RV8 porting

[blitzracing]

Does anyone have photos of a correctly ported head without valves? (say stage 1)The inlet and exhaust exit ports seem straight forward enough, but Im told there are big gains to be had by modifing the port shape behind the guides. Id also like to see what profile is used on the valve guide to improve the flow.

Thanks

[tahiti450]

I am just past half way through doing my pair of big valve heads 43mm inlet 38mm exhaust for my 450. From what Ive read and what Ive seen and done, the major restriction in the inlet port is just after the manifold gasket face opening (which as standard is 25 x 42mm) where the wall of the port intrudes into the port adjacent to the push rod hole and the roof dips also reducing the dims to 23 x 40 (xsa c900mm2) This seems to be the most restrictive section of the port. I have opened mine out to 46 x 28 (xsa c1290mm2) with these dims continuing to the start of the guide boss where things actually open up to 45 x 31 (xsa 1395mm2) and then 43 x 34 at the base of the guide (xsa 1460mm2 less the intrusion of the guide boss which is probably around 150mm2) so the minimum area of 1290 - 1300 is maintained. Guides shortened by 10mm and bulleted. Actual throat area - ID of valve seat is 36mm dia which is only 1020mm2 (less the valve stem of 50mm2) so this looks to be the limiting factor despite the big valves. I have avoided removing much material from the short side of the port (the floor) to avoid tightening the radius on the short side and to avoid getting too close to waterways and most of the height gain is from the roof. So in terms of the port itself there is a gain of about 40% in xsa.
I the case of the exhaust port the narrowest part is adjacent to the top of the guide boss, original dims 25 x 25mm (625mm2) mine now measure 28 x 33mm at this point (925mm2) and a gain of 48% with gains ranging from 44 to 56% along the length of the port. The seat ID lightly fettled from 29 to 30mm gives 710mm2. Again the guide is shortened by 10mm bringing it almost flush with the top of the boss. So again it appears that the port is not the limiting factor once modified.

So far I havent found fresh air either in waterways of push rod holes , phew - having carefully checked wall thicknesses with calipers wherever possible.

I have fought shy of removing substantial amounts of the guide bosses as once the ports are opened out these dont seem to be a huge intrusion and may have the benefit of smoothing flow around the guide itself.

Of course the real restriction in the system is the inlet manifold with runner sizes of 22 x 37mm (814mm2) as standard. I havent got the patience to do the manifold as well especially since V8 Developments do a modified one with 45mm throats for a very reasonable £195 +vat. If you want pics I can post some.
Whether these count as "properly modified" I have no idea but I expect them to show substantial gains in combination with the Stealth cam from V8D.

Edited by tahiti450 on Monday 16th October 19:29

[tahiti450]

PS when you say "behind the guides" what do you mean I tend to view the port as starting at the gasket face and ending at the valve I presume you are looking the other way, in which case yes - this is the port proper, rather than the throat. I suppose it all depends on valve sizes as to how much port enlargement is going to be appopriate.

[v8 racing]

Basically speaking you want to be aiming for the biggest possible valve size you can fit, dont try and technical on the port shape or you will end up possibly getting worse flow than standard, if you are running 4.6 heads just basically remove metal from the port roof and polish the rest, keep the guide boss there but blend it around the guide and fitted bulleted guides, the biggest gain over all will come from cutting the seats at a 3 angle, 45 seat 30 deg into chamber, and 60 deg into the seat from the port, blend the port to the seat, but you could leave a venturie on the long side if you want, just polis the rest of the port with a rough finish, dont fine polish it!

[tahiti450]

v8 racing said:

........ the biggest gain over all will come from cutting the seats at a 3 angle, 45 seat 30 deg into chamber, and 60 deg into the seat from the port, blend the port to the seat,

Fortunately in my case this had all already been done, so other than just some detail smoothing and blending and reseating the valves there was nothing to do in this department.

One area of considerable attention to detail is measuring and re-measuring of the ports at multiple points throughout the porting work to ensure that the inlet ports are all near enough identical in final shape and size to avoid uneven breathing and therefore mixture strength variation between cylinders. Obviously the same applies to the exhausts to ensure peak efficiency but clearly these wont have much impact on mixture distribution.

Edited by tahiti450 on Monday 16th October 20:17

[brummiewedge]

On my engine i had the bigger valves fitted, and the valve throats opened to match, no real porting although mine was a 2001 engine ( dont know which heads you have.). In the wedge the motor made 296 in 3rd or 313bhp in 4th. It pulls harder in the chim which can only be the exhaust being twice the size, as everything else is the same.

[boosted Ls1]

If you want to you can remove the guides and then remove material from the port roof. To ensure the ports all end up the same use a profiled tubuler template made from a piece of copper and fit that in place of the guide. Then remove material up to the bottom of the template. After that you can fit the bulleted guides confident that the port roofs/bowls are all the same.

Boosted.

[blitzracing]

Thanks for the general info. The comment about behind the guide ( as in the oposite side to the exit and entry to the port) was after a passing comment from Roy Burrell ex JE enginnering about this area having the biggest effect. On the guides front, I see V8 tuner do modified (billeted) exhaust guides for not a lot of money. Are the inlet and exhaust guides the same, and can you just drive them out with the head cold ?

Thanks
Mark

[tahiti450]

blitzracing said:

........ I see V8 tuner do modified (billeted) exhaust guides for not a lot of money. Are the inlet and exhaust guides the same, and can you just drive them out with the head cold ?

Thanks
Mark

I THINK the guides are the same but dont quote me, however the advice Ive seen about removal of guides is that driving them out from an alloy head is NOT a good idea presumably as this can cause some loss of material from the head and possibly compromise the security of the new guides plus the general risk of damaging the head or guide bore during what is a rather brutal process. It is best to machine them out until there is only a thin walled tube left and this is then easily pressed out - obviously this requires decent basic machine shop facilities. Fitting the new guides - chilled - to a warmed head is then relatively simple.

[boosted Ls1]

You would use a tool insert and press them out. A cast iron guide will break if you try to hammer it out. New guides won't drop if they have a step at the top.

Boosted.

[tahiti450]

blitzracing said:

......I see V8 tuner do modified (billeted) exhaust guides .....
Mark

PS: I think you mean BULLETED (meaning tapered and sort of bullet shaped at the end) rather than billet(ed) meaning machined from hot rolled metal stock as in "billet crankshaft" etc. Also the same applies for both guides, not just exhaust, in fact the reduced restriction is more important in the inlet side anyway.

[tahiti450]

v8 racing said:

Basically speaking you want to be aiming for the biggest possible valve size you can fit, dont try and get technical on the port shape or you will end up possibly getting worse flow than standard,

Thanks for the chat on the phone today Rob, I'm sorry for giving you the spanish inquisition on the details of the cam tho! Ive read many of your posts but I didnt realise who you were from your PH name. All the people I've spoken to at V8Developments have been really helpful.
I suspect, in the context of the original post, that I have probably been a bit over enthusiastic with my ports (although obviously I am committed now in terms of finishing the job) and that increasing the width in particular as much as I have is probably counter productive from the point of view of reduced gas speeds at low rpm due to the large xsa of the port. This may affect low speed drivablity adversely. On the other hand my driving style is definately not about low rpm slogging (i rarely maintain less than 2500rpm in any gear) and hopefully the large ports will promote mid and top end grunt, we shall see...

[David H]

tahiti450 said:

I rarely maintain less than 2500rpm in any gear

Do you only drive on track?

If not, how do you drive through built up areas?

I wouldn't consider myself someone who keeps the revs down but my my car is lumpy at 1800rpm and below, and this for me is borderline acceptable on the road. Driving in conjestion/built up areas is not ideal.

Edited by David H on Wednesday 18th October 11:39

[tahiti450]

David H said:

tahiti450 said:

I rarely maintain less than 2500rpm in any gear

If not, how do you drive through built up areas?

I wouldn't consider myself someone who keeps the revs down but my my car is lumpy at 1800rpm and below, and this for me is borderline acceptable on the road. Driving in conjestion/built up areas is not ideal.

Edited by David H on Wednesday 18th October 11:39

Change down?? I did say "rarely" and "maintain", I chose my words carefully in anticipation.

2500rpm in 2nd is about 27mph, 2400 rpm in 3rd c36mph. Don't do much town driving generally. IMHO <2000 rpm is mechanical sadists teritory.

Edited by tahiti450 on Wednesday 18th October 12:27

[tahiti450]

David H said:

I wouldn't consider myself someone who keeps the revs down but my my car is lumpy at 1800rpm and below, and this for me is borderline acceptable on the road. Driving in conjestion/built up areas is not ideal.

Edited by David H on Wednesday 18th October 11:39

Incidentally the griff rebuild looks great, its more or less what I have planned for the chim once my new garage is built.
I note you are running the H404 and I assume the above comments apply to this setup? The heads once finished will, it seems, be very similar to grif 500 heads - in that I am told TVR tend to take as much material out as they can get away - with hence the sometimes difficult low speed characteristics of the 500. The Stealth cam is I believe based on the H404 but tweaked to improve drivability (it has very modest overlap for instance)so the finished engine will probably not be disimilar in character to yours and if anything maybe have a smoother idle / low speed tractability. However that is all speculation at this point I will post with the outcome once (this phase) is all done and then I have a variety of induction mods in the pipeline.

[GreenV8S]

tahiti450 said:

I have a variety of induction mods in the pipeline.

[blitzracing]

Whilst we mention cams..I note that all the performance cams offer various power increases with durations of 260' (like the viper Hurricane) and over and various amounts of increased lift over the standard RV8 Cam. If you want a fast road cam they are 285' with power up to 6500 over the peak power of 5200 rpm for the standard cam. But on checking the standard cam duration this is already 285', but with fractionly less lift. A lot of perfomace cams offer less duration! I realise things like overlap and peak lift angles come into it, but has no one tried advancing (or is it retarding) the standard cam to move the powerband? We used to do this on Hillman Imp engines to good effect by simply moving the timing chain on the sprocket by one tooth!

On the porting front, Ill will proceed with caution, and just follow "best practice" to try and keep the port angles slight and not go over the top. I can probibly "bullet" the inlet guides in situ with carbide rotary files as I have done this quite successfully on Fiat engines in the past. Its only a 3.9 so does not suffer the breathing problems so badly as the larger engines. Im fitting a 270 piper cam and just want to make the most of it.

Thanks

[rev-erend]

It really makes a change to see someone questioning the real weakness of the RV8 (as far as power goes anyway )- it's head.

Here's a link to RPI - who actually show some flow figures
for their modified heads.
www.v8engines.com/engine-7.htm

It does show that the exhaust port makes big gains and the inlet side
gains hardly any top end and looses out lower down from a stage 3 port vs a stage 1.

Make what you want from this .. just for info.

[David H]

tahiti450 said:

Change down?? I did say "rarely" and "maintain", I chose my words carefully in anticipation.

2500rpm in 2nd is about 27mph, 2400 rpm in 3rd c36mph. Don't do much town driving generally. IMHO <2000 rpm is mechanical sadists teritory.

Fair enough, I guess you've thought it through.

I thought it wouldn't bother me being a bit lumpy low down (oo er) but it does. I only use my car for fun, never for mundane trips but when crossing Europe or hooning around the UK it's inevitable that you get caught up in traffic and you end up having to ride the clutch to stop any shuntyness.

Mine is borderline, when someone finally gets back to me with a good offer on a stand alone ECU I'll probably go for that and it should help a lot. But I wouldn't want to go hairier than my cam for road use and would recommend the 'Stealth' over mine ever time and am not overjoyed at being directed toward this cam when I clearly specified my requirements.

Let us know how you get on

[tahiti450]

GreenV8S said:

tahiti450 said:

I have a variety of induction mods in the pipeline.

oh yes excuse the pun! - they will definitely include some new pipelines in fact.

But specifically; 45mm trumpets, large throttle body, smooth bore induction pipes, Larger air flow meter (either the Bosch or the 20AM, I have one of each), ECU (emerald or Mark Adams).
I just want to get the basic engine sorted at this stage (its coming out and getting new shells - possibly with 270 degreee oiling - the cam, adjustable pushrods for preload setting, shim gaskets for a CR tweak, tuftrided rocker shafts (as an experiment to see if this stops the blasted things wearing and ruining the rockers) and then add the other bits as and when.