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I am thinking of installing a 1970 LT-1 cam in a 67 L-79 motor. The engine has been bored 30 with stock 11-1 pistons, other than that it is factory. If I swpped cams what kind of performance increase could be expected? I know this cam was used in the 65-65 FI 375hp. Would I need to go to a larger cfm carb such as the 800 cfm LT-1?
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Re: help on using a '70 LT-1 cam in a L-79 327 mot
The LT-1 cam wasn't used until 1970; '64-'65 fuelies used the earlier "30-30" cam. The LT-1 cam is an excellent solid-lifter cam, the last (and best) one Chevrolet made for the SB engine. You don't need a 780/800 CFM carb with an otherwise stock 327; a 600/650 will work fine. -
Re: help on using a '70 LT-1 cam in a L-79 327 mot
You probably won't feel much seat of the pants difference between the L79 and the LT1. If you have a 3.36:1 or a 3.08:1 with a close ratio you might be disappointed by the LT1 as it has less low end torque than the L79 camshaft - especially after spending many hours changing the cam and lifters.
Last winter I built a motor to 327/365 specs with the exception of the LT1 cam. My 3.36:1 and close ratio Muncie (2.20:1 first) left me wanting more low end torque so I am getting ready drop in a wide ratio Muncie (2.56:1 first) for some added oomph.
BrianComment
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Re: help on using a '70 LT-1 cam in a L-79 327 mot
I have a close ratio muncie and a 3.73 gear.Comment
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Re: help on using a '70 LT-1 cam in a L-79 327 mot
An owner of my acquaintance recently rebuilt a '65 L-79 with an LT-1 cam, nicely pocket ported/port matched 461 heads with a multiangle valve job (flow tested after rework), and Crower Sportsman rods (for a bullet proof bottom end) - OE inlet manifold, carb, and 2.5"exhaust manifolds. OE replacement (FM Speedpro) domed replacement pistons were used and the target CR was established at "no more than 10.5:1". After the chamber volumes were equalized and composition head gaskets choosen to equalize quench height, the final measured CR was 10.35 +/- 0.1.
The final assembled engine was tested on a lab dyno. The beginning of the eighty percent torque bandwidth was achieved at only 1600, but didn't begin to rise significantly until about 2500 and had a steep rise between 3000 and 4000 to a peak of about 332 lb-ft at 4500. The top end of the 80 percent bandwidth was beyond the 6500 rev limit used for the test. Peak power was also achieved at 6500 - 359 SAE gross.
Now you may think that this is only "9 HP more than stock", but if you took a production L-79 and tested it on a lab dyno, it would only make about 300 SAE gross HP. Those old advertised torque and power ratings were grossly exaggerated!
The combination of cam and head work increased peak power by about 20 percent, of which I attribute about half to the cam and half to the head work, but the two work synergyistically, so the whole is greater than the sum of the parts.
The loss of low end torque and tractability relative to the L-79 cam is slight and should not be that noticeable with your gearing, but improved power from 4000-up will be obvious
A Z-28/LT-1 manifold would add about anouther 15-20 HP and a massaged
Rochester FI system with a reworked air meter to 750 CFM would get this combination close to the 400 HP club. With the LT-1 cam and reworked heads, the old 327 SHP manifold is the limiting factor.
This engine should make between 250 and 275 RWHP on a Dynojet (corrected to SAE conditions), but the owner hasn't had an opportunity to run on one yet. A decent production L-79 should be in the 220s.
Results like this do not come without significant planning and system engineering up front and scrupulous attention to critical assembly clearances. Computer simulations were run with various proposed components, and a primary criterion was that the 80 percent torque bandwidth must start no higher than 2000 revs. After the final configuration was selected, the simulations were continuously updated with accurate informantion as it became available (such as head flow data). Specific tasks were identified and a vendor was chosen to do the machining and head work. This vendor also conducted the head flow and engine tests. The owner did all assembly work and was very meticulous, observing all critical assembly clearances, which were established up front in the planning stage.
DukeComment
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Re: help on using a '70 LT-1 cam in a L-79 327 mot
With a good set of aluminum aftermarket heads and 1.6:1 rockers, what kind of power and torque might be expected on a 10.5:1 327 with the L-79 cam?Comment
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Re: help on using a '70 LT-1 cam in a L-79 327 mot
I don't recommend higher ratio rocker arms. In fact, the only rocker arms I recommend are OE. Higher ratio rockers are not very cost effective because the top end power improvement is only marginal, but they considerably increase valvetrain loading, which is close to the reliablility limit with OE cams and rockers. Same applies to roller tip rockers - little if any improvement. Claims for reduced oil temperatures are meaningless on street engines because they don't spend a lot of time at high revs, which is what really heats up the oil. Budget for aftermarket valvetrain parts should be put into connecting rods to replace the dangerously weak 327 rods.
If an L-79 cam was installed in the engine I previously disussed in this thread, the low end torque curve would be slightly enhanced - say one to three percent - up to about 3500. Peak torque would be about the same, but would occur about 500 revs earlier and drop off faster above the peak. Top end power would be down about three percent, but the biggest loss would be the additional 500 revs power band sweet spot due to the L-79 cam's 6000 RPM safe rev limit, compared to 6500 for the LT-1 cam.
As you increase air flow, both power and peak power speed are increased, so the L-79 cam leaves some useble revs on the table instead of in the engine, which will have a greater impact on the loss of average power over the rev range for a maximum performance acceleration run, than the the loss of peak power alone.
"Good set of aluminum heads" doesn't mean much. There are a zillion on the market and their performance varies widely. Aftermarket heads may flow better out of the box, but most with reasonable port volume won't beat a set of well reworked OE heads, even if the aftermarket heads are reworked, and going too big on port volume will kill low speed/low load torque due to fuel vaporization and mixture distribution problems caused by low flow velocity.
The aftermarket doesn't sell and silver bullets!
DukeComment
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Re: help on using a '70 LT-1 cam in a L-79 327 mot
Thanks for your input Duke.Comment
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Re: help on using a '70 LT-1 cam in a L-79 327 mot
One more word on heads. When you get into big displacement SBs like 377s and up, more head (and inlet manifold ) flow is needed, so these are applications were big port volume aftermarket heads can be a signficant improvement. The bigger ports allow more flow, but flow velocity is maintained because the engine has a bigger appetite for air. Flow velocity is critical on carbureted engines to ensure adequate fuel vaporization and distribution. With port injection, distribution is very even and the better atomization from injection pressure enhances fuel vaporization, so you can use much bigger head ports and manifold runners without getting into low speed driveability problems.
The inlet system on the engine I discussed earlier in this thread is choked at about 6500 as indicated by an inlet Mach index of close to .550 at 6500 (which is computed by the Engine Analyser simlulation program). A higher flowing inlet system will improve top end power. but could negatively impact low speed driving characterisitics and low end torque, which is very important on a street engine. In the case of the example engine, the old SHP aluminum manifold is the biggest restriction at the top end, NOT the heads!
If you can meet your low end torque bandwidth criterion and the heads are close to choked at the rev limit, you have a highly optimized street high performance engine configuration.
DukeComment
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Re: help on using a '70 LT-1 cam in a L-79 327 mot
Thnaks for the additional into Duke. How much ar flow can be obtained from the 63-65 fuel injection intake manifold? I asume the manifold runers are the determining factor here.Comment
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Re: help on using a '70 LT-1 cam in a L-79 327 mot
A few months ago I developed a flow model of the Rochester FI system based on dimensions that were provided to me by folks on this forum and set it up in the Engine Analyser simulation program. Even without reworking the air meter for more flow, the FI showed a significant improvement in power WITH reworked heads.
With OE machined heads the power between FI and its SHP cousin is not much different because the heads are the limiting factor, but when you open up the heads, the SHP manifold is the big restriction and FI pulls away significantly at the top end. The FI manifold is a single plane type plus the runners are larger and straighter than manifold runners, so they have greater flow efficiency.
If you search the archives in the last year, you might find my post which has additional information.
DukeComment
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Re: help on using a '70 LT-1 cam in a L-79 327 mot
Thanks Duke. I'll look throught the archives and get that previous information.Comment
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