# Engine Question



## 68 GTO 4spd (Apr 26, 2014)

Hey all

Curious question here. In my 68 vert there is a 455 engine with the 670 pontiac heads. I dont really know the history of this engine and how, (or with what) it was built with internally. 

Being that these are high compression heads and the engine runs perfect on 91-93 pump gas I would assume it was rebuilt with low compression pistons to make up for the heads? Would that not be the easiest way to compensate?

If this was the case are there any aftermarket aluminum heads out there that could flow more and make a good jump in power? While still usiing pump gas? Again the engine runs perfect right now with a 750cmf vacume secendary holley, and with the twin spal fans never excedes 189 F even in bumper to bumper traffic. It pulls strong but you can never have enough:lol: Or should I leave well enough alone......


----------



## Pinion head (Jan 3, 2015)

An .030 455 with stock 670's should have above 11.5 CR, waaaay to much CR with cast iron heads to run pump gas. Are you 100% sure the block is a 455? I've bought numerous partscars and project cars over the years that the seller was hawking the car as having a 455 engine, and it didn't, Of course I knew that, instead the engines were Pontiac 400's and 350's.

Unless you can get ahold of paperwork on the shortblock build to figure out what pistons were used, and be able to tell if the 670 heads have had the open chamber mod to open the chambers up to 80cc chambers, not going to know what's going on. If it was mine, I'd drain quite a bit of coolant, then pull the intake, and pull a cylinder head and then note if the piston has a large dish. Take pics, post them here, several us are well aquainted with 455 builds and even 670 heads that have had the open chamber mod.


----------



## ALKYGTO (Mar 29, 2010)

If you can find a local shop that has one of these you won't have to tear down your engine. Maybe a local dirt track or NHRA track would be a source to ask.

Whistler « Katech Inc. 586-791-4120

Or you could buy one of these from Harbor Freight, stick it down the spark plug hole and see what you can see..... http://www.harborfreight.com/digital-inspection-camera-61839.html


----------



## PontiacJim (Dec 29, 2012)

68 GTO 4spd said:


> Hey all
> 
> Curious question here. In my 68 vert there is a 455 engine with the 670 pontiac heads. I dont really know the history of this engine and how, (or with what) it was built with internally.
> 
> ...


If it runs good and doesn't ping on the pump gas, most likely it was rebuilt using the 30CC dished pistons or some other custom piston size - my opinion.

Swapping to aluminum heads for HP gain might become a problem because your pistons, if dished, may now provide too low a compression with the aluminum heads. Aluminum heads like a higher compression as they absorb heat, so you typically go a point or more in compression over what you would use on an iron headed engine built to run on pump gas.

Many topics found here on the forums on all this if you do a search. That said, everything in a Pontiac engine should be matched to maximize performance. To effectively use the aluminum heads, you may now need to get different pistons. This costs, unless this is not a concern. There are other ways to pick up HP with what you have, but HP comes with a price in gas mileage and drivability.

For the price of the heads and new pistons (calling for an engine tear down -unless you were planning on it anyway), I would suggest you look into adding a TKO 5-speed. You would get increased acceleration due to the lower gear ratio's and then benefit from the OD in 5th gear that gives you comfortable highway cruising and improved gas mileage through lowered RPM's. You will have to cut/modify the floor as it is larger than the Muncie and this can be a concern to those who want to keep their car flooring original. A few other mods are required as well, but I think it a better gain in the long run over the add-on of aluminum heads. Just sayin' :thumbsup:


----------



## 68 GTO 4spd (Apr 26, 2014)

I appreciate the help everyone!

Very good ideas, That harber freight camera would have many good uses as well. ( That would also allow me to look at the cabon buildup on my direct injected DD turbo 4cyl )

The TKO 5-speed would be a outstanding upgrade, the gearing in the GTO really prevents me from ever taking a long road trip unless I want to do 50mph down the interstate.


----------



## frankrp (Jan 19, 2015)

*camera*

don't buy the $100 camera from harbor freight buy only the $200 one the cheaper one will not fit through a spark plug hole


----------



## geeteeohguy (Feb 2, 2008)

Late to the party here but my opinion? Leave well enough alone. It runs great. It doesn't ping. It doesn't get hot. Plenty of power. DRIVE IT. If it's an automatic car, slip a 2.78-2.93 rear end under it. It'll run great in town and on the freeway. At about 1/6 the cost of an overdrive trans conversion. ($3500+)


----------



## 68 GTO 4spd (Apr 26, 2014)

frankrp said:


> don't buy the $100 camera from harbor freight buy only the $200 one the cheaper one will not fit through a spark plug hole


Good to know! I have not purchased anything yet, seems like other things always come first.




geeteeohguy said:


> Late to the party here but my opinion? Leave well enough alone. It runs great. It doesn't ping. It doesn't get hot. Plenty of power. DRIVE IT. If it's an automatic car, slip a 2.78-2.93 rear end under it. It'll run great in town and on the freeway. At about 1/6 the cost of an overdrive trans conversion. ($3500+)


I think i will follow this logic for now :smile2: It is a original 4spd car though. Im not sure what would be the best gearing options for it. The way the budget seems to be, a simple rear end gear would work for now.


----------

