Sean Mckeown's 1.9 Engine

[PumaRacing 2]

The aim of this thread is not to continue the unpleasantness of recent days, which I'm sure everyone has had quite enough of, but to put on record the specification and some of the subtle details of how this engine build ended up. Firstly thank you to Anthony for facilitating the collection of the engine which had reached an impasse and for collecting it himself and even paying the balance due out of his own pocket pro tem to enable things to be resolved.

 

Despite the dispute that ensued during the build I always consider the engine itself to be my customer rather than the person paying the bill. To knowingly build something less than that which I think I could is an insult to the engine. The main bone of contention on this one was the cam choice given the standard bottom end and how much power that could cope with. In the end, for the main reason that it was a known quantity that had just been tested in CraigB's engine, the choice ended up as a Catcams 4900340 which has 255 degrees duration at 1mm lift and 12.25mm total lift. This has a useable power curve from about 3000 rpm to 8000 rpm. A PT28 had already been bought which has 283 degrees duration at 1mm lift and is therefore about 30 degrees or three steps hotter.

 

As cam duration goes up so does the required compression ratio and therefore swapping cams is not always a simple procedure if further engine machining has to take place. Also high lift cam lobes foul the inside of the cylinder head on the 8v engine (and many others). Although not really my problem or something I was being paid for I wanted to design a build which would allow the PT28 to be used in future once the basic engine had been proved reliable and warranty was no longer an issue.

 

Firstly the spec.

 

43mm inlet valve fully ported big valve XU9 head, standard exhaust valves.

Uprated valve springs to allow circa 8200 rpm to be used.

Standard 1.9 rods balanced to within 1 gram and with ARP bolts fitted.

New 1.6 Gti Karl Schmidt cast pistons.

Good s/h standard liners matched for deck height to within 1 thou, rehoned and with no measureable bore wear.

 

Solving the cam and compression ratio problem took a lot of time and calculation but eventually I hit on a solution. Firstly the head was machined so that the cam lobes of both the Catcam and also the PT28 would clear the top of the lifter bores. That also means that anything in between such as a PT27 (267 degrees at 1mm lift) should also clear unless the cam lobes are spaced differently lengthwise along the cam which sometimes happens and always needs checking. However I gave every area where the lobes cam close to the casting a little extra sideways clearance so that this hopefully won't be an issue.

 

To solve the compression ratio issue I designed the current build with the milder Catcam by using the thicker head gasket which is standard on the Mi16 rather than the standard gasket which came in the gasket set. With this in place the head was machined to give 11.25:1 CR and with a standard thinner gasket in place this would rise to 11.75:1 to better suit the PT28 or PT27. The valve spring clearance was also set so that any of those cams can be used with no further machining.

 

So in an afternoon the cam can be swapped, a thin gasket fitted and no further machining is required. I thought this was a fairly elegant way of maximising the utility of the engine and allowing it to be raised to a higher state of tune with very little work. Perhaps we can then all find out sometime what one of my big valve heads will do with a full race cam and TB's fitted. Of course if the PT28 is spotted on Ebay in the next few days then all my work and calculation has been wasted but such is life.

[boombang 2]

Without meaning to have a go at either part, but in fact out of curiousity, why was the engine not designed around that cam? Was it purely that Sean wanted to use the PT28 but you deemed it unsuitable due to the rest of the spec or that it was recommended to go for a stronger bottom end - which was ruled out for say cost reasons.

 

i.e. were you being the engine builder unhappy to let the PT28 be used with the given engine spec

 

You also say "power that could cope with" - does this mean too much for the pistons to cope with, rods, crank or purely that the bottom end is not up to revving as highly as the cam would require?

 

What recommendations would you put forward to someone using a "hotter" cam such as the PT28 and what spec would be advised?

 

Plus what power would this and the current spec be capable of?

[petert 587]

A couple of questions.

 

Q1. If you took the time to deck the liners, why didn't you take a bit more off (and the block), and push the pistons up into the gasket to maximise squish height, rather than taking metal off the head? (of course budget is a consideration here)

 

Q2. Which relates to Q1, why didn't you run the 4900340 at 11.75:1 anyway? I've seen milder cams run at 12:1 without problems on pump gas, Optimax 98. I'm assuming your fuel is similiar to ours.

Edited May 15, 2006 by petert

[PumaRacing 2]

A couple of questions.

 

Q1. If you took the time to deck the liners, why didn't you take a bit more off (and the block), and push the pistons up into the gasket to maximise squish height, rather than taking metal off the head? (of course budget is a consideration here)

 

I didn't deck them. I selected a nicely matched set of four out of the ones I had available. There was no money in the pot for machining blocks and liners. This was meant to be a cheap engine build until it somehow turned into a race engine along the way.

 

Q2. Which relates to Q1, why didn't you run the 4900340 at 11.75:1 anyway? I've seen milder cams run at 12:1 without problems on pump gas, Optimax 98. I'm assuming your fuel is similiar to ours.

 

I bet you haven't seen milder cams run at 12:1 with one of my BV heads and TB's. What I set things to was as far as I was prepared to push things without the budget to do a lot of R&D.

[PumaRacing 2]

I've seen milder cams run at 12:1 without problems on pump gas.

 

I take it the "I've seen" also means this is anecdotal based on someone else's measurements and not an engine you built yourself for reward. You see it's very easy to decide what CR to use on someone else's engine until you actually have to build that engine yourself and face it coming back to you at your expense if it blows up. Why would anyone in that situation push the CR to its bitter limit for the sake of another 1 or 2 potential bhp? In fact why would someone push anything to its bitter limit on a low budget engine build that isn't going to be actually racing against anything else?

[mfield 20]

In fact why would someone push anything to its bitter limit on a low budget engine build that isn't going to be actually racing against anything else?

 

So they know it's only them selves that can be improved ( taking into account budget )

 

Sounds like you've done a top job for the amount spent, it cost me about £2k for my old 8v which had std size valves.

[petert 587]

I take it the "I've seen" also means this is anecdotal based on someone else's measurements and not an engine you built yourself for reward.

 

No I didn't build it, but I sold him the BV head (not built by me either). It ran 45mm TB's and 244 deg. @ 0.050" cam. It ended up putting out 170hp at the wheels on nitrous. I was actually surprised myself, thinking it would detonate itself to bits. I guess you were also restricted with cast pistons. The engine above had forged. That's a valid point about it coming back.

[veloce200 3]

This post isn't convincing me that my proposed "grenade spec" build will even have a pin in it ! I guess the only thing will be by using std valve sizes in the xu9j2 head I am limiting flow and hence the PT28 will certainly not be as wild as it would be in a BV head. Clearly using less cam and having a better head is the sensible way to go, and I can see why with your head a PT28 would blow through 8000rpm with ease.

 

I have to say I've struggled on the Catcams site to find any other engine with options of 283 at 1mm. Is this a factor of design around comparatively undervalved Pug 8v engine or a consequence of the excellent lifter design as there are plenty of cams with much larger advertised durations and durations at .1mm? Kent say the Pt 28 powerband is 3000-7800. I expect that might be with a std head?!

 

riddle me this - what rpm do you think a std valve 1.9 with 40mm tb's and 8 injectors (4 firing as std to the back of the valve) and a pt28 cam and 12:1 compression would fall off the cam and also idle at? Any guesses?

 

thanks

[PumaRacing 2]

I have to say I've struggled on the Catcams site to find any other engine with options of 283 at 1mm. Is this a factor of design around comparatively undervalved Pug 8v engine or a consequence of the excellent lifter design as there are plenty of cams with much larger advertised durations and durations at .1mm? Kent say the Pt 28 powerband is 3000-7800. I expect that might be with a std head?!

 

The duration at 1mm lift isn't a function of lifter size or design. What the lifter diameter restricts is the maximum velocity of the valve, which will be reached at about half the full lift, and as a consequence the maximum lift that can be reached for a given seat duration. The duration at 0.1mm or 1mm is whatever the designer chose to grind into the cam.

 

All 16v engines and most other modern 8v engines have more valve area per cc than the XU so they don't need very long cams which is why you won't be finding many. However there are plenty with as much or more duration for older pushrod engines like the Chevy V8, Rover V8, MGB.

 

I wouldn't pay much attention to powerbands in cam catalogues. They won't have actually tested anything in an engine and the figures will be no more than a guess. Regardless of head mods the PT28 isn't going to do much below 4500 and the upper limit could easily be 9k with the right head and TBs.

 

Maximum useable duration in cams is very much a law of diminishing returns. At some point any extra duration just kills more of the bottom end power without gaining much at the top. Where the limit lies in any particular engine is one of the hardest things to gauge without a budget for actual dyno testing. However the basic rule is that the more valve area per cc the less cam duration you need.

 

It could be that the PT28 won't show much of an improvement over the PT27 but frankly I don't know. I wish there was some easy formula you could apply but there isn't. Choosing cam and compression ratio are probably the two hardest things to get right on an engine. If I'd had the budget to design a race engine from the start I might have made different choices on this one.

[veloce200 3]

The duration at 1mm lift isn't a function of lifter size or design. What the lifter diameter restricts is the maximum velocity of the valve, which will be reached at about half the full lift, and as a consequence the maximum lift that can be reached for a given seat duration. The duration at 0.1mm or 1mm is whatever the designer chose to grind into the cam.

 

All 16v engines and most other modern 8v engines have more valve area per cc than the XU so they don't need very long cams which is why you won't be finding many. However there are plenty with as much or more duration for older pushrod engines like the Chevy V8, Rover V8, MGB.

 

I wouldn't pay much attention to powerbands in cam catalogues. They won't have actually tested anything in an engine and the figures will be no more than a guess. Regardless of head mods the PT28 isn't going to do much below 4500 and the upper limit could easily be 9k with the right head and TBs.

 

Maximum useable duration in cams is very much a law of diminishing returns. At some point any extra duration just kills more of the bottom end power without gaining much at the top. Where the limit lies in any particular engine is one of the hardest things to gauge without a budget for actual dyno testing. However the basic rule is that the more valve area per cc the less cam duration you need.

 

It could be that the PT28 won't show much of an improvement over the PT27 but frankly I don't know. I wish there was some easy formula you could apply but there isn't. Choosing cam and compression ratio are probably the two hardest things to get right on an engine. If I'd had the budget to design a race engine from the start I might have made different choices on this one.

 

thanks for the reply. OK how about this angle. Downdraft port vs sidedraft port - generally speaking wouldn't a sidedraft respond better to more lift and the downdraft more duration? I guess I am just going to have to install the PT28 and find out what happens. PS don't suppose you need a set of Kent springs for your next Pinto rebuild - bloody springs they supply don't fit the Pug - I'd like a set of your single springs that fit the PUG! willing to pay extra as well!

[smckeown 1]

Perhaps we can then all find out sometime what one of my big valve heads will do with a full race cam and TB's fitted.

 

At the end of the day you chose the cam at the very early stages of the project, even after I questioned it. It was just after we agreed the build was a BV head on carbs/tbs (last summer time). You are doing a goood job convincing everyone you havent acrually made a mistake in cam choice. But I couldn't give a crap anymore, I see it as a good thing that I have a cam that will actually be usable in the rev range it can be used for.

 

Of course if the PT28 is spotted on Ebay in the next few days then all my work and calculation has been wasted but such is life.

 

Why would I want a cam I cannot use ? if I had the engine rebuilt in the future with forged pistons (to which you didn't want to use when you decided new pistons were needed) then i'd possibly look at a PT27. But that's not going to happen in the short or medum term.

 

It's great you future proofed the cam swap, but you are trying to discuise the fact you made the wrong choice in the first place. I don;t have a problem with you making a mistake, even though it only came to light recently we discussed it and moved on. I was surpised by all the years of engine building and calculation wizadry the cam choice went out the window based on feedback from your most recent head built, but there you go.

 

Anyway, I have my engine, and we'll all see what it generates soon enough. Let's hope i get more than your recently reduced pwoer targets on your site. Rally spec down from 175 bhp to 165 I see.

 

Any chance you can pop the receipt for the engine build in the post, as I don't have one.

[PumaRacing 2]

thanks for the reply. OK how about this angle. Downdraft port vs sidedraft port - generally speaking wouldn't a sidedraft respond better to more lift and the downdraft more duration?

 

Far more likely to be the other way round.

 

I guess I am just going to have to install the PT28 and find out what happens. PS don't suppose you need a set of Kent springs for your next Pinto rebuild - bloody springs they supply don't fit the Pug - I'd like a set of your single springs that fit the PUG! willing to pay extra as well!

 

I've come across those damn springs before when a customer sent a set along with his new cam. Tried to work out how the hell they fitted and finally phoned up Kent who said well they fit if you do lots of machining to remove the valve guide boss! Tossers.

 

I do my own Pinto and CVH springs so I don't really need another set but you can have a set of my XU singles. I've got plenty in stock.

[veloce200 3]

I do my own Pinto and CVH springs so I don't really need another set but you can have a set of my XU singles. I've got plenty in stock.

 

not only that but the caps to! how much please?

[PumaRacing 2]

not only that but the caps to! how much please?

 

I'll contact you off list.