1969 Jensen Interceptor drivetrain upgrade

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NigelK
Posts: 2
Joined: Wed Aug 19, 20 5:18 am

1969 Jensen Interceptor drivetrain upgrade

Post by NigelK »

Dear All

I’m just about to start a rebuild of the 383 HP engine in my 1969 Jensen Interceptor. My objective is to end up with a “polite” engine for the street consistent with the GT nature of the car, with a reasonable idle and enough vacuum for the brakes, and a 15-25% increase in power and torque over stock. CR should be no greater than 9.75:1 so I can use regular unleaded without pinking.

After long deliberations I have decided on a 438 stroker kit from 440Source, on the basis that the extra lower down torque from increased cu in is more in keeping with my objective than tuning the 383 to add power and torque at higher rpm.

I’m keeping the stock 906 heads for originality, reduced engine bay heat soak, and to remain as close as possible to the factory Interceptor 50/50 fore and aft weight distribution. I’ll get the heads ported, valve seats hardened for unleaded, and larger valves fitted. As far as I can tell the block has never been decked. With 0.019” steel shim head gaskets, static CR should be 9.6:1. Some minor milling of the heads should increase this to my target CR of 9.75:1.

440Source recommend the Comp Cams Xtreme Energy .477/.480” cam which has a 224/230 duration at 0.050” lift. I’ll probably follow Comp Cams recommendation to go up one notch to the Xtreme Energy .488/.491” cam which has a 230/236 duration at 0.050” lift.

For the carb, I’m thinking Edelbrock AVS2 650 cfm. Larger than the factory Carter AVS 4682S (625-630 cfm) but possibly a little small cf the factory 440 Carter TQs rated at 750 cfm. I reckon the improved low down driveability provided by the AVS2 primary annular booster is more in keeping with my overall objective than ensuring the engine can fully breathe above 5750 rpm.

For the exhaust, I’ll have custom 4-2-1 full length headers made with 1.75” primaries feeding 2” secondaries and 2.5” collectors. Then replicate the factory system (one pipe for each bank, with a single muffler and resonator) but maintain the 2.5” diameter and install an H-crosspiece abaft the transmission.

I’m getting the original A727B transmission rebuilt, probably with some upgrades to handle the expected 450-500 lbs-ft of torque. I’ll also retain the stock 10.75” high stall torque converter - the rated 2350-2650 rpm stall speed should give 2500-2800 stall speed behind the updated engine so just about right. The back end is the stock Salisbury 4HA with Pow-r-lok LSD, rebuilt with all new bearings.

Interested in any views on the above!

Best wishes,
Nigel

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Pete
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Re: 1969 Jensen Interceptor drivetrain upgrade

Post by Pete »

Welcome, Nigel; I look forward to your build and pictures with interest.

All the best.

Pete
Pete Wiseman; Cambridge.

Mopar by the grace of God

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DaveB
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Location: Thorne,Donny
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Re: 1969 Jensen Interceptor drivetrain upgrade

Post by DaveB »

Im doing a similar build for a customers 1960 Polara,383/434ci,although Ive used the 440 source heads,and decked the block to .002",using a .039" gasket,which will give a better quench than the open chamber 906 heads,it will be dynoed in the next couple of weeks,I expect itll make your predicted HP/TQ levels.
Oh yeah,Welcome :thumbright:

HarrySaggs
Posts: 20
Joined: Fri Sep 25, 20 8:50 am
Location: Tampa, FL

Re: 1969 Jensen Interceptor drivetrain upgrade

Post by HarrySaggs »

I'm excited to see the pictures as well. Something to look forward to during these slow, pandemic days.

NigelK
Posts: 2
Joined: Wed Aug 19, 20 5:18 am

Re: 1969 Jensen Interceptor drivetrain upgrade

Post by NigelK »

Slow but steady progress. All the required parts sourced from the States, engine stripped, block dipped and sent off for reboring. Thinking ahead, I’ll want the rebuilt engine tuned and dyno’ed so I have a power and torque curve to give to Burns Stainless so they can design my custom headers (none of the off the shelf header options will fit in an Interceptor). Can anyone recommend an engine tuner with an engine dyno in the West of England (Oxfordshire, Gloucestershire, Wiltshire, Somerset, Dorset) or in South Wales who could do this work? I’d go to John Sleath in Doncaster normally, but lockdown might make this tricky...
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mopar_mark
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Joined: Fri Jul 14, 06 8:01 pm
Location: Windlesham, Surrey

Re: 1969 Jensen Interceptor drivetrain upgrade

Post by mopar_mark »

I would speak to John S, he seems to be working at present. That said, who knows what’s coming, with Covid being on the rise.
"I spent a lot of money on booze, birds and fast cars. The rest I just squandered."

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