3.5 V8 High comp or Low comp?

Id always looked at the shallow intake runners and wondered how much more grunt id derive if I fitted a high rise manifold with longer intake run.

I remember pulling the intake system apart on an injected 3.5 and seeing the tuned length trumpets hidden inside the shoebox shaped alloy housing which brought a smile to my face as this confirmed to me that the Carbed Rangies were suffering with the shallow carby manifolds they came out with.

My experimental build would comprise of Porting, a special grind cam, Hypertec pistons with 5 thou bore clearance, standard rings (Not ChroMo), a high rise manifold and a suitably jetted 4 bbl down draught.

Add an electronic dissy dyno tuned to set the advance curve, 8 mm leads and a cap mounted coil pack to provide maximum spark and I suspect id have a reasonable performing engine with more torque.

The drawbacks are lack of height under the bonnet and the Hypertecs not enjoying a good rev as they expand if over revved and with 5 thou clearance any expansion would be catastrophic.

its a hypothetical spec By the way bt based on what I think would make a nice package.

Tony

Hypereutectic pistons dont expand when you get them hot , that is why they are used !
A special grind cam ? you going to degree it in properly when you fit ?
A High rise manifold ? What do you expect that to do ? dont you mean a Single or dual plain manifold ? A 4 barrel Carb ? that was suitably matched to the heads.
All of which wont do anything , unless you have the heads properly ported .
There is huge difference between all the home head port jobs and getting it done professionally . With severely port choked heads like yours , changing the rest wont make any difference , except chew alot more fuel .
A lttle something from a real Head Porter
How do you set up a port for the correct air speed vs Engine size & RPM? How do you determine your ports don’t end up in port choke? The cfm off the flow bench may not tell you! Neither will guessing or grinding by eye without measuring & setting the ports up to specific sizes. A modern cylinder head must be efficient, be it CFM / Sq in, Discharge co-eff’ velocity, Pressure Recovery, Mixture Motion. This is what CHT specialise in, with over 20 years experience of racing & cylinder head modifications. It’s experience that counts & that’s how CHT can help you. Correct sizing areas to set Mach speed velocity which is paramount to horsepower production at the desired RPM without going into port choke at the minimum cross sectional area or at the valve curtain area. Fine tuning of valve seats. Port mapping & designs. Combustion chamber modifications to control detonation. A popular saying is: Make it flow as much as possible! Sounds good, but it can be a torque and HP disaster if you don’t know what you’re doing! Too much CFM can be a bad thing if the min CSA is too small and the pitot pressure is higher that your test pressure. Port choke with a fairly large HP/ Trq loss will be the result.
Not hard to get your little 3.5 Heads out to 300HP potential , up to you how much of that you want !,only issue will be the $$$$$$$$$$$$$.

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Originally Posted by Squigs

Gday phillip I have just purchased a 76 2 Door Rangy non detox 3.5 what advise can you give me on making this motor perform better it has extractors already a non standard cam bought from rover tech standard carbys standard ignition this engine drinks fuel lacks power. prevoius ford v8 owner now wont to learn the v8 rover stuff by the way i am a mechanic of 30 yrs exp..cheeers Mike

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I had an after market cam in my V8 and it really lacked performance. I installed a pre-pollution cam from an early Range Rover (up to 1975) and it really improved the torque through the whole rev range.

Edward

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Originally Posted by I Love My Landy!

I had an after market cam in my V8 and it really lacked performance. I installed a pre-pollution cam from an early Range Rover (up to 1975) and it really improved the torque through the whole rev range.

Edward

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Try using Wade Cams 259a grind, works best with high compression. Brings max torque down from 3700rpm to a more usable 2500rpm.
Yes the intake manifold is shallow to keep motor under the fairly shallow bonnet height, keep the standard inlet rams horns to air cleaner this helps to keep air velocity up for improved torque. Keep your primary pipes on exhaust headers to 1 5/8" for mid range. My last 3.5 10:1CR with HS6 SU carbs regularly achieved 27-29MPG on the highway with the above cam and kept up with a mates 4.9l stoker!

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Originally Posted by PhilipA

Well this is a hard one to answer.
If you want torque then bigger capacity is really the only answer.

I often see posts on this forum that people are disappointed with aftermarket cams. I would (and just recently did in my injected 3.9 ) only fit a 3.9 injection cam as my research showed that even the mildest aftermarket cam was too radical for the reality of a 3.5 in almost 2tonnes.

You can gain about 7% modifying the heads as the exhaust ports are small and in many the casting so poor its a wonder anything gets through. I spent most time on the exhaust port bowls.

Extractors IMHO do not anything but noise and leaks to a 3.5. I had extractors on my 77 when I bought it , and got annoyed with the leaks. I was able to buy a complete injection exhaust system and it performed better.
You can fit larger carbs with 2inch SUs a possibility, but Rover tried them and rejected them early on as they cut down low rev torque.( and SU apparently couldn't supply enough). Some here fit Rochester carbs, but IMHO they would be very overcarbed.

My experience with particularly a fresh engine is that they are quite perky. they just get weaker over time as it is common with the old ones for head gaskets to leak into the valley., valves to leak etc etc .

My response to your comment on drinking is that it is all relative . Pushing 2tonnes and a brick ****house shape is never going to be fast or economical. Mine only ever got about 13.5L per100KM highway at its best with injection and Fairey overdrive. They are fast and economical in a TR8 or SD1 Vitesse.
So , if you do not think it is overcapitalising, the best bang for the buck is a 4.6., or even a Leyland 4.4 as it is actually legal in a 76. I think a 4.4 with nice heads and a 3.9 cam would be a really nice goer, but you may then like an overdrive.
Regards Philip A

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To clarify a point here, a P76 4.4 is not legal in any range rover without an engineers report as they were not fitted the the vehicle from the factory. They are not a straight swap as engine mounts have to be modified and flywheels redrilled. The best bet for extra cubes easily is a 4.6 or a stoker kit.