suppose any cam should be checked.

Here's a decent .454 lift cam. It MIGHT work in some of these apps.









Street Master Hydraulic Flat Tappet Cam - Pontiac V8 276/286


Hydraulic Flat Tappet Cam. Excellent for street performance with 455 c.i. motors. Works with stock valvetrain and all power accessories. Fair idle. ; Advertised Duration (Int/Exh): 276/286 ; Duration @ .050 (Int/Exh): 221/230 ; Gross Valve Lift (Int/




www.lunatipower.com





And here's a slightly smaller Howards. Looks like there is currently a supply problem. Anybody needing a cam right away may have to go with something that's on the shelf.









PONTIAC Howards Cams 410021-12 Howards Cams Street Force 2 Hydraulic Flat Tappet Camshafts | Summit Racing


Free Shipping - Howards Cams Street Force 2 Hydraulic Flat Tappet Camshafts with qualifying orders of $99. Shop Camshafts at Summit Racing.




www.summitracing.com


----------



## PontiacJim (Dec 29, 2012)

bigD said:


> You mention several times about a big cam possibly causing a valve to hit a 389 piston. So, have you done any testing/measuring to see EXACTLY how much cam can be safely used ?
> 
> There would obviously be several variables, just a couple of which would be: piston top to deck height & head gasket thickness. You'd need to measure exactly how far the lowest portion of the valve faces are, from the piston tops, when the pistons are at TDC. I suppose this could be easily measured by using really light valve springs to hold the valves up, then mashing the valves down & measuring the distance to the piston when @ TDC.
> 
> ...


*bigD*, as you have provided, no facts other than opinions. This is why I did this. 

Did you read this below?:









Pontiac Combustion Chamber Differences &amp...


PONTIAC HEAD DIFFERENCES 46 J312 - 350CI 4X 7H D143 - 400CI 4X 1H B163 - 455CI 96CC Press-in Studs 98CC Screw-in Studs 114CC Press-in Studs 1.96"/1.66" Valves 2.11"/1.66" Valves 2.11"/1.66"...




www.gtoforum.com





Yep, my next test will be the distance valve-to-piston. I have to get a 389 piston and will then fit/center it to a 400CI block I have. I will do a "valve drop"_ minus a head gasket_ to determine exactly what that distance is, but read my article as the valve drop would be a "*safe minimum*" but the valve chases the piston on both the down and up strokes, so the numbers can change based on the events of the cam - which could mean bigger lifts without hitting.

From my article above, I have the "valve drop" for one of the heads minus how much more additional drop I could go using the existing and mis-matched reliefs in the 389CI piston crown, "If you take .244" and add a .039" head gasket, and then add in a piston deck height (how far the piston top sits down in the bore) of .020", you get a grand total of .303". This is how much lift you could go before striking a piston if it did not have valve reliefs.

But keep in mind that the combustion chamber depth as I have shown in my other post may also have a bearing on "valve drop" because it may move the valve higher/lower in the valve seat itself

But, once I can establish a safe valve drop with a piston deck height of .020" and no head gasket, then you can juggle numbers around just as if you did your build, such as zero deck or a .027" head gasket versus a .060" head gasket. Then we will have "facts" and not guesstimates.

I would also like to measure the width of a 1968-1970 open combustion chamber and the width of the closed chamber "670" head. I may be able to get these numbers from a Pontiac friend as he is rebuilding a 1967 GTO 400 with the 670 heads.

Just having fun. So when I get around to the next step of my findings, I will add to this post.


----------

