inlet manifold port size?
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inlet manifold port size?
I have removed the heads on my classic range rover,its a 3.9,14 cux on an auto-box.I will be replacing the guides with the modified real steal ones sporting the valve stem seals,I will be using the waisted stem valves std dia /headman headers,matched to the exhaust port outlets.I have opened the inlet and exhaust port diameter at the valve, but am unsure regarding the inlet ports and manifold mating areas.I have twin 2&1/4" pipes all the way to the rear apart from an x pipe where the original y piece came together I have fitted a wide band o2 bung in the x pipe and would like to use an afr meter at some stage.The car runs LPG most of the time closed loop with the narrow band lambdas in the manifolds.Future mods I am contemplating are megasquirt/and some boost, twin turbo/super charger,not sure will see what develops.At this stage would like to now recommendations for the Inlet manifold mating areas/std or opened up a little,what would be best?all advice much appreciated thanks mark!!!
Hi
on the inlet side the area to open up is where the pushrod holes force the castings to narrow, this is the biggest restriction. If you decide to match the inlet port to the inlet manifold leave the port at the inlet face as close to original size as you can, really it is better to just leave this area alone but if you must attack it use templates of the inlet manifold, once you have fitted dowels, to match the two with minimal increase in sectional area.
Best regards
Mike
on the inlet side the area to open up is where the pushrod holes force the castings to narrow, this is the biggest restriction. If you decide to match the inlet port to the inlet manifold leave the port at the inlet face as close to original size as you can, really it is better to just leave this area alone but if you must attack it use templates of the inlet manifold, once you have fitted dowels, to match the two with minimal increase in sectional area.
Best regards
Mike
poppet valves rule!
thanks for the advice kiwicar,when you say inlet face do you mean the head side or the manifold side,they do not match to good on the std rover castings! I understand that going big will destroy the velocity,but would like to now your thoughts regarding any effects of the mismatch of head to manifold? thanks again Mark!!!!
Hi
realistically a mismatch is often preferable to opening the ports out too for on these heads, remember the gasket causes a double step between the inlet and the head which creates turbulance . . . unless that is you drop the gaskets and lap the manifold to the heads and in my opinion life is too short. The best quick solution is to radius both the inlet manifold face and the head face to about 1/32" 1/16" radius, around .8 to 1.5 mm but not the bit between the two adjacent ports.
On my chevy engine I have not bothered matching the inlet to the head, that is beyond shifting the whole manifold back and forth on the bolts to get minimal overall mismatch, this leaves any steps to about 1mm maximum if I have the heads ported later I will probably match them, however rhe runners on my inlet manifold are dead straight and I can get a tunstan carbide burr right down them so I don't have to muck about with templates. If I do match them I think it will be only worth 4 or 5 bhp on a unit producing well over 600bhp, to be honnest I think fitting 1 thou over main bearings and running the oil pump at a lower speed will gain me more.
Best regards
Mike
realistically a mismatch is often preferable to opening the ports out too for on these heads, remember the gasket causes a double step between the inlet and the head which creates turbulance . . . unless that is you drop the gaskets and lap the manifold to the heads and in my opinion life is too short. The best quick solution is to radius both the inlet manifold face and the head face to about 1/32" 1/16" radius, around .8 to 1.5 mm but not the bit between the two adjacent ports.
On my chevy engine I have not bothered matching the inlet to the head, that is beyond shifting the whole manifold back and forth on the bolts to get minimal overall mismatch, this leaves any steps to about 1mm maximum if I have the heads ported later I will probably match them, however rhe runners on my inlet manifold are dead straight and I can get a tunstan carbide burr right down them so I don't have to muck about with templates. If I do match them I think it will be only worth 4 or 5 bhp on a unit producing well over 600bhp, to be honnest I think fitting 1 thou over main bearings and running the oil pump at a lower speed will gain me more.
Best regards
Mike
poppet valves rule!
Hi
this may suprise you having read what I have just said about the inlet but I would recommend working on the exhaust side mis match, ideally you would blend the manifold face to match the header as much as you can over the upper 3/4 of the port face and have a step from the head to the header on the floor of the port. Here don't worry about going too big to achieve the match you can't on the rover without going into the water jacket. one way to achieve this is to fit an Ally plate between the head and the manifold and match each side to it's coresponging face (and on the head side you can extend this into the port. Here there are quite a few BHP to be gained and if you can get a big enough step from the heads to the header (try and mount the manifold lower on its studs) you can get quite an improvment in throttle response and a more stable mixture. If you look at the pictures of my engine herehttp://www.v8forum.co.uk/forum/viewtopic.php?t ... &start=210 you can see the plates on my engine, 20mm thick from what I remember, just before I blended them to the headers.
Best regards
Mike
this may suprise you having read what I have just said about the inlet but I would recommend working on the exhaust side mis match, ideally you would blend the manifold face to match the header as much as you can over the upper 3/4 of the port face and have a step from the head to the header on the floor of the port. Here don't worry about going too big to achieve the match you can't on the rover without going into the water jacket. one way to achieve this is to fit an Ally plate between the head and the manifold and match each side to it's coresponging face (and on the head side you can extend this into the port. Here there are quite a few BHP to be gained and if you can get a big enough step from the heads to the header (try and mount the manifold lower on its studs) you can get quite an improvment in throttle response and a more stable mixture. If you look at the pictures of my engine herehttp://www.v8forum.co.uk/forum/viewtopic.php?t ... &start=210 you can see the plates on my engine, 20mm thick from what I remember, just before I blended them to the headers.
Best regards
Mike
poppet valves rule!
Dont match exhaust ports and headers always make sure that there is a step so that port is smaller than the header.twinpipes wrote:...,I will be using the waisted stem valves std dia /headman headers,matched to the exhaust port outlets....
Opposite to the inlet where you want it matched or the head port bigger than the inlet
4.5L V8 Ginetta G27
Thanks for all the replies/info.Heads are back on + inlet manifold and headers,just another question,the engine was a low compression 38D suffix A. The head gasket was gone between pots 1 & 3 stripped thread in the block it was not even torqued up it was replaced some years before my purchase I have service history with it.It was rebuilt using composite gaskets,I have used tins to up compression,the heads skimmed by approx 10/15 thou.The combustion chambers are 32cc/std dished pistons/helicoiled block.Any idea what the comp ratio is likely to be now,and any recommended AFR gauges,probably prefer analogue,I already have a o2 sensor from a subaru and have fitted a bung in my x pipe,not to sure how many wires it has or if it would be suitable/I also have the turbo from the subaru and wonder if it would a good match if I take it a bit further and go for some boost,unsure until I dig it out what model it,I will take a peek tomorrow/Many thanks Mark/P.S. should be running tomorrow all being well cheers!!!
Hi Dark speed
"Dont match exhaust ports and headers always make sure that there is a step so that port is smaller than the header."
Interesting idea, what is the thinking behind this please? I have aways worked on blending the upper 3/4 of the port (when the header curves down after exiting the port) and putting a step at the bottom as described in the post above, the theory being that you retain laminar flow at the upper portion of the port where the gas velocity is high and can make use of the shock waves in the exhaust, But still prevent the flow reversing into the chamber using the step in the port/header juntion. This is also standard practice for Nascas headers and ports, well SB2 engines and those funny ones with blue ovals on them. Admittedly the RO4 heads just blend the port all round to the header as on my motorcycle engine but here the ports are at about 45 degrees to the bore centre line not horizontal as in the Rover and SBC.
Please can you tell me the thinking behind having the step all round, not just at the port floor as it would save a lot of mucking about during port prperation a lot simpler for me if I adopted it
Best regrads
Mike
"Dont match exhaust ports and headers always make sure that there is a step so that port is smaller than the header."
Interesting idea, what is the thinking behind this please? I have aways worked on blending the upper 3/4 of the port (when the header curves down after exiting the port) and putting a step at the bottom as described in the post above, the theory being that you retain laminar flow at the upper portion of the port where the gas velocity is high and can make use of the shock waves in the exhaust, But still prevent the flow reversing into the chamber using the step in the port/header juntion. This is also standard practice for Nascas headers and ports, well SB2 engines and those funny ones with blue ovals on them. Admittedly the RO4 heads just blend the port all round to the header as on my motorcycle engine but here the ports are at about 45 degrees to the bore centre line not horizontal as in the Rover and SBC.
Please can you tell me the thinking behind having the step all round, not just at the port floor as it would save a lot of mucking about during port prperation a lot simpler for me if I adopted it
Best regrads
Mike
poppet valves rule!
we all,perhaps some better than others understand the theory of the internal combustion engine,that is why we like the big v8,speed,performance,acceleration,its why we make these mods,or have them done by others.Getting as much in,a big bang at the optimum time & back out & using these pulses to pull the next cycle into the next cylinder is what we need!But its getting all these combinations to come together we are trying to achieve,some mods are better than others,you have to get the right combination for the desired effect.I am new to the rover v8 and no expert,so am on a learning curve and understand the theory of what Darkspeed as quoted,the steps help to stop any reversion. It would be perfect to have the inlets vertical on one side of the cylinder and the exhausts on the other side,the spark smack in the middle at peak time to create maximum cylinder pressure,upping the volumetric efficiency is what we are after,we have to get these factors to work with the confines of our engines and vehicles that we squeeze them into.The enjoyment I/we get is that if we make any mods that do work,we can share our experience and knowledge through these very forums and others/we can all benefit. I myself have a very good engineering understanding/experience,but it is the first rover v8 I have had,although I know own a stage one v8 109 station wagon too.So the experience and knowledge of you longer time lovers of the v8 is greatly enjoyed and appreciated.I am just trying to make mine better,but with very limited budget,so the more I learn & do myself the better! thanks to all involved Mark!!!
