Breaking in a new Sprint engine

[USASPRINTMAN]

I've just started driving my TR7 with the newly rebuilt Sprint engine.

I have to say I am a bit disappointed with the performance. For an engine with new 0.40 pistons, tubular exhaust, an STR091 cam and HS8s, I expected a bit more power. It performs about like an ordinary TR7.

The timing and carbs are set properly and the engine is running fine.
So, I was wondering if maybe the engine just needs to have some miles put on it before it loosens up a bit.

So far I've driven about 50 miles since the installation. Does it take awhile to run in a new Sprint engine?

Richard Truett
Detroit, Mich.

[Lewis]

It'll be about 500 miles before it starts to come together and about 1500 (?) before it's really settled in.

Probably worth getting it rolling-road tuned when it's bedded in as well to check everything is spot on and what it's actually making (which in turn could help identify any problems with it).

Remember to not load the engine up but DO rev it, not abusively but get some power down.

Did you break in the cam as per instructions? It's usually something like 2000-2500RPM for 10-20 minutes

Unforunately, if you've done 50 miles already and been a bit limp wristed with it you might never have the optimum from it but it'll still see you in good health

Hope it comes together nicely!

[Betty Swallocks]

It'll be about 500 miles before it starts to come together and about 1500 (?) before it's really settled in.

Probably worth getting it rolling-road tuned when it's bedded in as well to check everything is spot on and what it's actually making (which in turn could help identify any problems with it).

Remember to not load the engine up but DO rev it, not abusively but get some power down.

Did you break in the cam as per instructions? It's usually something like 2000-2500RPM for 10-20 minutes

Unforunately, if you've done 50 miles already and been a bit limp wristed with it you might never have the optimum from it but it'll still see you in good health

Hope it comes together nicely!

What difference does running a new cam in at 2-2500rpm for 10-20 minutes make? I'm intrigued as to why the performance would be any less. I can understand a newly built engine being a bit tight but the cam???

[USASPRINTMAN]

The cam didn't come with any running in instructions, but I did run the engine at varying speeds for a period of time close to that, so I should be in good shape there.

I changed the oil/filter after that first few minutes of running and now have Castrol 20W 50 GTX in the engine.

I have not loaded the engine and have revved her to about 5,000 RPM or so a few times.

The carb needles are UE and the plugs are nice light brown.

Richard

[Lewis]

Sounds alright then I'd stick with it and see how it improves. Doesn't sound like there's anything "wrong" as such

You could always do a leak down test or compression test to see what's the deal, may be that the rings haven't bedded well? Can loose you about 2-15% power overall if unlucky.

difference does running a new cam in at 2-2500rpm for 10-20 minutes make

Not necessarily any to the performance, as such - was more of a general question. However, if you run it at idle with a new cam you can damage the face of the cam lobes irreversibly, or wear them so much that it doesn't work as well as it should.

NEVER bed in a cam by letting it sit at idle for 10-20 minutes, will do nothing but ruin it

[DavePoth]

Ooh hang on, the tubular manifold's tuned for a certain rev range isn't it? How high have you revved in normal driving? I doubt it'll come properly alive below 3k.

[USASPRINTMAN]

I've been driving it pretty it easily at first. Revving to about 3500 or 4,000 most times and then shifting. Once or twice I have had it 5,000 or more.

My plan is to put about 30 miles a day on it until it gets to about 300 miles and then really start driving it harder.

Mart sold me a fast road cam a few years ago. With that one, you could really feel the power come on at around 3,000 rpm, it was like a mule kicked the car is the arse!

This new STR091 cam I bought from Jigsaw, has no peaks of performance at all and feels rather like a regular cam. She idles reasonable well at 1,000 rpm, too.

RT

[tinweevil]

The purpose of running a cam in for a specified time in one hit is to work harden it. Cant remember exactly but it goes something like: {tinweevil cobblers deleted, see link below}

[edit] I remember where I read it now - Puma racing lots of good articles on there.

Tinweevil

[Lewis]

Yup, spot on, loadings on the lobe tips is at it's highest at low speeds

Good website that!

[Jon Tilson]

needs to be timed correctly...at 106 ATDC inlet peak.
We've been here before...but a few degrees off wil loose you 30 bhp.

Jonners

[USASPRINTMAN]

I put on another 50 miles tonight, all on the highway.

She's definietly got more power now. It's a combination of two things: She's very tight, and I need slightly richer needles for the HS8s.

I am running UE's in there now. But at around 4,500 RPM she could use more fuel. At that speed, I pulled the choke out and felt a bit more power. So I will richen her up with different needles.

maybe this is just regular sorting.

I set the timing at 108 ATDC, as per the cam instructions. But I have a vernier sprocket, so I can easily reset it if need be.

There is one weird thing: The engine runs best when the timing mark on the pulley is at 24 degrees BTDC @idle at around 1,000 rpm.

I hope that's normal.

Richard

[SPRINTPARTS]

Hi Richard, I believe that the best way of running a motor in is just drive it normally, that is unless you abuse your motor. Sprint motors like to be nice and loose to get best performance. We have found over the years that it takes serveral race meetings before the motor performs as it should.

I believe that a road motor can take many thousand of miles before it is running at its best.

Motors usually perform best just before they go BANG!!!!!!!!!!

Is the harmonic balancer a Sprint unit? If it is a modified TR7 item I am not certain that the TDC mark is in the same postion on the pulley as a Sprint item. Also the out ring of the harmonic balancer can slip which will move the timing marks.


Mark

[USASPRINTMAN]

Mark:

I bought a Sprint front pulley from a club member, so I've got the right one on there. I have to say, though, that it is pretty skanky and I have another better one on the way.

I'm switching from UE to UO needles, which will richen up the mixture at higher engine speeds. I pulled the plugs after a highway run last night and they were a bit too light.

But the more miles I put on the engine, the better it performs. It's going to be a great engine.

Richard

[SPRINTPARTS]

I know that the "Green People" won't like this, but I have found that my Sprint's (road car on SU's and race car with EFI) before at their best when running on the rich side of mixture.

Even with the EFI, the race car showed best power on the dyno when running rich, a bit of black haze from the exhaust under acceleration.