Rough running problem

[JRMaroon]

Heidi,

You've already swapped your original motor for a higher performance crate engine. Is this advice based on the thought that you have the original from '78?

You also have the upgraded exhaust and it sounds awesome!

It's always tempting to go big but where is the cut-off. Good Luck with whatever you decide.

Jeff

 

[78SilvAnniv]

You've already swapped your original motor for a higher performance crate engine. Is this advice based on the thought that you have the original from '78?

You know...I don't know! I'll have to check my email message to Chris.
My GM crate engine is a 1997 250hp that was installed in late 1997.

I still think the advice is good and I do not like the idea of having to change so much routing over the top of the engine to make the vortec heads/manifold fit. I think I may just try to find a drop-in replacement for my heads.

How are heads 'graded'? Could I purchase the next-step-up heads and expect a little better (efficient) flow to the combustion chamber?
Heidi

 

[MoeJr]

Not to throw a wrench in anything but why not have the heads on the car now redone. A good valve job,replacement of the burnt valves and some mild porting would be satisfactory for what you want.

Heidi do you still have your original motor?

 

[78SilvAnniv]

Heidi do you still have your original motor?

Nope.
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Do not have original. Current is a 1997 GM crate, 250hp installed in '97.

 

[78SilvAnniv]

I think I need help...

I read the second link. I even printed it to pore over thoroughly and absorb the information.

I’m not sure I understand it all.
It appears that most of the heads that Bert/RacerGuy discussed have:
1.94/1.50” or 2.02/1.60” valves (is bigger better?)
64cc combustion chambers
intake volume of 161cc
exhaust port volume of 65cc

Some have, or do not have, accessory holes. (What are these? Holes for the brackets for parts on the engine’s front?)

What is double hump casting?

What is the difference between straight plugs vs angle plugs and how do I tell which ones I have?

I'm not sure I want to re-do the heads I have. The cost is similar to just buying new, so why not just get new ones? I am also feeling the bug to improve something, anything!
It's over, isn't it? I've got the disease.
At this point, I just want to improve flow of air/fuel to the combustion chamber and have the combustion be efficient for my application.

All of the info I checked out at the link appeared to be nearly the same for everything. I'm thinking of giving GM dealership a call tomorrow to see what I can see.

Thanks for the help everyone!
Heidi

 

[JRMaroon]

Re: I think I need help...

I am also feeling the bug to improve something, anything!
It's over, isn't it? I've got the disease.
At this point, I just want to improve flow of air/fuel to the combustion chamber and have the combustion be efficient for my application.

I see a new cam in your future to complement whatever heads you decide on.

It is over. There's no stopping now.

 

[Robin7TFour]

dann, that was an excellent explaination..but what would the preformance difference between 64 cc heads and 75 cc heads? another poser!

robin

 

[78SilvAnniv]

Re: Re: I think I need help...

...from the standpoint of moving air (remember an engine is just an air pump), usually bigger is better, as larger openings (valve size) means more volume is moved through the combustion chamber.
More air pumped = more power.
Again, all things equal, increased flow characteristics should translate into more power.

So, with my 1997 GM crate engine rated at 250hp with a 4 bolt main...what is the largest size head combination that will work efficiently with my lower end, without having to change the cam?

I am now leaning towards these numbers unless I can be informatively advised about exactly how much bigger I can go and not have it be overkill.
2.02/1.60" valves
64cc combustion chamber
161cc intake port volume
65cc exhaust port volume

Does anyone know what the specs would be for my 250hp engine? I don't have the paperwork from when I purchased it.
By specs, I mean...what would the cam be and what stats on the heads?
Heidi

 

[MoeJr]

I believe Heidis crate motor is 9:1 CR as it sits with 76 CC heads. 64 CC heads would drive the CR up past the safe zone for pump gas. Just my .02

 

[Mac]

There are a couple of traps to avoid, Heidi, and these are truly common sense but it's surprising how many fall into them.

Contrary to popular rumour, bigger is not always better! As you start changing componants, there's always the temptation to push the envelope but remember- each change reflects on the performance of the rest of the engine. The perfect example of this is the guy who throws on a new high CFM carb and then wonders why his performance and mileage drops dramatically. Well, go figure- the motor doesn't know what to do with all that extra gas, so it pumps it out the exhaust pipe. In your case, a change of heads without a change of cam and other componants won't likely make that big of a difference. That leads to the next point for consideration...

Consider the purposes you have in mind!If you spring for a set of Stage III heads (race equipment) and a wild cam but you never rev the motor higher than 4000 rpm, you've throw away thousands of dollars for nothing and don't be surprised when your engine won't idle below 1200 rpm and doesn't make power until 3000 rpm. Building a full-blown race engine is fun but if you're going to be driving it on the street, you won't be a happy camper because the true cost of all that horsepower is driveability.

Cost/benefit analysis! In a way, this is restating the previous point but it's different enough to justify saying. Do the benefits of replacing the heads justify the cost? Will the new heads work well with the existing motor or require more modifications? The existing heads, as part of a factory crate package, were designed to work with the rest of the engine. Replacing burnt valves isn't that big of a deal and it should be much less expensive than replacing the heads but staying with the old heads means no increase in hp.

Before you make any choices, figure out what your goals are and then take it from there. If you want a dependable driver with decent power but good manners, choose accordingly. If you want to increase the horsepower somewhat but not sacrifice driveability, choose accordingly. If you want to live life a quarter mile at a time, choose accordingly.

Take care!!

-Mac

 

[78SilvAnniv]

This is what I want:

If you want to increase the horsepower somewhat but not sacrifice driveability, choose accordingly.

After Dann's posts, Chris' email and everyone else who has taken the time to offer advice, I realized that I cannot radically change just a few pieces and expect great things.
It just won't happen. Everything must work well together.
I think I am making a conscious effort to learn all I can, but I'm getting a bit overloaded trying to figure out all these new ideas and assimilate the new information.


From what I've read above, I think I'd like the LS1, L98 or 462 heads. Am I on the right track?
I read the sheet I printed up by racerguy on SBC Heads and he commented that the "462" heads DO NOT have accessory holes. What would it take to put the holes in if I choose this head?
Goal: I would like to lightly increase hp and not sacrifice drieveability.
I am not so concerned with hp as I am with low end to midrange torque and responsiveness.

I'll have to look for my stamping numbers for the engine to determine exactly what I have. What is standard targetmaster OTC?

 

[MoeJr]

c5d the reason the LS1 can run 10:1+ CR is cause it has a modern computer system and fuel injection which makes it possible to run the CR that hi. Heidis Vette is a 78 with QJet and experience in with this stuff tells me keep it 9.5:1 or less or she'll hafta retard the timing too much to keep detonation away. hope you don't find this contentious.

 

[Bob Chadwick]

Aren't those higher compressions ratios achievable on an aluminum head without the detonation issues?

 

[bossvette]

From what I've read above, I think I'd like the LS1, L98 or 462 heads. Am I on the right track?

LS1 will not fit, it is a totally different small block,
462 the "old fueally heads" while they were the hot ticket in the sixetys-seventys do not have hard valve seats and will take a lot of work for a street car
l-98 If you are talking the aluminum Vette head would work, although I would use a thick head gasket to keep CR down as much as possible on a carb car and if you don't have the post 87 style small block you will require new intake and valve covers (centerbolt)
the "Vortec" head was designed as a "smog head" but was discovered to flow and make as much power as many "race heads" hence its popularity. They were cast in two combustion chamber sizes and have a heart shaped combustion chamber.
I believe the casting number was 906 and they were installed on the trucks with the 350 Vortec engine.

the question is how much do you want to spend and how fast do you want to go?

when you get it done bring it to Auburn and put it on the Dyno

Cruise-fest 2004

 

[MoeJr]

bobchad as a general rule you if you have a 9.5:1 motor on iron heads you can go 1 point higher on the CR with aluminum.

:bar

 

[Bob Chadwick]

Thanks Moe. I'm following this post with interest as I have the Performer manifold and want to upgrade my cam and heads. I think the stock compression ratio is 8.5:1.

It appears that I need to go with the Performer-Plus Cam Kit and the Performer RPM heads to match the manifold. I would have expected to go with the Performer head but it appears that the only difference is that the Perfomer heads have an exhaust crossover passage for emissions equipment compatibility. The EGR valve has been taken off already so I guess there is no sense at this point in trying to work within the emissions that were on the car from the factory.

The next questions I guess are whether to go with angled or straight plugs and 64cc or 70cc chamber sizes.

The Edelbrock web page says that "Performer heads with 64cc combustion chambers improve performance and retain stock compression ratio on 1970 and earlier small-blocks." I don't know what that means for me. All I know is that I want to be able to use pump gas.

Anybody have any estimates on the HP I will be pulling with this setup and true dual exhausts with 2 1/4 inch pipe and dual cats. Headers will come later. I have read how people have burned the ceramic coating off their headers breaking in the cam and felt that I should get this right before adding the headers.

Bob

 

[78SilvAnniv]

After Great Deliberation...

...here is what I have decided on and found that is within my budget.

Cast Iron heads
1.94/1.50 valves
67cc combustion chamber
170cc intake port
70cc exhaust port

SS valves, Z28 springs rated at 120# and steel retaining locks. Have also been told to pay the extra bit and ask for roller-tip rockers.
Will I need to also ask for hardened valve seats or are they done automatically on today's heads?

Changing only the heads and keeping the manifold and carb as is since I've been happy with it.
Heidi

 

[Bob Chadwick]

Thanks D.

 

[Robin7TFour]

greetings all, i am very impressed with all the info ,and i have a mild headache now too.
i wish i could have talked to the guy that built my engine. i could tune it much better. but hey! i'm doing the best with what i got.
the last engine i built from bare block was on my 68 camaro. it was the original 327. so i took all the 327/350 specs and put it together that way. i couldn't have been happier.
when engine time comes to ole blue, i do my homework the same way..

sorry if i am babbling

robin

 

[MoeJr]

Posted by bobchad:
"The next questions I guess are whether to go with angled or straight plugs and 64cc or 70cc chamber sizes.

The Edelbrock web page says that "Performer heads with 64cc combustion chambers improve performance and retain stock compression ratio on 1970 and earlier small-blocks." I don't know what that means for me. All I know is that I want to be able to use pump gas."

Bob 1970 and earlier SB's had CR of 10:1+ so in that respect on your 77 it would actually raise it to that amount where as on a 1970 or older it would be stock CR. With that in mind I suggest the 70CC versions and the difference in performance will be negligible. The stock manifolds on your Vette are pretty good so don't write those off yet. Headers are nice but the burn plug wires instantly if they contact each other. Performer RPM stuff is nice but may cause hood clearance problems with stock hood. Performer stuff is really better for street if ya have a automatic and hiway friendly gears. Just my .02. Please keep us posted as you start modifying your Vette.


Moe