[71C10]

Thinking about a cam and hedder swap to pick up some power in my 87-octane drinking 388. I don't know how much power it is making now as the closest chassis dyno is 200+ miles. Has anyone has done anything similar? What were your results? Here are the details:

Weight with driver 3950
Engine 9.25 compression SBC 388 built for 87-octane fuel
Milodon 6 quart oil pan
Eagle 3.750 crank
Eagle 5.7 rods
Probe forged pistons
Sealed Power plasma moly rings
Comp Cams Pro Mag 1.52 rockers
AFR 195 angle plug heads
Edelbrock Performer RPM Air-Gap
Pro Systems 780 DP Holley
MSD Pro Billet HEI
1 5/8 Hedman hedders now 1 3/4 after cam swap
TH400, Transmission Specialties 10 inch 2600-3200 converter
Gear Vendors overdrive
Denny's driveshaft
12 Bolt 4.10 Detroit Truetrac
B&M truck mega shifter

Current cam solid flat tappet specs:
Grind Number CS XS274S-10
________________________________________
Intake Exhaust
Valve Adjustment 0.016 0.016
Gross Valve Lift 0.501 0.510
Duration At 0.015 Tappet Lift 274 280
________________________________________
Valve Timing At 0.015
Open Close
Intake 31 63
Exhaust 74 26
________________________________________
These Specs Are For The Cam Installed At 106 Intake CL
Intake Exhaust
Duration At 0.050 236 242
Lobe Lift 0.334 0.340
Lobe Separation 110
________________________________________
Recommended Valve Springs 983-16

Proposed cam solid roller specs:
Grind Number CS XR274 R-10
________________________________________
Intake Exhaust
Valve Adjustment 0.016 0.018
Gross Valve Lift 0.564 0.570
Duration At 0.015 Tappet Lift 274 280
________________________________________
Valve Timing At 0.015
Open Close
Intake 31 63
Exhaust 74 26
________________________________________
These Specs Are For The Cam Installed At 106 Intake CL
Intake Exhaust
Duration At 0.050 236 242
Lobe Lift 0.376 0.380
Lobe Separation 110
________________________________________
Recommended Valve Springs 977-16

Current cranking compression is 175-PSI hot and interestingly enough the proposed cam has the same valve timing events. Comp Cams tech said that I could even step up to the next bigger roller (XR280R) and only lose about 10-PSI of cranking compression, "the 10.1 compression recommendation does not apply to your 87 octane engine build."

Please don't provide an uninformed "guess" if you have no experience in this area. Low octane performance can be done, I drove this thing half way across the country on 87-octane and think there is more HP in it waiting to be unleashed! The question is how much?

[71C10]

Here is the larger solid roller cam specs:

Grind Number CS XR280 R-10
Description
--------------------------------------------------------------------------

Intake Exhaust
Valve Adjustment 0.016 0.018
Gross Valve Lift 0.570 0.576
Duration At 0.015 Tappet Lift 280 286

--------------------------------------------------------------------------

Valve Timing At 0.015
Open Close
Intake 34 66
Exhaust 77 29

--------------------------------------------------------------------------

These Specs Are For The Cam Installed At 106 Intake CL
Intake Exhaust
Duration At 0.050 242 248
Lobe Lift 0.380 0.384
Lobe Separation 110

--------------------------------------------------------------------------------

Recommended Valve Springs 977-16

[GoneNova/406]

i have a 10.5-1 406 but with the gas prices now i opted to build another 9.4 motor to run on 87 octane.i've read alot of magazine articles by all kinds of engine builders and i agree hole heatedly that there is power to be had at that level of octane.the roller cams and alum. heads are a big plus in that area.if you go to AFR.COM,then click on articles,drop down down near the bottom of the sbc list you'll find one that says "412 H.P.350 c.i. afr 190 cc",hot rod ,june/97.the name of the article is,"the 350 engine chevrolet should have built".they build an engine under tight constraints money wise and performance wise but still come up in good shape for power and torque cheaply and use 87 octane.if you pay close attention you'll see where many performance parts can be swapped in to make big power still with 87 octane.

[71C10]

So nobody has any idea of the approx HP my current combo has? My guess about 425. How about after the proposed changes?

Anyone have any quarter mile estimates with 28x10.5 slicks? Depending the attained speed I could cross the finish line in 2nd over (1.15 to 1) instead of direct (1 to 1) due to the Gear Vendors OD.

The motor turns 6600 no problem but since I don't know where the HP peak is I could be shifting it too late.

Any good ideas or suggestions?

[onovakind67]

Please don't provide an uninformed "guess" if you have no experience in this area.

I guess there aren't many here who are qualified to guess.

[71C10]

Originally Posted by onovakind67

Please don't provide an uninformed "guess" if you have no experience in this area.

I guess there aren't many here who are qualified to guess.

LOL What I meant was no wild estimates from guys who have not built or dyno tested similar engines. Surely someone here has built and dyno tested a combo like this... if not I'll post results when I get on it a chassis dyno or to a drag strip this spring.

[xntrik]

Power is affected by more variables than we can see on your list. But your power should be very good.

Cranking compression is determined not only by static calculated compression ratio but also by the intake valve closing point. Your cam is advanced 4* as installed and lengthens the dynamic compression stroke. Retarding the cam to straight up will reduce cranking compression and bias the torque curve to a slightly higher (200) rpm.

Installing a longer duration cam will assist in moving the power peak upward, and if the (cam timing) intake valve closing point remains the same as the other cam, the cranking compression will remain the same since the dynamic compression stroke is still the same length, but of course the power curve will be moved higher and the low rpm might feel a little soggier.

Of course stepping up to a roller and its more agressive ramps will make more power across the board.

http://e30m3performance.com/myths/mo...comp_ratio.htm