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Cylinder Head Opinions Needed

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76spitspin Avatar
76spitspin John Erickson
Tolland, CT, USA   USA
Hey guys, I need some help deciding on what head would work well with my setup. I've recently rebuilt my 1500 engine. Internally I've got .20 flat top Nural pistons and a BPNW fast road cam. It's being fueled by HS4s. Exhaust wise, I believe its a Bell tubular 4-2-1 manifold, and a Rimmer Bros twin sports exhaust system from the manifold back. I was looking into the head that BPNW sells, but after reading through other threads, it seems like it would negatively impact my engine performance. I'm drawn in the middle between a late mkIV large valve head, or a head from a 76. I'd like to reach a CR of 9.0:1, or a 9.5:1, which ever would benefit my engine the most. Could someone please explain to me what would be more beneficial and why. Also, what is the point of double valve springs? I cant seem to quite wrap my mind around whats been said in other threads.

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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
The spec of your engine seems much the same as mine, with my large valve head. The head had the ports matched to the manifolds, and their was some work done to the the inside radius and minor clean up in the ports. Compression was left at about 9-1 and I find this works well with our mid grade gas, or even regular 'if need be' if I keep a light throttle. (I tour with the car so this was important)

Initally I had single valve springs. But after one spring broke and dropped a valve :-( I decided to fit the UK OE type double valve springs. The double valve springs did not alter my valve seat pressure, but the idea is that they alter the spring's harmonics and may prevent valve float at certain rpm.

My thoughts:
1) The Bean counters at Triumph did not spec them for fun.

2) I wanted a safeguard if another valve spring should break.

clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1511465 by 76spitspin Hey guys, I need some help deciding on what head would work well with my setup. I've recently rebuilt my 1500 engine. Internally I've got .20 flat top Nural pistons and a BPNW fast road cam. It's being fueled by HS4s. Exhaust wise, I believe its a Bell tubular 4-2-1 manifold, and a Rimmer Bros twin sports exhaust system from the manifold back. I was looking into the head that BPNW sells, but after reading through other threads, it seems like it would negatively impact my engine performance. I'm drawn in the middle between a late mkIV large valve head, or a head from a 76. I'd like to reach a CR of 9.0:1, or a 9.5:1, which ever would benefit my engine the most. Could someone please explain to me what would be more beneficial and why. Also, what is the point of double valve springs? I cant seem to quite wrap my mind around whats been said in other threads.

It's important to know what your deck clearance is, the distance from the piston crown to the top surface (aka 'deck') of the block.
This should be easy to measure since the head is off.
Check each piston at TDC. They are usually not exactly the same, but that's OK.
Unless you are seeking to squeeze every single HP out, any head will do, it's the compression ratio and the porting work (if any) that will make the difference.
Many folks obsess over valve sizes, but all they actually do is set the ultimate limit when everything else has been fully optimized.
Bigger valves can actually flow worse than smaller ones, especially at low and mid RPM.

For a street car you want the best performance for the conditions you drive in; stop/go traffic, cruising at fixed speeds, acceleration when overtaking or leaving a stoplight.
That means torque, not power.
Top speed?
Well, I suppose so if you enjoy flashing red/blue lights, sirens, and regular encounters with Law Enforcement.


One reason dual valvesprings are used is when single valvsprings would have to be operated near their fatigue limit.
The envelope (diameter, length) determines limit of how a coil spring can be operated, the seat pressure, the spring rate, the max opening distance, determine the fatigue life, in cycles.

The spring max diameter is limited by the spacing between the valves.
The spring height is limited by the length of the valvestem; or the geometry of the valvegear; or the clearance under the rocker arm cover; or the clearance under the hood, etc.
But with dual springs, the forces add together, so two 'weaker' springs can be used that operate with longer fatigue life, that together add up to the same spring force.

Another reason dual valvesprings are used is when the wire diameter of a single stronger spring is too large to permit the required opening distance (the coils bind, or touch, the spring goes solid).
This is common with a more aggressive cam, operated at higher RPM. To prevent the valves from hanging open at higher RPM (valve float), greater spring seat pressures and rates are needed.
And the cams also usually feature larger valve opening ('lift'). Both of these require stronger springs, either larger wire diameter, or different number of coils, or both.
When a single spring simply cannot handle both requirements, then dual springs must be used.

'Beehive springs' are a relatively new design that addresses the issue in three ways.
First, the conical shape allows more lift before binding because the coils are not directly on top of one another.
Second, they are would with 'ovate' wire, it's flattened instead of being round, giving even more lift without binding.
Third, the smaller diameter at the top yields less inertia, so less spring pressure is needed to prevent valve float.

Unfortunately, I'm not aware of any vendor offering these for our Spitfires.

It's something I'd like to experiment with, but there's not enough time for everything.
Anyone here tried them?
With what results?



Edited 1 time(s). Last edit at 2018-02-04 08:20 PM by clshore.

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GeorgeOhr Nonya Business
Yes, confused, USA   USA
In reply to # 1511465 by 76spitspin or a head from a 76.

No need, you would just cut yours "X" amount once you know deck height and chamber volume.

14GPDJENGINEERING Avatar
Silver Spring, MD, USA   USA
Go to this site:

http://auskellian.com/paul/links_files/performance_enhancements.htm#heads

Paul has a spreadsheet to calculate how much to mill your head.



Dennis smiling smiley

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