Discussion
I'm getting ready to rebuild a 907, the one in my Jensen Healey, not the Lotus, and am wondering if anyone knows of a shop that does these and knows them well?
I will probably do the job myself, but since the car is being prepped for SCCA ITS I need to get everything I can out of it but I am limited to what can be done. Essentially the engine can only be B&B'd, exhaust is free and that is it. I wouldn't mind sending the bottom end off to be balanced, as much weight removed and stay within rules, and then I'll complete the rest of the build.
Any suggestions? Thanks much,
Ron
I will probably do the job myself, but since the car is being prepped for SCCA ITS I need to get everything I can out of it but I am limited to what can be done. Essentially the engine can only be B&B'd, exhaust is free and that is it. I wouldn't mind sending the bottom end off to be balanced, as much weight removed and stay within rules, and then I'll complete the rest of the build.
Any suggestions? Thanks much,
Ron
Ron:
Contact Jeff Robinson at JAE Parts (www.JAEParts.com) for some insight and help with the 907 engine. There are likely secrets. Make sure you install the flat-top Euro spec higher compression pistons as the cars(Lotus anyway) had a lower compression piston to help meet emmissions. Probably some cams as well. You could install the larger valves (assuming regs allow it) from a 912 Lotus Esprit S4s engine.
Mark
Contact Jeff Robinson at JAE Parts (www.JAEParts.com) for some insight and help with the 907 engine. There are likely secrets. Make sure you install the flat-top Euro spec higher compression pistons as the cars(Lotus anyway) had a lower compression piston to help meet emmissions. Probably some cams as well. You could install the larger valves (assuming regs allow it) from a 912 Lotus Esprit S4s engine.
Mark
Can't install anything good, so:
*No different cams than stock
*only 0.5 compression over stock
*0.030 overbore/sleeve
*stock valve sizes
*NO PORTING beyong port matching to gaskets
No changes beyond stock specs. Now, I can use other cams that were in JHs during the production run and I'm checking that out to see if there are any different ones at any time during the produciton.
This class of SCCA is meant to be on the cheap for the everyday man, yeah right, like any racing is cheap.
*No different cams than stock
*only 0.5 compression over stock
*0.030 overbore/sleeve
*stock valve sizes
*NO PORTING beyong port matching to gaskets
No changes beyond stock specs. Now, I can use other cams that were in JHs during the production run and I'm checking that out to see if there are any different ones at any time during the produciton.
This class of SCCA is meant to be on the cheap for the everyday man, yeah right, like any racing is cheap.
Ron, the two best engine builders in these parts are Dennis Shaw (located right next to Pete Krause's shop near Carmax on Highway 70) and Sam Moore down in Charlotte/Mooresville.
I'd do two things. I'd call JAE and pick their brains, and buy parts from them, and then call Dennis Shaw and/or Sam Moore to see if they have any 907 experience. They can then do the work for you, if they know the motor.
You should also try calling Dave Bean of Dave Bean engineering (google him to get the number). He raced Elans for years and knows the 907 from a racing perspective. In fact, I would probably call him first.
I'd do two things. I'd call JAE and pick their brains, and buy parts from them, and then call Dennis Shaw and/or Sam Moore to see if they have any 907 experience. They can then do the work for you, if they know the motor.
You should also try calling Dave Bean of Dave Bean engineering (google him to get the number). He raced Elans for years and knows the 907 from a racing perspective. In fact, I would probably call him first.
Ron,
Check with the www.jensenhealey.com board for references. I've rebuilt a number of 907 engines for the members.
Judson
rjudman@bellsouth.net
Check with the www.jensenhealey.com board for references. I've rebuilt a number of 907 engines for the members.
Judson
rjudman@bellsouth.net
Judson, where are you located? Do you have any race experience with this motor? We are in a very limited prep class -- .5 bump in compression, free exhaust, some limited port matching, .040 over. Stock hp is 140 hp, we need to make 170, perferably 180 to be competitive. Possible? It sure seems like it. The IT "rule of thumb" is that you get at least a 25% bump in power with those mods, perhaps more if the car is older and the motor "sloppy."
What do you think?
What do you think?
rlearp said:
Can't install anything good, so:
*No different cams than stock
*only 0.5 compression over stock
*0.030 overbore/sleeve
*stock valve sizes
*NO PORTING beyong port matching to gaskets
No changes beyond stock specs. Now, I can use other cams that were in JHs during the production run and I'm checking that out to see if there are any different ones at any time during the produciton.
Ron,
J-H stock, or can you dip into Lotus stock? There is no J-H stock cam choice to consider. All stock set-ups used the Lotus C cam... only the MOP settings changed (115ret/115adv, 110nom/110nom, 100adv/115adv).
But stock Lotus Turbo cams (107) would be an improvement (used world wide) as would the 912HC intake cam (104... not used in the USA). Neither have radical timing, but they do offer much more lift. The 104 has essentially the same seat-to-seat duration as the stock cam (272 degrees), but 0.410" lift verses 0.340" and more aggressive opening ramps.
Can you play with adjustable cam pulleys? There would be some minor gains there, but it would require dyno time to optimize them.
Can you use a Turbo engine as a starting point? The block's bottom end is stronger and much more appropriate for racing. It also has a larger cooling jacket.
If not, can you dowel pin the 907's main bearing panel to the block? Lotus used only two dowel pins... one at the front and one at the rear (tubular sleeves in counterbores surrounding the stud). Dowel pinning all ten studs (ie, "shuffle pinning") significantly strengthens a 907's bottom end. No more power, but it won't break as readily.
Lotus permits fly-cutting the cylinder head up to 0.020" to correct flatness issues. I don't find a similar, specific reference in the J-H manual, but it's a common practice. It should be good for about half a point of compression. Along with the half a point allowed in the pistons, that could be worthwhile.
Cutting the head will lower the cams relative to the crank. Pulling the newfound slack out of the timing belt with the tensioner will retard the cams a bit. A 0.020" (.5mm) cut will retard the cams about 4.67 degrees. Are adjustable cam pulleys legal? If not, you could play musical chairs with the pulleys to get some of the timing back.
Installing a 100 MOP intake pulley from a North American engine (after engine No. 10480) would advance the intake cam 10 degrees... minus the retard due to milling the head = 5.33 degrees advance net.
Installing a 115 MOP exhaust pulley from an engine prior to No. 4030 would advance the exhaust cam 5 degrees. Minius the retard due to milling = 0.33 degree advanced net.
If you say, "No" to all those things, then I'm probably heading down the wrong path. "Yes", and we can talk about some possibilities. Or contact me off line... ;-)
Regards,
Tim Engel
Lotus Owners Oftha North
Minnesota, USA
Thanks on that. Pinning the dowels is legal. Adjusting cam timing is legal. Everything else...not so legal....sort of the key rule in IT is that you can use anything that came on the car over its lifespan, but what you use had to have been stock at some time in teh USA.
So it looks like the later intake is better, but that only one cam was used in the USA?
So it looks like the later intake is better, but that only one cam was used in the USA?
[quote=JeffYoung
So it looks like the later intake is better, but that only one cam was used in the USA?[/quote]
Jeff,
What do you mean by "the later intake is better"? The 100/115 timing? It depends upon what you want, since playing with the cam timing generally robs Peter to pay Paul.
You can get more high end horse power at the expense of low end torque. That may be beneficial on a fast course with lots of straights where you spend a lot of time at full scream. Torqueless, but fast if you have enough time to get up to speed... then hold it.
Or you can get more low end grunt which would be helpful on a tight, twisty course where you spend a lot of time accelerating out of corners.
In one engine for all courses, the nominal 110 INT /110 EXH timing would probably deliver the best overal flexibility.
If you shave the head, inherit the retarded timing that goes with that and just want to fix it, then the later 100/115 timing would advance both cams to offset the retard. The exhaust would just about zero-out at 0.33 advanced, while the intake would end up advanced by 5.33 degrees. Better? That depends upon what course you are designing for. But yeah, probably generally better.
There's a 104 MOP Lotus Pulley (107 and 104 cams... not legal) and an aftermarket 105 MOP pulley. They would get the retarded timing back closer to nominal. 104/115 would end up advanced about 1.33/0.33. 105/115 would end up advanced about 0.33/0.33.
Yes, only the Lotus C-cam was used in production.
272 degree duration seat to seat, and 0.340" lift.
100/115 MOP (advance intake 10 / advance exhaust 5)
North American engines only after Engine 10480
36 BTDC
56 ABDC
71 BBDC
21 ATDC
57 Overlap
110/110 MOP (Nominal, or design-correct)
From Engine 4030
26 BTDC
66 ABDC
66 BBDC
26 ATDC
52 Overlap
115/115 MOP (retard intake 5 / advance exhaust 5)
Prior to Engine 4030
21 BTDC
71 ABDC
71 BBDC
21 ATDC
42 Overlap
Regards,
Tim Engel
Lotus Owners Oftha North (LOON)
Minnesota, USA
So it looks like the later intake is better, but that only one cam was used in the USA?[/quote]
Jeff,
What do you mean by "the later intake is better"? The 100/115 timing? It depends upon what you want, since playing with the cam timing generally robs Peter to pay Paul.
You can get more high end horse power at the expense of low end torque. That may be beneficial on a fast course with lots of straights where you spend a lot of time at full scream. Torqueless, but fast if you have enough time to get up to speed... then hold it.
Or you can get more low end grunt which would be helpful on a tight, twisty course where you spend a lot of time accelerating out of corners.
In one engine for all courses, the nominal 110 INT /110 EXH timing would probably deliver the best overal flexibility.
If you shave the head, inherit the retarded timing that goes with that and just want to fix it, then the later 100/115 timing would advance both cams to offset the retard. The exhaust would just about zero-out at 0.33 advanced, while the intake would end up advanced by 5.33 degrees. Better? That depends upon what course you are designing for. But yeah, probably generally better.
There's a 104 MOP Lotus Pulley (107 and 104 cams... not legal) and an aftermarket 105 MOP pulley. They would get the retarded timing back closer to nominal. 104/115 would end up advanced about 1.33/0.33. 105/115 would end up advanced about 0.33/0.33.
Yes, only the Lotus C-cam was used in production.
272 degree duration seat to seat, and 0.340" lift.
100/115 MOP (advance intake 10 / advance exhaust 5)
North American engines only after Engine 10480
36 BTDC
56 ABDC
71 BBDC
21 ATDC
57 Overlap
110/110 MOP (Nominal, or design-correct)
From Engine 4030
26 BTDC
66 ABDC
66 BBDC
26 ATDC
52 Overlap
115/115 MOP (retard intake 5 / advance exhaust 5)
Prior to Engine 4030
21 BTDC
71 ABDC
71 BBDC
21 ATDC
42 Overlap
Regards,
Tim Engel
Lotus Owners Oftha North (LOON)
Minnesota, USA
We can't legally dip into Lotus stock, only what was on JHs. Now, that being said, there are some JH Rally Cams I'm told that are essentially the Lotus pieces sold on some JHs from the factory. I'm digging to get more info on the specs.
Jeff means the later intake casting were better, or so we're told.
>> Edited by rlearp on Wednesday 4th August 18:00
Jeff means the later intake casting were better, or so we're told.
>> Edited by rlearp on Wednesday 4th August 18:00
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