i bought 291 thumpr cam (part# 11-601-8) from comp cams after it was suggested to me, but i am now unsure of whether or not it will work with what i have. I need to know my compression ratio but i don't know how to find it. I have a 454 bored .030 with trw L2377 pistons. I have an eagle steel forged crank, and i have no heads yet. will this work descently with 119cc combustion chamber and if not will it even work with 110cc chambers?

http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=486&sb=2

well, it calls for/recommends a 9.0-1 compression ratio, 2400 stall, intake, gears and headers. it states it has somewhat of a rough idle...

the pistons you indicated show here with the CC sizes for approximate comp ratio. http://store.summitracing.com/partdetail.asp?part=TRW%2DL2377F30&autoview=sku

These pistons are not compatible with Gen V or Gen VI engines. Chamfer design. Approximate compression ratios: 8.72:1 with 100.9cc, 8.36:1 with 106.9cc, 8.22:1 with 109.4cc, 7.83:1 with 116.9cc, and 7.73:1 with 119cc head.

i'd say the comp ratio is kinda low with the pistons you're choosing...

is there any way that i can get 500 ft lbs of tourque and around 450hp with these pistons and a different cam?

i doubt it.

is there any way that i can get 500 ft lbs of tourque and around 450hp with these pistons and a different cam?

OK, to elaborate a bit more than my above "I doubt it" comment...


the '70 LS6 454 was one of the biggest baddest engines back in the day. it was rated at 450HP.

i did a google search for "LS6 specs" and found this... maybe it'll help ya a little.

http://www.popularhotrodding.com/tech/0707phr_big_block_chevy/index.html


with what you have so far i really think you're reaching for the stars without a spaceship. to reach that HP level you'll need compression, minimum of 10.5-1 (my estimate) your comp ratio is just way too low to get close to what you're asking.

is there any way that i can get 500 ft lbs of tourque and around 450hp with these pistons and a different cam?


gm has a crate 454 with 8.75 comp and it makes 425hp and 500 ft lbs trq. with the right heads and cam combo you could have a real torque monster.. the head cc is going to be a major factor with those pistons..

Sounds like you already have the pistons but if you go with some rectangle port closed chamber heads that will help get your compression back up around 9 or so. It would have been better to get the pistons after you knew what heads you were going to use. Closed chamber rectangle port heads are getting kind of hard to come by and bring a pretty penny these days too. But they rock! (at least I think so!) I think that cam would really like them.

Correction even the closed chamber heads with 109cc would only get you 8.22. Not enough unless you're planning on running a blower or Turbo.

i was given the lower end and parts of the top end so i was trying to fill in the blanks but apparently im not doing too great of a job. I think i may sell my pistons and get new ones.

Additionally the statement "These pistons are not compatible with Gen V or Gen VI engines" worries me when I hear "(I) was given the lower end and parts" which are generally out of late model pick-up trucks and if it is a 1991 and up block those pistons will hit the crank as the skirts are the wrong design.

All first generation Chevrolet motors such as the SBC and particularly the BBC motors were designed to run at or above 9.8:1 compression. When the EPA pulled the plug on 11.0:1 compression motors by removing tetraethyl-lead the rated horse power was drastically effected by the loss of compression. The BBC more so than the SBC with it's more efficient (at low compression) wedge shaped combustion chamber.

The BBC was breed to be a race engine first (roundy-round competition back in 1962 belonged to Ford and Pontiac) with 11.0:1 pistons. It was redesigned in 1967 to use a semi-hemi combustion chamber which requires extremely high compression to have any hope of generating power (the 12.5:1-14.0:1 hemispherical heads are based upon WWII fighter plane engine technology and used NOS and water injection to get there, in case anybody things this is new cutting edge stuff).

Just about every BBC piston will have at least some form of a positive dome. A flat top piston will only work with the small 90 cc heads found on the 18 degree, symmetrical port, Big Duke and Big Chief heads (which once again require special pistons because of the valve angle). To fill the semi-hemi open chambered 119 cc heads you are going to need to look for a 10.4:1 piston (static) and then bleed off compression with a longer duration cam (that sound you like). To get your actual (dynamic compression) to current pump gas limits of 9.2:1. This will effect your real displacement on a 454 cubic inches which is why so many choose to build a stroker (496) because the late closing valve is converting your 454 into a 427 (nothing wrong with a 427 as I used to get over 600 horse out of my old L-88 based 427's back in the days of Sunoco 260).

That is what low compression gets you. Which is why I celebrate converting to E-85 (at 120 effective octane or 105 research octane) I can build high compression motors again: in Florida at least because we have no smog inspection. If they do not sniff for nitrates and other nitrous compounds at your tail pipe you could also.

Heads define the motor as in "It's a "Hemi", a BBC or a SBC or a Gen III. Choose your heads first then, a pick a cam to compliment the heads in your desired RPM range of operation; only then fill the holes with the correct piston (even if it means going custom) to meet your compression goals for the fuel you want to burn. That is how you build for horse power.

Big Dave

As stated above, pick the heads you want first. Then match the cam and pistons for the perfect combination. Static compression makes absolutely no difference of whether or not it will run on pump gas. You need to be worried about dynamic compression ratio. A dynamic compression ratio of 8:1 is perfect for a high performance street motor. The motor will be a slouch if it is in the high 6:1 to low 7:1 range. My 406 I'm currently building for my 67 Camaro is going to have almost 11:1 static compression. However, the dynamic is going to be roughly 8.16:1. What kind of budget do you have for the motor? You could build a 600 HP pump gas 454 for a reasonable price. I'll be putting out close to 550 with my setup. This is a good website that explains dynamic compression in detail. http://www.empirenet.com/pkelley2/DynamicCR.html There is also a compression ratio calculator on that site you can download. Comp Cams has an engine dyno program you can download for free that will make the cam selection for you based on your engine build and use for the motor. It even numbers them from best to worst. Good luck:thumbsup:

But if you want to run on Kerosene, my 1947 John Deere model M has a whopping 6.0:1 dynamic compression. Two cylinders of 56.5 cubic inches each with little need for a spark plug (they usually oil foul, and I only clean them to start it). Yes sir, it rips to about 1600 RPM, idles at 20 RPM.

If you build a motor without enough compression to burn gasoline you will discover that getting tractor fuel (light weight kerosene) is tough.

Big Dave

would these heads work sufficiently with what i have http://store.summitracing.com/partdetail.asp?autofilter=1&part=EDL-60499&N=700+400065+4294908216+4294840133+4294867081+4294 784388+115&autoview=sku

It will give approximately 8.7:1 CR or would i benefit from these heads and camming down?

I think these would be an excellent choice head for your application and here are the flow numbers from Edelbrock. They are very respectable as compared to some others I compared to with larger intake runners such as World's Merlin Cast Iron and Aluminum, better than GM cast iron, comparable to Brodix 2Plus and others. Would give you very close to the compression your cam is wanting and should make good power for you. It would be cheaper however to buy a set of pistons but if you have to buy heads anyway these would be an excellent choice and good quality to boot. They are sold individually though and not as a pair so be prepared to drop $1839 on a pair but not bad for BBC Heads when Canfields outdated price is over $2100 and AFR's run $2400 to well over $3k. I like 'em! Good Choice!
FLOW DATA @ 28" H2O CYLINDER HEADS
#60499, #61459 (.100")74-73/71 (.200")143-143/128 (.300")207-208/153 (.400")250-251/178 (.500")284-284/200 (.600")309-299/218 –

Those are excellent heads for your flat top pistons. They will get you to your 450 horse goal easily with the right cam (you are looking for lift not a long duration cam as BBC hydraulic rollers are very, very heavy from the spring's point of view. So you will be all done making power by 5,800 RPM so choose your upper RPM to be there or below).

Note the very last line that requires special pistons. That statement will apply if you buy pistons with a dome to build more compression later (compression is free horse power adds 3% for every point you build).

Big Dave

yay finally some good news, haha. does the 11-601-8 cam sound like it will work well with these heads? I have an edelbrock performer 2-o and an 800cfm rochester carb. what kind of numbers will i have here? Im building this engine for tourque more than power.

This is what CompCams says, "High performance street/ strip, needs 9:1 CR, 2400+ stall, intake, gears, and headers, rough idle". Let us break it down a bit to see what they are telling you.

High performance-street/strip means an RPM operating range of 2200 to 5800 RPM which is perfect for a BBC running a hydraulic roller.

Advertised duration is advertising hype it means nothing and should be ignored. The actual duration @ .050'': Intake - 235°, Exhaust - 249° is what you should consider. These numbers are really big for the street but doable if you like a "rough idle", but it will have very little bottom end torque.

Valve Lift: Intake - 0.558", Exhaust - 0.542" is what you are looking for to get the air in and out.

Lobe Sep. Angle: 107° is extremely tight and will cause two problems it will need "gears" because it will have no bottom end torque, and it will require a 2400+ stall torque converter because it will have no bottom end torque. By the way bottom end torque is what gets your car to actually move which is only important if you want to drive it.

Finally intake and headers will be required to get the air in and out of any motor; and should be part of every one's build plans except for a concours restoration. I would recommend the Edelbrock RPM Air-Gap 2-O (1500-6500 rpm) non-EGR manifold #7561 with a Rochester to Holley adapter but it might not fit under the hood.

It is obvious tome that you are after a rough idle. Why; because everyone wants to sound just like their favorite Pro Stock car. But you have to ask yourself. Why do you suppose they trailer race cars to the track instead of drive them? It is because race cars have no bottom end torque. If you tried to drive one on the street (ignoring the Lenco planetary transmission problems) you would probably stall it at the first stop light.

Yes they do have incredible 60 foot times (with 500+ cubes making 2,600 horse power on gasoline turning 5.38 rear cogs they should); but only when you leave the line at 8,600 RPM. Most cops take a real dim view of that driving technique.

You can not have a "Rough Idle" and drivability. If this is a show car that lives on a trailer fine it will work.

Here are some Chevrolet factory hot rod cam specs:
L-88 427 430 HP Solid flat tappet 354° int 0.562" int
(Advertised) part # 3925535 360° exh 0.584" exh
Duration @ .050 Int./Exh. 264° / 269° Degree Lobe Separation 112°
Lash Hot Int./Exh. .024 .026 RPM operation 4400-7000
Open/Close @.050" Cam Lift Int./Exh. 24**** 60 70.5** 18.5

ZL-1 427 Solid flat tappet 262° int 0.580" int
@0.050 lift part # 3959180 273° exh 0.620" exh
Lobe separation angle 110°, lobe centerline 106°/114°
Intake opens/close 52 BTC/95 ABC, Exhaust 94 BBC/59ATC

LS6 454 450 HP solid flat tappet 242° int 0.496" Int
@0.050 lift 114° LBA 242° exh 0.492" exh
part number (3904362)

LS7 454 460 HP solid flat tappet valve lash 0.024" Int
Same cam as ZL-1 " " 0.026" Exh
Discontinued part number (3959180)
duration at lash point (advertised) 327° int/333° exh

502HO 450 HP Hyd Roller Cam 211° int 0.510" Int
@0.050 lift 112° LBA 230° exh 0.540" exh
part number (24502611)

ZZ502 502 HP Hyd Roller Cam 224° int 0.527" Int
@0.050 lift 110° LBA 234° exh 0.544" exh
part number (12366543)

I don't know if you have heard a ZZ502 idle but it thumps and yet it has a 224° intake duration and a 110° Lobe Separation Angle.

Duration and LSA determine the engines operating range and how rough the idle is. By the way, the idle is rough because both valves are open (off their seat) at the same time. It is really hard to build torque with both valves open as the air fuel mixture is leaking out both the intake (reversion) and the exhaust (wasted gas) at the same time. It does that because air is a fluid and it takes time to get it moving so they hold the valves open longer to get the air in and out at high RPM where you make the most horsepower and sacrifice drivability to obtain it.

In my youth I drove an L-88 427 Baldwin Motion Phase III 1968 Camaro on the street (motor was built by Don Yenko) with 5.13 rear cogs (ran consistent 10 teens back in 1971). I also had to get out of car and push it through the bank teller lines because I couldn't get it idle low enough to be heard by the teller or hold my place in line with out running into the car ahead of me. I also had to cruise on the interstate at 45-50 mph. So it can be done.

Big Dave

Go with a Potiac 455 block bore it out to 4.211 and stroke it to 4.5" and have your self a killer 501 cid engine that will make enough torque to pull a brick outhouse off its foundation. :D Just make sure you install a lifter brace and a rev limiter at about 5500 RPM.

Had to throw that out as the Poncho guy on the site! :beers:

yeah, but we still love ya... yer a GM brutha :thumbsup: ;)

It is obvious tome that you are after a rough idle. Why; because everyone wants to sound just like their favorite Pro Stock car. But you have to ask yourself. Why do you suppose they trailer race cars to the track instead of drive them? It is because race cars have no bottom end torque.

Is that why they trailer them? I thought it was because it takes takes them 2 gallons of fuel to drive a mile!:thumbsup:

Naw!!! 110 octane gas isn't gas at all; it is a drum full of chemicals, that's why it's so cheap. Unfourtunately we get all of our chemicals now from that land on the far side of the sea, so we can not get what we want when we want it, at a price we can afford that is why they trailer them.

Actually you have it bassackwards, it is closer to two gallons to the mile.

Big Dave

Isn't that what he said?????:confused:

Yea, isnt that what i said? :confused:

Ive said right from the start of this build that im going for tourque, but this is my first build and Im learning a tonne! Can you suggest a good cam for me to go with to get great tourque and still respectable power even with the lower compression ratio that i will have? Also what will the main difference between the intakes be? I am on a pretty tight budget (im 19 and a second year apprentice plumber) and would like to use the intake i have now and possibly upgrade it later.

Ok Kevan, I created an AirFlow File in Desktop Dyno for the Edelbrock Performer 100cc semi closed chamber heads 60499 from the advertised Data Edelbrock provided. With those heads and your flat top pistons @ 8.7:1 CR, dual plane performer intake, 800cfm carb, using your 291 camshaft it estimates with this combination you could make 457 HP at 5800-6000rpm and 470 lb/ft TQ at 4500. The TQ stumbles a little on the bottom and doesn't really come on until about 3000 and rises fair until about 4500 where it hits peak.

Now this is a classic example of how MORE isn't always better, because I used the exact same combo and same airflow file for the Edelbrock heads and dropped down to the 11-600-8 (283 Thumpr Cam) and it out performs the 291 hands down. The TQ curve kicks in much sooner and is much stronger with already 450 lb/ft at 3000 rpm staying at 472 from 3500, peaking at 487 at 4500 and holding 472 all the way through 5000 rpm before dropping down to 440 at 5500. Peak HP occured at 5500 at 465 and held to 461 through 6000 rpm before falling off. Much better overall performance for the combo we've discussed. I'd see about exchanging it for the 283 Thumpr! I've tried to do Print Screen shots of the charts and graph's from my desktop dyno program but it does't support that feature so I just have to try and explain to you what I'm seeing. :cool:

sweet thanks a lot I actually have that cam on summit racing in another window right now and was just about to ask about it. I wasn't sure if it was gonna be too much cam.

Yea, isnt that what i said? :confused:

Yup I read it wrong (again). Sorry for jumping to the wrong delusion.

My afore mentioned L-88 had twin Holley 660 center squirts on a large plenum Edelbrock tunnel ram and got two gallons to the mile every where I drove. But back then gas was only 63 cents a gallon for racing fuel (I was running 13.4:1 compression). Only thing left of that set up is my Mallory dual point four lobe distributor and the 427 emblems I kept when I sold the car.

Big Dave

Ah yes, sweet memories................LOL My teenage memories are of a 1963 Ford Pickup truck short wide bed with 3 in the tree and a 223 six cylinder in which I split the manifold and put dual exhaust on it. When I drove it through the mountains in Oklahoma (yes Southeastern Oklahoma has some mountains as the Ozarks run out of Arkansas into SE Oklahoma) I quickly realized that little 6 banger just didn't have enough oooomph to get up those hills very well so at 16 years old I performed my first engine swap with a 352 that I got from a friend who was sticking a 460 in his pickup (yes I've owned a couple of Fords over the years but that was before I saw the light.............LOL) There I was at the end of 6 mile lane working after school with the help of the local gas station guy there and we built custom motor mounts and I finished up the exhaust with flex pipe and off I went. Had a Motorcraft Holley 600 4 bbl on it and with the low rear geared 6 cylinder rear end in it, it was actually pretty quick. She wasn't for much on the top end but she could scoot pretty darn good. I will never forget the time I raced a really nice 67 Chevy pickup with a mildly built 327/automatic with lots of pretty goodies you know the cam, intake, valve covers carb etc. and my little 63 Ford with the phillips screwdriver for a shifter because the shift collars were notorious for breaking on those old trucks and my flexpipes.......LOL, jumped out of the hole on that ol' boy and left him at the line like there was no tomorrow, I held the lead all the way till right at the very end he finally caught up with me and beat me by about 1 to 1 1/2 lengths but I was pretty proud of my ol' Ford that day because the other guy really had a nice motor and all I had was my little 352 3 speed. What fun back in the day. Then there was my '71 Trans Am 455HO. But that's another story.................. ;)