upgrade choices


The Grumpy Grease Monkey mechanical engineer.
Staff member
Chevy 4 Life said:
Good morning Grumpy,

I really appreciate and respect the advice that you have given me and other on CT over the last year or so that I have been a member. I was duped into buying a rebuilt 68 350 with 882 smogger heads, and over cammed, even though I was told it was a built motor. The motor does run well though, just no low end TQ for the street and my 4000lb impala. I would like to install aluminum heads to lower the front weight. I am looking for reliable 375+hp, and over 400tq in the Idle-4500 range. It currently has 280h cam, performer intake, 882 heads with z28 springs, 1406 600 carb, long tubes, and 2 1/2" exhaust. 700r4 with 2200 stall,3.70s and 27" tires. My budget is 2k for parts, and do you think that I should stay flat tappet or roller. Rollers are pricey and I do like to lean towards the old school flat tappet route. Thanks for the help in advance.

with a 4000 lb car and a basically stock 350 short block youll want all the torque you can get in the lower and mid rpm bands, torque is the result of efficiently using cylinder pressure, great flowing heads are mandatory for max potential power and better heads tend to partially compensate for a slightly milder than ideal cam, but the current cams a bit too large in duration and the heads are restrictive ,given the budget limitations and reluctance to totally rebuild it as a 383 stroker config, and Id bet the reluctance to go with a flat tappet solid lifter cam, Id suggest going this route.(parts listed below)
the old chevy smogger 882 heads are very old and restrictive technology

even the more modern and fairly reasonable priced rhs heads flow much better
GM 882
Valve Exhaust Exhaust Open
Intake Lift w/ pipe
0.050 39 34 34
0.100 58,59,70

0. 200 125 108 109
0. 300 175 135 136
0.400 204 141 143
0.500 205 142 144
0. 600 206 142 145
E/I 69% 70%







I doubt youll quite reach 400 hp but youll darn sure have a more streetable combo with noticeably better low and mid rpm torque over the rpm band your using 90% of the time.
going with a roller cam and lifters would cost enough, of that $2K budget, to exclude the purchase of better heads and the heads are more critical to boosting operformance.

heads (low cost but noticeably better than current 882 heads)

SPEND A BIT MORE and get better heads (personally I think $240 extra,very well spent)

milder crower cam

rhoads lifters

1.6:1 erson rockers

youll learn a good deal by reading through








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The Grumpy Grease Monkey mechanical engineer.
Staff member
Chevy 4 Life said:
Thank you so much bud, boy do you have the knowledge. I emailed summit last week and this is what they recommended: Cam: http://www.summitracing.com/parts/cca-cl12-238-2

Heads: http://www.summitracing.com/parts/pmx-2168/overview/make/chevrolet

I informed them of my current setup and what I am kind of expecting and this is the setup that they recommended. It looks like it would work for the TQ and RPM range that I am looking for and they told me to keep the performer intake and carb. What good cheap Roller Rockers would you recommend thru Summit? Thanks again

yes you can find cheaper rockers , but remember your rockers take a constant beating and decent QUALITY is mandatory, and getting the valve train clearances, push rod lengths, and geometry correct MATTERS
these should work


but if it was my engine ID only consider these comp cams steel, roller rockers if limited to fairly low priced roller rockers from SUMMIT racing, steel has a noticeably longer fatigue stress life


Valve Spring Retainer to Rocker Arm Clearance
When installing the rocker arms, check to see that the inside of the rocker arms clear the spring retainers. Many rocker arms have a "relief" to accommodate large valve spring retainers.

yes youll want too use push rod guide plates on most heads when your not using self centering rockers

while your rocker wear marks on the valve tips look very close to ideal , you need to verify the push rod length, as getting that rocker geometry correct is important to durability , and a slight change in push rod length may improve that further, keep in mind that having the wear band centered is nice but not as important as keeping in narrow and close to center as possible as a narrow wear band tends to indicate minimal side thrust and as a result minimal wear results

"THAT PLASTIC THING" is a PUSH ROD LENGTH CHECKER, THE PUSH ROD LENGTH CHECKING, AND ROCKER GEOMETRY TOOL, ARE ENGINE SPECIFIC, so you MUST USE ONE DESIGNED FOR THE SAME STUD DIAM. SPECIFICALLY FOR YOUR particular ENGINE, and cylinder head design, to find the correct rocker geometry and push rod length. If you for example use one designed for 7/16" studs on a SBC and used it on a BBC with 7/16" rocker studs the result would not be close to correct, if the tool designed for one engine is used on the wrong engine, so be damn sure you use the correct tool.
if your seeing a .120-.150 gap between the push rod tip when the "PLASTIC THING" is inserted on the rocker stud ,with the cam lobe /lifter on the base circle AND IF ITS THE CORRECT CHECK TOOL FOR THE APPLICATION,and its resting on the valve tip, your push rods that much too short for the application, your measuring, if the tool rests on the push rod tip and its lets say .060 off the valve tip, that indicated the push rods that much too long for THAT particular application, get within .040 or less on either meassurment and your fine


yeah I know many guys would rather slash their wrists,
then read through a couple hours worth of links and sub links.....
try to avoid only reading links ,
only to find out WHY expensive parts need to be replaced AFTER they broke

but for the guys that want a durable engine ....heres help











spending a few days or even weeks doing careful research well before you start writing checks or pulling out a credit card, can save you thousands of dollars and months of work, understanding the difference in component quality ,correct clearances and how and why each component is supposed to perform and the potential stress its under helps you make far more intellegent choices and tends to allow you to get an engine built that far exceeds the quality and performance of the average crate engine assembly







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The Grumpy Grease Monkey mechanical engineer.
Staff member
Chevy 4 Life said:
I emailed Summit last week and they wrote back and recommended to keep my Performer intake and carb, swap to this Cam: http://www.summitracing.com/parts/cca-cl12-238-2

These Heads: http://www.summitracing.com/parts/pmx-2168/overview/make/chevrolet

All I need is Rockers, what good but cheap Roller Rockers do you guys recommend from Summit, and should I go with 1.5 or 1.6 Ratio?
rumrumm said:
Use 1.5 ratio rockers. You don't need the added stress 1.6 rockers on a street engine. I would highly advise calling CompCams and see if they would recommend the same cam as Summit did.

I'd tend to disagree, about the exclusion of the 1.6:1 rockers vs the 1.5:1 ratio rockers use, in this particular application, simply because with such a mild cam running at less than 6000RPM the vast majority of the time. the increased lift and minor increase in stress with that low lift, mild valve spring load rate is negligible compared to the minor but still useful gains in valve lift and air flow, vs the 1.5:1 rockers


graphing out the change in lift at the valve with a
1.5:1 vs 1.6:1 ratio rocker valve lift diagram would look similar too this
Rocker Arm Ratio Explained
You've heard of 1.5:1 ratio and 1.6:1 ratio rocker arms. What does that really mean? How can you make more horsepower by using the larger ratio rocker arms?

The ratio of a rocker arm refers to the amount of movement on the valve side of the rocker arm in comparison to the pushrod side. A 1.5:1 rocker arm will move a valve 1.5 times the lift of the cam, assuming all things are in proper working order. If your cam has a lift of .4 inches, multiply by 1.5 to get .6 inches of actual valve movement. With the same cam lift of .4 inches: If you do the math on a set of 1.6:1 rocker arms: Multiply 1.6 x .4 inches of cam lift. You get .64 inches of actual valve movement. Essentially, changing to a larger ratio rocker arm is the same as increasing the lift of your cam the same amount. Opening both valves further usually is a benefit in the power department as your engine is capable of moving more air and exhaust through it.


lets look at the cam & heads


at .469 max lift with a 1.5:1 ratio rocker, and a 90% port throat cross sectional area, your looking at a 1.219 square inch valve curtain

at .500 max lift with a 1.6:1 ratio rocker, and a 90% port throat cross sectional area, your looking at a 1.416 square inch valve curtain,
a roughly 16% gain in peak flow for roughly a 5-6% increase in applied peak valve spring pressure.

but whats the valve spring load rate PRESSURE?

looking at the info I can find , theres about 110lb seat and 310lb peak at .575 max lift, the valve spring load rate increases about 11 lbs from about 244 lbs at .469 lift to about 255 lbs at .500 lift or about .05%

calculate the engine increased power potential or power increase from the air flow change, shows its use of the higher ratio rockers should allow about a 15-20 hp advantage


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