antweave

Engine is newly built about 2 years ago. But this is a frame on restoration so the car just sits in the shop since the engine being built. My question is would it be a good idea to put a mild cam in just to get a little thumping sound. The engine is basically stock .30 over with stock heads and edelbrock hi-rise intake and carb. I just want a little noise

cutlassefi

Sure.

Uhh, we really need a whole lot more info than what you posted, C'mon help us out.

svnt442

Is it a 260? 455? Hell..a Honda 1.8? We don't know.

antweave

Sorry it is a stock 1970 stock 455 .30 over and a few aftermarket eternal parts like intake and carb

s i 442

Put in the comp cams Magnum 480/280.
And the info he gave other than the engine size is enough to pick a cam or it is for me anyway.

47 Convertible

________________________________
IMHO, No. It is not a good idea.

A "mild cam" isn't going to give you the thump.

You need a more radical grind camshaft to get "thump." Thump is the by-product of an engine choking on its own exhaust gases at idle because of increased valve timing overlap. Before the advent of variable valve timing (VVT) it was a gross inefficiency at low rpm that owners of performance engines put up with to get the extra power at higher rpms. Unfortunately 'thump' alone has become symbolic of high performance.

But what the heck, it is your money and you've already said it is about image. Just don't accept any race challenges the thump might invite.

Apologies in advance if any fans of thump are offended by my remarks. Thump for ego/image sake just doesn't seem serious or worthwhile.

cutlassefi

That's not really true. What you're hearing is actually the combustion process. You can have a whole bunch of overlap but if you don't have any cylinder pressure then consequently you won't hear squat. Ever hear a Prostock car? They idle at 800 and sound like your grandmas car without any mufflers, have 12.0:1ish compression but real big cams so consequently almost no low end cylinder pressure. That's why you don't hear them as much, they don't build much cylinder pressure at low rpms. You need compression/cylinder pressure in order to hear a "performance" cam. You're hearing the "bang".

s i 442

Thats strange, I had a 480/288 Crane cam in my stock 350 4 barrel Olds and it loped and I was out running cars with big blocks?
Some people just can't handle a lopey cam because they don't know how to tune an engine to run right in the first place. Lopey cam= scary place!

rootney

If anyone could give a real life example of a 455 build (comp. ratio, cam lift./dur, intake, carb) that gives a good lump, can smoke em up, and lives on pump gas, I would love to have the benefit of your experience.
I will be starting with a 455 in good shape and I'm up for spending moderate bucks for pistons, cam and valve train parts (I have "C" iron heads). I'd like some guidence on how high can I push the comp. ratio and what cam grind to use.
Can you retard the timing electronically to manage ping with pump gas and advance it when using high octane fuel?

George

svnt442

I put together a 455 about 20 years ago using TRW (now Speed Pro) L2323 .030 pistons (not forged, but only forged are available now), rebuilt J heads with no other work done to them and stock rockers and bridges, Performer intake, Edelbrock 1407 carb, an Erson JB100 camshaft installed 4° advanced and Flowtech headers through a flowmaster 2½" exhaust system.
specs:
JB100camspecs_zpsd5d345ef.jpg

It was in a 1970 Cutlass S with a TH400 using a B&M holeshot torque converter (adv 2500 rpm stall) and a 2.56 posi. It had a nice rumble at idle and 300' - 400' burnouts were easy peasy.

47 Convertible

______________________________

Receipt for rebuild of my '68 455 with small valve C heads in attached thumbnails. I would call it a budget build but think it will have added enough torque and hp to keep me happy and my 47 convertible won't be embarrassed too often. Cam is Comp Cams XE 268H flat tappet hydraulic. Comp Cams says it will have a slightly rough idle.

What is not on the build sheet: Sanderson shorty headers with ceramic coating, Edelbrock Performer Intake, original Q-Jet rebuilt and modified by Stans for the modified engine, later Olds HEI rebuilt and setup for modified engine, blocked heat crossover.

The caveat is the engine is still waiting for me to finish enough other stuff on the car to install it and the beefed up 700R4. Torque converter has also been strengthened but has stock stall. Car hobby moves along kinda slow due to financial constraints but it is getting there.

svnt442

Jerry Brown?!?!? Aren't you our governor?

47 Convertible

Nope. If I was I'd probably be having the State Motor Pool finish my project and I'd be behind the wheel a heck of a lot quicker than I will be up here in wet Western Washington State. Actually I like the build as much as the driving so it is not a bad thing that it is moving along slowly.

rootney

Ok to get my build started, for the bottom end (piston selection), can I shoot for 10 or 10.5:1 comp ratio with iron "C" heads without detonation issues on pump gas. I'd really appreciate some comments from guys who have been driving a higher comp ratio 455.

Thanks again,
George

marlar98

Maybe, maybe not. Depends on what your dynamic compression ratio is. Basically, you have to factor in the size of your cam. Bigger cams tend to bleed off more cylinder pressure which could allow higher static compression motors opperate without detonation. Cylinder head quinch and your altitude plays a part on how much compression you can run on pumped gas as well.

rootney

Thanks, I was headed toward higher comp. and longer duration cam and if I end up in the area of needing higher octane or retarding timing when on 93 gas, I guess I can live with that.
I just don't want to miss the runway and land in the weeds with something I'll hate.
So you believe a 10 or 10.5:1 by the piston selection chart is ok to start with, and then matched with a wider duration cam?
Thx,

George

Lee_A

George, are you going to be competitively racing this car, or will you mainly be driving on the street? Unless you need to make as much power as possible, I suggest you back on the compression ratio - more like 9.5:1, maybe even a tad less.

Many years ago, my Cutlass had an iron headed 455, CompCam 270 Magnum, Performer, headers, mildly ported G's, and about 10.0. LOTS of lowend, ran some 13.2's with 3.23 gears and a very mild converter. Sometimes it would ping, other times it wouldn't.

I also had a Firebird with a 455 Pontiac. It had an UltraDyne 288/296 (231/239 @ .050") on a 108 LSA, iron heads, just a tad under 10.0:1. That motor NEVER experienced detonation. BUT, it had a looser converter (about 3300), 3.42 gears, the pistons & combustion chambers had been massaged to round over all sharp edges, and I applied a thermal barrier coating to the pistons. It also had a very good cooling system. That car ran as quick as 11.27 @ 119.7, all motor & pump gas. [EDIT: It ran 11.5's at 116 with the 288/296 cam, the 11.2's happened with a slightly larger solid lifter cam - pardon my memory lapse!]

The higher the compression ratio, the larger the cam that will be required to run on pump gas. Bigger cams start trading lower-rpm power for more upper-rpm power - you can end up with a motor that makes a bunch of hp, but is so weak off-idle that it will be a dog off the line. In order to get the big-cam motor off the line (and to allow it to idle while in-gear) you have to run a loose (high stall) torque converter, and those can make the car miserable to drive on the street.

A 455 with about 9.25:1 and a cam like the one SVNT442 mentions will smoke the tires with ease, won't need a huge stall, and will be fun to drive around.

I recently helped a guy with a 400 Pontiac. I was basically a consultant for him, and also designed & degreed the camshaft, and helped him put the pieces together. One source provided the ported heads, another supplied the short block. We got the chamber volumes from the head porter, and the owner told these to the shortblock supplier so that he could build it to give us the compression ratio we wanted. Long-story cut short - the shortblock supplier got WAYYYYYY behind (delivery was about 10 weeks LATE) and didn't look at his notes. The pistons he used only gave us a bit over 8.0:1 (our target was 9.25)!! Due to shipping costs to return the motor, and the owners desire to actually drive the car, we went ahead and put it together. It will STILL smoke the tires, runs surprisingly well, and has no problem burning cheap gas :-)

rootney

Lee,
Just what I was looking for was a few real life examples.
Any more out there?
Thx,

George

68442CONVERTCO

Hi George,



Here's my build:



1968 455 block 40 over

Keith Black hyper. 277 pistons 10:1 CR

Comp Cams XE268H

Stock C heads

stamped roller rockers

guide plates

hardened push rods

Hooker 3902 headers

Carter AFB Competition 750 CFM

Edelbrock Performer intake

Ebay HEI

Dyno Results: 490 TQ 360 HP



Has a slight lope at idle 800 RPM.

68442CONVERTCO

It was dynoed on Pump gas @ 4658 feet.

I'm going to run 91 octane with 32oz. Torco Acclerator per 20 Gals. which should bump it up to 95 octane.

rootney

Tony,

Thanks. Your'e build is very close to what I'm setting sights on.
I appreciate the reply.

Thx,

George

jfb

I DID NOT READ ALL THE POSTS BUT CALL ENGLE CAMS AND GET THE PERFORMANCE ALSO BUDDY. i LOVE MY SOUND BUT I ALSO LOVE POWER AND HAVE BOTH.

455man

I've got a 455 .060 over with Keith Black hyper pistons, 9.7:1 compression, pocket ported E heads, crossovers welded shut and exhaust ports welded flush, flowtech headers into 2 1/2 exhaust 280H comp cam .490 @ 230. Performer intake with quadrajet. Right now, stock stall in a TH400 and open 2.73 gears. On 87 octane I have to back down the timing to 27 degrees. spins the single tire way too easy. Runs good up top. I'll put a posi 3.73 in with a 200R4 and about a 2300 stall eventually.