# Improving Top-End Power



## nestor moya (Jul 29, 2005)

I have a Datsun 510 with an L16 engine modified for high-performance street. The engine pulls very well in mid range but I had calculated that, in its state of tune, it should be good for 6300 to 6500 rpm.

In an effort to get better top-end, I switched from SU carburetors to Dual Weber 40 DCOE and addition to other intake improvements. To my dismay, there was absolutely no top-end performance gain. The engine pulls 5400 rpm in top gear (19.7 mph/1000 rpm); 6300 rpm in 4th (16.8 mph/1000 rpm) and seems out of breath in 3rd at 7200 rpm (12.8 mph/1000 rpm).

My question is: Will a custom exhaust header provide a significant improvement to justify its cost of over $500 or does this car produce so much aerodynamic drag that this is as good as it gets with this engine?

The engine details with the SU and Weber configurations are as follows:

Common Data (applies to both Configurations)

1)	Car: 1971 Datsun 510 with stock body and full interior, including air conditioning 
2)	The car is used for autocrossing and open highway
3)	Weight is approximately 2470 lbs. With driver
4)	Engine: L-16
5)	Total ignition advance 34°
6)	Cam: Isky L-480 Advertised timing @ 0.020” lift: 31-69/69-31; 0.480” lift.
7)	Valve springs: Crane valve springs matched (99# valves seated; 203# @ 0.480” lift)
8)	All valve stems at same height
9)	Compression: Approximately 9.5:1 using small chamber head (A87) and flat top pistons
10)	Combustion chambers volumes 40.6 +/- 0.1cc
11)	Intake port diameter: 1-1/2”
12)	Gearing: 19.7 mph/1000 rpm in top gear
13)	Exhaust: Stock cast iron manifold (4-2-1) with 2” diameter exhaust pipe and single MSL Maximum muffler P/N 6555 at end of tail pipe (muffler is same as used in stock ‘79-’81 Camaro Z28)

1st Configuration – SU Carburetors

1)	1.65” stock intake valves
2)	1.30” stock exhaust valves
3)	Manifolds/gasket matched to the head ports
4)	Dual SU (Hitachi) 38mm carburetors
5)	Aluminum-bronze valve guides
6)	Intake guides cut-back


2nd Configuration – Dual Weber DCOE

1)	1.69” intake and 1.38” exhaust Nissan Competition S/S valves
2)	New aluminum-bronze valve guides
3)	Intake and exhaust valve guides flush with port roofs
4)	Ported
5)	Cylinders eyebrowed for exhaust valve clearance
6)	Dual Weber 40 DCOEs with 33 mm chokes and the following jetting:
Main: 125 Air: 170 Idle: 50F8 Pump: 40 P. Bleed: closed Starter: 60F5
7)	Matched carburetor bores, insulators and manifold to head ports
8)	Carburetor throttle shafts aligned with each other
9)	Independent intake runners for each cylinder (no vacuum ports)
10)	No PCV provisions with Webers; currently using a Morosso extractor system connected to the exhaust pipe, just downstream of the collector

*My question is: Will a custom exhaust header provide a significant improvement to justify its cost of over $500*


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## B11sleeper (Oct 15, 2003)

I'd say the exhaust probably will help.

you seem to be running into the top of your power band. A better flowing exhaust will open up the topend, so you'd want 2" pipe all the way back.


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## 510Mods (Feb 21, 2005)

I have that same combo in my truck right now. Its funny cause I can pull past most normal cars after I did this:
1)Install a black box elec distributor from late 70's datsun trucks.
2)MSD blaster coil
3)Splitfire plugs
4)Tri-Y header
5)Magnaflow exhaust

The motor will stop beathing at 6500rpm no matter what your intake combo is, unless you port the head out and install larger valves. The next step is to turbo the motor. These L16 motors respond very well up to 8000rpm and pull all the way up to it. I believe 20psi stock it will handle no problems. If you slip on the rest of the mods, it will put you in the 180hp mark at the flywheel.


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