Glensgages

In the near-future, I hope to ****-can the Cross-Fire on my '82 Corvette, and am thinking about increasing the compression-ratio to about 10.2:1 via 64cc vortec iron heads with upgraded valve-springs, adding a CompCams 268H or 280H shaft, vortec RPM AirGap, and a 650 double-pump Holley carb:
wimpy 700-R4 will also be deep-sixed in-favor of a more durable THM350, and the OEM 2.87 rear-gears were relieved of duty 5 years-ago, and replaced with 3.73 gears.

While I'm not-looking for any specific HP/TQ numbers, and the car won't be drag-raced with any frequency, I'm expecting it to run more-like a CORvette instead of a CHEvette, like it does now:
car won't be taken on many long-trips, so highway RPM without the OD & 3.73s isn't a concern.

My question is regarding that-much squeeze with iron-heads, and how-well it will run on readily-available SUNOCO-93 pump-gas:
while I could get better aluminum heads for the same price, the deal from Scoggin-Dickey, including heads, intake, all bolts & gaskets for under $1100 is just too-good to not-consider.

http://www.sdparts.com/product/SD806...RPMAirGap.aspx

Will this thing ping & detonate itself to death with the compression on pump-gas with iron heads?


As-always, thanks-in-advance!!!!!

weimer20

The 268H will probably cause some issues. I would think you would need a bit more overlap to control your dynamic compression ratio. Search online for a DCR calculator and run the numbers. Someone can probably pop in and get you to a link for a good one. The 280 will probably be ok. Verify dynamic compression first though. JMO.

Little Mouse

Looked at the kit looks like a perfomer style manifold.
do vortec heads use different valve covers ?? You won't be able to
do it quite as cheap but you could use the IK180 brodix heads
BRO-1021004 = $1013.95. If you don't know anything about Brodix
the first aluminum head they made was in 1969 for a Hemi. Aluminum
head would give you the comfort zone your looking for, IK180 that I saw
tested just in one of the rags made more power over the vortec on the same engine. www.summitracing.com

Huum looked at the kit little harder if you have to spend $138.00 for a nice set
of valve covers to fit the head, brodix deal might start looking better money
wise. do you already have nice valve covers ?

stingr69

The 268H cam is good for a 8:1 motor but with 10:1 you will need more cam.

A 280H is probably better for that much compression. A GM 350/350 cam would also work with well with that much compression but will be a bit more "tame" as compared to the bigger Comp grind with 110 degree lobe separation. If you are running headers and a free flowing exhaust system you will do fine with the 280H.

-Mark.

Glensgages

I think all of the pictures that S-D uses for those kits show a Performer intake, but they will supply you with intake of your choice.

You are correct that the vortec heads uses center-bolt valve-covers, of-which I have none, but valve-covers won't sway me one-way or the other:
the Brodix IK heads are more head than I need for my modest goals, but I may end-up going with aluminum heads for the detonation-prevention factor

When I swapped the 76cc heads from the LM-1 on my '79 Z28 almost 30 years ago to 64cc iron heads, we had no-problem with a cam very-similar to the 268H, but the LM-1 was only 8.2:1 to begin-with, instead-of 9.1:1:
my Z28 is now 10.4:1 with iron heads, but uses the much-longer 292H (244* @ .050"-lift), and races on SUNOCO Ultra-94, which I can't find here in Floriduh

Little Mouse

Do you want a cam with more duration that raises the power band higher up just to bleed off compression so you can run the iron heads ?? Obviously the better the heads breath the less cam you need. less cam keeps low end torque stronger and the better breathing head still keeps things good up higher with the better breathing head. Old fulie heads as good as anything came off the assembly line only flowed 188 at .500 lift. chevy had to put a big 254 at .050 cam in it to get any power out of the engine, heads flow no air no problem throw a big cam in it, engine would not pull nothing below 4000.

Glensgages

That's just-it..... I won't be winding-out the stock, as-assembled 26 year-old short-block beyond 5500 RPM, so I don't need a big-cam (probably required with iron-heads), nor do I need good-flowing aluminum heads (probably required with a smaller cam):
for similar price as the IK-heads, I even considered using aluminum L98/ZZ4 heads,

http://paceperformance.com/index.asp...D&ProdID=22850

which have even smaller intake ports (163cc), and smaller combustion chambers (58cc), which I think would allow a smallish cam and make for a higher-compression (11:1? ) but low-RPM torque motor, but it's doubtful it'd run-well on pump-gas.....

stingr69

I have 10.4 C/R with Iron Eagle heads and a GM 350/350 cam and it runs just fine on pump gas. Your results may vary and it might not be the best setup for what you are wanting but it does work for me.

The smaller Comp 270H will also run on pump gas at the 10/1 ratio but I would not go any smaller on the cam. I would bet that Comp will probably tell you that as well if you give them a call.

-Mark.

Ganey

280H is for higher RPM. You need between the 2 cams, 270H or XE268.

Dalannex

There you go. If Ganey says that's what to use then that's what you should use. He has helped me out on a couple of different cam selections and was always spot on.

Look at what I am running in my sig. I have no problems with detonation on premium pump gas. (and in last fall's testing my car REALLY liked running on E85)


-Justin

Little Mouse

Well the vortec head flows air better then this head but summit has
a 67cc chamber head 202/160 valves 165 runner, Im only suggesting it as another option because its cheap $650.00 and uses standard intake
if nothing else to save money you could easly buy a good used manifold off fleabay for it. the 350/350 hp cam is good has a wide LSA 114,
wide LSA cams hold the intake valve open a little longer bleed off more compression, but the 222/222 at 050 duration is a little hot it had
11.0 compression to support it back when gas was good. What I would do if I was wanting the vortec head with a low end torque power band
is find a little lower duration but still has a wide LSA at least 112/114.
tight LSA cams give better overlap but they close the intake valve a little sooner the engine builds more compression thats what your trying to avoid.