#41  
Old 07-25-2022, 09:19 PM
amcmike's Avatar
amcmike amcmike is offline
Ultimate Warrior
 
Join Date: Oct 2004
Posts: 1,733
Default

Quote:
Originally Posted by amcmike View Post
Actually it is, and today's OEMs do.

Modern engines use much higher compression ratios, enabled by direct injection. The higher SCR increases efficiency even at part throttle, thus increasing fuel economy (in addition to increasing torque under wide open throttle). They can get away with these compression ratios due to the charge cooling as the fuel is injected directly into the combustion chamber (especially with multiple injection strategy at under medium loads and low-mid rpm). This then allows them to downsize the engine displacement (if desired) to further improve fuel economy. This is why OEMs use DI even on small economy cars, not just performance vehicles.

I should have said, one of the reasons. The other of course, being emissions (with the exception of particulate emissions, which is actually higher than port fuel).

__________________
"The Mustang's front end is problematic... get yourself a Firebird." - Red Forman
  #42  
Old 07-25-2022, 11:41 PM
GTOKIDRH's Avatar
GTOKIDRH GTOKIDRH is offline
Member
 
Join Date: May 2006
Posts: 37
Default

Quote:
Originally Posted by amcmike View Post
Actually it is, and today's OEMs do.

Modern engines use much higher compression ratios, enabled by direct injection. The higher SCR increases efficiency even at part throttle, thus increasing fuel economy (in addition to increasing torque under wide open throttle). They can get away with these compression ratios due to the charge cooling as the fuel is injected directly into the combustion chamber (especially with multiple injection strategy at under medium loads and low-mid rpm). This then allows them to downsize the engine displacement (if desired) to further improve fuel economy. This is why OEMs use DI even on small economy cars, not just performance vehicles.
So correct me if I'm wrong. The LS engines before DI were mostly if not all in the 10+ CR range. I understand this was largely due to the use of aluminum as well as the heart shaped combustion chamber with a centrally positioned spark plug tip. Yes DI helps immensely.

Sent from my SM-N950U using Tapatalk

  #43  
Old 07-26-2022, 12:53 AM
NeighborsComplaint's Avatar
NeighborsComplaint NeighborsComplaint is offline
Ultimate Warrior
 
Join Date: Aug 2009
Location: Elgin
Posts: 2,193
Default

I had a '65 Lemans w. 326 2bbl and single exhaust as a kid. A dual exhaust was a big upgrade in performance. I then added a 4 bbl intake and Carter AFB which also made it even better with no other changes. I was amazed at the transformation which included basic, quality tune up parts. It was a 3 spd w. Hurst linkage and would chirp the tires in 2nd and 3rd with ease. If you're up to a cam swap, a Summit 2801 kit with lifters and springs and a new timing set will give a nice performance return on investment. The 670 heads aren't needed for what is just a nice torquey cruiser. The rear gears would be a better investment than the heads if you had to make a choice.

__________________
Triple Black 1971 GTO "Cookie Cutter build" according to Honeyhush and Holley Carb coloring not up to Tom V's Standards ...
The Following 2 Users Say Thank You to NeighborsComplaint For This Useful Post:
  #44  
Old 07-26-2022, 03:40 AM
Formulabruce's Avatar
Formulabruce Formulabruce is offline
Ultimate Warrior
 
Join Date: Nov 2004
Location: North East of AMES PERFORMANCE, in the "SHIRE"
Posts: 8,877
Default

Quote:
Originally Posted by amcmike View Post
Actually it is, and today's OEMs do.

Modern engines use much higher compression ratios, enabled by direct injection. The higher SCR increases efficiency even at part throttle, thus increasing fuel economy (in addition to increasing torque under wide open throttle). They can get away with these compression ratios due to the charge cooling as the fuel is injected directly into the combustion chamber (especially with multiple injection strategy at under medium loads and low-mid rpm). This then allows them to downsize the engine displacement (if desired) to further improve fuel economy. This is why OEMs use DI even on small economy cars, not just performance vehicles.
While true on modern cars, The 60's and 70's and most of the 80's were built based on Torque And were built to run on the highway just below their torque peak in most cases, for passing power, and economy.
Would be interesting if ANYBODY started Dyno mapping at 1500 instead of 3K .
My Point is that some things were designed well, and do the job.. well....

__________________
"The Future Belongs to those who are STILL Willing to get their Hands Dirty" .. my Grandfather
The Following User Says Thank You to Formulabruce For This Useful Post:
  #45  
Old 07-26-2022, 08:03 AM
amcmike's Avatar
amcmike amcmike is offline
Ultimate Warrior
 
Join Date: Oct 2004
Posts: 1,733
Default

Quote:
Originally Posted by GTOKIDRH View Post
So correct me if I'm wrong. The LS engines before DI were mostly if not all in the 10+ CR range. I understand this was largely due to the use of aluminum as well as the heart shaped combustion chamber with a centrally positioned spark plug tip. Yes DI helps immensely.

It's a bit complicated, but I'll try to simplify.

The GENIII passenger vehicles (Corvette, Firebird, etc.) were in the low-mid 10s with aluminum block/heads premium. The small engine trucks 4.8/5.3 were mid-9s, the exception was the 5.3L HO which used an aluminum block and 9.9:1. The 6.0 LQ4 was only 9:1 but was meant for HD trucks that weighed more and would be used for heavier loads and 87 octane. There was a 6.0L LQ9 which was a 10:1 variant of the LQ4 but was used in Escalades and required premium.


The GENIV LS (debuting with the LS2) were still PFI, and saw a bump in compression with passenger cars adding about 1/2 point. For the GENIV trucks, the iron blocks (and some aluminum) were typically 9.5:1, but often had VVT which bumped up the dynamic compression below 3500rpm. Some larger aluminum blocks (like the L92) were as high as 10.5:1 but recommended premium.

With the GENV having DI, compression even with VVT, is typically 11:1 on trucks, and higher for passenger cars (but with premium recommended). And we haven't even talked about Super Charged cars, but the LT4 runs 10:1 with 9.4 lbs of boost.

__________________
"The Mustang's front end is problematic... get yourself a Firebird." - Red Forman
The Following User Says Thank You to amcmike For This Useful Post:
  #46  
Old 07-26-2022, 08:18 AM
PunchT37's Avatar
PunchT37 PunchT37 is online now
Ultimate Warrior
 
Join Date: Dec 2002
Location: Lafayette,LA
Posts: 3,000
Default

One canít talk about modern engine specs as a reference to old car building without realizing the fast and powerful computers running them.

  #47  
Old 07-26-2022, 08:24 AM
PunchT37's Avatar
PunchT37 PunchT37 is online now
Ultimate Warrior
 
Join Date: Dec 2002
Location: Lafayette,LA
Posts: 3,000
Default

Quote:
Originally Posted by 25stevem View Post
Scott, I think that it was your lack of experience / knowledge at age 18 that made your 2bbl to 4 bbl adventure a flop, especially if it was Q-Jet swap over you did!

If nothing else assuming having in the ball park jetting conditions and having full throttle available the car should have had better drivability at low speed and at least 10 to 12 more hp.
I know that would have been the case for me!
I agree. Even 301ís came with 4 bbl carbs and 2.41 gears without problems.

  #48  
Old 07-26-2022, 09:06 AM
25stevem's Avatar
25stevem 25stevem is offline
Ultimate Warrior
 
Join Date: Jan 2022
Posts: 1,229
Default

I killed a perfectly good 389 at age 16 when I rebuilt the carb.

The rebuild of my first carb went 100% fine, but then I found that I could get a bunch more idle rpm if a adjusted out the big center screw on the face of the AFB carb.

This I came to find was the idle air adjustment.

I left it that way and the motor ran so lean that the resulting detonation cracked two pistons!

So much for the knowledge of a fledgling 16 year old hot rodder!

__________________
You can cut out a manís tongue, but that does not mean heís a Liar, it just means you fear the truth that he might speak about you.
  #49  
Old 07-26-2022, 05:39 PM
GTOKIDRH's Avatar
GTOKIDRH GTOKIDRH is offline
Member
 
Join Date: May 2006
Posts: 37
Default

Quote:
Originally Posted by Formulabruce View Post
While true on modern cars, The 60's and 70's and most of the 80's were built based on Torque And were built to run on the highway just below their torque peak in most cases, for passing power, and economy.

Would be interesting if ANYBODY started Dyno mapping at 1500 instead of 3K .

My Point is that some things were designed well, and do the job.. well....
I would like to see that as well!

Sent from my SM-N950U using Tapatalk

  #50  
Old 07-26-2022, 05:41 PM
GTOKIDRH's Avatar
GTOKIDRH GTOKIDRH is offline
Member
 
Join Date: May 2006
Posts: 37
Default

Quote:
Originally Posted by NeighborsComplaint View Post
I had a '65 Lemans w. 326 2bbl and single exhaust as a kid. A dual exhaust was a big upgrade in performance. I then added a 4 bbl intake and Carter AFB which also made it even better with no other changes. I was amazed at the transformation which included basic, quality tune up parts. It was a 3 spd w. Hurst linkage and would chirp the tires in 2nd and 3rd with ease. If you're up to a cam swap, a Summit 2801 kit with lifters and springs and a new timing set will give a nice performance return on investment. The 670 heads aren't needed for what is just a nice torquey cruiser. The rear gears would be a better investment than the heads if you had to make a choice.
I already have the rear end as well as the 4BBL setup and the 670 heads. So.....

Sent from my SM-N950U using Tapatalk

  #51  
Old 07-26-2022, 07:00 PM
Scott Roberts's Avatar
Scott Roberts Scott Roberts is offline
Suspended
 
Join Date: Oct 2006
Posts: 3,170
Default

Quote:
Originally Posted by 25stevem View Post
Scott, I think that it was your lack of experience / knowledge at age 18 that made your 2bbl to 4 bbl adventure a flop, especially if it was Q-Jet swap over you did!

If nothing else assuming having in the ball park jetting conditions and having full throttle available the car should have had better drivability at low speed and at least 10 to 12 more hp.
I know that would have been the case for me!
I think I was actually 17 but non the less, you are probably right.. it was a carb and intake off of the original 400 that was in the car I blew up..
Never got it to take full throttle without rolling into it.

  #52  
Old 07-26-2022, 08:31 PM
NeighborsComplaint's Avatar
NeighborsComplaint NeighborsComplaint is offline
Ultimate Warrior
 
Join Date: Aug 2009
Location: Elgin
Posts: 2,193
Default

Quote:
Originally Posted by GTOKIDRH View Post
I already have the rear end as well as the 4BBL setup and the 670 heads. So.....

Sent from my SM-N950U using Tapatalk
Go for it. The potential for detonation will be reduced if you step up to an 067, 068 or Summit 2801 cam.

__________________
Triple Black 1971 GTO "Cookie Cutter build" according to Honeyhush and Holley Carb coloring not up to Tom V's Standards ...
The Following User Says Thank You to NeighborsComplaint For This Useful Post:
  #53  
Old 07-27-2022, 04:50 PM
lust4speed's Avatar
lust4speed lust4speed is offline
Ultimate Warrior
 
Join Date: Jul 2002
Location: Yucaipa, SoCal
Posts: 8,463
Default

Correct me if I'm wrong, but in '67 the only Pontiac engine with dished pistons was the "Export" engine, and all others had flat tops. If so, bolting on a set of 670's is going to raise the compression ratio too high. Sounds like a miserable swap to me unless you go with new dished pistons.

__________________
Mick Batson
1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon in progress.
The Following 2 Users Say Thank You to lust4speed For This Useful Post:
  #54  
Old 07-27-2022, 05:29 PM
b-man's Avatar
b-man b-man is offline
Moderator
 
Join Date: Sep 2002
Location: Sunny So Cal
Posts: 15,496
Default

Quote:
Originally Posted by lust4speed View Post
Correct me if I'm wrong, but in '67 the only Pontiac engine with dished pistons was the "Export" engine, and all others had flat tops. If so, bolting on a set of 670's is going to raise the compression ratio too high. Sounds like a miserable swap to me unless you go with new dished pistons.
Correct.

By that time the factory only used dished pistons on the 428 to maintain the same compression as 400 engines using the same heads.

Otherwise no dished pistons since the late Ď50s early Ď60s export engines with 7.6:1 compression.

__________________
1964 Tempest Coupe LS3/4L70E/3.42
1964 Le Mans Convertible 421 HO/TH350/2.56
2002 WS6 Convertible LS1/4L60E/3.23
The Following User Says Thank You to b-man For This Useful Post:
  #55  
Old 07-27-2022, 06:00 PM
GTOKIDRH's Avatar
GTOKIDRH GTOKIDRH is offline
Member
 
Join Date: May 2006
Posts: 37
Default

Quote:
Originally Posted by b-man View Post
Correct.



By that time the factory only used dished pistons on the 428 to maintain the same compression as 400 engines using the same heads.



Otherwise no dished pistons since the late Ď50s early Ď60s export engines with 7.6:1 compression.
It is my understanding that the lo po base 400 2 BBL (8.6:1 advertised) used in full size Pontiacs used different pistons. Am I misinformed? I see now that they are not dished as I previously stated. Apparently they are different however?

Sent from my SM-N950U using Tapatalk

  #56  
Old 07-27-2022, 06:14 PM
b-man's Avatar
b-man b-man is offline
Moderator
 
Join Date: Sep 2002
Location: Sunny So Cal
Posts: 15,496
Default

The 8.6:1 heads have a larger combustion chamber volume than the high compression heads.

Pontiac regulated the compression by modifying the heads, not the pistons at that juncture

What is the casting number on your heads?

__________________
1964 Tempest Coupe LS3/4L70E/3.42
1964 Le Mans Convertible 421 HO/TH350/2.56
2002 WS6 Convertible LS1/4L60E/3.23
The Following User Says Thank You to b-man For This Useful Post:
  #57  
Old 07-27-2022, 06:55 PM
GTOKIDRH's Avatar
GTOKIDRH GTOKIDRH is offline
Member
 
Join Date: May 2006
Posts: 37
Default

Quote:
Originally Posted by b-man View Post
The 8.6:1 heads have a larger combustion chamber volume than the high compression heads.

Pontiac regulated the compression by modifying the heads, not the pistons at that juncture

What is the casting number on your heads?
Stock 142s

Sent from my SM-N950U using Tapatalk

  #58  
Old 07-27-2022, 07:19 PM
lust4speed's Avatar
lust4speed lust4speed is offline
Ultimate Warrior
 
Join Date: Jul 2002
Location: Yucaipa, SoCal
Posts: 8,463
Default

Here is a photo showing pistons available in 1967. If your pistons are original then they are flat top. Notice the valve reliefs are different in the piston tops and your pistons would have the eyebrows in the wrong place for the 670 heads.

If you wanted to continue to use regular gas then the current 8.6:1 compression ratio is about perfect.
Attached Thumbnails
Click image for larger version

Name:	IMG_2268.JPG
Views:	33
Size:	114.7 KB
ID:	595060  

__________________
Mick Batson
1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon in progress.
The Following User Says Thank You to lust4speed For This Useful Post:
  #59  
Old 07-27-2022, 08:23 PM
Sirrotica's Avatar
Sirrotica Sirrotica is offline
Ultimate Warrior
 
Join Date: Jan 2005
Location: Catawba Ohio
Posts: 6,641
Default

Quote:
Originally Posted by lust4speed View Post
Here is a photo showing pistons available in 1967. If your pistons are original then they are flat top. Notice the valve reliefs are different in the piston tops and your pistons would have the eyebrows in the wrong place for the 670 heads.

If you wanted to continue to use regular gas then the current 8.6:1 compression ratio is about perfect.
Basically what I said earlier, but was met with, "I have 670 heads already". 670 heads aren't going to be the answer to the question, IMO.

Throughout the years the 670 head has been given a lot of ink, but there are better choices for the car in question. This is a cruiser, not a racecar. They surely wouldn't be my choice if I were going to try to wring power from a street car. They likely won't run on pump fuel, even premium fuel. I had a 67 engine for my 67 GTO racecar that I took off the 670 heads in favor of 62 heads before installing in my car, because I always felt the open chamber was superior to the closed chamber bathtub.

The regular fuel 400 basically used the 66 389 heads, hence the reason for one year only pistons with the older holdover valve inclination angle. In 68 the regular fuel engine became the same valve inclination angle as the premium fuel engines. I believe they gave up the bathtub combustion chamber also in all 1968 engines. When I worked at a Pontiac dealer in 1970 I remember a running change during the 1967 model year for broken valve springs, so depending on where in the model year the heads fell, they may have the old springs that were recalled.

If the car runs as poorly as the OP says, there has to be something fundamentally wrong with the engine, but I already have mentioned this in my previous posts. Putting hi compression heads on an engine that runs poorly is just a waste of time. Finding out why this engine runs so poorly would be my first priority, before pouring a bunch of money into a unknown quantity.

If the engine is worn out, or has low compression due to a mechanical defect, the OP might be ahead to find a 428/455 in running condition, and come out with more engine, for less money. Win, win

__________________
Brad Yost
1973 T/A (SOLD)
2005 GTO
1984 Grand Prix

100% Pontiacs in my driveway!!! What's in your driveway?

If you don't take some of the RACETRACK home with you, Ya got cheated


Last edited by Sirrotica; 07-27-2022 at 08:29 PM.
The Following User Says Thank You to Sirrotica For This Useful Post:
  #60  
Old 07-28-2022, 07:19 AM
25stevem's Avatar
25stevem 25stevem is offline
Ultimate Warrior
 
Join Date: Jan 2022
Posts: 1,229
Default

Here's one thing you can Bank on with factory iron heads!

The open chamber heads with there 14 degree valve inclination angle make for a shallower chamber then previously used,, this makes for for a lesser surface to volume ratio which is less detonation prone then the earlier 326/389/421 heads with there stepper valve angles.

The sharp edge change over ridge in the chamber also acts as a much needed fuel re atomizing ledge, and this too makes for lesser detonation issues for any given level of cylinder pressure and heat that's in play.

You guys who have in the process of cleaning up there open chamber Heads with a grinder loaded with a even just a polishing roll and have worked over that sharp lip a lot, or even as I have seen totally ground it the heck out of there thinking higher levels of Intake flow would be had have done yourself a great disservice!!

You have increased the likelihood of detonation.

Even the sharp edge on the Intake valve side of the plug hole should be left there, but just broken to the tune of .005".

This once again is to re-atomize wet flow .

__________________
You can cut out a manís tongue, but that does not mean heís a Liar, it just means you fear the truth that he might speak about you.
The Following User Says Thank You to 25stevem For This Useful Post:
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 08:37 AM.

 

About Us

The PY Online Forums is the largest online gathering of Pontiac enthusiasts anywhere in the world. Founded in 1991, it was also the first online forum for people to gather and talk about their Pontiacs. Since then, it has become the mecca of Pontiac technical data and knowledge that no other place can surpass.

 




Copyright © 2017