70sgeek

anyone know the stock cam specs? Getting ready to add a few suds to the motor and want to replace the cam with something a little more magical... Thinking about hitting the Crower or Lunati catalogs for a suitable tight duration/decent idle type replacment, maybe .450-.460 range?...

bobs77vet

don't know what they are and i'm running a comp xe268...and like it, others have bad things to say about this line of cam....but anyway how could you go wrong with a GM performance parts hot cam? let me get a part number hold on...

http://www.sdpc2000.com/catalog/540/...c-Camshaft.htm

in any event your heads are whats holding you back

MYBAD79

The heads and the cast manifolds don't let the engine breath. The stock valve springs don't allow for a lot of duration and lift, they're probably pretty weak after 100K (or how many miles) ???

The inexpensive Summit or Jegs heads ($500) are a nice upgrade if you don't want to spend the big bucks for aluminum heads, in combination with some $100 headers (shorty or long tube) you'll see a decent improvement.

Cam ? Something in the range of 218-224 advertized duration with .460 lift is a huge improvement over stock and will still idle good, the stock L-48 duration is somewhere around 204-210 with .400 lift.

sweethence

while the aftermarket does give some great stuff, if you are not gonna change the heads you wont get all the benefits as said earlier. but consider this the GM stock grind for a 70 Z28 is as follows

222/222 Duration, .447 lift 112 degrees lobe separation. i used this cam in a 67 350 camaro I had with very good results. The genereral spend millions developing parts so why not cash in on it right

I also picked up a set of magnum rockers bumping the ratio up to 1.6 from 1.5 another easy upgrade though with this one you should be very carefull about valve to piston clearance if done in conjuction with a cam swap

In any case, a new set of springs is worth the investment like said above. The best way to get consistent performancE across all 8 Cyl is to ensure each set of valves is set up as close to exact as possible. To do this get a new set of springs, (and if you want to takle the extra step , measure the compression height and spring force for each one). also a new set of rockers is not a bad idea on a higher milage engine, you be surprised about the differences in rocker ratio agross multiple cylenders due to casting and wear differences. some will say that this is minor for non racing applications, but for my 2 cents if your gonna buiild it to last may as well make sure you engine is a tight as possible. Building engines isnt magic, its a science. treat it so and be as precise as possible


have fun


tim

jackson

L48 cam is very small cam.


0.050" Duration 194*I / 203*E
Valve Lift .390"I / .410"E
Lobe Lift .260"I / .273"E

SAE Duration 260*I / 271*E
SAE Overlap 34*
108*ICL / 116*ECL
LSA (LDA) 112*

0.050" Valve Timing
IO 11*ATC, IC 25* ABC
EO 37* BBC, EC 14* BTC


Reference: Clevite Replacement Cam Specs for P/N 229-1274.

229-1274 interchanges w/ GM P/Ns 14060651, 14088839, 3733431, 3896929, 3918962.

Clevite 2005 Camshaft Catalog.

70sgeek

Love the feedback - many thanks!

The motor was said to have been rebuilt, timeframe and extent unknown but the valvesprings have overspray on them so my guess is the heads were touched at some point.

They're period factory castings so probably close to stock configuration - wanted to do something in that department but not sure what yet - main thing is I don't want to spend crate $$ on the rebuild but still want a healthy performance increase -

thinking about this in a crower cam - 270 HDP - 112 c-line, .210/.216, .445/.445 - coupled with a holley dual plane dominator and Avenger 670 carb. Might go alum on the heads rather than put any $$ into the oem's. Maybe I can sell the oem's to help offset the cost.

bobs77vet

i doubt it....

70sgeek

hey, 10 bucks is 10 bucks... - Steve Martin, 1978

comp

true,,so is 5

bobs77vet

and then theres shipping and you are into the negative territory

MYBAD79

you won't find many people who want these stock heads

and these are heavy.... can't ship them in one box, they're too heavy for UPS or FedEx

bobs77vet

well maybe for lunch and a beer

MYBAD79

yup... some people trade for food

Those two heads that magically appeared at my doorstep are cleaned up and will be prepped for the valve extraction shortly.... they'll receive new valve seals (maybe new springs, too) and will be mounted on top of my bone stock L-48 chevy SB some time in february... well, at least that's the plan right now....schedule may change.....

bobs77vet

hey that sounds great glad they could be used. those things weighed a ton.....

MYBAD79

the weight hasn't changed, they are still a little on the heavy side should I get some titanium valve spring retainers to drop the weight before I install them ?

Kidding aside, thanks again... the only other item I need to get the original L-48 complete is the cast iron intake. then I'll have the stock engine complete and running while I build the 383 ... the difference after the swap should then be very noticeable

jackson

70sgeek ... An avenger 670 has nothing to offer that's any better than freshening your OE 750 Qjet.

Your 76 L48's OE CR should be somewhere between 8:1 - 8.5:1 with OE dished L48 pistons ... OE dome volume about -11cc (that's neg 11cc).

Replacing your OE 76cc chamber heads w/a set of 64cc iron Vortec heads will raise CR about one whole number ... to about 9:1 - 9.5:1.

I suggest a set of iron Vortec heads, SpeedPro (sealed power) hyd flat tap cam P/N CS1013R (.443/.465 214*/224*, 112*cl), a low-rise dual-plane Vortec intake Professional Products "cyclone" P/N 52007, and your freshened OE Qjet carb & freshened OE HEI dist. Suggest you also change timing chain set along w/ cam. You will like FelPro P/N OS34510T one-piece oil pan gasket and Victor Reinz P/N 5746 head gaskets (composite but only 0.026" thick x 4.100" bore) ... if no block machinework ... and you do the work ... it'll EASILY be under $1K.
-edit- Clevite cam P/N 229-2205 is same as SP CS1013R ... & local parts houses can get these cams ... their quality is just as good as comp, lunati, crane etc ... but less$. FYI, Clevite & SP been supplying cams to OE for decades ... & offer nearly as many street/strip cam choices as those big name cam makers found in jeg's/summit etc.

glen242

The dish in my stock l-48 pistons looked a lot bigger than the dish in my Speed Pro D dish pistons and the Speed Pros claim -12cc. Where did you find the info on the stock pistons?

70sgeek

hmmn - hadn't thought about the vortec stuff - back to da catalogs!


The holley carb was a natural choice for me due to familiarity. That plus I got it brand new for under $300 thanks to a Summit price match...

The oe Cr is 8.5 according to the published specs. I think a little bump up is definitely in order, pump gas permitting...

MYBAD79

The Vortec heads are a good bang for the buck... You can find nice aluminum heads on Ebay for not a lot more $$$, take your time a shop around, the more patient you are the better the deal....

Assuming your Q-jet doesn't have any major issues it'll be fine - just have it cleaned and set up correctly. I am very happ with my cheap 600cfm Edelbrock-Carter clone carb on my 350... $240 at AZ and it works great right out of the box...

Without changing the pistons you'll be fine with 64cc heads which bump the CR to roughly 9.2:1 - you may want to look what head gaskets are avialable in what thickness.... a thinner gasket may get you to 9.5:1 CR without touching the pistons....

A cam like the RPM cam (edelbrock) with 234-244 duration requires more CR....been there, done that and replaced cam.... if you want a cheap RPM cam email me....

jackson

Both Sealed Power & SpeedPro catalogs ... look at xx423xx dished series. Amongst that dished series, dish volumes vary ALONG w/ compression heights (pin center-to-deck). Given same head cc and gasket thickness, effective CR remained about the same throughout. The dish volumes also vary via several combos of dish diameter & dish depth ... all within xx423xxx series. Again, end result CR of dished was about the same if same head cc & gasket thickness. Just like deck height & gasket thickness ... differences in dish dimensions are in thousandths ... it takes relatively much dish diameter change to offset a relatively small depth change ... relationship is inversely proportional ... but NOT 1:1. Looks can be deceiving.

If you have an 8.2:1 350 sbc motor w/ 76cc heads ... and replace w/ 64cc head & SAME type gasket, NO block decking, NO piston change ... CR will increase to right at 9.2:1. If you started w/ 8.5:1 and did same ... it'll become right at 9.5:1.

If you have typical composition head gasket and switch to thin steel shim head gasket ... that'll increase CR about 0.3-0.4. Simply switching from thick to thin gaskets on 8.5:1 CR sbc 350 will increase CR to about 8.8:1 - 8.9:1.