need to tame down my hp small block for everyday street use. Maybe replace High lift cam and use smaller carb? It has a roller cam and 750 carb and camel hump heads with headers I think higher compression pistons it’s a 4 bolt main block. All this is old school stuff .Trying to do this reasonably any ideas?
Detune hp small block
joes1111
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need to tame down my hp small block for everyday street use. Maybe replace High lift cam and use smaller carb? It has a roller cam and 750 carb and camel hump heads with headers I think higher compression pistons it’s a 4 bolt main block. All this is old school stuff .Trying to do this reasonably any ideas?
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2,501 Posts
Doesn't sound like you know which pistons are in the engine. The combination of compression ratio/heads/exhaust/intake/carb/rearend ratio/car weight/intended use will help determine which setup will suit you best. Can you supply as much of that information as you can? A tamer cam might get you to where you are wanting to go with the car, but if it has high compression pistons, a small cam may be a compromise for your intended goal that might no run the best and be picky on which gas you can use in the car.
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491 Posts
I had double hump heads on my small block, that had been machined 3 times in the years that I had them, and once before I had them. I don't know the exact CC that they were when done, but I do know with the .030 flat top pistons I was running that it absolutely would not run pump gas. So.... since I pulled the car out of service, and tore it apart to repair my tweaked frame from drag racing, the tweaked quarter panel from drag racing and other things, I chose to de tune the engine, and make changes, however my goals were to keep similar performance, but detune the engine enough to run pump gas. I tripped into a set of crazy lightly used Edelbrock aluminum heads for a price that I couldn't pass up (basically free), with 72CC to reduce compression, and i'm pulling out the cam that i've had in it for years, and going with a HYD roller with similar rpm range, and other characteristics, but will also produce actual vacuum so my power brakes will work once again YAY.... I'm intending to keep the same intake, carb, etc.. as i'll never use it for a daily, but I will drive it more than I used to. For your situation, i'd do similar heads as I have to lower compression a bit, change out that cam, and maybe go with a air gap intake, and slightly smaller carb, or re jet the carb that you already have.
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18,738 Posts
I did the same in 1979 getting ready to go away to school. It was an LT1. I put 882 "smogger" heads on with HUGE chambers and threw a " general kinetics" RV cam in it to boost TQ with 8.5:1 compression.
These days, alloy heads and a roller cam are the way to go aka DIABEL1969.
These days, alloy heads and a roller cam are the way to go aka DIABEL1969.
Yep ..just what you're suggesting i think .
Cam and carb swap bring er right back down to earth .
Do that and if compression is too high take the heads off figure out your compression and then either put different heads on it or go with a thicker head gasket
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12,324 Posts
Look into 76 cc aluminum heads.
Detune? Never heard of such a term.
Seriously though, why do you need to detune? What symptoms are you experiencing that you deem unfavorable?
Seriously though, why do you need to detune? What symptoms are you experiencing that you deem unfavorable?
Gene I am just gonna pretend that you did not do that to a LT1. I see nothing, I hear nothing!!!
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11 Posts
thanks again for all your replies I have two 71 Caminos one a super sport and will leave alone the other is the one I want to tame down for a daily driver. Too much done to that engine for me like no vacuum for brakes.erratic idle poor fuel mileage etc. so thanks for all the info you guys came up with that gives me more ideas. I did not mention earlier but I’m 75 and old school and don’t need two high output elkys. On the road
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6,051 Posts
Keep the carb and tune it.
You must be really aggressive in camshaft and compression in my book to not be able to use as every day street use.
Keep the heads slap in an old school 280 cam something with duration in the 230 range @ .050.
I have ran 11.9 compression as a daily driver tow vehicle with a 224@ .050 cam and 54cc heads 186 double humps milled a lot.
But a really good cam if you have flat tops and go with a larger chamber head is the 268 cam 218 @ .050
Easy to get 15-18 MPG from it.
The 230@ .050 cam I have got 15 mpg often and pulling a 20 foot pontoon I get 11.5 MPG with AC on.
57 cc finished chamber 601 casting heads. 350"
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You must be really aggressive in camshaft and compression in my book to not be able to use as every day street use.
Keep the heads slap in an old school 280 cam something with duration in the 230 range @ .050.
I have ran 11.9 compression as a daily driver tow vehicle with a 224@ .050 cam and 54cc heads 186 double humps milled a lot.
But a really good cam if you have flat tops and go with a larger chamber head is the 268 cam 218 @ .050
Easy to get 15-18 MPG from it.
The 230@ .050 cam I have got 15 mpg often and pulling a 20 foot pontoon I get 11.5 MPG with AC on.
57 cc finished chamber 601 casting heads. 350"
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11 Posts
I feel that what you are saying to me is right. I really don’t know what all has been done to this motor I know it sounds cool but no vacuum to operate the brakes properly. I did put on a different oil pan for clearance on the steering and it was a 4 volt main. Also I replaced the valve covers because there was not enough clearance for rocker arms and I checked the numbers on the heads and they are camel hump type. Whoever was souping up this engine is questionable in my mind but they we’re probably just learning but now the time has come to make the best of what can be done for street reliability by making it into a cool daily driver
Right ?? Threw me for a loop too lol
WOW lolGene I am just gonna pretend that you did not do that to a LT1. I see nothing, I hear nothing!!!
And to think I just threw some 882's in the scrap pile haha
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6,051 Posts
I have seen a lot of people reach for the big stick and vacuum would drop in the 5" range and power brakes were not happy.
11" vacuum and all will be well and some have ran 8-9" vacuum and had fine luck with brakes.
One deal is get idle speed up to 900-1100 rpm.
You mentioned it is a roller cam.
You can have that cam reground.
You need to pull the heads and see what type of piston is in there.. or a bore scope will also work.
If a flat top and double humps you are golden and I would run them.
They will not make too much compression for 91 octane gas.
I have ran them at 54cc with .028" and .051" piston to head clearance and at 64 cc with .051" no issues either way.
In fact the 54cc was less detonation prone.
Like others stated you can run a larger chamber head but less money out of pocket if you can keep the current ones.
Swap in a milder cam.
11" vacuum and all will be well and some have ran 8-9" vacuum and had fine luck with brakes.
One deal is get idle speed up to 900-1100 rpm.
You mentioned it is a roller cam.
You can have that cam reground.
You need to pull the heads and see what type of piston is in there.. or a bore scope will also work.
If a flat top and double humps you are golden and I would run them.
They will not make too much compression for 91 octane gas.
I have ran them at 54cc with .028" and .051" piston to head clearance and at 64 cc with .051" no issues either way.
In fact the 54cc was less detonation prone.
Like others stated you can run a larger chamber head but less money out of pocket if you can keep the current ones.
Swap in a milder cam.
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927 Posts
I have the same basic engine, 1970 LT-1 with solid cam, performer intake with 750 holley VA and stock exhaust manifolds,10:1 compression with turbos in a 69 Camaro. Brakes are fine. It has been driven for 35 years and I love it . . . . .hope I don't want to "detune" it when I am 75 in 2 years LOL
Bruce
Bruce
A cam producing more low end torque, less high end hp, is my recommendation.
Here's some info on selection:
Pete
Put a good streetable roller cam in the 215 duration with a lift under .500 with the correct springs in it and leave everything else the same. Maybe bring your carb down to a 650cfm or better yet put a quardrajet on it. Compression doesn't hurt anything unless you want to run 87 octane then I would suggest sell the motor and buy a Mr. Goodwrench basic motor for cheap money.
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7,406 Posts
Now that's a sleeper. I used to tell guys, if you want to de-tune your car put a 2bbl on it.
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18,738 Posts
It wasn't a real LT1 man, one I machined up is all. The 3.08 gears werent helping the original iteration!Gene I am just gonna pretend that you did not do that to a LT1. I see nothing, I hear nothing!!!
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