Cylinder head flow figures

[Darkspeed]

Just looking at the comparisons in the 3 types of valve used in the RV8

38mm P6 type - Tulip type valve
40mm SD1 - Flat back vale
40mm SD1 Flat back waisted stem

The valve seat on the 38mm is full valve diameter 38mm
The valve seat on the 40mm valves is not full valve, the seat diameter is 38.75mm

Just noted on a flow test on an older SD1 head some really poor low opening flow - on inspection this was being caused by a carbon build up on the unused .625mm edge of the valve.

The reason ported heads work so well with a rover is that the throat just behind the valve is a massive restriction that starts choking at well before maximum lift of a stock cam is achieved. The choke point starts having an effect at around 7.5mm (.300) lift


Any questions?

Andrew

[sidecar]

All good stuff, keep it coming!

One thing that is sort of related that I'd like to know is how do the likes of V8 Development fit bigger valves to the SD1 heads without removing the seats and replacing them with larger ones.

My heads are V8 Dev stage III jobbies, the valves are the ones that RS sell, (DWG 500 or something like that). The seat inserts have not been replaced and it does not look like they were bored out to a larger size either.

Infact even though they were done to stage III they still had a step where the valve seat insert joins the rest of the inlet or exhaust track. I ended up grinding out the step with tungsten burrs.

Pete

[CastleMGBV8]

Hi Pete.

It's standard procedure to recut the standard SD1, or later heads valve seat inserts, the Big Valve 1.63" inlet and 1.4" exhaust valve sizes are effectively dictated by the maximum amount the original seats can be opened up.

The larger Ultra Big Valve 1.695" inlet and 1.5" exhaust obviously require new larger seat inserts to be installed.

I'm a little surprised that the inserts were not opened up to valve seats size and the throats blended to size, as this is a cardinal sin in head modifying terms although I have seen some pics of V8D (Chesman?) head work that I thought was a little questionable.

People do get a little fixated re; fitting the biggets valves possible and this does not always give the results that may be expected.

It's interesting that a cast iron MGB 5 port head, 2 inlets and 3 exhaust can be made to flow enough in full race spec to produce 100 BHP per litre, you would need very good Rover heads to produce that figure even with 8 ports per head!

Kevin

[sidecar]

Hi Pete.

It's standard procedure to recut the standard SD1, or later heads valve seat inserts, the Big Valve 1.63" inlet and 1.4" exhaust valve sizes are effectively dictated by the maximum amount the original seats can be opened up.

The larger Ultra Big Valve 1.695" inlet and 1.5" exhaust obviously require new larger seat inserts to be installed.

I'm a little surprised that the inserts were not opened up to valve seats size and the throats blended to size, as this is a cardinal sin in head modifying terms although I have seen some pics of V8D (Chesman?) head work that I thought was a little questionable.

People do get a little fixated re; fitting the biggets valves possible and this does not always give the results that may be expected.

It's interesting that a cast iron MGB 5 port head, 2 inlets and 3 exhaust can be made to flow enough in full race spec to produce 100 BHP per litre, you would need very good Rover heads to produce that figure even with 8 ports per head!

Kevin

Hi Kevin,

I must admit I was slightly pi55ed off when I found out that the throats were not blended in properly. I had been running the stage III heads on my 3.5, when I then fitted them on a 4.6 I had to remove all the valves to in order to have the heads skimmed, that was when 'I clocked an eye' on the throats. The rest of the work looked OK. I used a dremel and a load of tungsten carbide burrs in order to sort it out. I'm sure that the inserts have not been bored out down the centres. According to Des Hammill JE Developments calls the valves that I have "mid size" valves and also stated that they are the largest valves that can be fitted to the standard inserts.

You are right in that it would need to be a very special head in order to get 100 BHP/Litre, I don't think that the combustion chambers are good enough even if the heads could be made to flow enough gas.

I feel that I might end up hijacking this thread, maybe I should start a new one.

Regards,

Pete

[jefferybond]

Surely fitting bigger valves to standard seats without even boring them out would make them worse?

The valve head basically 'gets in the way' of the gas flow, so surely bigger ones (on a standard seat!) just makes things worse? Am I right?

I'd be worried that boring out standard seats too much would make them a looser fit in the head, and prone to dropping out?

Jeff

[kiwicar]

In the case of the rover the first thing to do is open the throat behind the valve, this is the biggest restriction in the whole head. As valve lift is limited in the rover engine aswell the primary reason for fitting bigger valves on this engine is to open the throat area further, (as I said valve lift is limited so you are not going to fit larger valves to take advantage of excess lift! ). Whether you do this by boaring out the existing seats or fitting new inserts is dependent on if you can bore out the standard seats to take advantage of the bigger valves if not you need bigger inserts.
Sounds like a head designed by a marketing monkey not an engineer.
Best regards
Mike

[Darkspeed]

Thanks to Eppo (Speed I have finished flowing a brand spanking new - straight from the store Merlin head on the bench.

I need to do a few temperature conversions and convert to a graphical representation and check a few figures but we managed to get a representative run.

We only had a couple of hours to play and a fair bit of time was taken up with getting valve lifting fixtures sorted as the standard RV8 one that I have do not work on the Merlins. We also did not have the time to do many test runs because of the initial findings and wanting to try some investigations.

The is also a noise issue with a bench with the flow capacity that this bench has as I am sure Eppo will testify - when its flowing at 28" it gets a bit loud and at 10.30pm its antisocial

The heads are very nice castings and have the potential to produced some very big power numbers - But, and here's the catch - not without further work. As stock they have an issue.

The bench confirms MinorV8's findings on his swap over.

To be continued

Andrew

[minorv8]

Teaser

Yes I had to do a fair amount of cleaning in the ports, I removed the chamfered egde from the face of the intake port, there´s some mismatch between the throat and seat on both intake and exhaust ports that needed attention etc etc. Being too eager it only occurred me much later that it would have been nice to have the heads flow tested to see if my work had any impact. In total I have something like 6-8 hrs work in the heads.

I´m still curious about the fin or divided or whatever you call it that is in the intake port. I would understand if it would be in the roof just adjacent to the valve guide but it is in the floor of the port. Its function is not clear to me. I have not seen anything similar in aftermarket heads.

I would guess that at lower lifts these heads are pretty much equal to factory heads but should flow better at higher lifts. I think my engine has not enough lift and in fact needs more cam. But obviously somebody knows more than the rest of us

[Darkspeed]

Teaser

.....But obviously somebody knows more than the rest of us

I know enough at the moment that I would be reluctant to fit these heads to an engine without carrying out more bench investigation work.

To cut quickly to the chase the heads choked at .400" and flow dropped off above this lift - I removed the valve and flowed the port and it still flows the same figure as the .400" lift

Up until .400" the figures were looking impressive and I thought we were going to see something special - then the flow died.

Reducing bore shrouding by opening up the bore to 102mm made no difference - leading me to believe that the restriction is likely to be further into the port and most likely at the push rod turn

The heads would from stock benefit from some fettling and may pick up some small gains in lower lift flows but its the higher lifts that needs investigation.

I needed to get a velocity probe sorted out for the bench so that I can map port velocities to see where restrictions are - I should have this sorted in the next few weeks.

This is not to take anything away from the fact that for new castings these heads represent great value for money and "could" be a great foundation for a big horsepower motor - whether this potential can be extracted is one matter and having the courage to take a carbide to a brand knew head to find out is another.

At this moment in time I remain to be convinced that they would offer any significant improvement over well developed stage 3 heads - and I use the term well developed carefully.

Now where are those stage 3/4's for comparison peeps ?

Andrew

[kiwicar]

just a quick question, but what do you have up-stream of the inlet port face?
Mike

[Darkspeed]

just a quick question, but what do you have up-stream of the inlet port face?
Mike

Clay.....

Provides a 3/8" radius for entry to the port to reduce turbulence and give an accurate port flow figure.

As seen in the flow bench thread.

Andrew

[Speed 8]

Hi Andrew,

Just got back home. Very nice to meet you in person. Once again I would like to thank you for the warm welcome and your time. As expected you have a serious piece of equipment there and boy was it noise at full throttle. We arrived back in the hotel at 00:45, two junctions closed. Also enjoyed the Autosport International the day after.

We too were surprised to see the inlet choking at .400. Will investigate what’s going. Very strange indeed. We even double checked the results on the neighbouring cylinder.

Plans are as followed;
- Find a head tuner with flow bench in my area and take some further measurements.
- Ask the friendly people at RealSteel for an explanation.
- Get the old Dremel out?

Prior to visiting you we paid JE Developments a visit. To my surprise he had a pair of Merlins laying around. I asked him for his opinion. I noticed he had reworked the intake quite extensively. My goal with the 5.0 and the Merlins is to achieve around 300bhp. John said this would be easily achieved with the Merlins in standard trim. As one should expect of course.

I'll of course keep posted on any progress.

[Darkspeed]

Hi Eppo,

Sorry to hear of the long slog back to Birmingham - I really appreciate the opportunity to put the Merlins on the bench.

Marcus came up today with what is typically considered to be Stage3 - Ported with the largest valves for the standard seats - 41.5 and 35.5 be assured that Merlins outflowed them by a very significant margin.

Again having another ported/modified head on the bench provided some very interesting results that had me and Marcus scratching our combined heads and swapping heads back and forth. (Careful how you read that )

It sounds like John flows at 10"wg and 120CFM would be 200CFM at 28"WG which is where I thought we we heading until the brakes came on.

Interestingly whilst looking for some DJE information in an old file we found graphs for Vitesse, DJE stage 1 and DJE stage 3 heads flowing at what we are assuming is 28" as it relates very closely to what we were finding on the bench today.

Marcus has also been kind enough to leave the Stage 3 with me so that I can do some flows on another port as the port we ran the tests on was significantly smaller at the push rod pinch than the other 3

I have all the parts to recreate the Stage 3 port on a development head - bullet guides a seat grinder to widen the seats and enough burrs to remove material so in between testing all the stock variants I will be hogging out a head to see just how far stage 3 will go.

Lots to do.

Andrew

[HairbearTE]

Yes thanks to Andrew for a demo of the bench today. I was thoroughly impressed with it, consistent repeatable results and as mentioned above seemed to give accurate flow figures when compared with figures taken from DJE some time ago on a stock head. The stage 3 head had plenty of work in it but offered little or no advantage over a mildly modded (by Andrew) 3.9 head of the same casting type. We discovered afterwards that the port we tested on the stage 3 was smaller than the other three in the same head so further testing may reveal more, and the exhaust has yet to be tested but i'm now more sure than ever that a home built flowbench and a bit of home r+d is money better spent than just taking a chance on buying someone elses "stage 3" etc. heads.

[sidecar]

I suspect that you guys are just about to find out that there is a whole world of bull 5hit in the head tuning business!

Well done, I think that this thread is one of the best ever!