Disappointed by the BB
Drifting
Joined: Oct 2005
Posts: 1,528
Likes: 148
From: East London/SW Essex UK
Stock big block L36 427 (with oval ports) isn't happy revving past 4500 rpm. Gonna guess that early 454 with low rise inlet and 'soft' cam is much the same. TBH torque peak is over and done with before 3800 rpm - little point revving too much past. Old school rectangular ports are great for maximum HP capability at higher revs but not always so good for lower rpm driveability and efficiency.
Well designed oval port heads will have far better port velocity for good torque at low-end rpm. They are also the trick part for some higher rpm (not highest rpm) race engines too.
Well designed oval port heads will have far better port velocity for good torque at low-end rpm. They are also the trick part for some higher rpm (not highest rpm) race engines too.
Team Owner
Joined: Jul 2004
Posts: 40,408
Likes: 792
From: Redondo Beach, California
I'm aware that this critique is made about the rectangular ports. I, and a good friend at the time, we both had BB's with the rectangular ports. We never noticed any problem with low speed driving. Also, as for efficiency, I got good freeway cruising gas mileage. I had a 3.08:1 differential gear! I could drive the 300 miles to Las Vegas and get there with ample fuel...I think I was getting a little over 20 mpg. Fuel was a big issue though. I started out with a full tank of high octane Av Gas (130 octane?). After burning off some fuel from a full tank, I'd top it up again with 91 (?) octane auto gas .. and do this again to keep the overall octane up. Oh, about the 3.08:1. I had to get a 5 speed Doug Nash transmission just t get the car moving. The Nash was 1:1 in fifth gear, with an extra low first gear. The L88 clone had so little off-idle hp, I had to slip the clutch with the 4 spd Muncie to get moving..
Safety Car
Joined: Oct 2000
Posts: 4,080
Likes: 565
From: Allen TX
Great looking car. As others have said, get it on a chassis dyno and see what it is making. 500 flywheel HP, depending on the transmission and rear end, and all the accessories you're turning, may end up ~360-370hp at the rear wheels. but, as others have said, if it makes peak HP ~4500+, then you will be lower than that for sure. Could certainly be a tuning issue, but with your experience, you've probably checked out all of those potential "gotchas." (ignition timing, throttle blades fully and completely open at WOT, plugs/wires, cap n rotor).
It's too bad you don't know what parts were used to build the engine... that would probably tell you a lot, including how much actual potential it has.
It's too bad you don't know what parts were used to build the engine... that would probably tell you a lot, including how much actual potential it has.
Safety Car
Joined: Oct 2000
Posts: 4,080
Likes: 565
From: Allen TX
I'm aware that this critique is made about the rectangular ports. I, and a good friend at the time, we both had BB's with the rectangular ports. We never noticed any problem with low speed driving. Also, as for efficiency, I got good freeway cruising gas mileage. I had a 3.08:1 differential gear! I could drive the 300 miles to Las Vegas and get there with ample fuel...I think I was getting a little over 20 mpg. Fuel was a big issue though. I started out with a full tank of high octane Av Gas (130 octane?). After burning off some fuel from a full tank, I'd top it up again with 91 (?) octane auto gas .. and do this again to keep the overall octane up. Oh, about the 3.08:1. I had to get a 5 speed Doug Nash transmission just t get the car moving. The Nash was 1:1 in fifth gear, with an extra low first gear. The L88 clone had so little off-idle hp, I had to slip the clutch with the 4 spd Muncie to get moving..
Team Owner
Joined: Jul 2004
Posts: 40,408
Likes: 792
From: Redondo Beach, California
Panic: I think this might be close to the performance in your BB you are looking for. If you get the right stuff inside the engine you shouldn't be concerned about performance! You've got a 454 so you have a few extra cubic inches to play with. Also you can get a 454 crank internally balanced and use the neutral balance 427 crank damper and flywheel. Internally balanced helps keep the engine together at high rpma.
In 1968, Dick Guildstran driving a 67 L88 set a then track record of 171 mph on the Mulsanne Straightaway at Le Mans. I think a few years later, an L88 powered Corvette hit 191 mph....this car had a 2.56:1 differential!
....................................
BB aluminum BB heads with rectangular parts and the GM logo, may well be made by Edelbrock. I was on a Edelbrock factory tour, there were several pallets all stacked with BB heads with the GM logo.
In 1968, Dick Guildstran driving a 67 L88 set a then track record of 171 mph on the Mulsanne Straightaway at Le Mans. I think a few years later, an L88 powered Corvette hit 191 mph....this car had a 2.56:1 differential!
....................................
BB aluminum BB heads with rectangular parts and the GM logo, may well be made by Edelbrock. I was on a Edelbrock factory tour, there were several pallets all stacked with BB heads with the GM logo.
Last edited by 68/70Vette; Jul 5, 2020 at 06:05 PM.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
looks like an oval intake and stock GM iron heads. yes, you can get 500 out of GM iron ovals. but it takes a metric s#!t ton of porting. they could be truck peanuts. could be L29's. we need to see what you have for head casting numbers. and as i said earlier. valve lift will tell a lot about the cam. No Va. in spanish and italian means doesn't go...
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Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
When power falls off below the camshaft redline I look at weak valves springs. Not very expensive to try new springs and you can change them by just removing the valve covers and spark plugs.
Old Pro Solo Guy
Joined: Dec 2017
Posts: 8,094
Likes: 4,447
From: Marlton NJ
A 500 HP 454 does not have to rev like a SB to make that much power, it could easily peak at 5300-5600 like mine and WA2Fast do. If it revs real well to 6500 it's making way more than 500! More like 600+ The smaller BBs like the L78 396 and the L72 427 make peak HP 400 or 800 rpm higher with the same top end.
A 575 HP SB even a 406 probably rev'd really well. I'd guess 6500-7000.
But my LS6 454 has 555 ftlbs at only 3200 that a SB could only dream about.
My 400ish HP LT-1 rev'd real well to 6800, but the torque peak was 4800-5000, not a lot of bottom end, enough, just not tons. Maybe 400-420 tops tq. At 2-3000 the BB has double the TQ of that one.
Lots of cubic inches has a totally different feel. But speed is based on the HP and gearing it right.
So this engine you have is going to rev less for two reasons: because it has less HP and because it's bigger with more TQ.
You might want more heads and cam to get closer to 600HP. Those look like stock iron oval ports. Aluminum AFRs could net you 60-80HP in a head swap alone! BBs need to breathe.
A 575 HP SB even a 406 probably rev'd really well. I'd guess 6500-7000.
But my LS6 454 has 555 ftlbs at only 3200 that a SB could only dream about.
My 400ish HP LT-1 rev'd real well to 6800, but the torque peak was 4800-5000, not a lot of bottom end, enough, just not tons. Maybe 400-420 tops tq. At 2-3000 the BB has double the TQ of that one.
Lots of cubic inches has a totally different feel. But speed is based on the HP and gearing it right.
So this engine you have is going to rev less for two reasons: because it has less HP and because it's bigger with more TQ.
You might want more heads and cam to get closer to 600HP. Those look like stock iron oval ports. Aluminum AFRs could net you 60-80HP in a head swap alone! BBs need to breathe.
Last edited by leigh1322; Jul 6, 2020 at 11:49 PM.
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
Everyone claims they make 5 or 600hp.....Get a half decent head/cam that big block will rip.
Bet you got a stock truck engine with a small cam or perhaps weak valvesprings
Bet you got a stock truck engine with a small cam or perhaps weak valvesprings
Thread Starter
Team Owner
Joined: Nov 2004
Posts: 20,715
Likes: 25
From: Sorrento Italy
Heel & Toe
Joined: Jun 2017
Posts: 17
Likes: 7
From: Charlton, NY
Back in the day, the BB cylinder heads came with rectangular intake ports and oval port intakes. You need to have the rectanglar ports.....they are big. I had a piece part built L88 427 in a 1969 Coupe. The L88's were reputed to produce flywheel 550 hp...they of course had rectangular ports. The L88's had a 12.5 compression ratio, which needs 104 octane. I had the piston domes milled down 0.1 inches to get it down to 11:5 compression. I had sidepipe headers that were virtualy unmuffled. I think the carburetor I had flowed about 1000 cfm. It definately came alive at high rpms. It took a while before I could drive it without becoming frightened.
If your BB seems to be falling off at hgher rpm, first guess is it's running out of air. Rectangular ports? Free flowing exhaust? Big carburetor? Also, the cam? The L88 cam had a lot of overlap, so much so that the engine had very little off-idle power, but realy came alive at high rpm..
.............................
Stored the 69 in a sortage unit when I moved to Australia. It was stolen. I think the manager of the storage facility took it. He may have thought it was a real L88 car. 1969 L88's auction off at a little over $1 million today..
If your BB seems to be falling off at hgher rpm, first guess is it's running out of air. Rectangular ports? Free flowing exhaust? Big carburetor? Also, the cam? The L88 cam had a lot of overlap, so much so that the engine had very little off-idle power, but realy came alive at high rpm..
.............................
Stored the 69 in a sortage unit when I moved to Australia. It was stolen. I think the manager of the storage facility took it. He may have thought it was a real L88 car. 1969 L88's auction off at a little over $1 million today..
Racer
Joined: Oct 2001
Posts: 474
Likes: 64
From: Portage La Prairie Manitoba
I've owned for more then a decade a fully modded and lightened C3 (1260 kg), the engine was a 406 575 hp jewel built by American Speed of Ill... I've sold the vette and have recently bought a show conditions rebuilt 72 Nova, with a 454 engine with supposedly 1000 miles on the clock, seller claimed to have 500+ hp, 5 speeds trans (absolutely fantastic) and 4.11 gears...The car is beatiful, a true muscle car.
Just that Comparing my C3 SB with this new 454 I feel quite didappointed, the way it speeds up revs is totally different, it sounds thundering but the revs are not there, over 4k it becomes lazy, it just does not enjoy being over 5k, while my C3 406 raged up to 6k like a turbo motor...
I'm now thinking about changing the engine with a built low compression 406 race engine.
Your comments will be appreciated, tks.
Just that Comparing my C3 SB with this new 454 I feel quite didappointed, the way it speeds up revs is totally different, it sounds thundering but the revs are not there, over 4k it becomes lazy, it just does not enjoy being over 5k, while my C3 406 raged up to 6k like a turbo motor...
I'm now thinking about changing the engine with a built low compression 406 race engine.
Your comments will be appreciated, tks.
Big block makes massive torque but at a lower rpm then a small block
A taller gear will better utilize your torque curve
A dyno tune would also help.... maybe some power left untapped
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
May have a lopey cam but if the valvesprings arent the proper ones it can get into valve float early and feel like someones letting off the gas. BB valves are heavy. Not saying it is your problem but could be....say some guy puts a .600 lift cam in, shops ebay for a .600 lift spring
Doesnt mean it will work properly
Or could be float adjusment/fuel pump issue....check one thing at a time.
Doesnt mean it will work properly
Or could be float adjusment/fuel pump issue....check one thing at a time.