Yes, that would apply to solid lifter engines only. As you decrease lash lift and duration at the valve are increased. Keep in mind that, within a safe adjustment range, that increase won't be dramatic but it could provide a clue. The 365/375 hp 327's are listed at .025 lash in the AMA specs but .030 in the owner's manual. That was probably to make the cam a little more street friendly, especially in cars without low gears.

 

RACE ON!!!

 

Cool stuff!

I have a feeling I'll end up going with a popular cam... mainly because I dont have a complete understanding of all this stuff!

Duration makes a bit more sense thanks...

I am pondering an R/V and towing cam, because the bottom end of this motor hasnt been align bored, or balanced. Figuring that I probably shouldnt push it much past 5,500k. That is... unless yall have used any machine shops in the south east! But, if I'm going to have everything balanced I'd prefer to have a forged crank and get the rods cleaned up a bit...

While I'm asking questions, do yall know the stall rpm on a th400 torque converter? (1975 l48) That will play a part on the low end... l

Thanks again guys!

 

As I said, sometimes what you're thinking doesn't always come out the fingertips to the keyboard correctly.

Duke is right, the reversion is really best described by the late intake closing event where exhaust is pushed back into intake tract.

Lots of overlap can cause similar issues if backpressure is high. And it doesn't really have to be high like you may be thinking...anything above vacuum is high pressure in this respect. As long as ex flow out of the port is still helping create more intake flow it's a pretty good thing until it pulls excessive mixture out with it.

I saw some interesting tests once where they were trying to come closer to real running conditions in an engine vs just flowbench data. As mentioned, we don't race flwobenches either and often a set of heads runs better than they "should" against a higher flowing set. What they were doing was following the thought process that very low-lift (.100-.250-.300 maybe) flow wasn't as important as folks liked to talk about. The issue is that when the valve is actually in that position, the piston is actually moving the wrong direction. Think about it....the intake valve opens well before TDC and the only reason it has to be is so it will be open as much as possible as piston starts going down. So piston is climbing when the valve is .100 off the seat. And again when it is closing, the piston is aiming back up at it again.

The tests were evaluating the effects/benefits of a particularly poor flowing port at these lifts as being a good thing. They were manipulating valve job and valve head shape to impede reverse flow at those low lift points. They were actually flowing head in reverse for these measurements.

Also, when heads are ported/flowed, they usually flow them backwards on the exhaust side. They "suck" from the cylinder side. Apparently there is some benefit to flowing them the other way in a direction that the exhaust actually flows. Same thing with using superheated air that is dirty with particulates..it flows different than pure clean air. I suppose it's the same on the intake side since you are now seeing folks working with "wet" flowbenches.


Anyway, fun stuff to study and it always points out another way to look at things!


JIM

 

Interesting stuff!

What kind of exhaust system do I need to think about? I had (when first pulling the 75 apart...) been trying to replace the rusted out true duals with an emmissions legal exhaust. Thats how the "While your at its" set in...

Anyways, I have a set of the dual tip glasspack mufflers... you can see light looking through the pipes!

I'm pondering a side pipe exhaust, but I've heard that they are less efficient than an undercar exhuast with a crossover pipe.

If I recall... backpreasure can be tested with a gauge? Something that screws into the same bung as an oxygen sensor? I've done it before, but not with my own tools... on a LTD! Just cant remember what kind of gauge setup was used...

 

Well even if that 3896962 cam wasn't used in the LT1 mtrs it always made 50 more hp than the base L48 cam #3896929. It was designed for the same car using just ram exh manifolds - u can save urself the trouble of headers - and made 350 hp in 1970 (11:1 cr though). And GMPP still sells the 3896962. Its hydralic with 114 LSA. So if u wantr an easy 50 ponies there it is. I would recommend this cam for any mild engine using stock parts and if the block still has stock deck hieght using steel shim head gaskets will give the right qunech hieght for up to 15 more ponies - and save a few bucks too.
Good luck. cardo0

Found this and couldn't sleep. If ur VIN engine code is a "T" then u already have the #3896962 cam if using the original motor (VIN code "J" used 3896929 cam). Anyways emissions choked the "962" down to only 205 hp while the "929" became a 165 hp weezer in '75. So what i'm saying is that carb tuning and mostly ignition emissions timing with cat(s) is costing u big hp.
Maybe just a high flow cat and tuning will make it a new car.
Good night. cardo0

 

I doubt I can get over 300hp out of it... 8.62:1 compression if I go with a regular head gasket! I'm pondering the steel shim, but... I've never used one before.

Would the Crane cams Blueprint Muscle car cams fit the description of a 350hp sb?

SB-Chevy:
Hydraulic lifter replacement for 327/350 horsepower cam.
270-967601 Lift: .447''/.447''
RPM Range: 2200-5200 CartMe! $99.99

Not a lot of info besides that...

 

I'm using the .015" Felpro Performance coated steel shims...They've been sealing good for over 3 years

 

[QUOTE=ZD75blueSB-Chevy:
Hydraulic lifter replacement for 327/350 horsepower cam.
270-967601 Lift: .447''/.447''
RPM Range: 2200-5200 CartMe! $99.99

Not a lot of info besides that...[/QUOTE]

That's the L-79 cam, 3863151. Duration at .050" is 221/221 and centerlines are 110/118. The "962" cam was used in the '69 to '80 L-46 and L-82. Duration at .050" is 224 and centerlines are 114/114. This is essentially a L-79 cam with three degrees more duration and retarded 4 degrees. The "151" will make a little better low end torque, and the the "962" will make a little more top end power and is a good choice for a 350. If you want a little more low end torque, you can advance it four degrees to the same centerlines as the 151 and still get the benefit of the slightly more duration.

Duke

 

FYI 1 of our supporting vendors sells that cam # 3896962. Just click on the side bar of GMPartsDirect for:

GM PART # 3896962
CATEGORY: Engine Camshaft
PACK QTY: 1 CORE CHARGE: $0.00
GM LIST: $178.66
OUR PRICE: $125.06
DESCRIPTION: CAMS- 350

Good luck blue dude. cardo0

 

Duke- I'm setting up my new C2 engine as follows: 350ci, 10.5 cr, 2.5 inch ram's horn header w/ side exhaust, LT-1 cam setup per your instructions, 36 degrees total advance, Edelbrock al heads with 2.02 intakes, and quad WEBER 48 IDF's setup by Inglese. Any thought's on the combination?

 

Good long block - not sure about the Webers - 48s are a little on the small size for the cylinder displacement. Hope you have someone who can help you with setting up the Webers, but there are books on the subject.

If the Webers prove to be a PIA, A LT-1 manifold with a vacuum secondary 750 CFM carb. should work nicely.

Duke