Mclaren M8b replica (visual)

Thanks John,
I will go down the Holley path so will call John Harcourt and have a chat. Have put an add on trade me to see what comes up.
Question for Andrew, when you do the Holley carb size sums, they say 350cfm to 390cfm for a 3.5ltr Rover. So how can a substantially larger carb have good airflow for optimal fuel atomisation. Another problem for me would be that standard Rover heads (with basic port and polish) are far from `decent heads`. Love to know more.
Cheers
Russell
 
SUMPS
Whilst JacMac and others on the subject of sumps, I plan on cutting 25 mm out of the depth of my sump to match the gearbox to input centreline. The sump I am using is the standard Rover deep rear pan and as per my last build I was going to extend the front section, add trap doors to control oil surge and put in a horizontal plate about 60mm up from the floor. This is designed to also help oil stay own in the sump and would have some small holes and the minimum sized access hole for the oil pump pick up. Any comments.
Russell
Hi Russell, sorry must have missed this Q, don't see much of a problem with that but would suggest that you consider an external pickup from pan to pump plus some horizontal tubes in the pan to prevent oil surge from front to rear & vice versa. The OE pickup drilling in the block has caused a few re-priming issues with Rovers etc over the years, I'll have a look at a pump tomorrow to refresh the memory & draw a diagram or pic up.
 
Ruussell, mate for what its worth I had a 4.2 rover in the rear of a 20' cruiser with a duo prop Volvo leg, it was a Hartley so it wasn't a light weight, the engine was basically stock with a very mild cam, I used one of johns dual plane manifolds with a 390 4 barrel as he supplied it, just bolted it all on and it went like the proverbial shite of a shovel, and was real good on fuel to boot.
in all honesty I cant see any real gains by going much bigger, unless of course you intend to rev the ring out of it, which I doubt.
JMTBW
cheers John
 
Hi John,
I appears that Jc has moved on as both his numbers are now with other subscribers, not to worry, I will just call on Summit for a duel plane and 390 cfm.
Jac, I will not need to chop the sump now because as you can see, the motor and trans are sitting in their new home and the sump is the same level as the trans. I will just do the same surge mods I did to my other Mclaren which never gave any problems at all.
Jac, what sort of relative difference would there be between a 2 barrel 390 cfm and a 4 barrell 390cfm with the motor basically stock, extractors and a port and polish ? Remember that its not a full blown race car but I would like it to go!
Space is tight so again a plate over where the water pump was and this time I will run a Craig Davis to shift the water around. The gear change will be on the right hand side this time as it`s almost a direct line to the same side of the trans. The flywheel is ordered and the roll bar is being bent so plenty of work in front of me. I will buy the tube and bends for the extractors next time I am out Penrose way,as I can get them made whilst waiting for expensive bits. I need to start thinking about tyres at some stage now, I know the sizes that I need, its just a case of getting sticky ones to suit.
Good feeling to see progress but slowed the build today with lunch on Waiheke Island, all transport via Gold card, nice to get some of our taxes back.
Cheers
 

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Terry Oxandale

Skinny Man
Supporter
Russell,

The 4 barrel will provide better part-thottle being the smaller venturies until the secondary opens. I believe the 2 barrel and 4 barrel work comparably at WOT. I ran a 390 on my Pinto (2.3 L) and it ran fairly well, but it was a bit oversized. Have you considered the next size up in a 600 instead of the 390? When I was running the 289 a lot (4.7L), I either ran a dual 390 set-up, or a single 650-700 carb, and with the right staging, worked very well. Lastly, Holley is a great name in the carburetor business, but the Carter (now manufactured by Edelbrock) design has a lot going for it, IMHO has a better metering arrangement, and I believe has a 500 cfm carb. I've used both, and the Edelbrock is what I find more user friendly, with equal performance (until you get into the Barry Grant or Demon quality of carburetors).
 
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Hi Russel re the Harcourt manifold
John has moved by the look of it but a quick google found him
phone 03) 3497263

cheers John
 
Russell, good saves me doing a dwg, Holley use two different pressure ratings for 2bbl vs 4bbl carbs so 390cfm in 2bbl is not the same as 390 cfm in a 4 bbl. That said a 4bbl will/should give more favourable mixture distribution @ wide open throttle along with better response at part throttle for street use. Andrews point about using a larger cfm carb has some merit as long as you strike it right with the carb choice....one thing to remember which most carb tuners/experts cant tell you is how much potential flow is lost out the exhaust during the valve overlap period, not much in mild cam examples and a lot with wild cams , big ports etc.The beauty of the 4bbl square bolt pattern is a carb change is simple. How & where your going to operate it plays a big point here. Interesting Terry mentioned the Edelbrock/Carter AFB carbs, I tend to recommend those to anyone having power valve problems with Holleys these days on street cars, but that's more of a reflection of the fuel quality here in NZ.
 
What i still don`t understand is where all those extra cfm`s are going to be used! if the formula says around 390cfm for a 215 cu inch engine.
I also realized that I had not tagged on the pictures of the motor in situ.
John, I will check that number again but I had also rang the new number on google and got a private person(correct number).
Cheers Russell
 

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John
Just had a look on Google street view and 559 springs rd is now a tyre shop, its the same phone number also.
Cheers
He must have collected his gold card and moved on!
 
Most formulae work/assume a percentage of VE, some unrestricted naturally aspirated stuff can exceed 100% VE with the right conditions and well thought out sources for air intakes etc, eg your 215 rover is 497 cfm @ 100% at 8000rpm.
 
Thanks Jac, I will probably only rev it to 6 to 6500 rpm so that equates to some where around the 400 plus cfm. I think for the moment I may just modify a Rover dual plane and fit a 2 barrel carb. Then if that was not to my liking, I could then go the correct 4 barrel carb and manifold. Would you think there would be much difference between the two set ups. I have that set up in Carol`s car and I must admit it goes really well.
Regards
Russell
 

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Hi Russell, good to see you motoring along with your build. Are you going to build your own uprights again for the rear or do you have something else planned. if you are interested I'd be happy to do some alloy ones for you and they can be set up to take what ever hub you want to use. I have a new pattern and they will be much lighter and can be hollow core if you wish.

Cheers Leon
 
Leon
Thanks for that offer, I may take you up on it yet. I have already started down the steel fabrication road already and welded the brake mounting plate to the turned hub housing, hopefully there will not have been to much shrinkage. I am using Subaru bearings, drive flanges and axel`s so hope that it will all work out. Spent some time looking at how tight my engine install is and see that I have to relocate 1 brace behind my seat and scallop the rear subframe to clear the left hand universal rubber boot, apart from that its looking good. I will cut new axels once I have the rear suspension set up and sorted, Audi 1 end...Subaru the other. The gear change shaft has almost a clear run from its first turn by my RH shoulder so have stuck a dummy tube there so that the headers can be built to accommodate its passage. Got plenty to work with at the moment so work to be done.
Cheers
Russell
 
Hi Russell, sorry I wasn’t paying attention to your earlier questions on carb CFM and I’ll respond because it is an interesting area that I've mucked around with a bit.

I reckon it’s useful to ponder a bit on how carbs are rated. At rated airflow capacity a 4bbl carb will lose about 5% of mass airflow across it, and a 2bbl about 10%. That’s oxygen the engine is capable of turning into power that is not delivered to it because of pressure drop across the carb. This means that an engine that is capable of pulling 750cfm through a 750 4bbl would theoretically pull 790cfm through the mythical zero loss intake system, and an engine pulling 350cfm through a 350 2bbl would pull 390cfm through the mythical zero loss set-up.

The “rule of thumb” carb sizing calculators are all based on assumptions about what is an acceptable compromise in mass airflow loss at the top end in order to be confident that the carb will do a decent job of metering and distributing fuel at low airflows and on transitions. As has been pointed out, a really healthy 215ci mill getting its ring rev’d out might pull 400 cfm depending on its VE. It’s not going to see about 40 of those pulling through a 350 cfm 2bbl, and will miss about 20 of them pulling through a 390 cfm 4bbl, and might miss out on 5 or 10 pulling through a 750 cfm 4bbl.

It’s obviously no good thinking theorectically about this if the larger carb can’t perform properly at lower airflows, however in my experience there is a substantial difference between the ability of similar rated Holleys and Holley-clones in this area, and it’s usually related to the quality of design and manufacture of the carb main body and the boosters. My rule of thumb for a mill that must be flexible and responsive at normal engine speeds is to use the biggest carb I can get away with that will deliver decent idle, low speed and transition performance. That’s because I don’t like the idea of leaving up to 10% of airflow on the table at the top end. Manifold choice is critical as is tuning but in most cases you can probably avoid losing any more than a few %. You’ll generally end up with a carb that might, on the face of it, appear a bit big for the engine.

Having said all that, something decent in the 390-500 cfm range is a safe bet and would work just fine!

Cheers, Andrew
 
Back on deck now...light duties.
So first thing up was exhausting! fabricated up the drivers side headers which also had to allow for the gear shift shaft to fit thru the same hole. I had made some subtle changes from the last car, I have run the rear diagonal opposite and found that it compromised the exhaust passage. I have also made this chassis some 50mm taller so that prevented me from bringing the headers up inside the chassis rails and then over the rear bulkhead.The pipes would also be too close to the body work with heat issues. After much head scratching, I figured out that a snake pit would work if I was careful with my lengths( all within 10%), some 5 u bends later and all into the collector which will fit snug with a bit of panel beating.The system will be much the same as the other car with the mufflers crossing over the trans axel and exiting under the rear clip as per the real thing. The real clip did not tilt on my first car and I will be working hard to have that feature on this.The materials have arrived for my fabricated rear uprights so they are next to be worked on.
Cheers
 

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Terry Oxandale

Skinny Man
Supporter
Looking forward to seeing what you do with the uprights.

I put a lot of energy into the tilt front and rear, and it has been a lifesaver in terms if easy access for any work that must be done either in a hurry, or for normal maintenance.
 
I like the look of your headers Russell. I would like to do a set of 180s on my car just for the look and sound but not sure its the right move (originality wise) Keep the progress coming.

Terry, waiting for some more colour parts mate, no pressure.

Cheers Leon
 

Terry Oxandale

Skinny Man
Supporter
Slow your jets Leon. The part you saw was only a practice shot to see if the colour was proper. I'm going over the entire car right now with 400 wet/dry and a final primer/sealer before the finer grit wet-sand and paint.
 
You know I live vicariously through you and Russell because mine is taking so long, Hell Russell is on to his second car and will probably have that finished before mine. So forgive my impatience I just love reading these post's LOL.
Cheers Leon
 
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