Hesitating over starting a 455 build for a manual transmission car. It'll have 3x2, ported iron B heads, headers, a/c, PS, PB. Is a 235/241 cam on a 114 LSA too big for
a low compression .030 over 455? Will be using the forged TRWs with the big dish for a sub 9:1 compression ratio. Suppose I advance the cam 4 degrees and use Rhoads lifters? The trans is a Richmond Gear 5 speed and there'll be 3.23s out back. 5th is OD. Use will be cruising, touring.

 

Exactly which cam are you looking at ?

 

Since you have overdrive, you can put more gear in the car, at least 4.10 but the cam will not smooth out until over 2000 rpm.

 

what ratio is 1st and 2nd in the Richmond? overall ratios when in 1st and 2nd mean a lot

 

You might not have enough vacuum for your power brakes to operate properly. I have a 30 over low compression 455 . It had a similar cam that I changed out for a much smaller one and increased my vacuum and drivability. I had 3:91 gears, but not enough compression to make good power.

 

1st gear in the 5 speed is like 3:1. Thank you everyone for your contributions. I think I should probably go down to maybe 225/235 on a 112 or 114.
I want to use the 3.23s because its a freshly rebuilt 10bolt and I want very low highway rpms. I had 2.56s in a 455 Trans Am at one time. Its quieter, better mpg (range) and cooler as a 455 revving at 3000 all the time gets hot here in Florida.

 

For what it's worth, I'm running a well tuned 226/230 @ .050, with 110 LSA, and there is not enough vacuum generated to properly operate front discs without a vacuum canister or pump.

 

In an engine with 55 fewer cubic inches.

 

your overall first ratio is 9.69

that’s more than enough for a low compression big block to pull hard out of the hole with that cam. I would out it in at +6. it’s a wide LSA cam..it’ll idle very smooth

you have a dual plane intake…it’ll make good vacuum.

to put your combo into perspective…you have more overall first gear ratio, TQ multiplication , than a Muncie close ratio with 4:33 gears which is only 9.53

 

No such thing as too much cam, just not enough engine!!!! 😁

 

what intake manifold, cubic inch and compression?

 

how do you know that?

from his name?

 

'67 400ci E block, professionally ported and polished C heads, Edelbrock 2151 Performer, original flat top pistons, 10.5 compression using copper gaskets

 

Hmmm, how is that possible?
My Dyno mule is a 350 with a 222/228@.050 roller on a 110 with 9.5:1 and it makes plenty of vacuum for power brakes.
Hmmmmm.

 

not even comparable

 

Mark - I don't know a 1/10th of what many of you guys know, I just know the components in the motor/driveline of my car. I have the cam card. Did you see my post #13 above? Car starts easily and runs extremely strong. Idle is very lopey, but doesn't struggle to maintain idle. I don't own a vacuum gauge, but the motor seems to run flawlessly. Former owner said despite optimal tune, it would not generate enough vacuum to operate the front disc's without a collector. I didn't know enough then to question him on it, I still don't.

 

Gotcha.

 

How do you test for idle vacuum on your dyno?

 

Same way anyone does, load no load.

 

when you load it to simulate at idle in gear ..what change have you seen on the vac reading on one of your engines with a healthy cam?

 

A healthy cam or my mule, which imo is fairly mild?

 

whatever you want to talk about..what’s the drop in idle vac.

What’s the biggest drop you’ve seen?

 

Typically a few inches. I put about 40lbft of load against it. That seems to be pretty close in most cases.

 

I’ve seen the same, which can make or break the cam for power brakes in an automatic app

depending on how tight the converter is.

 

Curious: how would that affect vacuum for power brakes?

 

a stock type tight converter will load the motor more at idle which will reduce idle vac.

if the cam makes borderline idle vac in neutral like say 12 or 13”, it may drop to 10” or less when in gear. I’ve found anything less than about 11” idle in gear is about the limit for factory pwr brake boosters to still work good

 

So a tight converter won't actually change vacuum @ a given RPM (which is where I thought you were going), it'll just reduce idle RPM altogether when put in gear thereby reducing vacuum.

Got it, thanks.