The V8 Owners Forum -

Hi
Can you tell me with a few questions regarding upgrading my RV8. I currently have a standard bored 3.5 SD1 with a Hurricane cam, duplex timing chain, standard heads and a a weber 500 carb. My question is, can I put on stage 1 or 2 heads without any other mods and if so will I get a noticeable performance increase (BHP)? I had thought of getting a pair of old heads and trying to port them myself, with a bit of help to get the valve seats done etc.
Any comments and advice would be greatly appreciated.

Martin

Heads are almost always worth it IMO.

As to what spec....depends on your budget. But I say always buy the best you can afford. that way you wont regret doing it later, and want to buy better.

Depends on budget. Cheapest - file exhaust ports to match the manifold. Or send the heads to Roland Marlow at ACR Automotive for a proper doing. he did mine - there is not much he doesn't know about V8's.
My 4.8 v8 pulls 300 hp at 6150 rpm. Same torque at 4000.

Stephen Leckie wrote:Depends on budget. Cheapest - file exhaust ports to match the manifold. Or send the heads to Roland Marlow at ACR Automotive for a proper doing. he did mine - there is not much he doesn't know about V8's.
My 4.8 v8 pulls 300 hp at 6150 rpm. Same torque at 4000.

No don't file the exhaust ports to match the manifold. You need a step to catch the reflected wave coming back up the exhaust. Unless of course your doing an all out high rev for a track.

katanaman wrote:

Stephen Leckie wrote:Depends on budget. Cheapest - file exhaust ports to match the manifold. Or send the heads to Roland Marlow at ACR Automotive for a proper doing. he did mine - there is not much he doesn't know about V8's.
My 4.8 v8 pulls 300 hp at 6150 rpm. Same torque at 4000.

No don't file the exhaust ports to match the manifold. You need a step to catch the reflected wave coming back up the exhaust. Unless of course your doing an all out high rev for a track.

You can also create the step by not matching the round header tube with the square exhaust port flange. (You can sort of flattern the tube so that the sides match but not the top and/or bottom).



Pete

That engine sounds like it's crying out for a decent pair of heads, having already had some sensible mods already. It would be fair to expect a gain of 25+hp over the standard 3.5 heads and you can add another 10 at least with some good headers.

By increasing the size of the inlet ports, ie stage 1 or stage 2 depending, you will increase the ability of the heads to breath better at higher revs, but of course there is a trade off, torque in the lower rev band will be reduced.

Torque equals acceleration, so until the revs rise sufficiently, acceleration will suffer.

Fuel consumption will also increase quite considerably.

These are my understanding of such modifications.

I recall seeing a graph of torque and horsepower between a 4.6 with standard heads, and the same engine with stage 3 heads.
Up to 3500rpm, the standard engine delivered more power and more torque, which for a road car is exactly what you need.

Beyond the 3500rpm point, the 4.6 with stage 3 heads pulled right away in both power and torque.

RoverP6B wrote:By increasing the size of the inlet ports, ie stage 1 or stage 2 depending, you will increase the ability of the heads to breath better at higher revs, but of course there is a trade off, torque in the lower rev band will be reduced.

Torque equals acceleration, so until the revs rise sufficiently, acceleration will suffer.

Fuel consumption will also increase quite considerably.

These are my understanding of such modifications.

I recall seeing a graph of torque and horsepower between a 4.6 with standard heads, and the same engine with stage 3 heads.
Up to 3500rpm, the standard engine delivered more power and more torque, which for a road car is exactly what you need.

Beyond the 3500rpm point, the 4.6 with stage 3 heads pulled right away in both power and torque.

I guess really what my question is, is that can these heads bolt straight on or will I need to make other mods to accomodate the uprated heads??

Thanks

Martin

RoverP6B wrote:By increasing the size of the inlet ports, ie stage 1 or stage 2 depending, you will increase the ability of the heads to breath better at higher revs, but of course there is a trade off, torque in the lower rev band will be reduced.

Torque equals acceleration, so until the revs rise sufficiently, acceleration will suffer.

Fuel consumption will also increase quite considerably.

These are my understanding of such modifications.

I recall seeing a graph of torque and horsepower between a 4.6 with standard heads, and the same engine with stage 3 heads.
Up to 3500rpm, the standard engine delivered more power and more torque, which for a road car is exactly what you need.

Beyond the 3500rpm point, the 4.6 with stage 3 heads pulled right away in both power and torque.

So you say that std 4,6engine delivered more power and torgue at low rews than stage 3?

Have a look my stage3 4,6efi torque curve. (it´s not my best power/torque curve, but i cant find any better now.) My best torgue curve is 350Nm @ 1000-1100rpm and 440Nm@3800. Curve depends lot of ignition timing..
This graph shows about 325Nm@1000rpm.
1500rpm is about 375Nm.




Rpi says:
http://www.rpiv8.com/engine-3.htm

1500rpm = 340Nm.. Mine has got over 35Nm @ 1500rpm.