I have a 385" sbc. 6" rods, 254@.050 intake, 262@.050 exhaust solid cam. Thinking of milling the alum. heads this winter to go from 11:1 to 12.25:1 compression. I run race gas anyway & when e 85 comes my way i'll be ready. What are thoughts here?

4 sp. car 4:11 r.p. & street strip

 

If you're running race gas anyway no reason not to go for 13.0. Sounds like fun!!

Might be able to throw a little more cam in it with the added compression and really fly!

JIM

 

I have considered a new cam, but need to keep an eye on the dollars for now...

 

Compression ratio has the law of diminishing returns. With gasoline once your over 11ish compression additional points might only be 1-2 % of power change.

Why would you run race gas with a big cam and only 11:1 C/R? My 383 runs very nice on a less duration SR cam and 11.24:1 compression on our 91 mandated super unleaded.

Your money might be better spent finding oz of power else where.

Picture of 13.8 compression pistons for a racing 396 ci small block I put together. I can't remember if they were an 7 or 9 cc dome for 3.875 stroker, 6 inch Manley rods Dart 227cc heads 2.08/1.625 with .750 max lift roller springs

 

Hi "73", we do a "bunch" of these style units over here and I gotta' tell you that if you run/plan-to-run "fuel" you are as we say here "in-no-mans-land" if your between 11:1 and 14:1. This is a good area to merely burn up some decent fuel and actually get NOTHING in return. This is my opinion, and most of my customer's as well, you'll also gain nothing with "milling the heads".

A number of our "better" street units up here are at 15.5 minumum! All (larger) SB's. Thanks, Gary in N.Y.

P.S. George, while I'm here if you are using the heads in the photo, and I'm saying this merely from what I can "see" there, I would suspect you MAY, more than likely be "shy" a 100 HP. I'll put a photo here of recent 11:1, 93 octane 406" made 600+ (using our 4500 carb) in the dyno room, but was delivered at 580. Customer has since changed carb and has his 600 back. Nothing fancy, in-house ported 235 Pro-Toplines, wet-sump, "standard" box pistons/ring-pack, and a small roller. The photo is the only one I have showing the exhaust's. Not the best shot, but kind of the ports you need "going out".

 

Go fast, are you saying that you're "better street engines" run 15:1 & greater? Is this on 110 octane? What is the cam duration to make one of these "street" engines? survive with out rattling to death? With that much compression does the 235 cc intake head have decent velocity for lower rpm running? Finally, what power & torque numbers & rpm curves are generated by one of these monsters? Also, what kind of cranking psi does this generate? thanks much!

 

gkull, sorry, missed the post & thanks for feedback. I know i don't really need the race gas & have run on premium. But i have to admit that i like the smell & the pyschological feel good of this non-essential money burn; crazy, i know. I miss my 2 stroke racing days when we bought it by the barrel & it makes me smile to pump & run it, sad now that i hear my self think out loud about it...

 

I know that logic tells you that a large "D" port exhaust maximizes flow. What you don't see in the Dart photo is that port is .600 raised. So in effect you could never grind a stock location exhaust .600 "D" shaped port. If you go to the Dart head site check out the claimed CFM. When you get up around 230 CFM exhaust is very respectable. Another thing that you can't see is that port is so big that a 1 3/4 hooker super comp primary pipe has to be opened up on the top and sides to even get close to size of that port. The bottom of course is a anti-reversion

Without a flow bench............ I would not get in and take a chance on screwing up an already good thing

 

The size of the combustion chamber and the compression ratio have nothing to do with port flow velocities.

What I question is why if "This is a good area to merely burn up some decent fuel and actually get NOTHING in return. This is my opinion, and most of my customer's as well, you'll also gain nothing with "milling the heads"" do "A number of our "better" street units up here are at 15.5 minumum!"? That appears contradictory.

RACE ON!!!

 

Hi George, first, Happy Thanksgiving!

To the post, understood, and agree totally. I do stand by my original statement, soley BASED ON THE PHOTOS, don't care about the "raised" port deal, but the ports themselves "appear" to have 100 "ponies" lying in their. Unless I had the heads on a bench this is pure conjecture still!

I have used just about ALL the brands in the market place, with the exception of the "Canfields", and I still have some issues with BOTH the "Dart" and the "AFR" lines. The unit you see pictured had the 230 Darts on there, removed them and used the "Pro's" and picked up about 30+ HP. More recently removed a set of (early) BB Dart 360's from a 540 Blown unit and replaced them with some "2X" Brodix's and picked up a full 1/2 second! Went from 9.90's straight to 9.30's with only the head change. I will add here the Dart's were the original 360's series from the days of the Maskin's/Mitchell era. The flow numbers were very similar on all 4 units, the SB above and the BB mentioned. Port shape AND design are more critical to making power than overall flow numbers. We run 2 (Superflow) benches much of the work week over here. I do have 3 but only use 2. Thanks, Gary in N.Y.

(Add) To answer EFI-CFI, if you're going to buy fuel for $5.00+? per gallon it makes sense to use a C.R. of 15 in place of 12, the torque numbers climb dramatically from the C.R. itself. Also if he manages to get his C.R. up by (angle) milling he will most definitely have the wrong cam in there. Been down that road with a few of my own customers. If you
"jump" around with that C.R. spread, the "base" combo becomes all wrong! We see this in the dyno room constantly. Trying to maintain adequate torque numbers on pump-gassers while making the required power is difficult. It comes down to the fact Compression = Torque, it's that simple. That 730+HP SB (mentioned below) made only 640 torque due to the 11:1 C.R. In our opinion, weak torque BUT runs/races fine on the 93! You get increases in torque with stroker's, but with stroker's AND high C.R. ratios it's more dramatic.

P.S. In answer to the C.R. above, up here in N.Y., the street cars are more like registered track cars. But they do meet the criteria. These 15+ C.R. units will not run on 110 but we pay the same for higher octane. Now I'll go one further here, we do have a 100% street car here that has a 468" SB runs on 93, N.A., and came off the dyno at 730+ at under 6600 and sat in the dyno room idling around 800/900 if I remember correctly. This car is driven to and from his job every day in the nice weather. Pulls into the local station and "fill's-it-up".These are NOT 23 degree units, 18's or under! We have an upcoming 11 degree almost at the dyno door!

 

Yeah, that was sorta my point. No reason not to throw real compression in it. I guess I should have said 13.0+++++!!

Adding compression with no other changes doesn't add lots of power if it's pretty decent anyway. But it DOES allow more cam and THAT will add real power. Plus there is a distinct ability of the engine to "gain" rpm quicker. A dyno doesn't always tell you that, but you can tell a high compression motor at the track by the way it comes out of the corners or pulls through the gears and in high gear on the other end.

Plus they sound really cool!!


JIM

 

thanks to all. may pull my heads before snow flies for a look. also, going to look to see if the cross section can be opened up a bit...