Optimum Compression Ratio for 383/432 Stroker Build

[TorRed]

Hi All,

I'm about to get serious about restoring my 70 Roadrunner and have a question about what compression ratio I should shoot for. What I have so far: 440source CNC'd Stealth heads, Doug's 1 3/4" headers, new six pack setup either vacuum or full mechanical linkage carbs (or Mopar M1 dual plane or Holley Street Dominator intakes), Lunati Hydraulic Roller Cam (Advertised Duration (Int/Exh): 282/290 ;Duration @ .050 (Int/Exh): 231/239 ;Gross Valve Lift (Int/Exh): .535/.550 ;LSA/ICL: 110/106 ;Valve Lash (Int/Exh): Hyd/Hyd ;RPM Range: 2200-6200). 3000 stall FTI torque converter, Gear Vendors Overdrive, 8 3/4 with 4.10 gears. I'm also sticking with a 2.5" exhaust for clearance and sound.

When I order my 432 stroker kit the highest compression ratio listed for my 80cc heads is 9.8, if I shave the heads to 75cc it jumps to 10.3 which I think is closer to what I want. Opinions? Worth the cost of shaving the heads (haven't priced it yet)? Is 9.8 to 1 fine with everything else I'm running?

Thanks in advance for your input,
Jim

 

[6PKRTSE]

With today's gas I would stick with the 9.8. Several of my street engines are 10.5 to 10.75:1 with no issues. However, I run all of them on 93 octane.

 

[PurpleBeeper]

Yeah, 6pk is right. It depends on what gas you can get. I’m shooting for 9.5:1 for my next motor so I can drive cross country where I might get not be able to get 93 octane

 

[33 IMP]

I sure wouldn't go higher than 9.8 for a mild combo like yours. I'd probably shoot for 9-9.5 for a street car, considering best gas around here is 91, 10% cat piss.
A half point too little is MUCH better than a half point too much, imo. A half point might lose 1%, but I think less. I'd gladly give that up to run pump gas anywhere.

 

[hunt2elk]

9.5 to 9.6 is the max I go anymore with todays crappy gas, and I'm sure it will be getting no better in the future. 91 octane 100% gas with aluminum heads is what I run.

 

[TorRed]

Thanks for the input, I really like the 'bark' of the exhaust note with the current build with TRW pop up pistons and around 11 to 1 compression. In Georgia and now Florida 93 octane is readily available but with the government working hard to get these and other ICE vehicles off the road, one thing they could do is make 93 and even 91 not available in the future. I guess I could go with the 9.8, that way with no milling there's no concern about intake manifold aligning with the intake ports on the heads.

 

[TorRed]

Second question: any estimates what this combo would make in HP & TQ? I'm thinking close to or slightly over 500 HP and maybe 525 TQ? Opinions?

 

[RemCharger]

Maybe even closer to 550hp

 

[TorRed]

Maybe even closer to 550hp

Cool beans, thanks for the optimistic reply!

 

[RemCharger]

Cool beans, thanks for the optimistic reply!

My cousin built a 451 a while ago very similar, but unported stealths. It was showing about 520

 

[TorRed]

My cousin built a 451 a while ago very similar, but unported stealths. It was showing about 520

I'll have a few less cubes but better flowing heads so it should be interesting to see if I end up above or below your cousin's number. I'd be very happy with 500-550 HP, with my cam & exhaust both being more street oriented than track. Thanks for the reply.

 

[rumblefish360]

10-1 to 10.5-1 max. Although currently I have a 360 @ 11.3-1 using 93 with TF heads and TTI headers with a hyd roller cam that is small. 224@050 intake w/1.6 rockers.
Read it below;

 

[451Mopar]

The 9.8:1 would be a good ratio with those heads, camshaft, and pump gas.

 

[TorRed]

10-1 to 10.5-1 max. Although currently I have a 360 @ 11.3-1 using 93 with TF heads and TTI headers with a hyd roller cam that is small. 224@050 intake w/1.6 rockers.
Read it below;

View attachment 1602702

I have the Crane cams card from back in 70's somewhere, I think I remember it spelling out the 'overlap' between the intake & exhaust, but

 

[TorRed]

The 9.8:1 would be a good ratio with those heads, camshaft, and pump gas.

Thanks for the input, I think the chorus of replies telling me to leave it at 9.8 has me feeling pretty good about not shaving the heads for more compression.

 

[rumblefish360]

Thanks for the input, I think the chorus of replies telling me to leave it at 9.8 has me feeling pretty good about not shaving the heads for more compression.

Please do so show it and explain it for us all if you can.
It would be of great help I think for those here.

Here’s my small block Crane Hyd flat tappet cam card.

 

[TorRed]

Please do so show it and explain it for us all if you can.
It would be of great help I think for those here.

Here’s my small block Crane Hyd flat tappet cam card.

View attachment 1605217

I know I didn't throw it away but it's been years since I remember seeing it so it may take me a while to dig it out. When I do I'll absolutely post it. My Roadrunner was the fastest street car in Griffin, Georgia back in the mid 70's. There were a couple of cars with big slicks, gutted interiors and open exhaust people would race for big money, I never raced those.