High Comp 120cc Build

dave brode

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The caddy uses very tall springs. Most of the cheap straight springs sold by the vendors use normal sbc retainers and "minus" locks [typically for sbchev and go in at 1.750" or so, some go in at 1.700"!!]. The minus locks move the retainer DOWN, and the "chev" style retainer also sits lower than the caddy retainer. Even then, you still may need to shim under the springs to get the installed height needed when using short springs.

Point: in any case, you MUST have the locks and retainers that you will use when measuring from bottom of retainer to seal.

The comp 787-16 retainers for beehive springs normally need a "minus" lock too. The exception are the taller LS7 springs, which may work with std locks.

viewtopic.php?f=3&t=8224&p=171214&hilit=+value+priced+springs#p171214

:twocents: Most tunnel ram guys will tell you that a single carb top is far from ideal, as far as cyl to cyl distribution. If you know what type engine the top is from, you might be able to find a 2x4 top. If you did this, I would NOT run wee small carbs. I would try 750 cfm carbs.

Fwiw, my slide chart says;

If a big chamber head 507" with a 5cc dish piston started as a 8.4-1 CR engine, removing 20cc of combustion space [the 5c dish and the 15cc dome] would make it 9.6-1.

If it stated as 8.65-1, removing 20cc from the combustion space would make it right at 10-1.

Dave
 

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No way.

Essentially the same architecture, but notice the huge positive dome? Small chamber 10:1's look more like mine.



 

samIam

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Thanks 85 and Dave, looks like I have some work to do. The problem is...I don't have a cam/spring kit picked out yet.

Been talking to Mad Cad about a cam grind....! What do y'all think? I only get to drive this thing on the street maybe 20/30 days a year, the rest is at the track where its gonna be in the street eliminator class, 13.00 or slower. I do like the 1/8 mile track too because its not so harsh on the car. Gotta stay 8 sec or slower on the 1/8th.

I'll take the top of the tunnel ram off.
 

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Erring towards the bigger side helps tolerate pump fuel to some degree.
 

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I have a cutsom grind with just about identical flow numbers to yours on the cylinder heads. Its basically the MTS#20 cam with earlier timing on the valve events for higher DCR.

It works good for the little bit that i have driven it. Take the next few comments with a heavy grain of salt, since i have very little seat time with this combo, and alot of it could just be bad tuning.

It takes about 2000rpm for it to wake up. However the off-idle torque is NOTICEABLY greater than my previous combo (stock 472 high comp, with MTS#15). But once its there, this engine revves so fast, i just about cant process whats happening. I have some youtube videos of it on the engine stand, and the tach cant keep up with how quickly it revs. I thought it was just because it was on the stand, but in the car, with a transmission and rear end attached it didnt slow down much. I was going about 50mph on the highway for a short blast, downshifted to 2nd, and pinned the throttle to feel the torque, but it pinned the rev limiter. I let off, and shifted to third, grab traction, mat it again, and again it pinned the rev limiter. To give you an idea of the off idle torque feeling from butt dyno, my 3500ish lbs regal with the 472 felt like i was driving a little hatchback with a V6, now with the 512, it feels like im driving a shopping cart with a v8. The car feels weightless cuz theres so much torque.


Even still, when its all said and done and in the car, it doesnt sound that extreme or cammy. I thought it was going to sound a lot more aggressive than it does. If i were to do it over again, i would have gone roller, with alot more lift, and alot more duration.
 

The Mad Cadder

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frankenregal84 said:
I have a cutsom grind with just about identical flow numbers to yours on the cylinder heads. Its basically the MTS#20 cam with earlier timing on the valve events for higher DCR.

What are the specs on your grind ?? isn't the lift a bit more then the 20 ??

Of course this is just a experienced guess.. Given his head flow I would say to stay under 245@.05 .. of course with as much lift as you can get..
Maybe go for a 106-108 LSA.. I think about .590 is about all you can get in a hydraulic flat at that
.05..

I can look some up if you'd like
 

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The Mad Cadder said:
I think about .590 is about all you can get in a hydraulic flat
And thats exactly why to do it again, i would have gone with a roller.

I'll have to look up the specs, can never remember them off hand. Yes the lift is different, but the duration is the same (almost).

The Mad Cadder said:
Of course this is just a experienced guess.. Given his head flow I would say to stay under 245@.05 .. of course with as much lift as you can get..
Maybe go for a 106-108 LSA.. I think about .590 is about all you can get in a hydraulic flat at that

Its funny, cuz what you just said is exactly what i did, and thats the cam i got.
 

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Julius;

My reasons for 245 duration were probably different than yours. How did you come up with 245? By that i mean, what characteristic or behavior does staying at 245 control?



EDIT:
Its a custom Lunati Cam. 245*@ 050, with a .342" Lobe. 288* adv, 110LSA. Single pattern. <-----Thats .582 lift for my setup.
Heres a video of the cam with no exhaust (manifolds only).
https://www.youtube.com/watch?v=7Oh2qRdBvPY

Heres a video of it in the car with mufflers.
https://www.youtube.com/watch?v=owrd63I8a6Y
 

The Mad Cadder

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frankenregal84 said:
Julius;

My reasons for 245 duration were probably different than yours. How did you come up with 245? By that i mean, what characteristic or behavior does staying at 245 control?

EDIT:
Its a custom Lunati Cam. 245*@ 050, with a .342" Lobe. 288* adv, 110LSA. Single pattern. <-----Thats .582

Looks like you have a excellent grind..
Low hydraulic intensity (quick opening/closing ramp .05 and less)
Excellent lobe intensity..

They do have a .359 lobe lift same 159*@.200 just more total lift

Trying to match rpm potential of cam duration to head flow ..And lift to same

His heads overall (total cfm under the curve) flow about what a stock
76cc head..

In my experience 236@.05 was the best performing duration I used with
stock unported 76cc heads.. I went to 250@.05 but it didn't perform
as good .. Granted this was all with a factory dual plane .

So I kind of extrapolated from that.. more might be better but I would stay close
to the same

From Stan Weiss flow data
902 unported
.100 -- 83
.200 -- 134
.300 -- 180
.400 -- 215
.500 -- 248
.600 -- 263
.700 -- 277
 

samIam

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So I did my little combustion chamber CC tester and got 127cc. Pretty cool little tool but my phone wasn't working to take pictures. Also took the tunnel ram apart..





 

The Mad Cadder

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It appears that the runners taper inward as they get close
to the head .. that's good imo it allows the air to stack up
and compress.. but I also think that's like a 7000 plenum.
Small individual plenums I bet work better .. of course Iam
just guessing never ran one like that..
Will try to find pic of the tunnel ram I had..

I dont think your gonna like it very much especially with one carb..
2 650 or 750's .. Vac secondary unless you put a big stall and cam in it.
 

The Mad Cadder

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Here it is.. From what I recall the plenum was split.. as in one side for one carb .. signal did not cross over..
I did not make much use of it..

Car ran faster with a 460 Victor with no mods to it

jf7oes.jpg
 

The Mad Cadder

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4.330 bore
15cc dome
Zero deck
Fel Pro .039 thick 4.350 fire ring
127cc chamber

9.55 to 1

Are you sure dome is 15cc ??
Did you have those heads decked ??

If not check dome clearance in chamber and I would have em cut another .08 assuming they were cut maybe .010 when you took them in the first time
 

samIam

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I'll have to look at it. I know the first and last are on one side of the oil galleys and the middle ones are on another side...looking down at the main caps.
 

dave brode

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samIam said:
I'll have to look at it. I know the first and last are on one side of the oil galleys and the middle ones are on another side...looking down at the main caps.

Correct.

Looking at the main saddles, and assuming that you can look down through the feed holes and see a hole in the bearings, the holes must be 180* apart, not 90*, as stated above. If this is true, it's less than idea positioning, but still better than having stock cam bearings.
 

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samIam said:
So i checked the cam bearings and they look to be back grooved with two holes 90 degrees apart.

I can see 2,3,4 in the picture you posted and they appear to be about 11 which
puts the second hole about 5 oclock..

Unless you have put different ones in since ??

Cadco's are .090 holes .. 180* apart.. the back groove is .02 dp .190 wide
 
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