Building a 427 (L-88) engine

[Steve Antonucci]

Good evening all,

Over the past few years, I have seen numerous threads on this site regarding
rebuilding SHP big block engines that take into account todays fuel octane
ratings. I recently finished a totally stock L/89 ( L/78 ) project and
started having second thoughts soon after. I would like to pose a related
question from another point of view.

It has been a dream of mine to build an L-88 engine for a project car for some
time. I now have all of the original components I need ( less pistons & cam )
for this project. I am torn between building this powerhouse engine back to
the way it came from the factory ( original solid lifter cam, 12:1 comp. ), or
building it with 9?:1 compression and either a hot hydraulic or roller cam.
There are as many opinions as days of the year......

Many topics have been covered here regarding the use of octane boost, AV-gas,
etc. in SHP engines to get them to operate "properly". I would like to enlist
the assistance of the members here as to whether I should consider lower
compression pistons ( what compression to be exact ) with the original solid
lifter cam, or a roller type cam. Also, can I get away with the original L-88
distributor, or will I need to make modifications there as well.

As anyone who has been around an L-88 knows, there is no substitute for the
unique sound ( not to mention power ) of these engines. This question really
wants to address the practicality of building an L-88. Essentially, what
should the internal configuration be so that the engine will run its pants off
using todays unleaded pump gas. Assuming this is even possible.

Thanks everyone.

Steve

[Verle R.]

Re: Building a 427 (L-88) engine

Steve,

What do you intend to do with this engine/car?
Drive it on the street, shows only, race it?

Answer that question and it will help with responses.

Verle

[Steve Antonucci]

Re: Building a 427 (L-88) engine

Thanks for the request for clarification Verle. I should have included it.

This would be for show & drive occasionally. However, I just want to add that
if this was 1970, it would absolutely be an original L-88. Yes, I know it is
not 1970, last time I checked anyway, but I want this to be as close to an L-88
as is possible today.

Steve

[Clem Z.]

Re: Building a 427 (L-88) engine

check near where you live to see if anyone is selling 100 octane no lead at the pump. union 76 and sunoco both market it for street use. check their websites for location

[Michael H.]

Re: Building a 427 (L-88) engine

Clem has a good idea. If you find the fuel, you can live with the 12-1 CR, if that's what you want. If you take out the L88 cam and the 12-1 comp pistons, you've pretty much taken the L88 out of the L88. Just about everything else inside is designed for durability, not power. The few remaining items, such as open plenum intake manifold and special stagger jetted Holley carburetor are designed to work with the cam at high RPM but would most likely be a negative factor without the original L88 cam and CR ratio.

The racing fuel would be a lot cheaper, even at it's current outrageous price, than switching to 9-1 comp ratio, although I would guess that within a few months of driving on the street, you would tire of the L88 engine.

If you do install a shorter duration cam, you should also change the distributor cent advance curve specs back to something close to a stock 425 or 435 HP.

[Clem Z.]

L-88 with stock exhaust do not run wery well

i would at least use headers with muffled 4" side pipes to get as much power as possible

[Patrick H.]

Re: Building a 427 (L-88) engine

I know the thought. I think it would be neat, too.

But, with today's technology and knowing the L-88's reputation, I'd make a few changes. Those would include a roller camshaft, dual plenum intake (likely 1966 425 if I'm staying GM unless there's a better one now) and a Demon carb with a choke. Using today's aluminum heads, I'd bet that you could get close to the 12:1 if not right on and still build it for the street with the right camshaft. And, if they'd fit under some type of stock appearing valve cover, I'd use roller rockers.

But, that's just me. The only "give away" externally might be a logo on the end of a cylinder head and the Demon carb. But with an air cleaner on top, most people would never notice.

I'd also buy dyno time. Why go that far and not have it tuned right on?

Patrick

[Duke W.]

Re: Building a 427 (L-88) engine

The key to L-88's high top end power in the upper rev range is its high overlap cam with a very late closing inlet valve combined with high compression ratio, and even the 103 RON super premiums from the sixties were barely adequate The amount of overlap was specifically designed to take advantage of the wave dynamics generated by a properly designed header and open exhaust system to increase VE in the mid to upper range, so headers AND very low backpressure, preferably open exhaust, are a must to get the most out of the cam.

OE manifolds and mufflers will just kill output across the entire rev range, and high overlap combined with low compression ratio will cause such a high exhaust gas residual that VE and power will be poor, even at high revs, not to mention that low speed throttled operating characteristics will be absolutely atrocious. The L-88 equivalents in the SB world are 302's that are "built" with the 140 or 754 cam, and the 2 x 4 cross flow manifold induction system makes them even worse. Yeah, it sure looks neat, but doesn't run worth a damn below at less than WOT and 4500 revs.

You might as well pour water in the gas as run a L-88 cam with 9:1 compression It will be a dog!

A good performing engine is the result of good engine system engineering. Valve timing, CR, head flow and inlet and exhaust systems must be engineered to be synergistic - the whole should be more than the sum of the parts, but install one "off tune" component" and the whole symphony is going to sound like a junior high music class in their first year of instruction.

The L-88 was designed for racing where idle quality, low end torque and low speed driveability were of no concern - everything else was sacrificed for maximum WOT power in the 4500-7000 range. Expecting the L-88 configuration to work well in the normal street and highway driving environment is just a futile attempt to pound a square peg into a round hole.

The SHP mechanical lifter BBs are the epitome of good street high performance engine system engineering. They produce high specific output with reasonable idle quality, acceptable low speed driving characteristics and torque bandwidth, but they are certainly more high strung than the milder hydraulic lifer cam versions - too high strung for some. The best way to screw them up is install a L-88 cam or some aftermarket "racing cam" that has way too much overlap.

Aluminum heads on a SHP BB are even better because they can take as much as a half-point higher compression on the same octane, and the vintage or modern aluminum heads will flow better than sixties vintage iron heads with similar rework effort. An iron head closed chamber L-72/71 will operate without significant detonation on the best pump premiums with a CR of no more than about 10.25:1 and this is achievable with production machined components and judicious head gasket selection. On a L-72 cammed engine, open chamber heads should be held to 10:1, but aluminum open chamber heads should be okay up to close to 10.5:1. "Modern" moderate duration, aggressive action hydraulic roller street cams have earlier closing inlet valves than L-72, so DCR is higher and static compression should be held to about 9.5:1, 9.0:1 with iron heads.

Head flow is critical to engine performance, and properly reworked heads will produce 5-10 percent more power on any given configuration without affecting normal driving characteristics including, idle quality, low end torque, and normal speed driveability. If you didn't get your previous project's heads reworked for better flow you left 30-50 HP sitting on the table, so your best course of action would be to go back and pick it up.

I watched the NASCAR race from Watkins Glen yesterday, and it was interesting to observe the in-car camera/audio during caution laps. You could hear the engines surging and the drivers had to keep modulating the throttle to maintain speed and position. Those carbureted, big cam engines just can't handle part load constant speed operation. Imagine having to deal with that continuously as you drive down the freeway. L-88s and 302 Tran-Am engines are going to be equally cantakerous.

Guys have been dreaming about L-88s for over 30 years, but it's a pipe dream. It's just not a practical configuration unless you are building a serious race car or want a hanger queen that looks cool.

Duke

[Clem Z.]

if you want a wild sounding street engine

i would build or buy a GM 572 cubic inch crate engine with a wild sounding cam because the cubic inches will make up for the loss of low RPM power. most of the people back then with L-88s or cammed 302s used 4.56 or 4.88 rear gears

[Duke W.]

Re: if you want a wild sounding street engine

If you're going to "build" a good street engine, the best way to start is by packing as many cubic inches into the package as possible, so for a vintage BB I would use a 4" stroke crank to make it a 454 - even a restoration engine. Nobody will know unless you tell.

The new LS7 is certainly a study on how to build a great street engine. They started with the biggest displacement they could pack into the LS architecture.

Valve timing is relatively conservative for a 4" stroke engine - 211/230 at .050" lifter rise, 0.6" max valve lift, (with a wide LCA although I have not seen it specified), and the light weight valve train components (including titanium inlet valves) allow very aggressive dynamics.

The CNC machined head ports have HUGE flow - 360 CFM @ 28" at max valve lift on the inlet side. The exhaust ports are restrictive relative to the inlet ports, which is why the exhaust duration is considerably longer than the inlet, and the extra duration is all on the front end via an early opening exhaust valve - just like the vintage LT-1 cam. The valve timing is specifically tailored to the head flow characteristics. This is good system engineering.

Even with relatively conservative valve timing such huge ports would not work well with a carburetor and manifold, but with a modern engine control system including port fuel injection, you can get away with high port flow without compromising drivability and emissions.

So the hot setup to achieve broad torque bandwidth with high top end power while achieving good idle quality and driveability boils down to the following three "rules".

1. As much displacement as possible from the external package size.

2. High flow ports with high flow inlet and exhaust systems.

3. Conservative valve timing specifically matched to flow characteristics for good idle quality and driveability characterisics.

The same basic philosophy applies to a vintage engine, but you can't have as high flowing inlet ports and manifold with a carburetor or port velocity will be insufficient to achieve good fuel distribution, vaporization, and mixing, however, you can compensate somewhat with a bigger cam because there is no emissions requirement and most will accept somewhat poorer idle quality and driveability on a vintage engine.

Also, modern engines can have much higher CRs than vintage engines because the engine control system has all kinds of sensors and control algorithms to keep it right on the ragged edge of detonation, which is the most efficient operating regime under many operating conditions, including WOT. (The high CR on modern engines is a big factor in their excellent fuel economy.) On a vintage engine, with their crude control systems, you have to be much more conservative in selecting CR in order to keep it out of detonation.

Duke

[Dick W.]

Re: if you want a wild sounding street engine

Old adage "Only substitute for cubic inches is cubic money". Go real fast =cubic inches+cubic money. First rule of engine building.

[Joe L.]

Re: if you want a wild sounding street engine

clem-----

The 572 certainly has the cubic inches. However, it's built on the 10.2" "tall deck" truck block. So, unless you go with a radical hood modification, it won't fit in a C3. I don't know if it will fit in a C2, but I doubt it unless the hood is modified, also. The extra "wideness" of the engine might cause other fitment problems, too, with peripheral components.

[Clem Z.]

Re: if you want a wild sounding street engine

a friend had a 540 cu in BBC in a 69 vette and i think they use the same 10.2" block and if i remember correctly the power brake booster was the problem. he used a stock BBC intake with intake to head spacers to get the hood clearance with a L-88 type hood. all the after market intakes manifolds that fit the "tall block" without spacers were too tall. it was not a direct drop in but it did fit. if you want it bad enought you can make it work. i helped put a 425 HP 409 into a 56 vette. talk about a tight fit

[Everett Ogilvie]

Here's the deal...

If you de-cam and de-compression the L88 it is not an L88. You answered your own question - you mentioned occasional use and if that is really the case, build it all the way, buy racing fuel (106+ octane, which is available but expensive), and enjoy driving the car occasionally.

As a prior owner of a real L88, I think there are too many myths around this engine. Duke's info is good info about the extensive cam overlap, and the rest of the technical details, but as an owner I am telling you that these cars can be driven (with good fuel), and with an exhaust system in place (granted, my car had the factory off-road pipes and mufflers). All the old myths (the engine won't idle at less than 2000 rpm, it was so cammy that it was impossible to manage, etc.) are not true. I have owned 7 solid lifter 427s, and the L88 even without headers will destroy the L78 and L72. Period. The only issue I had with the car is the overheating at slow speeds due to no fan shroud. If you are only building the L88 engine, and not duplicating all the other items (for example, if you add a fan shroud), you won't have any issues if you are willing to put good fuel in it. I am sure the other L88 owners on this board will concur with most of this info, as they have done with me offline through emails etc.

I have written an article for the Restorer regarding L88 Mythology, but have not submitted it yet b/c I recently sold the car.

[Dick W.]

Re: Here's the deal...

I too previously owned an L/88 and occassionally drove it on the street. It even had the across the counter ZL-1 cam. Engine idled at about 1,000 rpm's after I adjusted the secondary throttle plates. Only problem other than heating was that with the cam all the vacuum system was a little slow. Passed the PV though. I did not age Bill Clupper over 10-15 years when we did the PV.