what CR do i need?

[sabre67]

Hello all hope your keeping safe Im building a 440 for a street driven Dart automatic . I have purchased Edelbrock Performer RPM heads #60929 (84cc). The Lunati cam and kit I purchased #(771977PR-16) has these specs
Advertised duration (int/ext) 268/276
[email protected] (int/ext) 226/234
Gross Valve Lift 494/513
LSA/ICL (110/106)
RPM Range (1800-6200)
My question is What compression should i be aiming for to use these parts?
Thank you very much for any help Sabre67

 

[diesel_lv]

I'd call Lunati and see what their recommendations are for CR. They should know their cams best.

 

[justcruisin]

I would be shooting for around 10:1. If you build a stock stroke short block I would get the block machined for zero deck. With a flat top piston with 4-6cc reliefs that will net you just a little over with a 0.039" gasket depending on the piston relief. Tuned properly you will have no problem at sea level on pump gas.

 

[440Coronet500]

I run a similar duration cam with slightly less lift. You should run about 10:1 CR. 440'

 

[dadsbee]

What is your plan for fuel?

 

[sabre67]

92 is the best around where i live

 

[dadsbee]

Then you'd be wise to read through hunt2elk 's thread on "engine advise" if you aren't gonna mix that 92 with something a little more potent.

 

[Beekeeper]

Then you'd be wise to read through hunt2elk 's thread on "engine advise" if you aren't gonna mix that 92 with something a little more potent.

Wayne you have a link to the thread?

 

[Nate S]

I’d go 9.5 or maybe 9.75. Over that with 92 octane you’ll be knocking if you set the timing and advance curve properly. Wrong timing to fix too much compression will hurt you more than lower compression. Be sure you calculate it all properly. Do it yourself, don’t trust an online calculator, I’ve seen many be wrong. Did you measure deck height and pin to top on the old pistons? Much easier than measuring crank centerline to deck.

 

[dadsbee]

Wayne you have a link to the thread?

https://www.forbbodiesonly.com/moparforum/threads/need-some-engine-advice.194871/

 

[sabre67]

Thanks dadsbee ill look at that

 

[sabre67]

Nate S i dont have a engine yet still looking for a good rebuilder

 

[beanhead]

If 'street car' means today's 92, with that cam, safer is better in my lowly opinion. (I'm over in Crapgas-afornia though...I don't know how your fuel quality is up there?) Gearing and converter will kill a cam and performance quicker than a few tenths of SCR, in my opinion, so hopefully those are well-matched...I'd be thinking keep it nice and safe. There just isn't a big difference in performance with a couple tenths of SCR at that level...so why push it. Along the lines of what "Nate S." stated above, you don't want to have to reduce the timing or monkey around with the tune to keep it from pingin'...
Sophia Loren is an all-timer by the way

 

[33 IMP]

I agree with those above who urge restraint. I would shoot for 9-9 1/4. That cam is a little small, imo, for more than 9.5. Ever since i used wallace calculator to see how much(little) power is lost by lowering compression, i have become more conservative. Not much worse than having to crutch a tune for a motor that rattles. You specified a street driver. There is no need to push the compression envelope.

 

[wyrmrider]

9.7 = 264 with tight quench
9:1 = 256 say 460 intake lift 112LCA
so 10 should work al heads help as does the combustion chamber
LCA makes a difference
whats your intake close abdc?
if lunati does not show it look up a comp 268 it will have the .006 timing
but you have the better cam
what 33 imp said
tall gears, towing back it off a little
you need cold air
and dist curve work
tight quench is one key
good flowing exhaust is another
so there are still some unknowns

 

[sabre67]

Thanks for all your good info,I think ill take the conservative approach and stay below 10.1

 

[33 IMP]

Wallace calculator says a 400hp engine with 10 to 1 compression, if you drop compression to 9 to 1, the horsepower plummets to only......395. A nine to one motor will be a lot happier on crap gas.

 

[69 GTX]

The piston will make all the difference. With that big of a chamber it'll be prone to knock even with alum heads at 10:1 on anything less than 93 in my opinion. I'd shoot for 9 with a flat top and 9.5 with a good piston to get good quench and squish. Then you can run 88-90 and not have to run the expensive gas. Even more so if your not going to the track. More fun and less$!

Also depends on your altitude. If your at 4-5000 ft that'd help..........

 

[1 Wild R/T]

Wallace calculator says a 400hp engine with 10 to 1 compression, if you drop compression to 9 to 1, the horsepower plummets to only......395. A nine to one motor will be a lot happier on crap gas.

That number is deceptive... Yes the peak HP doesn't change much but the torque and throttle response will be noticeable lower....

Aluminum heads & pay attention to getting a tight quench and I'd stay closer to 10-1...

No mention or the gear, 3:55 or more definitely will take more compression, 3:23 with an A body I'd still build for 9.5+ 2.76 stay safe & build for 9-1

The fact car is a Dart means it's light, which means the engine won't be working hard... Pushing a heavy B/C or Truck you need to be conservative, pushing a A body is less of an issue.... Personally I would have looked at a little more camshaft but it shouldn't be an issue...

 

[justcruisin]

I run a similar combo, 440-448ci, 10.2:1 with a 0.039" quench, eddy rpm's, slightly bigger cam, I run 18/35 ignition timing and run it on 93 but it will run fine on 91. No hint of detonation regardless of weather either audibly or visually with regular plug inspections and a endoscope down the holes. Mostly at sea level, 4050lbs, 11" converter and 3.23 rear gear. Been running that way for 8 years. If you want to run less compression you will need to run a dish piston, a thicker head gasket or have the pistons down the bore a bit, not sure if that is a good move to fight off detonation. As 1 wild R/T said with a light car you could afford to run a bigger cam, it would help with cylinder pressure bleed off.