# Streetability of stock 67 400ci 335 HP 4BBL 670 Heads HEI Distributor 3.36 posi



## goat671 (Apr 13, 2019)

Hello
I am wondering if I will be able to run this safely on the street with todays gas.

All comments and suggestions are welcome.


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## Sick467 (Oct 29, 2019)

My 67, like yours except it had a points dizzy and a higher rear (maybe 3.08), would run well on 91 octane (no ethanol content), prefers the 93 however. On the hottest of summer days, the 91 might do a little dieseling when shut off at full operating temps (might). I have not run it on the streets since ethanol was added and cannot tell you what 10% would do.


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## Honeyharbour62 (Jul 15, 2018)

Same set up with MSD ignition and 670 heads. Engine is 0.030 over with hardened seats, 3 angle valve job, and TRW advertised 10.5 to 1 forged pistons. I run on 91 octane zero ethanol with Lucas octane boost, as well as Red Line lead substitute just for lubricity for the Rochester and I've yet to hear any pinging. On days over 80° F I drive conservatively, cool days I stretch her out. Would prefer the Torco octane boost but can't find it here in Ontario.


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## armyadarkness (Dec 7, 2020)

67 400 with 670's, Dougs headers, MSD dizzy, Edelbrock 800 cfm carb, 30 over, runs all day on 93, in 98 degree temps with 90% humidity.


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## armyadarkness (Dec 7, 2020)

BTW, 336 posi, too and I did have HEI


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## ylwgto (Oct 27, 2009)

'68 400 350HP with 72cc #16 heads, Holley 750, mild cam, Hedman headers, MSD controlled timing, 3.25 rear. 

Very streetable as long as you have dished pistons to bring the compression ratio down to compensate for model fuels. I've been having dieseling at shut off for some time that I am trying to resolve (might be a timing issue, might be not enough octane for higher compression #16 heads), but otherwise it runs all day long as a daily driver on 93...no issues.


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## armyadarkness (Dec 7, 2020)

ylwgto said:


> '68 400 350HP with 72cc #16 heads, Holley 750, mild cam, Hedman headers, MSD controlled timing, 3.25 rear.
> 
> Very streetable as long as you have dished pistons to bring the compression ratio down to compensate for model fuels. I've been having dieseling at shut off for some time that I am trying to resolve (might be a timing issue, might be not enough octane for higher compression #16 heads), but otherwise it runs all day long as a daily driver on 93...no issues.


I think my 670 heads are much worse than yours and I dont have dished pistons. Id be curious as to what your timing is at.


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## goat671 (Apr 13, 2019)

Thanks for all the info on you rides.

So it seems I can run it with 93 Octane is the 10% ethanol any issue? Or should I use the ethanol free?

When I got the car it had a fresh rebuild that was back in 1989. I drove it very briefly before I started the restro.
I do not know if the heads had any work done on them to work with the unleaded fuel.

Any way I can check to see if anything has been done to the heads?

When did we stop being able to buy leaded fuel asking because if the heads were done they probably would have addressed this when they had the work done.


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## ylwgto (Oct 27, 2009)

armyadarkness said:


> I think my 670 heads are much worse than yours and I dont have dished pistons. Id be curious as to what your timing is at.


I think 670s basically flow the same as 16s, but just have a strange chamber shape that is a bit different than the standard iron 72cc casting. Again, I'm no expert!

I cannot remember what pistons I put in when I rebuilt the engine many years ago, but I do not think they were dished. I'm fairly certain my static compression is around 10:1. If I get my idle RPM even a bit too high (anything over 750ish) I get dieseling even with 93. 

I'm convinced it is a timing issue and it's related to a lack of vacuum advance on my MSD distributor (which I need to address soon one way or another).


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## PontiacJim (Dec 29, 2012)

ylwgto said:


> I think 670s basically flow the same as 16s, but just have a strange chamber shape that is a bit different than the standard iron 72cc casting. Again, I'm no expert!
> 
> I cannot remember what pistons I put in when I rebuilt the engine many years ago, but I do not think they were dished. I'm fairly certain my static compression is around 10:1. If I get my idle RPM even a bit too high (anything over 750ish) I get dieseling even with 93.
> 
> I'm convinced it is a timing issue and it's related to a lack of vacuum advance on my MSD distributor (which I need to address soon one way or another).


At the higher idle RPM's, your throttle blades are cracked open allowing the engine to pull gas through the primaries and keep it running-on, or dieseling. This is where an electric solenoid can come in that will raise idle speeds of the carb to keep the engine running when activated, then drop RPM's, thus closing down the throttle baldes, and the engine quits. Later Pontiacs did use these, not sure what year that began.

Dieselling will break rings/pistons and take out main/rod bearings.


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## armyadarkness (Dec 7, 2020)

ylwgto said:


> I think 670s basically flow the same as 16s, but just have a strange chamber shape that is a bit different than the standard iron 72cc casting. Again, I'm no expert!
> 
> I cannot remember what pistons I put in when I rebuilt the engine many years ago, but I do not think they were dished. I'm fairly certain my static compression is around 10:1. If I get my idle RPM even a bit too high (anything over 750ish) I get dieseling even with 93.
> 
> I'm convinced it is a timing issue and it's related to a lack of vacuum advance on my MSD distributor (which I need to address soon one way or another).


Buy that Summit Dizzy that I mentioned. It's cheap as Hell, and it's just a rebranded MSD.


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## ylwgto (Oct 27, 2009)

armyadarkness said:


> Buy that Summit Dizzy that I mentioned. It's cheap as Hell, and it's just a rebranded MSD.


Yeah, I know. Haven't done that yet because I am right on the fence in buying a Holley Sniper system, which they now make a Pontiac Hyperspark distributor for. It's a bit $$, so have not pulled the trigger yet, but if I don't I will definitely drop that Summit 850084 unit it.


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## BearGFR (Aug 25, 2008)

goat671 said:


> Hello
> I am wondering if I will be able to run this safely on the street with todays gas.


Truth is, NO ONE can promise you that, or even make a reasonable guess without knowing a lot more about your engine. Which head gaskets are in it and how thick are they? More importantly, which pistons are in it and are they "flat tops" or dished? If they're dished, how big are the dishes, volume wise? And, how much deck clearance is there? 

All those dimensions play a part in actual compression ratio. 

Bear


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## goat671 (Apr 13, 2019)

BearGFR said:


> Truth is, NO ONE can promise you that, or even make a reasonable guess without knowing a lot more about your engine. Which head gaskets are in it and how thick are they? More importantly, which pistons are in it and are they "flat tops" or dished? If they're dished, how big are the dishes, volume wise? And, how much deck clearance is there?
> 
> All those dimensions play a part in actual compression ratio.
> 
> Bear


Never expected ANYONE to promise me anything  .Your questions are all very good, as I did not do the rebuild I can not answer any of them IIRC the person I bought it from stated that it had been rebuilt. No real details. But when I had it running it sounded stock no lope in the cam or any add ons. The AIR Reactor (California model) was installed and all associated emission pieces present including snorkeled air cleaner base with chrome cover.
If I had to guess I think it was rebuilt using fully stock pieces, but this is only I guess.

If it was a completely stock never rebuilt would it run on todays gas?

I ran it back in the late 80s with premium gas and did not have any issues that I recall. 
You are right the only way to now exactly what I got is to pull the heads I would rather not but it is not a bad idea. Just be getting some gaskets.

Thanks for taking the time to respond.


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## PontiacJim (Dec 29, 2012)

goat671 said:


> Never expected ANYONE to promise me anything  .Your questions are all very good, as I did not do the rebuild I can not answer any of them IIRC the person I bought it from stated that it had been rebuilt. No real details. But when I had it running it sounded stock no lope in the cam or any add ons. The AIR Reactor (California model) was installed and all associated emission pieces present including snorkeled air cleaner base with chrome cover.
> If I had to guess I think it was rebuilt using fully stock pieces, but this is only I guess.
> 
> If it was a completely stock never rebuilt would it run on todays gas?
> ...


If you have the "670" heads, these are the closed chamber heads and seem to be a little less prone to detonation than open chamber heads used 1968 andnup, excluding the early 1967 061 heads.

Will it run on todays premium 93 octane? It might. You may simply want to add a little octane booster and be good with it. You can drop/retard timing a little, but too much will hurt engine power and it can cause engine temps to rise. But, we used to do this back in the 80's, right?

The 335HP engine won't have any big cam lope or sound "souped". Most Pontiac don't sound like a Chevy, but they have their own sound which can seem mild - until you nail the gas and lay down some rubber. 

Your 335 HP engine has the factory "067" cam - Duration: Int 273 Ex 289 Lift .406" on both intake and exhaust. Lobe Separation Angle (LSA) 113 degrees.

A step up to the factory 360 HP engine used the "068" cam - Duration: Int 288 Ex 302 Lift .406" on both intake and exhaust. LSA 116 degrees. This cam has the more aggressive sound to it.


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## goat671 (Apr 13, 2019)

PontiacJim said:


> If you have the "670" heads, these are the closed chamber heads and seem to be a little less prone to detonation than open chamber heads used 1968 andnup, excluding the early 1967 061 heads.
> 
> Will it run on todays premium 93 octane? It might. You may simply want to add a little octane booster and be good with it. You can drop/retard timing a little, but too much will hurt engine power and it can cause engine temps to rise. But, we used to do this back in the 80's, right?
> 
> ...


Thanks for the reply I do remember what the engine sounded like and it did not have a aggressive cam in it pretty sure it is a stock cam. I will never know about the pistons until I pull a head to see if it was bored and what pistons were used if it was bored at all. I would figure a stock thickness head gasket. Like I said the PO said it just had an engine rebuild done on it but not much more.

Now off subject................

My first car was a 67 Lemans Mariner Turquoise with a black vinyl top I purchased from my Uncle for $100.00 when I was 15. The 326 was tired so my father who worked at Norms auto scrounged me up a 350 out of a 70 firebird looking back at it wish it was a 455 lol, anyhow I built this one bored 30 over new pistons rings and bearings with a crower cam and springs headers and Holley 650 during the winter of 1975. My father guided me along the way.

Completely finished I was stuck on how I was going to get it off the engine stand and up the stairs from the basement 😁 Well did I say my father worked at a junk yard yea thats what we called them...
A tow truck backed up to the side door of the house with a straight shot to the bottom of the stairs where the 350 was standing was pulled out engine stand and all. With my father telling we how this was not the smartest move.

Yea I know the difference between a stock sounding engine and a built one. That engine lasted 3 years and got me from Minnesota to Huntsville AL I was in AIT at Redstone I beat that poor engine I was never afraid to see what it would do. My father rebuilt manual transmissions he built a M21 with close ratio gears at least that is what he told me 3.08 rear end gears so it would pull to 55 in first at least that is what the spedo said... The day I sold it to a friend it spun a bearing, not sure what exactly as I was shipping out to Germany and did not pull it apart. Missed that car from the day I sold it.

Now Today my friend is having a 67 Lemans built it will be a tribute car it will have pieces of a GTO but will keep the side Gills from the 67 he had these welded in to the new quarters. A stroked 455 putting out loads of torque. He is not sparing any expense on this. He has also had a 67 all along.

He has been egging me on so I finally decided it is time to do something with mine that has been sitting in the same place in the garage for 30 years.


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## 67ventwindow (Mar 3, 2020)

goat671 said:


> Now Today my friend is having a 67 Lemans built it will be a tribute car it will have pieces of a GTO but will keep the side Gills from the 67 he had these welded in to the new quarters.


  Heres to keeping the gills!!!!! 

I may have to start a 501c "KEEP the GILLS"


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## geeteeohguy (Feb 2, 2008)

goat671 said:


> Hello
> I am wondering if I will be able to run this safely on the street with todays gas.
> 
> All comments and suggestions are welcome.


I've had the same combination as you for the past 39 years except for the stock points distributor. Even back in the early 1980's with leaded 94 octane, I was not able to run this combo without detonation. I had to retard the timing so far that the car was a total slug. The only way to run 670 heads these days on pump gas is to install dished pistons. On my '67 400, I installed bigger- chambered heads.


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## BearGFR (Aug 25, 2008)

geeteeohguy said:


> I've had the same combination as you for the past 39 years except for the stock points distributor. Even back in the early 1980's with leaded 94 octane, I was not able to run this combo without detonation. I had to retard the timing so far that the car was a total slug. The only way to run 670 heads these days on pump gas is to install dished pistons. On my '67 400, I installed bigger- chambered heads.


Hey! Welcome back!
Bear


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## geeteeohguy (Feb 2, 2008)

BearGFR said:


> Hey! Welcome back!
> Bear


Thank you, Sir! I was finally able to log on without joining any social media platforms, etc. I was basically locked off the forum (likely due to my own IT incompetence) for a couple of years. Good to be back! As stated by others, this is a more personal forum with folks that just want to help out, etc. I see you're doing your engine again? Or for a different car, perhaps?


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## Scott06 (May 6, 2020)

goat671 said:


> Thanks for all the info on you rides.
> 
> So it seems I can run it with 93 Octane is the 10% ethanol any issue? Or should I use the ethanol free?
> 
> ...


Running 93 ( with 10% ethanol) and a lead substitute in my stock 65 389 w theoretically 10.75:1 no issue for typical weekend cruise work... about 36 deg total timing and a tad rich jetting.


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## armyadarkness (Dec 7, 2020)

PontiacJim said:


> A step up to the factory 360 HP engine used the "068" cam - Duration: Int 288 Ex 302 Lift .406" on both intake and exhaust. LSA 116 degrees. This cam has the more aggressive sound to it.


My new cam has an 112 LSA , and I swear it sounds more mild than that Bullet 4/7 swap I had, which was 110, I believe.


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## PontiacJim (Dec 29, 2012)

armyadarkness said:


> My new cam has an 112 LSA , and I swear it sounds more mild than that Bullet 4/7 swap I had, which was 110, I believe.


Get rid of your H-pipe. Install glass packs. Then get some cut-outs.


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## armyadarkness (Dec 7, 2020)

PontiacJim said:


> Get rid of your H-pipe. Install glass packs. Then get some cut-outs.


H pipe is out tkx is going in tomorrow


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