Exhaust Manifolds for 'Fast Burn' Crate Heads

[Elm Zobens]

OK- Here I go again ;-)
I have a 69' Corvette Coupe with a ZZ3 crate engine. I'm considering installing the Fast Burn heads, Hot Cam w/1.6 Rockers and GM Vortec style intake.
The question I have is for the exhaust manifolds- I am currently using the factory cast iron 'Ram Horn' manifolds, but rumor has it they won't fit properly on the Fast Burn heads.
Is there any truth to this?
If the ram horns won't work, what are my options from a factory standpoint?
I'm not big on headers and would prefer to keep everything GM.
Can I use LT1 manifolds from a C4 Vette? Will they fit the heads and chassis properly?
Any advice would be greatly apprecited.
Thanks!
Elm

[John H.]

Re: Exhaust Manifolds for 'Fast Burn' Crate Heads

Before I got into exhaust manifolds, I'd want to check hood clearance very carefully first; those heads and Vortec intake push the carb up higher than the stock arrangement.

[Frank H.]

Re: Exhaust Manifolds for 'Fast Burn' Crate Heads

The exhaust ports are suppost to be higher then stock so,maybe porting a spare set of rams horns or slotting the holes on a set of those shorty street rod hedders,seen on E-bay in chrome and other finishes.There is the SS 80-82 type manifolds that are similer but with a/r tubes with matching head pipes.????
FH

[Elm Zobens]

Re: Exhaust Manifolds for 'Fast Burn' Crate Heads

The heads themselves aren't any 'taller' than the standard SBC heads and the vortec intake has a different bolt pattern and port spacing- But since the intake side of these heads is in the same place as on any other SBC, I don't envision the low-rise dual plane intake to be any higher than the ZZ4 intake that I am currently running. Obviously, I will need to verify before I order anything.

These heads even go as far as having 'dual' bolt patterns for the Vortec (4 bolt)and traditional SBC (6 bolt) intakes- Which asks the question why they did this if they are turning around and saying you should use a Vortec style intake?

Anyway, I am having a hard time just figuring out where all these engines fall-
Are the 'ZZ' motors considered Gen I with mods, Gen II like the LT1 and LT4 or some sort of hybrid? Is 'Vortec' considered as Gen I, Gen II or?? Is the Vortec design similar to the LT1 and LT4 designs?

If there was any documentation that clears all this up, my decisions would be much easier ;-)

Thanks!

[Joe L.]

Re: Exhaust Manifolds for 'Fast Burn' Crate Heads

Elm-----

As far as I know, the stock GM cast iron manifolds will work ok with the fast burn heads. There will be a very slight port mismatch between the fast burn heads and the GM "ram's horn"-type exhaust manifolds. However, this mis-match is slight and should cause you no problems, at all. It is possible to "port match" the manifolds and heads by some slight grinding, but I would't do it. I'd leave them just as they are.

The term "Vortec" for engines can be misleading. "Vortec" has been applied to both Gen I and Gen III and, now, Gen IV small blocks. However, it was never applied to any Gen II small block and it doesn't apply to all Gen I small blocks, either. Gen II small blocks are the rarest of all small blocks, although they are not rare, per se. They were used only for 92-96 Corvettes, 93-97 Camaros, and some 93-96 full size RWD GM cars. They were never used in PRODUCTION for any truck application and ALL "Vortec"-labeled engines are truck engines.

The Votec heads that you are talking about are applicable to Gen I small blocks ONLY. They cannot be used on any Gen II or Gen III/IV small blocks.

A Vortec style intake will give better performance when used with heads which can accept them (like the fast burn which are dual drilled) than will non-Vortec manifolds. However, the difference is not great and you can use either style manifold with fast burn aluminum heads.

ALL ZZ-series engines are Gen I engines. NONE are Gen II and, to date, none are Gen III or Gen IV.

[Elm Zobens]

Re: Exhaust Manifolds for 'Fast Burn' Crate Heads

Joe,
Thanks so much for clearing things up!
So even though the ZZ engines have the roller cams and 1 piece rear main, they are still considered Gen I? Good to know...
What adds to all the confusion is that the 'HOT' cam used in these engines are from the LT4 (Gen II) and the Fast Burn heads appear to be similar to the L31 'Vortec' design- Which is what lead me astray originally.
Does GM publish some sort of guide or anything that explains all of this stuff in detail?
Seems like there is much room for interpretation and error in picking and choosing the right components for any particular generation SBC.

Thanks Again!
Elm.

[Joe L.]

Re: Exhaust Manifolds for 'Fast Burn' Crate Heads

Elm------

Yes, the one piece rear seal and roller cams are not exclusive to Gen II and later. All 1955-91 Corvette small blocks were Gen I engines. However, 1986 and later had one piece rear seals and 1987 and later had roller cams. The change to 1 piece rear seals and roller cams did not cause a "Gen" change for the small block. These changes were PART of the changes that accompanied the "Gen" change for big blocks, though.

The Gen I small blocks were actually used in PRODUCTION vehicles from 1955 through about 2002, or so. They preceded the Gen II and they continued to be manufactured and used in PRODUCTION at the same time as the Gen II and, even, after the Gen II was out of production.

The "fast burn" heads are Gen I heads and can be retrofitted to just about any Gen I engine. They cannot be used on Gen II engines. The "fast burn" heads were never used in PRODUCTION, though. They are SERVICE-only pieces. However, they are somewhat similar to the 87-91 Corvette heads. They also incorporate some Vortec head features. Vortec cylinder heads (all were cast iron) were used only on trucks with Gen I small blocks. These were used in PRODUCTION right up to the time that the Gen I engines were phased completely out of PRODUCTION trucks and replaced by the Gen III ("LS1 style") small block.

The Gen I engines and major components thereof are still produced for SERVICE by GM in Toluca, Mexico. They are also produced for marine and industrial applications. They are produced in only 305 and 350 cid configurations. However, a 383 cid configuration is assembled in this country from components manufactured in Mexico. GM never used a 383 cid configuration in a PRODUCTION vehicle EVER, though.

The Gen II small block is out of production.

The cams used in Gen I and Gen II are, essentially, interchangeable. The only difference relates to the length of the dowel pin on the front of the cam. While all Gen II engines used a roller cam, most Gen I engines used a roller cam from 1987 onward. PRODUCTION-style roller cams cannot be used in pre-1987 Gen I engines.

Believe me, the world of GM small block engines is anything but simple. Some information can be found in the GM Performance Parts Catalog. Unfortunately, nowhere near all of it is there.

[Elm Zobens]

Re: Exhaust Manifolds for 'Fast Burn' Crate Heads

Whew!
Thanks again for the education Joe!
So one last question(s) (for now LOL):
The LT1 and LT4 are the ONLY 'Gen II' engines ever produced?
What was the major difference(s) between the Gen I and Gen II engines?
Is the 'reverse cooling' something that was introduced in the Gen II engines or was this another late Gen I enhancement as well.

Thank you so much for patience-
Elm.

[Joe L.]

Re: Exhaust Manifolds for 'Fast Burn' Crate Heads

Elm------

There were 3 basic variants of the Gen II engine. The first was the LT1 which was used in 92mid-90's Cadillac Broughams, and 94-96 Impala SS. The second was the LT4 used only for some 1996 Corvettes. All of the preceding were 350 cid. The third was a smaller cid engine which, if I recall correctly, was ABOUT 280 cid and called the L99. It was used in some Caprices and other similar GM cars (Buick Roadmaster, Olds Custom Cruiser wagon). Most LT1 engines (but not all) used aluminum heads. All "L99" used cast iron heads.

The major difference between Gen I and Gen II engines involves the cooling system configuration (i.e. "reverse flow"), ignition system, and induction system. All of this required significant changes to the block and cylinder heads and Gen I and Gen II blocks and cylinder heads are, consequently, not interchangeable. The ignition and induction system components are also unique to Gen II engines and were never used on any Gen I engine.

Gen II engines were never used for any truck application---they were used for cars only. Gen I engines were/are used for cars, trucks, marine, and industrial engine applications.

"Reverse flow" cooling is a feature unique to Gen II engines and is ONE of the reasons for so many unique, major components on the Gen II engines. No Gen I engine ever used this cooling system configuration. In fact, Gen III and Gen IV small blocks don't use "reverse flow" cooling, either.

[Joe L.]

Correction

Somehow, the second sentence in my first paragraph got "chopped off" as a result of something I did wrong. It should read as follows:

The first was the LT1 which was used in 92-96 Corvettes, 93-97 Camaros/Firebirds, 93-96 Caprices with police package, some mid-90s Cadillac Broughams, and 94-96 Impala SS.