What kind of head are you using are they aluminum?

 

11-1 (approx) compression with short duration cam equals detonation, no doubt.

I agree about a bigger cam (more duration) to reduce detonation, but a bigger cam will be happier at higher rpms, thus your 2.73 rear will be border-line IMHO.

Are you leaning towards flat tappet or roller? Hyd or solid?

-

 

they are 64cc double humpers
flattappet hydraulic is preferred

the 2.73 rearend might be changed in the future, so it wont be an issue

 

11-1 (approx) compression with short duration cam equals detonation, no doubt.

Yep...when guys run high compression they usually have cams that are high rpm /high duration that in effect lowers the dynmamic compression ratio at low street rpms and can run pump gas ok...
Add to it that u have 273 gears makes things even worse, even going up to say 37s rear end will not make any or much differnce to knock on the street /highway.
There is just too much compression for pump gas

Bottom line if u put it on LPG , changed the dizzy curve, a 160 F thermost you would have a damn quick low rpm economical car.

Solns
1/ fit a Impco system
2/Fit a higher and you will need quite a higher duration cam...at the expense of stretabilty and economy
3/Change the heads.

 

F*CK!

ill just put in the isky 244/244 .450/.450 106 degree cam in it and see what happens.

i must be the worst engine builder in town, Jeez..

 

Good luck. That cam might well do the trick. But maybe give the cam tech (at Comp, Isky or Crane) guys a call and see what they say. They might have a reasonable solution for ya. I'm guessing you'd want a cam that has a later intake closing, but still won't kill you on the street.

I'm pretty sure you can fix this and still be happy. You have a good starting point.

 

Please come back and tell us how it runs w/ the 244/106 Isky cam in it.

And good luck, we are pulling for you to get her going the way you want it!

pdq67

 

i must be the worst engine builder in town, Jeez..

No not at all...I bet 99% of the old hands here , waaay back in their early days all made such similar mistakes mismatching power parts....
My 1st build had single plane manifold, hi compession, and a cam that didnt match..thu that was in the days of high octane leaded pump gas, so detonation wasnt the issue...just couldnt afford to run on long trips and didnt have the go I thought it should

Couldnt afford to do much about it for a couple yrs, thu did swap the manifold for a performer...Then the Gov came to the resuce...they planed to mess with the pump gas
It was then, to the absolute horror of the guys in the Hot rod Club!!! I started to think outside the square....and went to LPG..it was cheaper and had more potentaul to go that route for fuel.
The 1st day out at inter hot rod club drags...a few jaws dropped and where silenced.
It was DYO I took out the prize for the club and ran consistant 14.2s in drive undrer 5000rpm with a 308 diff on old hard street tyres.

 

I could be wrong but I don't think that Isky will be much better, you don't want 106ls, 110 or even 112 might work, whats the advertised duration? 292? But it still won't work very well with high gears.

I would probably run this cam if I were in your situation: Power Max H-284, 284/284 222/222 .450/.450 114ls. I think it would be a good compromise between your gears and compression. Or maybe the H-288-2, 288/296 226/234 .458/.473 114ls, this will have less chance of pinging.

http://www.cranecams.com/pdf/Page236-257.pdf

What is the advertised duration and lobe separation of your 216 cam?

 

thats 272/272 advertised and 110 degree lobe sep.

 

What about this cam?

rpm range looks okay to me, 107 lsa for loosing some compression, i think....?


Brand: COMP Cams
Product Line: COMP Cams Thumpr Hydraulic Flat Tappet Camshafts
Part Type: Camshafts
Part Number: CCA-12-600-4
Cam Style: Hydraulic flat tappet
Basic Operating RPM Range: 2,000-5,800
Intake Duration at 050 inch Lift: 227
Exhaust Duration at 050 inch Lift: 241
Duration at 050 inch Lift: 227 int./241 exh.
Advertised Intake Duration: 279
Advertised Exhaust Duration: 297
Advertised Duration: 279 int./297 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.479 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.465 in.
Valve Lift with Factory Rocker Arm Ratio: 0.479 int./0.465 exh. lift
Lobe Separation (degrees): 107
Camshaft Gear Attachment: 3-bolts
Intake Valve Lash: 0.000 in.
Exhaust Valve Lash

 

Bottom line...what is the design/use of the engine for
Strip, circuit, Street strip, Sat night street, or weekend highway cruising, general daily around town...
From this info, correct cam selection and mods can then be suggested with some accracy

At this stage, if used for street, no matter what diff or cam you put in, unless u run expensive high octane fuel with low milage, there is still a good chance you will still get detonation....

More info.

 

I think the Comp 280H would work great with 10.8 to 1's and still be fine with 2.73's. Doug H was running a very similar combo as your with 2.73's. He was still running bottom 13's with it.
It specs...280/280.....230/230.....480/480......110

 

Imho, you can bleed compression off at three timing events.

At overlap around TDC, by widing the LCA to move intake valve closure and by retarding the cam so that the intake closes later, thus trapping less charge.

The only problem here is that I HAVE to concur to somebody like UDHarold, Chris and others to tell me which override's the other two??

pdq67

 

I'll have to disagree with "bleeding compression".
You are "traping" less at lower RPM where your cam is not efficient, but once you get in the operating range where it becomes efficient, you are back to traping the same amount. This is why cams move your peak numbers higher.
In addition, at higher rpms, you get a slight cooling effect from the intake charge (it is a little coole because it has less time to absorb heat on its way to the cylinder), so it does help a little with pre-ignition, but, I would still monitor it closely. You may not hear it at 5000rpm either!
The only guys that I have personaly seen running very high cr (12.5-13-1) on pump gas are the Fuel injected LT1/LSx guys. I'm not sure I'd want to try it with our older technology and on a carb (unless the combo is very well thought out: coated piston, chambers, valve and one heack of a cooling systm to keep things extra cool)
I'm not saying it is impossible, I'm saying it's tricky and takes more than off the shelves parts thrown together.

 

I'll have to disagree with "bleeding compression".

I agree bleeding is a long shot...and if lucky will work
But with such a high compression and reasons stated above its less than a 50/50 chance will work..
Drop the compression with bigger chambers...and It WILL sort the issue...and dont have to change the cam or touch anything else..
Go the cam way and the likely hood heads etc will have to be done...which means a hell ove a lot of double work and expense.

 

I have an engine im doing in my neighbors garage thats 10.75:1 with a .450 lift rule 110 cam and 230/236 duration. it will run fine with proper tuning. Its got DBL humps.
Look into a circle track cam. I LOVE those for street motors. If you think about it, the usable RPM range on the street is where the circle track cams make their power. Always made sense to me. Its worked so far. I rarely use drag cams on a street car.
ALL IMHO of course.

 

I/m w/ wiskee here, lift-limited roundy-round cams are fine for lift-limited heads!

Like the old double humps and stock Vortec's and such.

pdq67

 

i just ordered an ISKY cam with 234/234 duration en .450 lift at 106 lsa
(278/278 advertised)

with some Lunati hydr. lifters, i hope the 106 lsa is not too much...

 

Its gonna have a rumity rump idle thats for sure!

 

Should sound WAY cool!

pdq67

 

Just wondering if you had checked what your cranking compression is.
You can also install a methanol injection kit.

MBHD

 

Robert,

You have the lobe separation angle vs. cylinder pressure "bleed off" concept backwards. If you had two identical engines, with the same cam and you only changed the lobe separation angle, the cam with the wider LSA would have lower cylinder pressure. The cam characteristic that effects cylinder pressure is the Intake Valve Close timing (or IVC) not LSA or overlap.

My recommendation for a cam based on US octane gasoline would be something like the Comp 292H -- 292* advertised, 244* duration @ .050, 110* LSA, installed on a 106* intake center line. This cam will work with power brakes in a 383 like yours and will make power from 3000 to 6000-6500 RPM.

If your gasoline is 98 octane, R+M/2 method, then the 230* cam that you originally planned on would work well with better street manners and a slightly lower RPM power band.

Hope that helps. There is also some good information in a few of the threads you originally started when you were building this engine a year or so ago. You can find them by searching by your user name and "383"

 

Hi Robert:

One thing you might try is running an old 30-30 Z/28 cam. THis closes the intake valve at 59 deg a.b.d.c. I have talked to guys who run this in their 302's with 11:1 and can run on pump gas. I run one in my 68 Z with a 302, and can run pump gas. Just remember this is an old school cam, and power range is 4000-7000 r.p.m. Might be 500 r.p.m. lower in a 383. If you call Crane and talk to their tech. dept; Steve is really sharp and very helpful. Good Luck

 

well ill just install that isky i allready ordered, can i advance or retard that cam a little for bleeding compr. off?

 

You need to have a good quench area.
Have close to zero deck as possoble even a positive deck height will work.
I ran 12-1 ,had 220 cold cranking cylinder pressure & ran pump gas,,,but I had zero to positive + .003-.004 deck height.

MBHD

 

Is it a 278/234, 106/106, .450" lift cam?

If it is, install it at 106/110, or four degree's retarded so that the intake closes later.

pdq67