Hello to all you Big Block guys. I know there are a lot of BBC combos in the archives of this board. I ran a search and spent a couple nights looking for ideas. The only thing I'm worried about is "pump gas" seems to mean 91-93 octane for you guys. To me, pump gas is 87-89 octane. Prices are high here in California, and some stations around here don't even carry 91 octane anymore. Nobody seems to be buying it anymore, and when it is around, I hear it is stale. My brother now runs 89 in his '01 Malibu because he says the 91 stuff has been iffy lately, and he REALLY didn't like having to run 89 for some reason.

As some of you know, my brother has a '69 Nova we plan to drop a 454 into sometime in the next year or year and a half.

He wants somwhere between 425HP and 450HP, and I think 425HP will get the lightweight nova moving just fine.

We're looking to re-use the 781 heads that are already on the motor. Have a good valve job done, probably use stock-diameter valves, will do bigger if that's what is needed.

Hopefully the block/crank/rods will be usable, if so, we would be re-using it all. Block bored minimum amount. Rods re-sized with good bolts installed. Crank ground/polised minimum as needed. New bearings everywhere, of course.

The pistons/compression ratio are still undecided on, because we don't know what it'll take to meet our goal on 87 octane. But we would like to use a budget Forged piston.

We'll probably use a windage tray/crank scraper also, they're relatively cheap for the job they do.

We're doing all this on a budget, it isn't specified but "cheap as possible without building a wreck" is our motto. So we have to stick to off-the-shelf parts as far as cam/valvetrain. Looking to use a solid flat tappet cam.

We're also thinking of using a 800cfm Qjet carb we have already to get the engine running an until we can afford a different carb.

We're thinking of using an RPM manifold or Weiand Stealth, whatever is most common at swapmeets.

Cheapest full length headers (Summit?), 2.5in exhaust, dumps before rear end.

The car is a stock-bodied 1969 Nova, No options except power disk brakes and a new 4-row radiator(no AC, radio, bench seat, etc). Bolt-on CE sub-frame connectors. 200 pound driver.

The rest of the drivetrain will likely be a rebuilt TH350 w/shift kit and cooler, stock driveshaft if re-usable, 3.73/posi 12bolt rear, Drag radials or slicks small enough to fit in stock wheel wells.

Lookin' for at least 12's with a rookie driver.

Just need some help to get on the right path, just some general info on CR range we should shoot for, size of cam needed in general, what kind/size of valves to run, etc.

I don't know squat about big blocks, so I just need to be pointed in the right direction so I can start doing my own research.

87-89octane/12s/budget build are the main requirements.

Thanks in advance.

Enrique, have you got any info from Pat Kelley's website on what effective compression ratio allows 87 octane? 7.2-7.5 maybe? Then pick a cam based on operating range.Using that cam's valve event timing in the effective compression calculation, back into your static compression ratio. It won't be perfect, but will net you a motor in the intended rpm range and 87 octane capability.

Off the cuff, a 8.8 to 9.1 454with a Comp270S should run on 87. Some of the 'cheap'generic grinds are 114LSA, which would want maybe 9.5:1

There is plenty of info here in this forum to achieve your goals.Small dome piston (.095-.100) with your 781's will get you 8.5 to 9.0 to 1 depending on deck height,final combustion chamber size,head gasket thickness,etc.
As Gene mentioned,the Comp 270H will certainly work,or even a small solid.You have 3.73's too,which will certainly help with your 12 second goal.

Chris, I was thinking the 270S which is a really small 224/224 on a 110 solid cam. I've never run calc's on a 9:1 454 with a small solid cam. Peak HP at 5300? Maybe the XS268 is closer to 5500.(230/236) and the XS274 with 236/242, which should make peak HP close to 6000.

So Enrique, you see the 'solution' as a system of simultaneous equations, cam powerband/rpm range ( set by gearing/tire dia and stall), and static compression.

Seems like with 3.73s in back, you might want just a bit more squeeze, like 9.3-9.5:1 and a cam similar to the XS274.

First thing I would do is set the operating band by using the current gearing ratios/tire dia and max rpm crossing the 1320 stripe, back into a cam that provides the 454 given its smaller heads the correct rpm band ( with those ovals I'd like to see you move into a decent sized bumpstick), and then back into your desired final CR. Try and keep the LSA short, duration in the 230 range ( solid), and CR in the 9.25:1 range.

Fancy juggling is another way to look at it. Simultaneous equations implies there is a 'correct' solution. No, there are a 'range of good solutions'. HPH.

It 'aint' rocket science.

Gene, Pat's site doesn't have anything for 87-89 octane. At the bottom of the page it asks for people running 87-89 octane successfully to email him so that he can compile some estimates.

Chris, Thanks for your help.

So I'm guessing a solid cam in the range of 220-230degrees @ .050 lift would be in the area of what I'm looking for? Would 108LSA be too tight for power brakes?

I like what Isky has in their Z-66 solid: .520/.520 268/268 228/228 108LSA

Wiseco, SRP, and TRW all have some (21-23cc) dome pistons that would bring the CR to about 9.6-7:1 with a .040" quench.

Hmmmm, lots of new stuff to learn.

Thanks Gene,

Actually, the gearing isn't set yet. But I figure since this is his "hot rod" and not a daily driver by any means (but will see lots of street cruising, hence the 87octane), 3.55-4.10 is the gear range we should shoot for.

It'd also be nice to keep the engine under 6000rpm as he wants it to be a long-lasting engine.

He wants to get pretty deep into the 12s, although I think he doesn't realize how fast that really is. But to each his own.

I just get a little confused because of the weight factor, I could help him build a copy of one of the many combos on TC and predict how fast his car would run if it was a 3800 pound Chevelle, but it seems like the Nova would be somewhere in the 34-3500 range?

I would think that an 11-second timeslip would be reasonably easy to achieve. We ran a mild 454 in a 71 Nova to some 11.20's a few years back - nothing special. It's not the peak horsepower you want to focus on, it's the torque in the range you are going to operate the engine.

Not to be the naysayer here, but motor is only a fraction of it. We all have motors in cars that should be running 11.XX or 12.XX or 13.XX but wind up running 12.XX, 13.XX or 14.XX. Tell you first hand, 12.XX, especially a low 12 will take some good chassis tuning, although a Nova is probably easier to deal with than a Chevelle body.

Just copy our GM crate 454 425hp with your heads and you will have a good combo!! :D

..another thing..when you run low compression,you want to have a steeper gear (3.55-3.73)

Thought about that already, LOL. Pretty sure that crate engine has a roller cam though, no?

Chris, why the steeper gears when running low compression? Steeper means higher or lower numerically?

Just go a tad bit steeper but similar on specs or go exact since you have ovals you'll have more power anyway. A roller adds about 20-25 more HP than a flat tappet of equal specs but if you go over but near the same specs it should eqaul out. But like I said you have the ovals which make up a bunch right there!! :D

I built my 454 with 87 in mind, about 8.75:1 compression and a CompCams XE 4x4 270 cam. I used Merlin heads which have 120cc chambers - same as 718's and a small dome pisto.n

-Ryan

My 454 runs happily on 89 octane. 9.5:1 compression with aluminum heads. I guess EFI helps as I can precisely control fuel and spark. Running lots of advance and no pinging. 40 dgr at 1500 rpm cruise. 48 dgr @ 2500 rpm cruise. Cam is a small hydroller, 224/230 on a 114 LSA.

who can tell me what pat's site is.

Where does one come up with the idea that compression is used for rear gear tuning? I've never heard of anyone doing that.

You optimize your gearing based on the power your engine has as well as the set up of the car to go through the traps at your optimum RPM's regardless of your compression.

If your engine makes peak power at a given RPM, then your gearing should be based on that(and tire size, car weight,etc., NOT what the engines compression is. Gearing is used for torque multiplication not compression multiplication.

Get your engine done see where it like it's power and then set up your rear end.

I have a feeling that the Isky Z-66 solid cam along with a set of old closed chambered large ovals and low domed pistons such that you can make about 9.25 to 9.5 to 1 CR, should do nicely on the low priced gas.. Use the 800 cfm carb. you want along with a cheap set of 1.75" four tube long headers..

The closed chambered heads are dirtier, smog-wise, then opens but are less knock sensitive if not mistaken..

pdq67

Originally posted by mfsr:
Where does one come up with the idea that compression is used for rear gear tuning? I've never heard of anyone doing that..low compression needs an equalizer,especially if he wants to run in the 12's
A low compression combo needs all the help it can get.Car Craft did a great article years ago on how to make a low compression combo run well.
The methods aren't what you think..a larger cam (for the compression anyway) in an 8.5 to 1 with plenty of gear and some convertor is what was suggested.Remember,its the whole combo that matters..and gear certainly helps.
I highly doubt my motor build with 8.5 to 1 comression vs. my current 10.5 to 1 would be capable of running low 13's/high 12's with 2.56's

Power is Power regardless of what your compression is. If you have 2 identical power curves, the car doesn't care what the CR is. All the car cares about is the power at the flywheel going to the rear end. Hence torque multiplication.

You need to set up your rear for the power band NOT the CR, dynamic or static.

Compression has very little to do with overall power gains as well. The % is miniscule compared to other modifications.

Did Car Craft run a side by side test under the exact same conditions? Did they even build a car to try it or was it just a bunch of what if theories like most of those magazines do?

Okay guys, lets not get our panties in a bunch here.

I think what Chris means is that the lower the CR, the lower the output of the engine, typically, when compared to an engine of equal size and basic design. So the deeper gears will help accelerate the engine faster, the worst thing you could do to an already low-output engine would be to put bonneville gears in the rear. Trust me, I run an 8.3:1 355 with 2.73 gears in a 3800ish pound car, and it is a dog compared to my friend's car that also has a similar 8.3:1 355 in a 3800ish pound car, and his car with 3.36 gears eats mine alive at the track.

mfsr, you're totally correct, you should gear according to your power output. But sometimes the power output doesn't vary too much across the RPM range so you gear it so that it uses the whole RPM range where it makes power, rather than worry about gear to exact peak power RPM.

Paul, we have to stick with the open chambers we already have. I totally understand why closed chambers and a flat top/small dome are preferred when using the same CR, but BBC stuff isn't that easy to come by, and the closed chamber stuff brings more money because they came on earlier, more nostalgic engines, so people want money for them. Plus, the 781s are really good heads as far as stock GM pieces go.

I think I'm going to shoot for 9.5:1 to 9.7:1, something like the z-66 cam or some other similar solid, and gear it accordingly. We'll see if it runs on 87 or not. I just don't want to get stuck having to do a piston swap to raise the compression later when the "more power, scotty" bug bites him. I'd rather be able to mill a little off the heads.

Thanks everyone for the help so far.

Whatever mfsr smile.gif
Answer me this,is an 8.0-8.5 454 with my cam and 2.56's going to run the same number as my combo?
I don't think so! If it did,building motors would certainly be cheaper!

Originally posted by Slowpoke70:
I think what Chris means is that the lower the CR, the lower the output of the engine, typically, when compared to an engine of equal size and basic design. So the deeper gears will help accelerate the engine faster, the worst thing you could do to an already low-output engine would be to put bonneville gears in the rear. Trust me, I run an 8.3:1 355 with 2.73 gears in a 3800ish pound car, and it is a dog compared to my friend's car that also has a similar 8.3:1 355 in a 3800ish pound car, and his car with 3.36 gears eats mine alive at the track.
Enrique,thats exactly what I was trying to say.
Learned about this a long time ago with some low compression Olds 455's in a friends 442

heres a simple bbc i built some years back....

completely stock 100,000 plus bottom end 454
removed the heads oval ports of normal size, cleaned up a few places in the runners and bowls believe me there was just a few hours of this clean up nothing like a full port, regrind the stock valves put a 20 degree back cut on them and 3 angle valve job slapped on some hd 427 springs, ground down the tops of the guides with a grinder....lol for retainer clearence
took the stock cam out. put a comp cam 305 hyd . in there and felpro head gaskets, used some roller tip rockers that had laying around , put on a victor jr intake a 850 holley.

with 4.56 gears out back and a 4000 stall it ran 12.80's with open headers....125 hp nitrous pushed it to 11.80's.

nothing fancy ran the cr@p out of it until the stock oil pump pick up fell off.....no oil pressure...... never figured the compression ...didnt care at the time cause i was just building a cheap fun motor...the heads where open chambered so the compression would have been in the 8.0 to 1 range somewhere.


granted my 414 has smaller bore/shorter stroke.....but with 10.5 to 1 true compression ratio...with a 233/239 @ .050 cam and even the rhoads lifters there is no ping or knock on 87 octane fuel with my 2.73 gears.......this engine could be built the same with a 454 and you would be seriously in the low 12's with a very mild combo.....with 107+ mph out of my 414ci its not a slug.....in a 3900 lbs car.......just imagine what a 454 would be like with the extra cubes...

O.K. 4 speed, read my other posts really slowly.

I was not comparing compression, I was comparing power curves.

Do you really think that 2 motors with IDENTICAL power, but with 2 different CR are going to neccesitate completely different rear end set ups?

""..another thing..when you run low compression,you want to have a steeper gear (3.55-3.73)""

I would never equate my rear end gears to what my compression is, but what my power/RPM band is.

Rob

I would never equate my rear end gears to what my compression is, but what my power/RPM band is. compression can directly affect the power/rpm band.

for example

a 8:1 454 with a 280 advertised cam will make less low speed torque than a 10:1 454 with the same cam. the 10:1 engine will accelerate faster and will peform better in the lower rpms even though the two engines may make similar HP numbers.

the 8:1 engine will need more gear to achieve the same acceleration, its plain and simple.

so your point about Chris choosing the gear ratio based on the compression is false. he is selecting the gear based on the power band, it just so happens the compression is low and extra gear is needed as a crutch. besides its not like hes recommending 4.56s!!

Rob,I'm not talking about motors with identical power..a low compression motor isn't going to make the same power as a higher compression motor with the same cam,and that where a little extra gear will help.

Slowpoke,

My full weight 69 Malibu (got to be way close to 4000 lbs with my big a** in the seat!)is running a pump gas motor. It's got angle milled 049's (112cc chambers) using TRW 2399 pistons, around 9.5 to 1. This thing loves 90 octane, run it hard at the strip. No problem putting a Nova way into the 11's IF you can hook. I run the ignition at 38 total for best performance. I am sure that I could back out a few degrees timing and run regular pump gas all day long, and would never know the difference on the street.

Try it, you will love it. I fixing to yank the current carb and add a little more gear. 11's come spring!!!

Dont even bother with the larger vavles if you want to save the cash, this combo made 490 horse on the dyno with stock valve size 049's.

I would love to find a Nova for a mill like this, looking for a 68-72.

Originally posted by RatONaStick:
[QUOTE]I would never equate my rear end gears to what my compression is, but what my power/RPM band is.
[QUOTE]
...so your point about Chris choosing the gear ratio based on the compression is false. he is selecting the gear based on the power band,... Do I hear an echo in here.

Go back and re-read my post

IDENTICAL power curves repeat IDENTICAL

The car knows no difference to what the CR is.

Build your motor first then figure out what gear you need.

Don't pick a gear based on what "crutch" you might think your CR might be.

Rob

Slowpoke, fwiw, and its NOT a race car, my chassis is near stock, but well thought out, and it runs deep 12s pretty easily. So please don't think it needs to be trick or high dollar. Just solid.

And while I haven't read Chris' comments, since we're buds,I'm quite sure all he meant to add is that gears 'make' torque. Band-aid if you will. But it's common fact.

( also makes a retro hp-builtmotor run just as strong as a torque-built motor )

Gears, the great equalizer! smile.gif

Slapper bars,bolt in frame connectors, and 3.73's is about all the chassis work a Nova needs. Its not rocket science to get a early Camaro or Nova in the 12's with a mild 454.

Originally posted by mfsr:
Do I hear an echo in here.

Go back and re-read my post

IDENTICAL power curves repeat IDENTICAL [/QB]i read your reply as i read every reply in this post and no one is talking about identical power curves but YOU, maybe YOU need to go back and re-read. your the one who invaded this post trying to discredit someone who did nothing but state a fact.

the fact is an 8:1 engine will need more gear to run the same numbers as a 10:1 engine with the same cam, same car, blah blah blah. graemlins/boring.gif

theres that echo again. im done, have a nice day graemlins/waving.gif

I find it hard to believe that an 8:1 engine could ever develop an IDENTICAL power curve as a 10:1. Just doesn't seem likely. Unless the 8:1 is blown or juiced, still wouldn't be IDENTICAL. I'm pretty sure that an 8:1 motor's torque curve graph will be drastically different than a 10:1.

Anyway, I'm thinking small solid cam, 9.5:1 to 9.7:1 CR with a matchin stall and 3.73 gear will get this little chevy moving down the strip pretty quick.

We're actually planning on taking a look at the bearings, doing a compression/leakdown test and if it is in decent shape, drop it in stock w/ an RPM or Stealth, either the big Qjet or 600cfm Holley and just run it as-is to see what the 255HP rated Big Block can run through the stock tranny and rear, just for fun.

FWIW,

if everything is identical, changing CR from say 8 to 1 to 10 to 1 will create almost identical power curves except the higher CR. motor's curves will be higher above the lower CR. motor's curves!!

AND I expect the same thing would happen if you added a roots blower to the same lower CR. motor and created a 10 to 1 CR. motor at boost..

pdq67

425 BHP out of 454 cid, 87-octane, low compression....
Put an 264/264 at .020, 232/232 at .050, .532/.532 gross lift/.510/.510 net lift cam cut on either 110 LSA or 112 LSA, either one in 4° to 6° advanced....
Then pull off nr 7 plug wire.....

UDHarold

Harold,
You crack me up!
Ron

I'm pretty sure by the numbers my old 454 in my Shovel was 8.75:1. Flat tops down .025, 107cc heads and a .039 gasket.
It managed high 11,s in an all stock weight 70SS.
I have to admit though, I never tried it on 87 octane.
I believe a Nova with a rat and a 200lb driver will be right around 3600lbs.
Rapid Robert was correct, slapper bars, sub frame connectors and some decent shocks with slicks and it will hook well. Don't forget the front end of the car btw, you need to get the front end to rise. Make sure the slapper bars extend so the snubber hits under the front spring eye. Monoleaf springs are just dandy.
One more thing, Qjets can work real well. But it will take some mods. If you can find the HP book called Rotchester Carburetors, it details all of the mods required to make the Qjet work. These days, the hardest part will be finding the jets, rods and hangers to get the most out of it. They haven't made dem carbs forever. Edlebrock may be a source.
Have fun!
Ron

I run 89 octane an da bottle of booster in 10.25/1 454 and have zero problems in at least 1000 miles. if it pings I have never heard it.