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tips, technology, tools and techniques related to vehicle driveline components

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turbodave
dave cox

(13 posts)

Registered:
04/30/2018 03:00PM

Main British Car:


Re: Prepping head for high lift cam - springs? Stem seals?
Posted by: turbodave
Date: May 07, 2018 04:28PM

Lots of great info here. Thanks everyone.

Appreciate the heads up on Rimmers; for $210 I just bought a set of big valves :-)
You really can't complain about that price for a whole set of oversized valves can you?

Appreciate the note on the 11-degree angle (I would have double-checked before purchasing) but found two references that said 7 degrees... I guess that the interwebs were wrong again!

This is not going to be a road engine - it'll only be used on the track.
Will be in 3.9 using vitesse plenum with welded and ported plenum base (instead of the trumpets) and aftermarket management.

This cam has been recommended to me by someone who has used it for many years in many 3.9 engines, but they also use every part of 7000 rpm. I was looking for keeping to a 6100 rpm redline, using the factory 3.9 pistons while I shake down the car, and get a feel for the drivability of the cam, but know this cam (with a suitable CR) will still be pulling very hard at my redline once dialled in. I was told i needed every bit of flow the heads could give me, but was going to keep them standard initially, but then realised the spring issue - and of course, have just bought some valves, so will instead get the heads up to snuff.
Jim, I'm curious what your "desktop dyno" says about timing for this cam? Also, that 10:1 seems a shade low static CR for a cam like this doesn't it?


turbodave
dave cox

(13 posts)

Registered:
04/30/2018 03:00PM

Main British Car:


Re: Prepping head for high lift cam - springs? Stem seals?
Posted by: turbodave
Date: May 07, 2018 04:33PM

And as far as how much I can cut the seat pockets down - I've got a scrap pair of 3.9 heads I'm going to section to aid my porting exercise, and will also look at the area under the spring pocket. I can laser cut as many shims as i need to at work to bring it back, so once I've figured out what I think I need pocketwise, I'll probably go deeper and shim back, as that'll allow me to play with the loads more easily.


mgb260
Jim Nichols
Sequim,WA
(1915 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Prepping head for high lift cam - springs? Stem seals?
Posted by: mgb260
Date: May 07, 2018 04:37PM

Dave, I assumed street motor. Racing with good fuel more likely 11 to 12.5. I'll run the program with fuel injection and 12:1 compression on a 3.9. Cam has 5 degrees advance ground in when installed straight up. So with a 3 keyway timing set retarded 4 degrees will actually be 1 advanced. It will move up the powerband. Probably a little more HP @7000RPM and a little less Tq @ 5000RPM



Edited 1 time(s). Last edit at 05/07/2018 04:53PM by mgb260.


mgb260
Jim Nichols
Sequim,WA
(1915 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Prepping head for high lift cam - springs? Stem seals?
Posted by: mgb260
Date: May 07, 2018 04:48PM

Dave, Ran the program at 12:1 for 3.9 injected motor. 342HP@6500RPM, 307TQ@5000. 1000RPM idle @20 degrees initial timing, 34 total and 11.5 Vacuum. The fuel injection helps there. This is just a simulation and probably optimistic. I just ran it 4 degrees retarded(actually 1 degree advanced). 347HP@7000RPM, TQ stayed the same 307@5000. Recommended initial timing moved up to 24 degrees. Total stayed at 34.



Edited 2 time(s). Last edit at 05/07/2018 05:02PM by mgb260.


mgb260
Jim Nichols
Sequim,WA
(1915 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Prepping head for high lift cam - springs? Stem seals?
Posted by: mgb260
Date: May 07, 2018 05:09PM

Dave, Where are you at? If in Britain, do you know Perry Stephenson? Haven't heard from him in a while on this board or V8Owners.


turbodave
dave cox

(13 posts)

Registered:
04/30/2018 03:00PM

Main British Car:


Re: Prepping head for high lift cam - springs? Stem seals?
Posted by: turbodave
Date: May 07, 2018 05:31PM

Appreciate the info Jim. Just so we're on the same page - when you say "good fuel" do you mean premium or something more? Premium is all I'll be running.

Also - maybe I'm slow on the uptake here - what do you mean by "installed straight up" on the cam timing?

Finally, I left the UK many years ago; I'm not familiar with that name to be honest, but I was never really into the RV8 before I left that side of the pond, so wouldn't know anyway.


mgb260
Jim Nichols
Sequim,WA
(1915 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Prepping head for high lift cam - springs? Stem seals?
Posted by: mgb260
Date: May 07, 2018 05:56PM

Dave, On a typical aftermarket timing set there are 3 keyways. Some have 9. The 3 keyways correspond to 4 degrees advance, 0/straight up, and 4 degrees retarded. If you set up your cam at 0/straight up you are really 5 degrees advance because that is ground into the cam. So if you retard the timing 4 degrees you are still 1 degree advanced because of the 5 degrees advance ground into the cam. If you advance the cam you will lower the power curve, retard and you raise the power curve in RPM's. I figured the fuel as 91-93 Premium with added octane booster to 104. If you are just running premium limit your compression to 10.5. I figured you might be from the UK because you ordered those valves so quick. Perry frequented this site and is a Drag racer that had his MBGT into the 9's. I would not get rid of the trumpets but shorten them so the flare is flush with the bottom of the intake, it will help flow transition. Or you could use a sheetmetal intake like this for 444HP@7500RPM on my program. Similar to what Tim Lanocha uses in his TR7 race car.
custintakeQ.jpg



Edited 4 time(s). Last edit at 05/07/2018 06:18PM by mgb260.



turbodave
dave cox

(13 posts)

Registered:
04/30/2018 03:00PM

Main British Car:


Re: Prepping head for high lift cam - springs? Stem seals?
Posted by: turbodave
Date: May 07, 2018 06:27PM

ahhh, my experience of cams in other engines is that the keyway is only a guide, and that only degree-ing in the cam, preferably using a vernier or 1-degree dowel adjustment is the preferred approach. I've not even looked at timing gear yet, so don't know what folks commonly use.

I got them ordered quick as I already had stuff in my cart with Rimmers...

I've had many conflicting opinions on the trumpets - the TVR guys are all over the place on opinions on them as well - but I've understood that building them back with weld to give a flush surface (sans trumpets), and then opening up the throats, plus blending to the inlet, is pretty much a known solution that works (sure it could be optimised more), but the stock dia trumpets being a little too small for a well ported head.



Edited 1 time(s). Last edit at 05/07/2018 06:28PM by turbodave.


mgb260
Jim Nichols
Sequim,WA
(1915 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Prepping head for high lift cam - springs? Stem seals?
Posted by: mgb260
Date: May 07, 2018 07:03PM

Dave, I still degree the cam to verify where it is, but using the keyways to put the power band where I want. You could remove the trumpets and mill a 45 degree transition to the port. Usually use the Buick V6 timing set. Have you done the recommended oiling mods? I would use the oil pump booster plate, T/A 60lb relief spring(or adjustable relief valve), larger 5/8"Buick V6 pickup and the T/A front cam bearing also. The clearance on the rod and main bearings is best at .0015 instead of .002 like Ford and Chevy.



Edited 1 time(s). Last edit at 05/07/2018 07:06PM by mgb260.


turbodave
dave cox

(13 posts)

Registered:
04/30/2018 03:00PM

Main British Car:


Re: Prepping head for high lift cam - springs? Stem seals?
Posted by: turbodave
Date: May 08, 2018 10:09AM

I'm using the 94/95 "interim" front cover with the crank mounted pump, so hope to have little of the typical Rover V8 oiling issues. I will be making an adjustable pressure cap however.

I will be putting the restriction in the rocker feed (or going for full roller rockers).

Not sure what the T/A front cam bearing modification is? Can you advise? Thanks!


mgb260
Jim Nichols
Sequim,WA
(1915 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Prepping head for high lift cam - springs? Stem seals?
Posted by: mgb260
Date: May 08, 2018 11:37AM

The front cam bearing is grooved on the back side to move the oil feed hole to a better location to improve the oil wedge and reduce the load from the distributor and early oil pump. Years ago Phil Baker told me to lengthen the slots in the stock bearing from 1 to 3 o clock and 7 to 9 o clock installation for better oil distribution. There is also a front cover mod to put a squirt hole to the distributor gear.

[www.youtube.com]



Edited 1 time(s). Last edit at 05/08/2018 12:15PM by mgb260.


turbodave
dave cox

(13 posts)

Registered:
04/30/2018 03:00PM

Main British Car:


Re: Prepping head for high lift cam - springs? Stem seals?
Posted by: turbodave
Date: May 08, 2018 01:51PM

ahhh, that's becuase the dizzy drive gear is also driving the oil pump?

I won't need any of that as the dizzy gear turns only the dizzy shaft.

I always like to maximize the oiling of all journal bearings by chamfering and smoothing as needed, so will take a look at the cam shells as well.

I understand that the later crank driven pumps are night and day better at moving oil than the gear driven pumps and can run higher pressures without the issues of higher pressures on the gear-driven pumps. The only downside is they are a swine to prime (i know that from experience with a 4.6 disco motor i rebuilt previously.
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